Research Article Microstructure-Based Interfacial...

9
Research Article Microstructure-Based Interfacial Tuning Mechanism of Capacitive Pressure Sensors for Electronic Skin Weili Deng, 1 Xinjie Huang, 2 Wenjun Chu, 2 Yueqi Chen, 2 Lin Mao, 2 Qi Tang, 2 and Weiqing Yang 1 1 Key Laboratory of Advanced Technologies of Materials (Ministry of Education), School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu 610031, China 2 School of Mechanical Engineering, Southwest Jiaotong University, Chengdu 610031, China Correspondence should be addressed to Weiqing Yang; [email protected] Received 30 November 2015; Revised 17 January 2016; Accepted 20 January 2016 Academic Editor: Stefania Campopiano Copyright © 2016 Weili Deng et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In order to investigate the interfacial tuning mechanism of electronic skin (e-skin), several models of the capacitive pressure sensors (CPS) with different microstructures and several sizes of microstructures are constructed through finite element analysis method. e simulative pressure response, the sensitivity, and the linearity of the designed CPS show that the sensor with micropyramids has the best performance in all the designed models. e corresponding theoretically predicted sensitivity is as high as 6.3 × 10 −7 fF/Pa, which is about 49 times higher than that without any microstructure. Additionally, these further simulative results show that the smaller the ratios of / of pyramid, the better the sensitivity but the worse the linearity. When the ratio of / of pyramid is about 2, the sensitivity and the linearity could reach a balance point. e simulative results evidently provide the important theoretically directive significance for the further development of -skin. 1. Introduction Electronic skin (e-skin) is usually referred to as “the new flexi- ble wearable tactile biomimetic sensor.” e rapid progress of an e-skin with human-like sensory capabilities has been made by the possibility of such large, multisensory surfaces being highly applicable for autonomous artificial intelligence, med- ical diagnostics, and replacement prosthetic devices capable of providing the same level of sensory perception as the organic equivalent [1]. e working mechanisms of human machine interfacing for e-skin reported mainly focused on the piezoresistivity [2, 3], capacitance [4, 5], piezoelectricity [6, 7], optics [8, 9], and so on. Among them, capacitive sensors based e-skin simplifies device design and analysis owing to the simple governing equation = 0 / [10], where 0 is the free space permittivity, is the relative permittivity, is the opposite area, and is the distance between electrodes. Moreover, capacitive sensors for tactile sensing of e-skin have demonstrated high strain sensitivity, compatibility with static force measurement, and low power consumption [10–12]. Aſter the first monolithic capacitive pressure sensor was designed for medical-research applica- tions in 1980 [13], silicon solution tablets technology and etch-stop technique were put forward to make the capacitive sensor [14]. Aſterwards, the CPS with different microstruc- tures had been deeply studied due to the introduction of MEMS (microelectromechanical systems) technology [15– 18]. Ji et al. [19] made the capacitive pressure sensor by a combination of a standard CMOS (Complementary Metal Oxide Semiconductors) process and bulk micromachining technology. Tian and coworkers [20] designed a flexible capacitive pressure sensor with pyramids in 2010 and they analyzed its response time by experimental studies. ese results showed that the pyramid structure had the advan- tage of short response times, evidently demonstrating the superbly capably tuning action of microstructure interface between human skin and e-skin on the performance of the CPS. erefore, of important significance for the great improvement of pressure sensor performance is making clear the interfacial microstructure-tuning mechanism. However, Hindawi Publishing Corporation Journal of Sensors Volume 2016, Article ID 2428305, 8 pages http://dx.doi.org/10.1155/2016/2428305

Transcript of Research Article Microstructure-Based Interfacial...

Page 1: Research Article Microstructure-Based Interfacial …downloads.hindawi.com/journals/js/2016/2428305.pdfResearch Article Microstructure-Based Interfacial Tuning Mechanism of Capacitive

Research ArticleMicrostructure-Based Interfacial Tuning Mechanism ofCapacitive Pressure Sensors for Electronic Skin

Weili Deng1 Xinjie Huang2 Wenjun Chu2 Yueqi Chen2 Lin Mao2

Qi Tang2 and Weiqing Yang1

1Key Laboratory of Advanced Technologies of Materials (Ministry of Education) School of Materials Science and EngineeringSouthwest Jiaotong University Chengdu 610031 China2School of Mechanical Engineering Southwest Jiaotong University Chengdu 610031 China

Correspondence should be addressed to Weiqing Yang wqyangswjtueducn

Received 30 November 2015 Revised 17 January 2016 Accepted 20 January 2016

Academic Editor Stefania Campopiano

Copyright copy 2016 Weili Deng et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

In order to investigate the interfacial tuningmechanism of electronic skin (e-skin) several models of the capacitive pressure sensors(CPS) with different microstructures and several sizes of microstructures are constructed through finite element analysis methodThe simulative pressure response the sensitivity and the linearity of the designed CPS show that the sensor withmicropyramids hasthe best performance in all the designed modelsThe corresponding theoretically predicted sensitivity is as high as 63 times 10minus7 fFPawhich is about 49 times higher than that without any microstructure Additionally these further simulative results show that thesmaller the ratios of 119871119867 of pyramid the better the sensitivity but the worse the linearityWhen the ratio of 119871119867 of pyramid is aboutradic2 the sensitivity and the linearity could reach a balance pointThe simulative results evidently provide the important theoreticallydirective significance for the further development of 119890-skin

1 Introduction

Electronic skin (e-skin) is usually referred to as ldquothe newflexi-ble wearable tactile biomimetic sensorrdquoThe rapid progress ofan e-skinwith human-like sensory capabilities has beenmadeby the possibility of such large multisensory surfaces beinghighly applicable for autonomous artificial intelligence med-ical diagnostics and replacement prosthetic devices capableof providing the same level of sensory perception as theorganic equivalent [1] The working mechanisms of humanmachine interfacing for e-skin reported mainly focused onthe piezoresistivity [2 3] capacitance [4 5] piezoelectricity[6 7] optics [8 9] and so on Among them capacitivesensors based e-skin simplifies device design and analysisowing to the simple governing equation 119862 = 120576

0

120576119903

119878120575 [10]where 120576

0

is the free space permittivity 120576119903

is the relativepermittivity 119878 is the opposite area and 120575 is the distancebetween electrodes Moreover capacitive sensors for tactilesensing of e-skin have demonstrated high strain sensitivitycompatibility with static force measurement and low power

consumption [10ndash12] After the first monolithic capacitivepressure sensor was designed for medical-research applica-tions in 1980 [13] silicon solution tablets technology andetch-stop technique were put forward to make the capacitivesensor [14] Afterwards the CPS with different microstruc-tures had been deeply studied due to the introduction ofMEMS (microelectromechanical systems) technology [15ndash18] Ji et al [19] made the capacitive pressure sensor by acombination of a standard CMOS (Complementary MetalOxide Semiconductors) process and bulk micromachiningtechnology Tian and coworkers [20] designed a flexiblecapacitive pressure sensor with pyramids in 2010 and theyanalyzed its response time by experimental studies Theseresults showed that the pyramid structure had the advan-tage of short response times evidently demonstrating thesuperbly capably tuning action of microstructure interfacebetween human skin and e-skin on the performance ofthe CPS Therefore of important significance for the greatimprovement of pressure sensor performance is making clearthe interfacial microstructure-tuning mechanism However

Hindawi Publishing CorporationJournal of SensorsVolume 2016 Article ID 2428305 8 pageshttpdxdoiorg10115520162428305

2 Journal of Sensors

there is scarcely any report to theoretically and systematicallyinvestigate the interfacial tuning mechanism of e-skin todate Here we employ the traditional COMSOL Multi-physics models using finite element analysis method [21ndash24] to construct four different microstructures and severalsizes of microstructures for the detailed study of interfacialmicrostructure-tuning mechanism between human skin andPVDF (polyvinylidene fluoride) The theoretical model ofthe CPS with microstructure decorated is proposed And thepressure response the sensitivity and the nonlinear errorof the designed sensors are analyzed Both the results fromtheoretical analysis and simulation calculation could be usedas theoretical guidance in e-skin processing

2 System Design and Characterization

As we know the capacitance of parallel plate capacitors is

119862 =

120576119878

120575

=

1205760

120576119903

119878

120575

(1)

where 120576 is the dielectric permittivity of dielectric medium 1205760

is the vacuum dielectric constant 120576119903

is the relative dielectricconstant 119878 is the opposite area of the electrodes 120575 is thedistance between the electrodes According to (1) 119878 and 120575 arethe two important factors to tune the sensitivity of the CPSExperimentally the microstructures surface modificationsof the middle dielectric layers were usually employed toeffectively control the opposite area 119878 and the distance 120575 ofelectrodes to improve the performance of the CPS Hereinin order to obtain their theoretical mechanisms we havedesigned the middle layers with four different microstruc-tures to get a systematic insight of microstructures surfacemodifications into the tuning process of the CPS The sketchof the CPS for e-skin is shown in Figure 1

In this model both the top and bottom electrodes arethe copper thin film materials and the dielectric materialis PVDF with excellent dielectric property and flexibility[25]The substrate is PET (polyethylene terephthalate) whichis transparent and has excellent physical and mechanicalproperties and electrical insulating properties [5] Its initialcapacity value should be demonstrated as

1198620

=

120576119878

1205750

(2)

in which 1205750

is the initial distance between the electrodes and1198620

is the initial capacitance When the plate moves

Δ119862 =

120576119878

1205750

minus Δ120575

minus

120576119878

1205750

=

120576119878

1205750

sdot

Δ120575

1205750

minus Δ120575

= 1198620

Δ120575

1205750

minus Δ120575

(3)

where Δ120575 is the variation of the plate spacing The relativevariation of capacitance can be presented as

Δ119862

1198620

=

Δ120575

1205750

minus Δ120575

=

Δ1205751205750

1 minus Δ1205751205750

(4)

The Taylor expansion of (4) is shown as

Δ119862

1198620

=

Δ120575

1205750

[1 +

Δ120575

1205750

+ (

Δ120575

1205750

)

2

+ (

Δ120575

1205750

)

3

+ sdot sdot sdot] (5)

PolyimideCopperPVDF

Polyacrylic resinPET

Figure 1The sketch of the CPS for 119890-skinThe sensor has six layersnamely polyimide copper PVDF copper polyacrylic resin andPET The upper end uses polyimide material as the cover layer thetwo pieces of copper used as the electrode polyacrylic resin as theadhesive coating and all the devices put on the PET base

When Δ1205751205750

≪ 1 the result (omitting the high-order)can be simplified as

Δ119862

1198620

asymp

Δ120575

1205750

(6)

The sensitivity119870 [26] can be defined as

119870 =

Δ119862

Δ120575

=

1198620

1205750

=

120576119878

1205750

2

prop

1

1205750

2

(7)

Nonlinear error 119903 [27 28] namely linearity is usuallymeasured in terms of a deviation from an ideal straight lineand it is typically expressed in terms of percent of full scalewhich can be explained as

119903 =

Δ119862max1198620

times 100 =Δ120575max1205750

times 100 (8)

3 Results and Discussion

In this paper the middle layers with four microstruc-tures for CPS were designed to investigate the interfacialmicrostructure-tuning mechanisms of surface modificationAs shown in Figure 2 the sketches of these structures arerespectively flat panel (Figure 2(a)) cuboids (Figure 2(b))cylinders (Figure 2(c)) and pyramids (Figure 2(d))

In order to investigate the effect of middle dielectric layermicrostructure on the sensitivity of pressure sensor all hem-line lengths (119871) of the above microstructures are identicallyfixed to be 10 120583m and their heights (119867) are designed to thesame size of about 707120583mThe corresponding ratios of 119871119867are controlled to be about radic2 As shown in Figure 2 underthe same pressure of 1MPa the simulative pressure responses

Journal of Sensors 3

4 35

3 25

2 15

1 05

0

(120583m)

998771002

998786 142times10minus5

(a)

0

(120583m)

998771007

998786 866times10minus5

006

005

004

003

002

001

(b)

998771006

times10minus4

0

(120583m)006

007

005

004

003

002

001

998786 133

(c)

02

018

016

014

012

01

008

006

004

002

0

(120583m)

99877102

times10minus4

998786 392

(d)

Figure 2 Different profile structures of the CPS (a)The flat panel (b) the cuboids (c) the cylinders and (d) the pyramidsThe 3D diagramsof the CPS the cross-sectional view of sensors the vertical view of the functional layer of the sensor and the deformations of the functionallayer are listed in the figure from top to bottom

Table 1 Sensitivity and nonlinear error of the CPS with differentmicrostructures

Structure Sensitivity119870 (fFPa) Nonlinear error 119903Flat panel 128273E minus 8 0001646Cuboids 805555E minus 8 0000681Cylinders 100342E minus 7 0000476Pyramids 629792E minus 7 0008034

of CPS evidently show that the sensitivity 119870 of the CPSwith microstructures should be better than that without anymicrostructure and that of pyramids-based CPS is obviouslythe best one among four microstructures Furthermore thedetailed characteristic analyses of the above four structureswithin the ambient pressure range of 0sim1MPa through thefinite element software COMSOL Multiphysics are shown inFigure 3

Figures 3(a)ndash3(d) represent the obvious deformation ofthe CPSwith the increasing pressureThe central areas of CPShave the largest deformation in each model The capacitancepressure characteristic curves of all the models are shownin Figure 3(e) The comparisons of the sensorsrsquo sensitivity119870 and nonlinear error 119903 between different microstructuresare shown in Figure 3(f) and Table 1 showing the sensitiv-ities of pyramids-based and flat panel pressure sensors are

63 times 10minus7 and 128 times 10minus8 fFPa respectively That is theformer is about 49 times higher than the latter evidentlyrevealing the excellent capacity for microstructure-controlof middle dielectric layer to tune the sensitivity of CPSFrom Figure 3(f) the nonlinear error 119903 of pyramids is greaterthan that of other models but still less than 1 evidentlyshowing the designed CPS has very good linearityThis resultis consistent with the discussion of the literature [26] Thiscan be explained by considering the stress distribution ofthe different geometrical shapes In a flat panel structure thestress distribution is fairly constant throughout the heightof the panel to the force contact area However when theshape changes from the flat panel to cuboids cylindersand pyramids the stress distribution is nonuniform and isconcentrated at the pointed tips due to the smaller contactarea rather than the broad bases of the structures Thusthe pyramid tips compress more resulting in the highermechanical deformations at the top Therefore the pyramidsshapes are more sensitive

In order to further study the performance of sensor dec-orated with pyramids a series of simulations were performedwith different 119871 of pyramids the sketches and simulationresults of the models are shown in Figure 4

In the simulation 119871 changes from 8 120583m to 12 120583m withconstant height (119867 = 707 120583m)The pressure responses of theCPS with different hemline lengths of pyramids are shown in

4 Journal of Sensors

998771002

998786 142 times 10minus5

times10minus2

004081216

(120583m

)

(a)

998771007

998786 696 times 10minus60001002003004005006

(120583m

)

(b)

998771006

998786 324 times 10minus60001002003004005

(120583m

)

(c)

Pressure

99877102

9987861 times 10minus4000400801201602

(120583m

)

1MPa08MPa06MPa04MPa02MPa0MPa(d)

PyramidCylinder

CuboidFlat panel

00

02

04

06

08

10

Capa

cita

nce d

iffer

ence

(fF)

02 04 06 08 10 1200Pressure (MPa)

(e)

Kr

Kr

Flat panel Cuboids Cylinders

times10minus7

times10minus7

K(fF

Pa)

K(fF

Pa)

00

20

40

60

0000

0002

0004

0006

0008

0010

r (

)

Cuboids Cylinders PyramidsFlat panelMicrostructures

00

10

0000

0005

r (

)

(f)

Figure 3The pressure responses of the CPS with different microstructuresThe deformations of the CPS were shown as (a) the flat panel (b)the cuboids (c) the cylinders and (d) the pyramids In the same model the top part is the surface deformation of the CPS the bottom partis the partial detailed view of the microstructure (e) The capacitance-pressure characteristics of the sensors with different microstructures(f) The sensitivity and nonlinear error of the sensors with different microstructures

Journal of Sensors 5

99877103

998786161 times 10minus4000501015

02502

(120583m

)

12120583m11120583m10120583m

7 0711120583m

9120583m8120583m

(a)

L = 12120583mL = 11120583m

L = 10120583mL = 9120583mL = 8120583m

00

02

04

06

08

10

Capa

cita

nce d

iffer

ence

(fF)

02 04 06 08 10 1200Pressure (MPa)

(b)

Kr

000

001

002

003

r (

)

9 10 11 128L (120583m)

times10minus7

00

40

80

K (fF

Pa)

(c)

Figure 4The pressure responses of the CPS with different lengths of hemline of pyramids (a)The profile structures of sensors with differentlengths of hemline of pyramid from 8 120583m to 12 120583m and the same height 70711 120583m at 1MPa (b) The comparison of capacitance-pressurecharacteristics of the sensors with different lengths (c) The sensitivity and nonlinear error of the sensors with different lengths

Table 2 Sensitivity and nonlinear error of the CPS with differenthemline lengths of pyramids

Length ofhemline 119871 (120583m) Sensitivity 119870 (fFPa) Nonlinear error 119903

8 881355E minus 7 00176219 735721E minus 7 001206810 629792E minus 7 000803411 548525E minus 7 000527112 485630E minus 7 0004066

Figure 4(b) and the sensitivities and the nonlinear errors ofCPS were shown in Figure 4(c) and Table 2

From Table 2 both the sensitivity and the nonlinear errordecrease with the increasing 119871 When hemline length 119871 andheights 119867 are 8120583m and 707 120583m the sensor has the bestsensitivity of 881 times 10minus7 fFPa In this case in order to

obtain greater sensitivity we hope the hemline length is assmall as possible In other words the smaller the ratios of119871119867 of pyramid the better the sensitivity of the CPS Butits nonlinear error would reach 0018 As the change ofratios of 119871119867 we should balance the sensitivity of CPS fore-skin against the nonlinearity error to effectively tune theperformance of CPS through choosing different parametersaccording to the required demands

In analogy with the research between the pyramidsrsquolengths of hemline and the sensorrsquos performance we have alsomade a series of simulations about the pyramidsrsquo heights Inthe simulation the height changes from5120583mto9120583mwith thesame length of hemline (119871 = 10 120583m) the schematic diagramis shown in Figure 5(a)

From this schematic diagram all the models have thesame distance between the two electrodes when the heightof pyramids changes the bottom of the pyramid will befilled with dielectric material Likewise the outside pressurechanges from 0 to 1MPa too the pressure responses of

6 Journal of Sensors

99877104

998786174 times 10minus4

00501015

0350302502

(120583m

)

6120583m 7120583m 9120583m8120583m5120583m

10120583m

(a)

00

02

04

06

08

Capa

cita

nce d

iffer

ence

(fF)

02 04 06 08 10 1200Pressure (MPa)

6120583m7120583m

9120583m8120583m

H =H =H = H =

H =5120583m

(b)

000

001

002

003

r (

)

6 7 8 95

Kr

H (120583m)

times10minus7

00

40

80

K (fF

Pa)

(c)

Figure 5 The pressure responses of the CPS with different heights of pyramids (a) The profile structures of sensors with different heights ofpyramid from 5120583m to 9120583m and the same lengths of hemline 10 120583m at 1MPa (b)The comparison of capacitance-pressure characteristics ofthe sensors with different heights (c) The sensitivity and nonlinear error of the sensors with different heights

the sensor are obtained and the capacitance-pressure curvesof sensors are shown in Figure 5(b) The sensitivity and thelinearity of sensors are shown in Figure 5(c) and Table 3

From Figure 5 and Table 3 it is easy to find that thesensitivity increases with the height increases from 5 120583m to9 120583m but the linearity is decreased In the simulation ofthis series when the length of hemline of pyramid is 10 120583mand the height of pyramid is 9 120583m the sensor has the bestsensitivity that is 700589119864minus7 fFPa In this case in order toobtain the greater sensitivity we hope the height of pyramidis as large as possible In other words in order to obtain thegreater sensitivity we expect that the length of hemline ofpyramid is more thanradic2 times the height

From what has been discussed above it is obvious thatthe performance of the sensor is affected by the length ofhemline and the height simultaneously Considering thesetwo contradictory parameters a compromise method isproposed to obtain the optimal performance of the sensor

Table 3 Sensitivity and nonlinear error of the CPS with differentheights of pyramids

Height119867 (120583m) Sensitivity 119870 (fFPa) Nonlinear error 1199035 398334E minus 7 00051116 404683E minus 7 00051357 409844E minus 7 00053848 412467E minus 7 00060559 700589E minus 7 0022813

if the medians of 119871 and 119867 are selected at this point boththe sensitivity and linearity have good values Through theanalysis of the relationship between 119871 and 119867 the authorcomes to the conclusion that in order tomake the sensor havebetter performance the ratios of 119871119867 should beradic2

Journal of Sensors 7

4 Conclusions

In this paper we employ the traditional COMSOL Mul-tiphysics models based on finite element analysis methodto construct four different microstructures (flat panelcuboids cylinders and pyramids) CPS for the detailed studyof microstructure interfacial tuning mechanism betweenhuman skin and PVDF The simulative results show thatCPS with micropyramids structures has the best measuringsensitivity K (= 63 times 10minus7 fFPa) which is about 49 timeshigher than that without any microstructure Through thesimulation of pyramids with different ratios of 119871119867 theresults show that the smaller the ratios of 119871119867 of pyramidthe better the sensitivity but the nonlinear error will increaseWhen the ratio of 119871119867 of pyramid is aboutradic2 the sensitivityand the linearity could reach a balance pointThismethod canbe used as theoretical guidance for the e-skin processing

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the National University StudentInnovation Program (201510613009) of China SichuanProvince Science and Technology Plan Project (no2015JQ0013) and the Fundamental Research Funds forthe Central Universities (A0920502051408-10)

References

[1] M L Hammock A Chortos B C-K Tee J B-H Tok andZ Bao ldquo25th Anniversary article the evolution of electronicskin (E-Skin) a brief history design considerations and recentprogressrdquo Advanced Materials vol 25 no 42 pp 5997ndash60382013

[2] T W Tombler C Zhou L Alexseyev et al ldquoReversible elec-tromechanical characteristics of carbon nanotubes under local-probe manipulationrdquo Nature vol 405 no 6788 pp 769ndash7722000

[3] B Zhu Z Niu H Wang et al ldquoMicrostructured graphenearrays for highly sensitive flexible tactile sensorsrdquo Small vol 10no 18 pp 3625ndash3631 2014

[4] D J Cohen D Mitra K Peterson and M M MaharbizldquoA highly elastic capacitive strain gauge based on percolatingnanotube networksrdquo Nano Letters vol 12 no 4 pp 1821ndash18252012

[5] S C BMannsfeld B C-K Tee RM Stoltenberg et al ldquoHighlysensitive flexible pressure sensors with microstructured rubberdielectric layersrdquo Nature Materials vol 9 no 10 pp 859ndash8642010

[6] W Zhang and R-G Xiong ldquoFerroelectricmetal-organic frame-worksrdquo Chemical Reviews vol 112 no 2 pp 1163ndash1195 2012

[7] L Persano C Dagdeviren Y Su et al ldquoHigh performancepiezoelectric devices based on aligned arrays of nanofibersof poly(vinylidenefluoride-co-trifluoroethylene)rdquo Nature Com-munications vol 4 article 1633 2013

[8] M Ramuz B C-K Tee J B-H Tok and Z Bao ldquoTransparentoptical pressure-sensitive artificial skin for large-area stretch-able electronicsrdquo Advanced Materials vol 24 no 24 pp 3223ndash3227 2012

[9] R Koeppe P Bartu S Bauer and N S Saricifici ldquoLight-and touch-point localization using flexible large area organicphotodiodes and elastomer waveguidesrdquo Advanced Materialsvol 21 no 34 pp 3510ndash3514 2009

[10] R Puers ldquoCapacitive sensors when and how to use themrdquoSensors and Actuators A Physical vol 37-38 pp 93ndash105 1993

[11] J A Dobrzynska and M A M Gijs ldquoFlexible polyimide-basedforce sensorrdquo Sensors and Actuators A Physical vol 173 no 1pp 127ndash135 2012

[12] H BMuhammad C Recchiuto CMOddo et al ldquoA capacitivetactile sensor array for surface texture discriminationrdquo Micro-electronic Engineering vol 88 no 8 pp 1811ndash1813 2011

[13] C S Sander J W Knutti and J D Meindl ldquoA monolithiccapacitive pressure sensor with pulse-period outputrdquo IEEETransactions on Electron Devices vol 27 no 5 pp 927ndash9301980

[14] H-L Chau and K DWise ldquoAn ultraminiature solid-state pres-sure sensor for a cardiovascular catheterrdquo IEEE Transactions onElectron Devices vol 35 no 12 pp 2355ndash2362 1988

[15] S S Kumar and B D Pant ldquoPolysilicon thin film piezoresistivepressuremicrosensor design fabrication and characterizationrdquoMicrosystem Technologies vol 21 no 9 pp 1949ndash1958 2015

[16] K Takahata Y B Gianchandani and K D Wise ldquoMicroma-chined antenna stents and cuffs for monitoring intraluminalpressure and flowrdquo Journal of Microelectromechanical Systemsvol 15 no 5 pp 1289ndash1298 2006

[17] T G S M Rijks P G Steeneken J T M van Beek et alldquoMicroelectromechanical tunable capacitors for reconfigurableRF architecturesrdquo Journal of Micromechanics and Microengi-neering vol 16 no 3 pp 601ndash611 2006

[18] K I Arshak DMorris A Arshak O Korostynska and E JaferldquoDevelopment of a wireless pressuremeasurement systemusinginterdigitated capacitorsrdquo IEEE Sensors Journal vol 7 no 1 pp122ndash129 2007

[19] J Ji S T Cho Y Zhang K Najafi and K D Wise ldquoAnultraminiature CMOS pressure sensor for amultiplexed cardio-vascular catheterrdquo IEEE Transactions on Electron Devices vol39 no 10 pp 2260ndash2267 1992

[20] H Tian Y Shu X Wang et al ldquoA graphene-based resistivepressure sensor with record-high sensitivity in a wide pressurerangerdquo Scientific Reports vol 5 article 8603 pp 1ndash6 2015

[21] C Tao Z Zhaohua R Tianling et al ldquoA novel dual-functionalMEMS sensor integrating both pressure and temperature unitsrdquoJournal of Semiconductors vol 31 no 7 Article ID 074013 2010

[22] X Huang and D Zhang ldquoA high sensitivity and high linearitypressure sensor based on a peninsula-structured diaphragm forlow-pressure rangesrdquo Sensors andActuators A Physical vol 216pp 176ndash189 2014

[23] N J Madduri G Lakkoju B L Kasturi S Sravanam andT Satyanarayana ldquoDesign and deformation analysis of MEMSbased piezoresistive pressure sensorrdquo International Journal ofAutomotive Engineering and Technologies vol 7 pp 521ndash5312014

[24] B A Ganji and M Shahiri-Tabarestani ldquoA novel high sensitiveMEMS intraocular capacitive pressure sensorrdquo MicrosystemTechnologies vol 19 no 2 pp 187ndash194 2013

8 Journal of Sensors

[25] K Hosoda Y Tada and M Asada ldquoAnthropomorphic roboticsoftfingertipwith randomly distributed receptorsrdquoRobotics andAutonomous Systems vol 54 no 2 pp 104ndash109 2006

[26] J CHelton J D JohnsonC J Sallaberry andC B Storlie ldquoSur-vey of sampling-based methods for uncertainty and sensitivityanalysisrdquo Reliability Engineering and System Safety vol 91 no10-11 pp 1175ndash1209 2006

[27] J Y ZhaoDetection and Sensing Technology Southwest JiaotongUniversity Press Chengdu China 2007

[28] L Lin H-C Chu and Y-W Lu ldquoSimulation program forthe sensitivity and linearity of piezoresistive pressure sensorsrdquoJournal of Microelectromechanical Systems vol 8 no 4 pp 514ndash522 1999

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Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Page 2: Research Article Microstructure-Based Interfacial …downloads.hindawi.com/journals/js/2016/2428305.pdfResearch Article Microstructure-Based Interfacial Tuning Mechanism of Capacitive

2 Journal of Sensors

there is scarcely any report to theoretically and systematicallyinvestigate the interfacial tuning mechanism of e-skin todate Here we employ the traditional COMSOL Multi-physics models using finite element analysis method [21ndash24] to construct four different microstructures and severalsizes of microstructures for the detailed study of interfacialmicrostructure-tuning mechanism between human skin andPVDF (polyvinylidene fluoride) The theoretical model ofthe CPS with microstructure decorated is proposed And thepressure response the sensitivity and the nonlinear errorof the designed sensors are analyzed Both the results fromtheoretical analysis and simulation calculation could be usedas theoretical guidance in e-skin processing

2 System Design and Characterization

As we know the capacitance of parallel plate capacitors is

119862 =

120576119878

120575

=

1205760

120576119903

119878

120575

(1)

where 120576 is the dielectric permittivity of dielectric medium 1205760

is the vacuum dielectric constant 120576119903

is the relative dielectricconstant 119878 is the opposite area of the electrodes 120575 is thedistance between the electrodes According to (1) 119878 and 120575 arethe two important factors to tune the sensitivity of the CPSExperimentally the microstructures surface modificationsof the middle dielectric layers were usually employed toeffectively control the opposite area 119878 and the distance 120575 ofelectrodes to improve the performance of the CPS Hereinin order to obtain their theoretical mechanisms we havedesigned the middle layers with four different microstruc-tures to get a systematic insight of microstructures surfacemodifications into the tuning process of the CPS The sketchof the CPS for e-skin is shown in Figure 1

In this model both the top and bottom electrodes arethe copper thin film materials and the dielectric materialis PVDF with excellent dielectric property and flexibility[25]The substrate is PET (polyethylene terephthalate) whichis transparent and has excellent physical and mechanicalproperties and electrical insulating properties [5] Its initialcapacity value should be demonstrated as

1198620

=

120576119878

1205750

(2)

in which 1205750

is the initial distance between the electrodes and1198620

is the initial capacitance When the plate moves

Δ119862 =

120576119878

1205750

minus Δ120575

minus

120576119878

1205750

=

120576119878

1205750

sdot

Δ120575

1205750

minus Δ120575

= 1198620

Δ120575

1205750

minus Δ120575

(3)

where Δ120575 is the variation of the plate spacing The relativevariation of capacitance can be presented as

Δ119862

1198620

=

Δ120575

1205750

minus Δ120575

=

Δ1205751205750

1 minus Δ1205751205750

(4)

The Taylor expansion of (4) is shown as

Δ119862

1198620

=

Δ120575

1205750

[1 +

Δ120575

1205750

+ (

Δ120575

1205750

)

2

+ (

Δ120575

1205750

)

3

+ sdot sdot sdot] (5)

PolyimideCopperPVDF

Polyacrylic resinPET

Figure 1The sketch of the CPS for 119890-skinThe sensor has six layersnamely polyimide copper PVDF copper polyacrylic resin andPET The upper end uses polyimide material as the cover layer thetwo pieces of copper used as the electrode polyacrylic resin as theadhesive coating and all the devices put on the PET base

When Δ1205751205750

≪ 1 the result (omitting the high-order)can be simplified as

Δ119862

1198620

asymp

Δ120575

1205750

(6)

The sensitivity119870 [26] can be defined as

119870 =

Δ119862

Δ120575

=

1198620

1205750

=

120576119878

1205750

2

prop

1

1205750

2

(7)

Nonlinear error 119903 [27 28] namely linearity is usuallymeasured in terms of a deviation from an ideal straight lineand it is typically expressed in terms of percent of full scalewhich can be explained as

119903 =

Δ119862max1198620

times 100 =Δ120575max1205750

times 100 (8)

3 Results and Discussion

In this paper the middle layers with four microstruc-tures for CPS were designed to investigate the interfacialmicrostructure-tuning mechanisms of surface modificationAs shown in Figure 2 the sketches of these structures arerespectively flat panel (Figure 2(a)) cuboids (Figure 2(b))cylinders (Figure 2(c)) and pyramids (Figure 2(d))

In order to investigate the effect of middle dielectric layermicrostructure on the sensitivity of pressure sensor all hem-line lengths (119871) of the above microstructures are identicallyfixed to be 10 120583m and their heights (119867) are designed to thesame size of about 707120583mThe corresponding ratios of 119871119867are controlled to be about radic2 As shown in Figure 2 underthe same pressure of 1MPa the simulative pressure responses

Journal of Sensors 3

4 35

3 25

2 15

1 05

0

(120583m)

998771002

998786 142times10minus5

(a)

0

(120583m)

998771007

998786 866times10minus5

006

005

004

003

002

001

(b)

998771006

times10minus4

0

(120583m)006

007

005

004

003

002

001

998786 133

(c)

02

018

016

014

012

01

008

006

004

002

0

(120583m)

99877102

times10minus4

998786 392

(d)

Figure 2 Different profile structures of the CPS (a)The flat panel (b) the cuboids (c) the cylinders and (d) the pyramidsThe 3D diagramsof the CPS the cross-sectional view of sensors the vertical view of the functional layer of the sensor and the deformations of the functionallayer are listed in the figure from top to bottom

Table 1 Sensitivity and nonlinear error of the CPS with differentmicrostructures

Structure Sensitivity119870 (fFPa) Nonlinear error 119903Flat panel 128273E minus 8 0001646Cuboids 805555E minus 8 0000681Cylinders 100342E minus 7 0000476Pyramids 629792E minus 7 0008034

of CPS evidently show that the sensitivity 119870 of the CPSwith microstructures should be better than that without anymicrostructure and that of pyramids-based CPS is obviouslythe best one among four microstructures Furthermore thedetailed characteristic analyses of the above four structureswithin the ambient pressure range of 0sim1MPa through thefinite element software COMSOL Multiphysics are shown inFigure 3

Figures 3(a)ndash3(d) represent the obvious deformation ofthe CPSwith the increasing pressureThe central areas of CPShave the largest deformation in each model The capacitancepressure characteristic curves of all the models are shownin Figure 3(e) The comparisons of the sensorsrsquo sensitivity119870 and nonlinear error 119903 between different microstructuresare shown in Figure 3(f) and Table 1 showing the sensitiv-ities of pyramids-based and flat panel pressure sensors are

63 times 10minus7 and 128 times 10minus8 fFPa respectively That is theformer is about 49 times higher than the latter evidentlyrevealing the excellent capacity for microstructure-controlof middle dielectric layer to tune the sensitivity of CPSFrom Figure 3(f) the nonlinear error 119903 of pyramids is greaterthan that of other models but still less than 1 evidentlyshowing the designed CPS has very good linearityThis resultis consistent with the discussion of the literature [26] Thiscan be explained by considering the stress distribution ofthe different geometrical shapes In a flat panel structure thestress distribution is fairly constant throughout the heightof the panel to the force contact area However when theshape changes from the flat panel to cuboids cylindersand pyramids the stress distribution is nonuniform and isconcentrated at the pointed tips due to the smaller contactarea rather than the broad bases of the structures Thusthe pyramid tips compress more resulting in the highermechanical deformations at the top Therefore the pyramidsshapes are more sensitive

In order to further study the performance of sensor dec-orated with pyramids a series of simulations were performedwith different 119871 of pyramids the sketches and simulationresults of the models are shown in Figure 4

In the simulation 119871 changes from 8 120583m to 12 120583m withconstant height (119867 = 707 120583m)The pressure responses of theCPS with different hemline lengths of pyramids are shown in

4 Journal of Sensors

998771002

998786 142 times 10minus5

times10minus2

004081216

(120583m

)

(a)

998771007

998786 696 times 10minus60001002003004005006

(120583m

)

(b)

998771006

998786 324 times 10minus60001002003004005

(120583m

)

(c)

Pressure

99877102

9987861 times 10minus4000400801201602

(120583m

)

1MPa08MPa06MPa04MPa02MPa0MPa(d)

PyramidCylinder

CuboidFlat panel

00

02

04

06

08

10

Capa

cita

nce d

iffer

ence

(fF)

02 04 06 08 10 1200Pressure (MPa)

(e)

Kr

Kr

Flat panel Cuboids Cylinders

times10minus7

times10minus7

K(fF

Pa)

K(fF

Pa)

00

20

40

60

0000

0002

0004

0006

0008

0010

r (

)

Cuboids Cylinders PyramidsFlat panelMicrostructures

00

10

0000

0005

r (

)

(f)

Figure 3The pressure responses of the CPS with different microstructuresThe deformations of the CPS were shown as (a) the flat panel (b)the cuboids (c) the cylinders and (d) the pyramids In the same model the top part is the surface deformation of the CPS the bottom partis the partial detailed view of the microstructure (e) The capacitance-pressure characteristics of the sensors with different microstructures(f) The sensitivity and nonlinear error of the sensors with different microstructures

Journal of Sensors 5

99877103

998786161 times 10minus4000501015

02502

(120583m

)

12120583m11120583m10120583m

7 0711120583m

9120583m8120583m

(a)

L = 12120583mL = 11120583m

L = 10120583mL = 9120583mL = 8120583m

00

02

04

06

08

10

Capa

cita

nce d

iffer

ence

(fF)

02 04 06 08 10 1200Pressure (MPa)

(b)

Kr

000

001

002

003

r (

)

9 10 11 128L (120583m)

times10minus7

00

40

80

K (fF

Pa)

(c)

Figure 4The pressure responses of the CPS with different lengths of hemline of pyramids (a)The profile structures of sensors with differentlengths of hemline of pyramid from 8 120583m to 12 120583m and the same height 70711 120583m at 1MPa (b) The comparison of capacitance-pressurecharacteristics of the sensors with different lengths (c) The sensitivity and nonlinear error of the sensors with different lengths

Table 2 Sensitivity and nonlinear error of the CPS with differenthemline lengths of pyramids

Length ofhemline 119871 (120583m) Sensitivity 119870 (fFPa) Nonlinear error 119903

8 881355E minus 7 00176219 735721E minus 7 001206810 629792E minus 7 000803411 548525E minus 7 000527112 485630E minus 7 0004066

Figure 4(b) and the sensitivities and the nonlinear errors ofCPS were shown in Figure 4(c) and Table 2

From Table 2 both the sensitivity and the nonlinear errordecrease with the increasing 119871 When hemline length 119871 andheights 119867 are 8120583m and 707 120583m the sensor has the bestsensitivity of 881 times 10minus7 fFPa In this case in order to

obtain greater sensitivity we hope the hemline length is assmall as possible In other words the smaller the ratios of119871119867 of pyramid the better the sensitivity of the CPS Butits nonlinear error would reach 0018 As the change ofratios of 119871119867 we should balance the sensitivity of CPS fore-skin against the nonlinearity error to effectively tune theperformance of CPS through choosing different parametersaccording to the required demands

In analogy with the research between the pyramidsrsquolengths of hemline and the sensorrsquos performance we have alsomade a series of simulations about the pyramidsrsquo heights Inthe simulation the height changes from5120583mto9120583mwith thesame length of hemline (119871 = 10 120583m) the schematic diagramis shown in Figure 5(a)

From this schematic diagram all the models have thesame distance between the two electrodes when the heightof pyramids changes the bottom of the pyramid will befilled with dielectric material Likewise the outside pressurechanges from 0 to 1MPa too the pressure responses of

6 Journal of Sensors

99877104

998786174 times 10minus4

00501015

0350302502

(120583m

)

6120583m 7120583m 9120583m8120583m5120583m

10120583m

(a)

00

02

04

06

08

Capa

cita

nce d

iffer

ence

(fF)

02 04 06 08 10 1200Pressure (MPa)

6120583m7120583m

9120583m8120583m

H =H =H = H =

H =5120583m

(b)

000

001

002

003

r (

)

6 7 8 95

Kr

H (120583m)

times10minus7

00

40

80

K (fF

Pa)

(c)

Figure 5 The pressure responses of the CPS with different heights of pyramids (a) The profile structures of sensors with different heights ofpyramid from 5120583m to 9120583m and the same lengths of hemline 10 120583m at 1MPa (b)The comparison of capacitance-pressure characteristics ofthe sensors with different heights (c) The sensitivity and nonlinear error of the sensors with different heights

the sensor are obtained and the capacitance-pressure curvesof sensors are shown in Figure 5(b) The sensitivity and thelinearity of sensors are shown in Figure 5(c) and Table 3

From Figure 5 and Table 3 it is easy to find that thesensitivity increases with the height increases from 5 120583m to9 120583m but the linearity is decreased In the simulation ofthis series when the length of hemline of pyramid is 10 120583mand the height of pyramid is 9 120583m the sensor has the bestsensitivity that is 700589119864minus7 fFPa In this case in order toobtain the greater sensitivity we hope the height of pyramidis as large as possible In other words in order to obtain thegreater sensitivity we expect that the length of hemline ofpyramid is more thanradic2 times the height

From what has been discussed above it is obvious thatthe performance of the sensor is affected by the length ofhemline and the height simultaneously Considering thesetwo contradictory parameters a compromise method isproposed to obtain the optimal performance of the sensor

Table 3 Sensitivity and nonlinear error of the CPS with differentheights of pyramids

Height119867 (120583m) Sensitivity 119870 (fFPa) Nonlinear error 1199035 398334E minus 7 00051116 404683E minus 7 00051357 409844E minus 7 00053848 412467E minus 7 00060559 700589E minus 7 0022813

if the medians of 119871 and 119867 are selected at this point boththe sensitivity and linearity have good values Through theanalysis of the relationship between 119871 and 119867 the authorcomes to the conclusion that in order tomake the sensor havebetter performance the ratios of 119871119867 should beradic2

Journal of Sensors 7

4 Conclusions

In this paper we employ the traditional COMSOL Mul-tiphysics models based on finite element analysis methodto construct four different microstructures (flat panelcuboids cylinders and pyramids) CPS for the detailed studyof microstructure interfacial tuning mechanism betweenhuman skin and PVDF The simulative results show thatCPS with micropyramids structures has the best measuringsensitivity K (= 63 times 10minus7 fFPa) which is about 49 timeshigher than that without any microstructure Through thesimulation of pyramids with different ratios of 119871119867 theresults show that the smaller the ratios of 119871119867 of pyramidthe better the sensitivity but the nonlinear error will increaseWhen the ratio of 119871119867 of pyramid is aboutradic2 the sensitivityand the linearity could reach a balance pointThismethod canbe used as theoretical guidance for the e-skin processing

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the National University StudentInnovation Program (201510613009) of China SichuanProvince Science and Technology Plan Project (no2015JQ0013) and the Fundamental Research Funds forthe Central Universities (A0920502051408-10)

References

[1] M L Hammock A Chortos B C-K Tee J B-H Tok andZ Bao ldquo25th Anniversary article the evolution of electronicskin (E-Skin) a brief history design considerations and recentprogressrdquo Advanced Materials vol 25 no 42 pp 5997ndash60382013

[2] T W Tombler C Zhou L Alexseyev et al ldquoReversible elec-tromechanical characteristics of carbon nanotubes under local-probe manipulationrdquo Nature vol 405 no 6788 pp 769ndash7722000

[3] B Zhu Z Niu H Wang et al ldquoMicrostructured graphenearrays for highly sensitive flexible tactile sensorsrdquo Small vol 10no 18 pp 3625ndash3631 2014

[4] D J Cohen D Mitra K Peterson and M M MaharbizldquoA highly elastic capacitive strain gauge based on percolatingnanotube networksrdquo Nano Letters vol 12 no 4 pp 1821ndash18252012

[5] S C BMannsfeld B C-K Tee RM Stoltenberg et al ldquoHighlysensitive flexible pressure sensors with microstructured rubberdielectric layersrdquo Nature Materials vol 9 no 10 pp 859ndash8642010

[6] W Zhang and R-G Xiong ldquoFerroelectricmetal-organic frame-worksrdquo Chemical Reviews vol 112 no 2 pp 1163ndash1195 2012

[7] L Persano C Dagdeviren Y Su et al ldquoHigh performancepiezoelectric devices based on aligned arrays of nanofibersof poly(vinylidenefluoride-co-trifluoroethylene)rdquo Nature Com-munications vol 4 article 1633 2013

[8] M Ramuz B C-K Tee J B-H Tok and Z Bao ldquoTransparentoptical pressure-sensitive artificial skin for large-area stretch-able electronicsrdquo Advanced Materials vol 24 no 24 pp 3223ndash3227 2012

[9] R Koeppe P Bartu S Bauer and N S Saricifici ldquoLight-and touch-point localization using flexible large area organicphotodiodes and elastomer waveguidesrdquo Advanced Materialsvol 21 no 34 pp 3510ndash3514 2009

[10] R Puers ldquoCapacitive sensors when and how to use themrdquoSensors and Actuators A Physical vol 37-38 pp 93ndash105 1993

[11] J A Dobrzynska and M A M Gijs ldquoFlexible polyimide-basedforce sensorrdquo Sensors and Actuators A Physical vol 173 no 1pp 127ndash135 2012

[12] H BMuhammad C Recchiuto CMOddo et al ldquoA capacitivetactile sensor array for surface texture discriminationrdquo Micro-electronic Engineering vol 88 no 8 pp 1811ndash1813 2011

[13] C S Sander J W Knutti and J D Meindl ldquoA monolithiccapacitive pressure sensor with pulse-period outputrdquo IEEETransactions on Electron Devices vol 27 no 5 pp 927ndash9301980

[14] H-L Chau and K DWise ldquoAn ultraminiature solid-state pres-sure sensor for a cardiovascular catheterrdquo IEEE Transactions onElectron Devices vol 35 no 12 pp 2355ndash2362 1988

[15] S S Kumar and B D Pant ldquoPolysilicon thin film piezoresistivepressuremicrosensor design fabrication and characterizationrdquoMicrosystem Technologies vol 21 no 9 pp 1949ndash1958 2015

[16] K Takahata Y B Gianchandani and K D Wise ldquoMicroma-chined antenna stents and cuffs for monitoring intraluminalpressure and flowrdquo Journal of Microelectromechanical Systemsvol 15 no 5 pp 1289ndash1298 2006

[17] T G S M Rijks P G Steeneken J T M van Beek et alldquoMicroelectromechanical tunable capacitors for reconfigurableRF architecturesrdquo Journal of Micromechanics and Microengi-neering vol 16 no 3 pp 601ndash611 2006

[18] K I Arshak DMorris A Arshak O Korostynska and E JaferldquoDevelopment of a wireless pressuremeasurement systemusinginterdigitated capacitorsrdquo IEEE Sensors Journal vol 7 no 1 pp122ndash129 2007

[19] J Ji S T Cho Y Zhang K Najafi and K D Wise ldquoAnultraminiature CMOS pressure sensor for amultiplexed cardio-vascular catheterrdquo IEEE Transactions on Electron Devices vol39 no 10 pp 2260ndash2267 1992

[20] H Tian Y Shu X Wang et al ldquoA graphene-based resistivepressure sensor with record-high sensitivity in a wide pressurerangerdquo Scientific Reports vol 5 article 8603 pp 1ndash6 2015

[21] C Tao Z Zhaohua R Tianling et al ldquoA novel dual-functionalMEMS sensor integrating both pressure and temperature unitsrdquoJournal of Semiconductors vol 31 no 7 Article ID 074013 2010

[22] X Huang and D Zhang ldquoA high sensitivity and high linearitypressure sensor based on a peninsula-structured diaphragm forlow-pressure rangesrdquo Sensors andActuators A Physical vol 216pp 176ndash189 2014

[23] N J Madduri G Lakkoju B L Kasturi S Sravanam andT Satyanarayana ldquoDesign and deformation analysis of MEMSbased piezoresistive pressure sensorrdquo International Journal ofAutomotive Engineering and Technologies vol 7 pp 521ndash5312014

[24] B A Ganji and M Shahiri-Tabarestani ldquoA novel high sensitiveMEMS intraocular capacitive pressure sensorrdquo MicrosystemTechnologies vol 19 no 2 pp 187ndash194 2013

8 Journal of Sensors

[25] K Hosoda Y Tada and M Asada ldquoAnthropomorphic roboticsoftfingertipwith randomly distributed receptorsrdquoRobotics andAutonomous Systems vol 54 no 2 pp 104ndash109 2006

[26] J CHelton J D JohnsonC J Sallaberry andC B Storlie ldquoSur-vey of sampling-based methods for uncertainty and sensitivityanalysisrdquo Reliability Engineering and System Safety vol 91 no10-11 pp 1175ndash1209 2006

[27] J Y ZhaoDetection and Sensing Technology Southwest JiaotongUniversity Press Chengdu China 2007

[28] L Lin H-C Chu and Y-W Lu ldquoSimulation program forthe sensitivity and linearity of piezoresistive pressure sensorsrdquoJournal of Microelectromechanical Systems vol 8 no 4 pp 514ndash522 1999

International Journal of

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Control Scienceand Engineering

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RotatingMachinery

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Submit your manuscripts athttpwwwhindawicom

VLSI Design

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Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

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Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Page 3: Research Article Microstructure-Based Interfacial …downloads.hindawi.com/journals/js/2016/2428305.pdfResearch Article Microstructure-Based Interfacial Tuning Mechanism of Capacitive

Journal of Sensors 3

4 35

3 25

2 15

1 05

0

(120583m)

998771002

998786 142times10minus5

(a)

0

(120583m)

998771007

998786 866times10minus5

006

005

004

003

002

001

(b)

998771006

times10minus4

0

(120583m)006

007

005

004

003

002

001

998786 133

(c)

02

018

016

014

012

01

008

006

004

002

0

(120583m)

99877102

times10minus4

998786 392

(d)

Figure 2 Different profile structures of the CPS (a)The flat panel (b) the cuboids (c) the cylinders and (d) the pyramidsThe 3D diagramsof the CPS the cross-sectional view of sensors the vertical view of the functional layer of the sensor and the deformations of the functionallayer are listed in the figure from top to bottom

Table 1 Sensitivity and nonlinear error of the CPS with differentmicrostructures

Structure Sensitivity119870 (fFPa) Nonlinear error 119903Flat panel 128273E minus 8 0001646Cuboids 805555E minus 8 0000681Cylinders 100342E minus 7 0000476Pyramids 629792E minus 7 0008034

of CPS evidently show that the sensitivity 119870 of the CPSwith microstructures should be better than that without anymicrostructure and that of pyramids-based CPS is obviouslythe best one among four microstructures Furthermore thedetailed characteristic analyses of the above four structureswithin the ambient pressure range of 0sim1MPa through thefinite element software COMSOL Multiphysics are shown inFigure 3

Figures 3(a)ndash3(d) represent the obvious deformation ofthe CPSwith the increasing pressureThe central areas of CPShave the largest deformation in each model The capacitancepressure characteristic curves of all the models are shownin Figure 3(e) The comparisons of the sensorsrsquo sensitivity119870 and nonlinear error 119903 between different microstructuresare shown in Figure 3(f) and Table 1 showing the sensitiv-ities of pyramids-based and flat panel pressure sensors are

63 times 10minus7 and 128 times 10minus8 fFPa respectively That is theformer is about 49 times higher than the latter evidentlyrevealing the excellent capacity for microstructure-controlof middle dielectric layer to tune the sensitivity of CPSFrom Figure 3(f) the nonlinear error 119903 of pyramids is greaterthan that of other models but still less than 1 evidentlyshowing the designed CPS has very good linearityThis resultis consistent with the discussion of the literature [26] Thiscan be explained by considering the stress distribution ofthe different geometrical shapes In a flat panel structure thestress distribution is fairly constant throughout the heightof the panel to the force contact area However when theshape changes from the flat panel to cuboids cylindersand pyramids the stress distribution is nonuniform and isconcentrated at the pointed tips due to the smaller contactarea rather than the broad bases of the structures Thusthe pyramid tips compress more resulting in the highermechanical deformations at the top Therefore the pyramidsshapes are more sensitive

In order to further study the performance of sensor dec-orated with pyramids a series of simulations were performedwith different 119871 of pyramids the sketches and simulationresults of the models are shown in Figure 4

In the simulation 119871 changes from 8 120583m to 12 120583m withconstant height (119867 = 707 120583m)The pressure responses of theCPS with different hemline lengths of pyramids are shown in

4 Journal of Sensors

998771002

998786 142 times 10minus5

times10minus2

004081216

(120583m

)

(a)

998771007

998786 696 times 10minus60001002003004005006

(120583m

)

(b)

998771006

998786 324 times 10minus60001002003004005

(120583m

)

(c)

Pressure

99877102

9987861 times 10minus4000400801201602

(120583m

)

1MPa08MPa06MPa04MPa02MPa0MPa(d)

PyramidCylinder

CuboidFlat panel

00

02

04

06

08

10

Capa

cita

nce d

iffer

ence

(fF)

02 04 06 08 10 1200Pressure (MPa)

(e)

Kr

Kr

Flat panel Cuboids Cylinders

times10minus7

times10minus7

K(fF

Pa)

K(fF

Pa)

00

20

40

60

0000

0002

0004

0006

0008

0010

r (

)

Cuboids Cylinders PyramidsFlat panelMicrostructures

00

10

0000

0005

r (

)

(f)

Figure 3The pressure responses of the CPS with different microstructuresThe deformations of the CPS were shown as (a) the flat panel (b)the cuboids (c) the cylinders and (d) the pyramids In the same model the top part is the surface deformation of the CPS the bottom partis the partial detailed view of the microstructure (e) The capacitance-pressure characteristics of the sensors with different microstructures(f) The sensitivity and nonlinear error of the sensors with different microstructures

Journal of Sensors 5

99877103

998786161 times 10minus4000501015

02502

(120583m

)

12120583m11120583m10120583m

7 0711120583m

9120583m8120583m

(a)

L = 12120583mL = 11120583m

L = 10120583mL = 9120583mL = 8120583m

00

02

04

06

08

10

Capa

cita

nce d

iffer

ence

(fF)

02 04 06 08 10 1200Pressure (MPa)

(b)

Kr

000

001

002

003

r (

)

9 10 11 128L (120583m)

times10minus7

00

40

80

K (fF

Pa)

(c)

Figure 4The pressure responses of the CPS with different lengths of hemline of pyramids (a)The profile structures of sensors with differentlengths of hemline of pyramid from 8 120583m to 12 120583m and the same height 70711 120583m at 1MPa (b) The comparison of capacitance-pressurecharacteristics of the sensors with different lengths (c) The sensitivity and nonlinear error of the sensors with different lengths

Table 2 Sensitivity and nonlinear error of the CPS with differenthemline lengths of pyramids

Length ofhemline 119871 (120583m) Sensitivity 119870 (fFPa) Nonlinear error 119903

8 881355E minus 7 00176219 735721E minus 7 001206810 629792E minus 7 000803411 548525E minus 7 000527112 485630E minus 7 0004066

Figure 4(b) and the sensitivities and the nonlinear errors ofCPS were shown in Figure 4(c) and Table 2

From Table 2 both the sensitivity and the nonlinear errordecrease with the increasing 119871 When hemline length 119871 andheights 119867 are 8120583m and 707 120583m the sensor has the bestsensitivity of 881 times 10minus7 fFPa In this case in order to

obtain greater sensitivity we hope the hemline length is assmall as possible In other words the smaller the ratios of119871119867 of pyramid the better the sensitivity of the CPS Butits nonlinear error would reach 0018 As the change ofratios of 119871119867 we should balance the sensitivity of CPS fore-skin against the nonlinearity error to effectively tune theperformance of CPS through choosing different parametersaccording to the required demands

In analogy with the research between the pyramidsrsquolengths of hemline and the sensorrsquos performance we have alsomade a series of simulations about the pyramidsrsquo heights Inthe simulation the height changes from5120583mto9120583mwith thesame length of hemline (119871 = 10 120583m) the schematic diagramis shown in Figure 5(a)

From this schematic diagram all the models have thesame distance between the two electrodes when the heightof pyramids changes the bottom of the pyramid will befilled with dielectric material Likewise the outside pressurechanges from 0 to 1MPa too the pressure responses of

6 Journal of Sensors

99877104

998786174 times 10minus4

00501015

0350302502

(120583m

)

6120583m 7120583m 9120583m8120583m5120583m

10120583m

(a)

00

02

04

06

08

Capa

cita

nce d

iffer

ence

(fF)

02 04 06 08 10 1200Pressure (MPa)

6120583m7120583m

9120583m8120583m

H =H =H = H =

H =5120583m

(b)

000

001

002

003

r (

)

6 7 8 95

Kr

H (120583m)

times10minus7

00

40

80

K (fF

Pa)

(c)

Figure 5 The pressure responses of the CPS with different heights of pyramids (a) The profile structures of sensors with different heights ofpyramid from 5120583m to 9120583m and the same lengths of hemline 10 120583m at 1MPa (b)The comparison of capacitance-pressure characteristics ofthe sensors with different heights (c) The sensitivity and nonlinear error of the sensors with different heights

the sensor are obtained and the capacitance-pressure curvesof sensors are shown in Figure 5(b) The sensitivity and thelinearity of sensors are shown in Figure 5(c) and Table 3

From Figure 5 and Table 3 it is easy to find that thesensitivity increases with the height increases from 5 120583m to9 120583m but the linearity is decreased In the simulation ofthis series when the length of hemline of pyramid is 10 120583mand the height of pyramid is 9 120583m the sensor has the bestsensitivity that is 700589119864minus7 fFPa In this case in order toobtain the greater sensitivity we hope the height of pyramidis as large as possible In other words in order to obtain thegreater sensitivity we expect that the length of hemline ofpyramid is more thanradic2 times the height

From what has been discussed above it is obvious thatthe performance of the sensor is affected by the length ofhemline and the height simultaneously Considering thesetwo contradictory parameters a compromise method isproposed to obtain the optimal performance of the sensor

Table 3 Sensitivity and nonlinear error of the CPS with differentheights of pyramids

Height119867 (120583m) Sensitivity 119870 (fFPa) Nonlinear error 1199035 398334E minus 7 00051116 404683E minus 7 00051357 409844E minus 7 00053848 412467E minus 7 00060559 700589E minus 7 0022813

if the medians of 119871 and 119867 are selected at this point boththe sensitivity and linearity have good values Through theanalysis of the relationship between 119871 and 119867 the authorcomes to the conclusion that in order tomake the sensor havebetter performance the ratios of 119871119867 should beradic2

Journal of Sensors 7

4 Conclusions

In this paper we employ the traditional COMSOL Mul-tiphysics models based on finite element analysis methodto construct four different microstructures (flat panelcuboids cylinders and pyramids) CPS for the detailed studyof microstructure interfacial tuning mechanism betweenhuman skin and PVDF The simulative results show thatCPS with micropyramids structures has the best measuringsensitivity K (= 63 times 10minus7 fFPa) which is about 49 timeshigher than that without any microstructure Through thesimulation of pyramids with different ratios of 119871119867 theresults show that the smaller the ratios of 119871119867 of pyramidthe better the sensitivity but the nonlinear error will increaseWhen the ratio of 119871119867 of pyramid is aboutradic2 the sensitivityand the linearity could reach a balance pointThismethod canbe used as theoretical guidance for the e-skin processing

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the National University StudentInnovation Program (201510613009) of China SichuanProvince Science and Technology Plan Project (no2015JQ0013) and the Fundamental Research Funds forthe Central Universities (A0920502051408-10)

References

[1] M L Hammock A Chortos B C-K Tee J B-H Tok andZ Bao ldquo25th Anniversary article the evolution of electronicskin (E-Skin) a brief history design considerations and recentprogressrdquo Advanced Materials vol 25 no 42 pp 5997ndash60382013

[2] T W Tombler C Zhou L Alexseyev et al ldquoReversible elec-tromechanical characteristics of carbon nanotubes under local-probe manipulationrdquo Nature vol 405 no 6788 pp 769ndash7722000

[3] B Zhu Z Niu H Wang et al ldquoMicrostructured graphenearrays for highly sensitive flexible tactile sensorsrdquo Small vol 10no 18 pp 3625ndash3631 2014

[4] D J Cohen D Mitra K Peterson and M M MaharbizldquoA highly elastic capacitive strain gauge based on percolatingnanotube networksrdquo Nano Letters vol 12 no 4 pp 1821ndash18252012

[5] S C BMannsfeld B C-K Tee RM Stoltenberg et al ldquoHighlysensitive flexible pressure sensors with microstructured rubberdielectric layersrdquo Nature Materials vol 9 no 10 pp 859ndash8642010

[6] W Zhang and R-G Xiong ldquoFerroelectricmetal-organic frame-worksrdquo Chemical Reviews vol 112 no 2 pp 1163ndash1195 2012

[7] L Persano C Dagdeviren Y Su et al ldquoHigh performancepiezoelectric devices based on aligned arrays of nanofibersof poly(vinylidenefluoride-co-trifluoroethylene)rdquo Nature Com-munications vol 4 article 1633 2013

[8] M Ramuz B C-K Tee J B-H Tok and Z Bao ldquoTransparentoptical pressure-sensitive artificial skin for large-area stretch-able electronicsrdquo Advanced Materials vol 24 no 24 pp 3223ndash3227 2012

[9] R Koeppe P Bartu S Bauer and N S Saricifici ldquoLight-and touch-point localization using flexible large area organicphotodiodes and elastomer waveguidesrdquo Advanced Materialsvol 21 no 34 pp 3510ndash3514 2009

[10] R Puers ldquoCapacitive sensors when and how to use themrdquoSensors and Actuators A Physical vol 37-38 pp 93ndash105 1993

[11] J A Dobrzynska and M A M Gijs ldquoFlexible polyimide-basedforce sensorrdquo Sensors and Actuators A Physical vol 173 no 1pp 127ndash135 2012

[12] H BMuhammad C Recchiuto CMOddo et al ldquoA capacitivetactile sensor array for surface texture discriminationrdquo Micro-electronic Engineering vol 88 no 8 pp 1811ndash1813 2011

[13] C S Sander J W Knutti and J D Meindl ldquoA monolithiccapacitive pressure sensor with pulse-period outputrdquo IEEETransactions on Electron Devices vol 27 no 5 pp 927ndash9301980

[14] H-L Chau and K DWise ldquoAn ultraminiature solid-state pres-sure sensor for a cardiovascular catheterrdquo IEEE Transactions onElectron Devices vol 35 no 12 pp 2355ndash2362 1988

[15] S S Kumar and B D Pant ldquoPolysilicon thin film piezoresistivepressuremicrosensor design fabrication and characterizationrdquoMicrosystem Technologies vol 21 no 9 pp 1949ndash1958 2015

[16] K Takahata Y B Gianchandani and K D Wise ldquoMicroma-chined antenna stents and cuffs for monitoring intraluminalpressure and flowrdquo Journal of Microelectromechanical Systemsvol 15 no 5 pp 1289ndash1298 2006

[17] T G S M Rijks P G Steeneken J T M van Beek et alldquoMicroelectromechanical tunable capacitors for reconfigurableRF architecturesrdquo Journal of Micromechanics and Microengi-neering vol 16 no 3 pp 601ndash611 2006

[18] K I Arshak DMorris A Arshak O Korostynska and E JaferldquoDevelopment of a wireless pressuremeasurement systemusinginterdigitated capacitorsrdquo IEEE Sensors Journal vol 7 no 1 pp122ndash129 2007

[19] J Ji S T Cho Y Zhang K Najafi and K D Wise ldquoAnultraminiature CMOS pressure sensor for amultiplexed cardio-vascular catheterrdquo IEEE Transactions on Electron Devices vol39 no 10 pp 2260ndash2267 1992

[20] H Tian Y Shu X Wang et al ldquoA graphene-based resistivepressure sensor with record-high sensitivity in a wide pressurerangerdquo Scientific Reports vol 5 article 8603 pp 1ndash6 2015

[21] C Tao Z Zhaohua R Tianling et al ldquoA novel dual-functionalMEMS sensor integrating both pressure and temperature unitsrdquoJournal of Semiconductors vol 31 no 7 Article ID 074013 2010

[22] X Huang and D Zhang ldquoA high sensitivity and high linearitypressure sensor based on a peninsula-structured diaphragm forlow-pressure rangesrdquo Sensors andActuators A Physical vol 216pp 176ndash189 2014

[23] N J Madduri G Lakkoju B L Kasturi S Sravanam andT Satyanarayana ldquoDesign and deformation analysis of MEMSbased piezoresistive pressure sensorrdquo International Journal ofAutomotive Engineering and Technologies vol 7 pp 521ndash5312014

[24] B A Ganji and M Shahiri-Tabarestani ldquoA novel high sensitiveMEMS intraocular capacitive pressure sensorrdquo MicrosystemTechnologies vol 19 no 2 pp 187ndash194 2013

8 Journal of Sensors

[25] K Hosoda Y Tada and M Asada ldquoAnthropomorphic roboticsoftfingertipwith randomly distributed receptorsrdquoRobotics andAutonomous Systems vol 54 no 2 pp 104ndash109 2006

[26] J CHelton J D JohnsonC J Sallaberry andC B Storlie ldquoSur-vey of sampling-based methods for uncertainty and sensitivityanalysisrdquo Reliability Engineering and System Safety vol 91 no10-11 pp 1175ndash1209 2006

[27] J Y ZhaoDetection and Sensing Technology Southwest JiaotongUniversity Press Chengdu China 2007

[28] L Lin H-C Chu and Y-W Lu ldquoSimulation program forthe sensitivity and linearity of piezoresistive pressure sensorsrdquoJournal of Microelectromechanical Systems vol 8 no 4 pp 514ndash522 1999

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Page 4: Research Article Microstructure-Based Interfacial …downloads.hindawi.com/journals/js/2016/2428305.pdfResearch Article Microstructure-Based Interfacial Tuning Mechanism of Capacitive

4 Journal of Sensors

998771002

998786 142 times 10minus5

times10minus2

004081216

(120583m

)

(a)

998771007

998786 696 times 10minus60001002003004005006

(120583m

)

(b)

998771006

998786 324 times 10minus60001002003004005

(120583m

)

(c)

Pressure

99877102

9987861 times 10minus4000400801201602

(120583m

)

1MPa08MPa06MPa04MPa02MPa0MPa(d)

PyramidCylinder

CuboidFlat panel

00

02

04

06

08

10

Capa

cita

nce d

iffer

ence

(fF)

02 04 06 08 10 1200Pressure (MPa)

(e)

Kr

Kr

Flat panel Cuboids Cylinders

times10minus7

times10minus7

K(fF

Pa)

K(fF

Pa)

00

20

40

60

0000

0002

0004

0006

0008

0010

r (

)

Cuboids Cylinders PyramidsFlat panelMicrostructures

00

10

0000

0005

r (

)

(f)

Figure 3The pressure responses of the CPS with different microstructuresThe deformations of the CPS were shown as (a) the flat panel (b)the cuboids (c) the cylinders and (d) the pyramids In the same model the top part is the surface deformation of the CPS the bottom partis the partial detailed view of the microstructure (e) The capacitance-pressure characteristics of the sensors with different microstructures(f) The sensitivity and nonlinear error of the sensors with different microstructures

Journal of Sensors 5

99877103

998786161 times 10minus4000501015

02502

(120583m

)

12120583m11120583m10120583m

7 0711120583m

9120583m8120583m

(a)

L = 12120583mL = 11120583m

L = 10120583mL = 9120583mL = 8120583m

00

02

04

06

08

10

Capa

cita

nce d

iffer

ence

(fF)

02 04 06 08 10 1200Pressure (MPa)

(b)

Kr

000

001

002

003

r (

)

9 10 11 128L (120583m)

times10minus7

00

40

80

K (fF

Pa)

(c)

Figure 4The pressure responses of the CPS with different lengths of hemline of pyramids (a)The profile structures of sensors with differentlengths of hemline of pyramid from 8 120583m to 12 120583m and the same height 70711 120583m at 1MPa (b) The comparison of capacitance-pressurecharacteristics of the sensors with different lengths (c) The sensitivity and nonlinear error of the sensors with different lengths

Table 2 Sensitivity and nonlinear error of the CPS with differenthemline lengths of pyramids

Length ofhemline 119871 (120583m) Sensitivity 119870 (fFPa) Nonlinear error 119903

8 881355E minus 7 00176219 735721E minus 7 001206810 629792E minus 7 000803411 548525E minus 7 000527112 485630E minus 7 0004066

Figure 4(b) and the sensitivities and the nonlinear errors ofCPS were shown in Figure 4(c) and Table 2

From Table 2 both the sensitivity and the nonlinear errordecrease with the increasing 119871 When hemline length 119871 andheights 119867 are 8120583m and 707 120583m the sensor has the bestsensitivity of 881 times 10minus7 fFPa In this case in order to

obtain greater sensitivity we hope the hemline length is assmall as possible In other words the smaller the ratios of119871119867 of pyramid the better the sensitivity of the CPS Butits nonlinear error would reach 0018 As the change ofratios of 119871119867 we should balance the sensitivity of CPS fore-skin against the nonlinearity error to effectively tune theperformance of CPS through choosing different parametersaccording to the required demands

In analogy with the research between the pyramidsrsquolengths of hemline and the sensorrsquos performance we have alsomade a series of simulations about the pyramidsrsquo heights Inthe simulation the height changes from5120583mto9120583mwith thesame length of hemline (119871 = 10 120583m) the schematic diagramis shown in Figure 5(a)

From this schematic diagram all the models have thesame distance between the two electrodes when the heightof pyramids changes the bottom of the pyramid will befilled with dielectric material Likewise the outside pressurechanges from 0 to 1MPa too the pressure responses of

6 Journal of Sensors

99877104

998786174 times 10minus4

00501015

0350302502

(120583m

)

6120583m 7120583m 9120583m8120583m5120583m

10120583m

(a)

00

02

04

06

08

Capa

cita

nce d

iffer

ence

(fF)

02 04 06 08 10 1200Pressure (MPa)

6120583m7120583m

9120583m8120583m

H =H =H = H =

H =5120583m

(b)

000

001

002

003

r (

)

6 7 8 95

Kr

H (120583m)

times10minus7

00

40

80

K (fF

Pa)

(c)

Figure 5 The pressure responses of the CPS with different heights of pyramids (a) The profile structures of sensors with different heights ofpyramid from 5120583m to 9120583m and the same lengths of hemline 10 120583m at 1MPa (b)The comparison of capacitance-pressure characteristics ofthe sensors with different heights (c) The sensitivity and nonlinear error of the sensors with different heights

the sensor are obtained and the capacitance-pressure curvesof sensors are shown in Figure 5(b) The sensitivity and thelinearity of sensors are shown in Figure 5(c) and Table 3

From Figure 5 and Table 3 it is easy to find that thesensitivity increases with the height increases from 5 120583m to9 120583m but the linearity is decreased In the simulation ofthis series when the length of hemline of pyramid is 10 120583mand the height of pyramid is 9 120583m the sensor has the bestsensitivity that is 700589119864minus7 fFPa In this case in order toobtain the greater sensitivity we hope the height of pyramidis as large as possible In other words in order to obtain thegreater sensitivity we expect that the length of hemline ofpyramid is more thanradic2 times the height

From what has been discussed above it is obvious thatthe performance of the sensor is affected by the length ofhemline and the height simultaneously Considering thesetwo contradictory parameters a compromise method isproposed to obtain the optimal performance of the sensor

Table 3 Sensitivity and nonlinear error of the CPS with differentheights of pyramids

Height119867 (120583m) Sensitivity 119870 (fFPa) Nonlinear error 1199035 398334E minus 7 00051116 404683E minus 7 00051357 409844E minus 7 00053848 412467E minus 7 00060559 700589E minus 7 0022813

if the medians of 119871 and 119867 are selected at this point boththe sensitivity and linearity have good values Through theanalysis of the relationship between 119871 and 119867 the authorcomes to the conclusion that in order tomake the sensor havebetter performance the ratios of 119871119867 should beradic2

Journal of Sensors 7

4 Conclusions

In this paper we employ the traditional COMSOL Mul-tiphysics models based on finite element analysis methodto construct four different microstructures (flat panelcuboids cylinders and pyramids) CPS for the detailed studyof microstructure interfacial tuning mechanism betweenhuman skin and PVDF The simulative results show thatCPS with micropyramids structures has the best measuringsensitivity K (= 63 times 10minus7 fFPa) which is about 49 timeshigher than that without any microstructure Through thesimulation of pyramids with different ratios of 119871119867 theresults show that the smaller the ratios of 119871119867 of pyramidthe better the sensitivity but the nonlinear error will increaseWhen the ratio of 119871119867 of pyramid is aboutradic2 the sensitivityand the linearity could reach a balance pointThismethod canbe used as theoretical guidance for the e-skin processing

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the National University StudentInnovation Program (201510613009) of China SichuanProvince Science and Technology Plan Project (no2015JQ0013) and the Fundamental Research Funds forthe Central Universities (A0920502051408-10)

References

[1] M L Hammock A Chortos B C-K Tee J B-H Tok andZ Bao ldquo25th Anniversary article the evolution of electronicskin (E-Skin) a brief history design considerations and recentprogressrdquo Advanced Materials vol 25 no 42 pp 5997ndash60382013

[2] T W Tombler C Zhou L Alexseyev et al ldquoReversible elec-tromechanical characteristics of carbon nanotubes under local-probe manipulationrdquo Nature vol 405 no 6788 pp 769ndash7722000

[3] B Zhu Z Niu H Wang et al ldquoMicrostructured graphenearrays for highly sensitive flexible tactile sensorsrdquo Small vol 10no 18 pp 3625ndash3631 2014

[4] D J Cohen D Mitra K Peterson and M M MaharbizldquoA highly elastic capacitive strain gauge based on percolatingnanotube networksrdquo Nano Letters vol 12 no 4 pp 1821ndash18252012

[5] S C BMannsfeld B C-K Tee RM Stoltenberg et al ldquoHighlysensitive flexible pressure sensors with microstructured rubberdielectric layersrdquo Nature Materials vol 9 no 10 pp 859ndash8642010

[6] W Zhang and R-G Xiong ldquoFerroelectricmetal-organic frame-worksrdquo Chemical Reviews vol 112 no 2 pp 1163ndash1195 2012

[7] L Persano C Dagdeviren Y Su et al ldquoHigh performancepiezoelectric devices based on aligned arrays of nanofibersof poly(vinylidenefluoride-co-trifluoroethylene)rdquo Nature Com-munications vol 4 article 1633 2013

[8] M Ramuz B C-K Tee J B-H Tok and Z Bao ldquoTransparentoptical pressure-sensitive artificial skin for large-area stretch-able electronicsrdquo Advanced Materials vol 24 no 24 pp 3223ndash3227 2012

[9] R Koeppe P Bartu S Bauer and N S Saricifici ldquoLight-and touch-point localization using flexible large area organicphotodiodes and elastomer waveguidesrdquo Advanced Materialsvol 21 no 34 pp 3510ndash3514 2009

[10] R Puers ldquoCapacitive sensors when and how to use themrdquoSensors and Actuators A Physical vol 37-38 pp 93ndash105 1993

[11] J A Dobrzynska and M A M Gijs ldquoFlexible polyimide-basedforce sensorrdquo Sensors and Actuators A Physical vol 173 no 1pp 127ndash135 2012

[12] H BMuhammad C Recchiuto CMOddo et al ldquoA capacitivetactile sensor array for surface texture discriminationrdquo Micro-electronic Engineering vol 88 no 8 pp 1811ndash1813 2011

[13] C S Sander J W Knutti and J D Meindl ldquoA monolithiccapacitive pressure sensor with pulse-period outputrdquo IEEETransactions on Electron Devices vol 27 no 5 pp 927ndash9301980

[14] H-L Chau and K DWise ldquoAn ultraminiature solid-state pres-sure sensor for a cardiovascular catheterrdquo IEEE Transactions onElectron Devices vol 35 no 12 pp 2355ndash2362 1988

[15] S S Kumar and B D Pant ldquoPolysilicon thin film piezoresistivepressuremicrosensor design fabrication and characterizationrdquoMicrosystem Technologies vol 21 no 9 pp 1949ndash1958 2015

[16] K Takahata Y B Gianchandani and K D Wise ldquoMicroma-chined antenna stents and cuffs for monitoring intraluminalpressure and flowrdquo Journal of Microelectromechanical Systemsvol 15 no 5 pp 1289ndash1298 2006

[17] T G S M Rijks P G Steeneken J T M van Beek et alldquoMicroelectromechanical tunable capacitors for reconfigurableRF architecturesrdquo Journal of Micromechanics and Microengi-neering vol 16 no 3 pp 601ndash611 2006

[18] K I Arshak DMorris A Arshak O Korostynska and E JaferldquoDevelopment of a wireless pressuremeasurement systemusinginterdigitated capacitorsrdquo IEEE Sensors Journal vol 7 no 1 pp122ndash129 2007

[19] J Ji S T Cho Y Zhang K Najafi and K D Wise ldquoAnultraminiature CMOS pressure sensor for amultiplexed cardio-vascular catheterrdquo IEEE Transactions on Electron Devices vol39 no 10 pp 2260ndash2267 1992

[20] H Tian Y Shu X Wang et al ldquoA graphene-based resistivepressure sensor with record-high sensitivity in a wide pressurerangerdquo Scientific Reports vol 5 article 8603 pp 1ndash6 2015

[21] C Tao Z Zhaohua R Tianling et al ldquoA novel dual-functionalMEMS sensor integrating both pressure and temperature unitsrdquoJournal of Semiconductors vol 31 no 7 Article ID 074013 2010

[22] X Huang and D Zhang ldquoA high sensitivity and high linearitypressure sensor based on a peninsula-structured diaphragm forlow-pressure rangesrdquo Sensors andActuators A Physical vol 216pp 176ndash189 2014

[23] N J Madduri G Lakkoju B L Kasturi S Sravanam andT Satyanarayana ldquoDesign and deformation analysis of MEMSbased piezoresistive pressure sensorrdquo International Journal ofAutomotive Engineering and Technologies vol 7 pp 521ndash5312014

[24] B A Ganji and M Shahiri-Tabarestani ldquoA novel high sensitiveMEMS intraocular capacitive pressure sensorrdquo MicrosystemTechnologies vol 19 no 2 pp 187ndash194 2013

8 Journal of Sensors

[25] K Hosoda Y Tada and M Asada ldquoAnthropomorphic roboticsoftfingertipwith randomly distributed receptorsrdquoRobotics andAutonomous Systems vol 54 no 2 pp 104ndash109 2006

[26] J CHelton J D JohnsonC J Sallaberry andC B Storlie ldquoSur-vey of sampling-based methods for uncertainty and sensitivityanalysisrdquo Reliability Engineering and System Safety vol 91 no10-11 pp 1175ndash1209 2006

[27] J Y ZhaoDetection and Sensing Technology Southwest JiaotongUniversity Press Chengdu China 2007

[28] L Lin H-C Chu and Y-W Lu ldquoSimulation program forthe sensitivity and linearity of piezoresistive pressure sensorsrdquoJournal of Microelectromechanical Systems vol 8 no 4 pp 514ndash522 1999

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Page 5: Research Article Microstructure-Based Interfacial …downloads.hindawi.com/journals/js/2016/2428305.pdfResearch Article Microstructure-Based Interfacial Tuning Mechanism of Capacitive

Journal of Sensors 5

99877103

998786161 times 10minus4000501015

02502

(120583m

)

12120583m11120583m10120583m

7 0711120583m

9120583m8120583m

(a)

L = 12120583mL = 11120583m

L = 10120583mL = 9120583mL = 8120583m

00

02

04

06

08

10

Capa

cita

nce d

iffer

ence

(fF)

02 04 06 08 10 1200Pressure (MPa)

(b)

Kr

000

001

002

003

r (

)

9 10 11 128L (120583m)

times10minus7

00

40

80

K (fF

Pa)

(c)

Figure 4The pressure responses of the CPS with different lengths of hemline of pyramids (a)The profile structures of sensors with differentlengths of hemline of pyramid from 8 120583m to 12 120583m and the same height 70711 120583m at 1MPa (b) The comparison of capacitance-pressurecharacteristics of the sensors with different lengths (c) The sensitivity and nonlinear error of the sensors with different lengths

Table 2 Sensitivity and nonlinear error of the CPS with differenthemline lengths of pyramids

Length ofhemline 119871 (120583m) Sensitivity 119870 (fFPa) Nonlinear error 119903

8 881355E minus 7 00176219 735721E minus 7 001206810 629792E minus 7 000803411 548525E minus 7 000527112 485630E minus 7 0004066

Figure 4(b) and the sensitivities and the nonlinear errors ofCPS were shown in Figure 4(c) and Table 2

From Table 2 both the sensitivity and the nonlinear errordecrease with the increasing 119871 When hemline length 119871 andheights 119867 are 8120583m and 707 120583m the sensor has the bestsensitivity of 881 times 10minus7 fFPa In this case in order to

obtain greater sensitivity we hope the hemline length is assmall as possible In other words the smaller the ratios of119871119867 of pyramid the better the sensitivity of the CPS Butits nonlinear error would reach 0018 As the change ofratios of 119871119867 we should balance the sensitivity of CPS fore-skin against the nonlinearity error to effectively tune theperformance of CPS through choosing different parametersaccording to the required demands

In analogy with the research between the pyramidsrsquolengths of hemline and the sensorrsquos performance we have alsomade a series of simulations about the pyramidsrsquo heights Inthe simulation the height changes from5120583mto9120583mwith thesame length of hemline (119871 = 10 120583m) the schematic diagramis shown in Figure 5(a)

From this schematic diagram all the models have thesame distance between the two electrodes when the heightof pyramids changes the bottom of the pyramid will befilled with dielectric material Likewise the outside pressurechanges from 0 to 1MPa too the pressure responses of

6 Journal of Sensors

99877104

998786174 times 10minus4

00501015

0350302502

(120583m

)

6120583m 7120583m 9120583m8120583m5120583m

10120583m

(a)

00

02

04

06

08

Capa

cita

nce d

iffer

ence

(fF)

02 04 06 08 10 1200Pressure (MPa)

6120583m7120583m

9120583m8120583m

H =H =H = H =

H =5120583m

(b)

000

001

002

003

r (

)

6 7 8 95

Kr

H (120583m)

times10minus7

00

40

80

K (fF

Pa)

(c)

Figure 5 The pressure responses of the CPS with different heights of pyramids (a) The profile structures of sensors with different heights ofpyramid from 5120583m to 9120583m and the same lengths of hemline 10 120583m at 1MPa (b)The comparison of capacitance-pressure characteristics ofthe sensors with different heights (c) The sensitivity and nonlinear error of the sensors with different heights

the sensor are obtained and the capacitance-pressure curvesof sensors are shown in Figure 5(b) The sensitivity and thelinearity of sensors are shown in Figure 5(c) and Table 3

From Figure 5 and Table 3 it is easy to find that thesensitivity increases with the height increases from 5 120583m to9 120583m but the linearity is decreased In the simulation ofthis series when the length of hemline of pyramid is 10 120583mand the height of pyramid is 9 120583m the sensor has the bestsensitivity that is 700589119864minus7 fFPa In this case in order toobtain the greater sensitivity we hope the height of pyramidis as large as possible In other words in order to obtain thegreater sensitivity we expect that the length of hemline ofpyramid is more thanradic2 times the height

From what has been discussed above it is obvious thatthe performance of the sensor is affected by the length ofhemline and the height simultaneously Considering thesetwo contradictory parameters a compromise method isproposed to obtain the optimal performance of the sensor

Table 3 Sensitivity and nonlinear error of the CPS with differentheights of pyramids

Height119867 (120583m) Sensitivity 119870 (fFPa) Nonlinear error 1199035 398334E minus 7 00051116 404683E minus 7 00051357 409844E minus 7 00053848 412467E minus 7 00060559 700589E minus 7 0022813

if the medians of 119871 and 119867 are selected at this point boththe sensitivity and linearity have good values Through theanalysis of the relationship between 119871 and 119867 the authorcomes to the conclusion that in order tomake the sensor havebetter performance the ratios of 119871119867 should beradic2

Journal of Sensors 7

4 Conclusions

In this paper we employ the traditional COMSOL Mul-tiphysics models based on finite element analysis methodto construct four different microstructures (flat panelcuboids cylinders and pyramids) CPS for the detailed studyof microstructure interfacial tuning mechanism betweenhuman skin and PVDF The simulative results show thatCPS with micropyramids structures has the best measuringsensitivity K (= 63 times 10minus7 fFPa) which is about 49 timeshigher than that without any microstructure Through thesimulation of pyramids with different ratios of 119871119867 theresults show that the smaller the ratios of 119871119867 of pyramidthe better the sensitivity but the nonlinear error will increaseWhen the ratio of 119871119867 of pyramid is aboutradic2 the sensitivityand the linearity could reach a balance pointThismethod canbe used as theoretical guidance for the e-skin processing

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the National University StudentInnovation Program (201510613009) of China SichuanProvince Science and Technology Plan Project (no2015JQ0013) and the Fundamental Research Funds forthe Central Universities (A0920502051408-10)

References

[1] M L Hammock A Chortos B C-K Tee J B-H Tok andZ Bao ldquo25th Anniversary article the evolution of electronicskin (E-Skin) a brief history design considerations and recentprogressrdquo Advanced Materials vol 25 no 42 pp 5997ndash60382013

[2] T W Tombler C Zhou L Alexseyev et al ldquoReversible elec-tromechanical characteristics of carbon nanotubes under local-probe manipulationrdquo Nature vol 405 no 6788 pp 769ndash7722000

[3] B Zhu Z Niu H Wang et al ldquoMicrostructured graphenearrays for highly sensitive flexible tactile sensorsrdquo Small vol 10no 18 pp 3625ndash3631 2014

[4] D J Cohen D Mitra K Peterson and M M MaharbizldquoA highly elastic capacitive strain gauge based on percolatingnanotube networksrdquo Nano Letters vol 12 no 4 pp 1821ndash18252012

[5] S C BMannsfeld B C-K Tee RM Stoltenberg et al ldquoHighlysensitive flexible pressure sensors with microstructured rubberdielectric layersrdquo Nature Materials vol 9 no 10 pp 859ndash8642010

[6] W Zhang and R-G Xiong ldquoFerroelectricmetal-organic frame-worksrdquo Chemical Reviews vol 112 no 2 pp 1163ndash1195 2012

[7] L Persano C Dagdeviren Y Su et al ldquoHigh performancepiezoelectric devices based on aligned arrays of nanofibersof poly(vinylidenefluoride-co-trifluoroethylene)rdquo Nature Com-munications vol 4 article 1633 2013

[8] M Ramuz B C-K Tee J B-H Tok and Z Bao ldquoTransparentoptical pressure-sensitive artificial skin for large-area stretch-able electronicsrdquo Advanced Materials vol 24 no 24 pp 3223ndash3227 2012

[9] R Koeppe P Bartu S Bauer and N S Saricifici ldquoLight-and touch-point localization using flexible large area organicphotodiodes and elastomer waveguidesrdquo Advanced Materialsvol 21 no 34 pp 3510ndash3514 2009

[10] R Puers ldquoCapacitive sensors when and how to use themrdquoSensors and Actuators A Physical vol 37-38 pp 93ndash105 1993

[11] J A Dobrzynska and M A M Gijs ldquoFlexible polyimide-basedforce sensorrdquo Sensors and Actuators A Physical vol 173 no 1pp 127ndash135 2012

[12] H BMuhammad C Recchiuto CMOddo et al ldquoA capacitivetactile sensor array for surface texture discriminationrdquo Micro-electronic Engineering vol 88 no 8 pp 1811ndash1813 2011

[13] C S Sander J W Knutti and J D Meindl ldquoA monolithiccapacitive pressure sensor with pulse-period outputrdquo IEEETransactions on Electron Devices vol 27 no 5 pp 927ndash9301980

[14] H-L Chau and K DWise ldquoAn ultraminiature solid-state pres-sure sensor for a cardiovascular catheterrdquo IEEE Transactions onElectron Devices vol 35 no 12 pp 2355ndash2362 1988

[15] S S Kumar and B D Pant ldquoPolysilicon thin film piezoresistivepressuremicrosensor design fabrication and characterizationrdquoMicrosystem Technologies vol 21 no 9 pp 1949ndash1958 2015

[16] K Takahata Y B Gianchandani and K D Wise ldquoMicroma-chined antenna stents and cuffs for monitoring intraluminalpressure and flowrdquo Journal of Microelectromechanical Systemsvol 15 no 5 pp 1289ndash1298 2006

[17] T G S M Rijks P G Steeneken J T M van Beek et alldquoMicroelectromechanical tunable capacitors for reconfigurableRF architecturesrdquo Journal of Micromechanics and Microengi-neering vol 16 no 3 pp 601ndash611 2006

[18] K I Arshak DMorris A Arshak O Korostynska and E JaferldquoDevelopment of a wireless pressuremeasurement systemusinginterdigitated capacitorsrdquo IEEE Sensors Journal vol 7 no 1 pp122ndash129 2007

[19] J Ji S T Cho Y Zhang K Najafi and K D Wise ldquoAnultraminiature CMOS pressure sensor for amultiplexed cardio-vascular catheterrdquo IEEE Transactions on Electron Devices vol39 no 10 pp 2260ndash2267 1992

[20] H Tian Y Shu X Wang et al ldquoA graphene-based resistivepressure sensor with record-high sensitivity in a wide pressurerangerdquo Scientific Reports vol 5 article 8603 pp 1ndash6 2015

[21] C Tao Z Zhaohua R Tianling et al ldquoA novel dual-functionalMEMS sensor integrating both pressure and temperature unitsrdquoJournal of Semiconductors vol 31 no 7 Article ID 074013 2010

[22] X Huang and D Zhang ldquoA high sensitivity and high linearitypressure sensor based on a peninsula-structured diaphragm forlow-pressure rangesrdquo Sensors andActuators A Physical vol 216pp 176ndash189 2014

[23] N J Madduri G Lakkoju B L Kasturi S Sravanam andT Satyanarayana ldquoDesign and deformation analysis of MEMSbased piezoresistive pressure sensorrdquo International Journal ofAutomotive Engineering and Technologies vol 7 pp 521ndash5312014

[24] B A Ganji and M Shahiri-Tabarestani ldquoA novel high sensitiveMEMS intraocular capacitive pressure sensorrdquo MicrosystemTechnologies vol 19 no 2 pp 187ndash194 2013

8 Journal of Sensors

[25] K Hosoda Y Tada and M Asada ldquoAnthropomorphic roboticsoftfingertipwith randomly distributed receptorsrdquoRobotics andAutonomous Systems vol 54 no 2 pp 104ndash109 2006

[26] J CHelton J D JohnsonC J Sallaberry andC B Storlie ldquoSur-vey of sampling-based methods for uncertainty and sensitivityanalysisrdquo Reliability Engineering and System Safety vol 91 no10-11 pp 1175ndash1209 2006

[27] J Y ZhaoDetection and Sensing Technology Southwest JiaotongUniversity Press Chengdu China 2007

[28] L Lin H-C Chu and Y-W Lu ldquoSimulation program forthe sensitivity and linearity of piezoresistive pressure sensorsrdquoJournal of Microelectromechanical Systems vol 8 no 4 pp 514ndash522 1999

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Page 6: Research Article Microstructure-Based Interfacial …downloads.hindawi.com/journals/js/2016/2428305.pdfResearch Article Microstructure-Based Interfacial Tuning Mechanism of Capacitive

6 Journal of Sensors

99877104

998786174 times 10minus4

00501015

0350302502

(120583m

)

6120583m 7120583m 9120583m8120583m5120583m

10120583m

(a)

00

02

04

06

08

Capa

cita

nce d

iffer

ence

(fF)

02 04 06 08 10 1200Pressure (MPa)

6120583m7120583m

9120583m8120583m

H =H =H = H =

H =5120583m

(b)

000

001

002

003

r (

)

6 7 8 95

Kr

H (120583m)

times10minus7

00

40

80

K (fF

Pa)

(c)

Figure 5 The pressure responses of the CPS with different heights of pyramids (a) The profile structures of sensors with different heights ofpyramid from 5120583m to 9120583m and the same lengths of hemline 10 120583m at 1MPa (b)The comparison of capacitance-pressure characteristics ofthe sensors with different heights (c) The sensitivity and nonlinear error of the sensors with different heights

the sensor are obtained and the capacitance-pressure curvesof sensors are shown in Figure 5(b) The sensitivity and thelinearity of sensors are shown in Figure 5(c) and Table 3

From Figure 5 and Table 3 it is easy to find that thesensitivity increases with the height increases from 5 120583m to9 120583m but the linearity is decreased In the simulation ofthis series when the length of hemline of pyramid is 10 120583mand the height of pyramid is 9 120583m the sensor has the bestsensitivity that is 700589119864minus7 fFPa In this case in order toobtain the greater sensitivity we hope the height of pyramidis as large as possible In other words in order to obtain thegreater sensitivity we expect that the length of hemline ofpyramid is more thanradic2 times the height

From what has been discussed above it is obvious thatthe performance of the sensor is affected by the length ofhemline and the height simultaneously Considering thesetwo contradictory parameters a compromise method isproposed to obtain the optimal performance of the sensor

Table 3 Sensitivity and nonlinear error of the CPS with differentheights of pyramids

Height119867 (120583m) Sensitivity 119870 (fFPa) Nonlinear error 1199035 398334E minus 7 00051116 404683E minus 7 00051357 409844E minus 7 00053848 412467E minus 7 00060559 700589E minus 7 0022813

if the medians of 119871 and 119867 are selected at this point boththe sensitivity and linearity have good values Through theanalysis of the relationship between 119871 and 119867 the authorcomes to the conclusion that in order tomake the sensor havebetter performance the ratios of 119871119867 should beradic2

Journal of Sensors 7

4 Conclusions

In this paper we employ the traditional COMSOL Mul-tiphysics models based on finite element analysis methodto construct four different microstructures (flat panelcuboids cylinders and pyramids) CPS for the detailed studyof microstructure interfacial tuning mechanism betweenhuman skin and PVDF The simulative results show thatCPS with micropyramids structures has the best measuringsensitivity K (= 63 times 10minus7 fFPa) which is about 49 timeshigher than that without any microstructure Through thesimulation of pyramids with different ratios of 119871119867 theresults show that the smaller the ratios of 119871119867 of pyramidthe better the sensitivity but the nonlinear error will increaseWhen the ratio of 119871119867 of pyramid is aboutradic2 the sensitivityand the linearity could reach a balance pointThismethod canbe used as theoretical guidance for the e-skin processing

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the National University StudentInnovation Program (201510613009) of China SichuanProvince Science and Technology Plan Project (no2015JQ0013) and the Fundamental Research Funds forthe Central Universities (A0920502051408-10)

References

[1] M L Hammock A Chortos B C-K Tee J B-H Tok andZ Bao ldquo25th Anniversary article the evolution of electronicskin (E-Skin) a brief history design considerations and recentprogressrdquo Advanced Materials vol 25 no 42 pp 5997ndash60382013

[2] T W Tombler C Zhou L Alexseyev et al ldquoReversible elec-tromechanical characteristics of carbon nanotubes under local-probe manipulationrdquo Nature vol 405 no 6788 pp 769ndash7722000

[3] B Zhu Z Niu H Wang et al ldquoMicrostructured graphenearrays for highly sensitive flexible tactile sensorsrdquo Small vol 10no 18 pp 3625ndash3631 2014

[4] D J Cohen D Mitra K Peterson and M M MaharbizldquoA highly elastic capacitive strain gauge based on percolatingnanotube networksrdquo Nano Letters vol 12 no 4 pp 1821ndash18252012

[5] S C BMannsfeld B C-K Tee RM Stoltenberg et al ldquoHighlysensitive flexible pressure sensors with microstructured rubberdielectric layersrdquo Nature Materials vol 9 no 10 pp 859ndash8642010

[6] W Zhang and R-G Xiong ldquoFerroelectricmetal-organic frame-worksrdquo Chemical Reviews vol 112 no 2 pp 1163ndash1195 2012

[7] L Persano C Dagdeviren Y Su et al ldquoHigh performancepiezoelectric devices based on aligned arrays of nanofibersof poly(vinylidenefluoride-co-trifluoroethylene)rdquo Nature Com-munications vol 4 article 1633 2013

[8] M Ramuz B C-K Tee J B-H Tok and Z Bao ldquoTransparentoptical pressure-sensitive artificial skin for large-area stretch-able electronicsrdquo Advanced Materials vol 24 no 24 pp 3223ndash3227 2012

[9] R Koeppe P Bartu S Bauer and N S Saricifici ldquoLight-and touch-point localization using flexible large area organicphotodiodes and elastomer waveguidesrdquo Advanced Materialsvol 21 no 34 pp 3510ndash3514 2009

[10] R Puers ldquoCapacitive sensors when and how to use themrdquoSensors and Actuators A Physical vol 37-38 pp 93ndash105 1993

[11] J A Dobrzynska and M A M Gijs ldquoFlexible polyimide-basedforce sensorrdquo Sensors and Actuators A Physical vol 173 no 1pp 127ndash135 2012

[12] H BMuhammad C Recchiuto CMOddo et al ldquoA capacitivetactile sensor array for surface texture discriminationrdquo Micro-electronic Engineering vol 88 no 8 pp 1811ndash1813 2011

[13] C S Sander J W Knutti and J D Meindl ldquoA monolithiccapacitive pressure sensor with pulse-period outputrdquo IEEETransactions on Electron Devices vol 27 no 5 pp 927ndash9301980

[14] H-L Chau and K DWise ldquoAn ultraminiature solid-state pres-sure sensor for a cardiovascular catheterrdquo IEEE Transactions onElectron Devices vol 35 no 12 pp 2355ndash2362 1988

[15] S S Kumar and B D Pant ldquoPolysilicon thin film piezoresistivepressuremicrosensor design fabrication and characterizationrdquoMicrosystem Technologies vol 21 no 9 pp 1949ndash1958 2015

[16] K Takahata Y B Gianchandani and K D Wise ldquoMicroma-chined antenna stents and cuffs for monitoring intraluminalpressure and flowrdquo Journal of Microelectromechanical Systemsvol 15 no 5 pp 1289ndash1298 2006

[17] T G S M Rijks P G Steeneken J T M van Beek et alldquoMicroelectromechanical tunable capacitors for reconfigurableRF architecturesrdquo Journal of Micromechanics and Microengi-neering vol 16 no 3 pp 601ndash611 2006

[18] K I Arshak DMorris A Arshak O Korostynska and E JaferldquoDevelopment of a wireless pressuremeasurement systemusinginterdigitated capacitorsrdquo IEEE Sensors Journal vol 7 no 1 pp122ndash129 2007

[19] J Ji S T Cho Y Zhang K Najafi and K D Wise ldquoAnultraminiature CMOS pressure sensor for amultiplexed cardio-vascular catheterrdquo IEEE Transactions on Electron Devices vol39 no 10 pp 2260ndash2267 1992

[20] H Tian Y Shu X Wang et al ldquoA graphene-based resistivepressure sensor with record-high sensitivity in a wide pressurerangerdquo Scientific Reports vol 5 article 8603 pp 1ndash6 2015

[21] C Tao Z Zhaohua R Tianling et al ldquoA novel dual-functionalMEMS sensor integrating both pressure and temperature unitsrdquoJournal of Semiconductors vol 31 no 7 Article ID 074013 2010

[22] X Huang and D Zhang ldquoA high sensitivity and high linearitypressure sensor based on a peninsula-structured diaphragm forlow-pressure rangesrdquo Sensors andActuators A Physical vol 216pp 176ndash189 2014

[23] N J Madduri G Lakkoju B L Kasturi S Sravanam andT Satyanarayana ldquoDesign and deformation analysis of MEMSbased piezoresistive pressure sensorrdquo International Journal ofAutomotive Engineering and Technologies vol 7 pp 521ndash5312014

[24] B A Ganji and M Shahiri-Tabarestani ldquoA novel high sensitiveMEMS intraocular capacitive pressure sensorrdquo MicrosystemTechnologies vol 19 no 2 pp 187ndash194 2013

8 Journal of Sensors

[25] K Hosoda Y Tada and M Asada ldquoAnthropomorphic roboticsoftfingertipwith randomly distributed receptorsrdquoRobotics andAutonomous Systems vol 54 no 2 pp 104ndash109 2006

[26] J CHelton J D JohnsonC J Sallaberry andC B Storlie ldquoSur-vey of sampling-based methods for uncertainty and sensitivityanalysisrdquo Reliability Engineering and System Safety vol 91 no10-11 pp 1175ndash1209 2006

[27] J Y ZhaoDetection and Sensing Technology Southwest JiaotongUniversity Press Chengdu China 2007

[28] L Lin H-C Chu and Y-W Lu ldquoSimulation program forthe sensitivity and linearity of piezoresistive pressure sensorsrdquoJournal of Microelectromechanical Systems vol 8 no 4 pp 514ndash522 1999

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Page 7: Research Article Microstructure-Based Interfacial …downloads.hindawi.com/journals/js/2016/2428305.pdfResearch Article Microstructure-Based Interfacial Tuning Mechanism of Capacitive

Journal of Sensors 7

4 Conclusions

In this paper we employ the traditional COMSOL Mul-tiphysics models based on finite element analysis methodto construct four different microstructures (flat panelcuboids cylinders and pyramids) CPS for the detailed studyof microstructure interfacial tuning mechanism betweenhuman skin and PVDF The simulative results show thatCPS with micropyramids structures has the best measuringsensitivity K (= 63 times 10minus7 fFPa) which is about 49 timeshigher than that without any microstructure Through thesimulation of pyramids with different ratios of 119871119867 theresults show that the smaller the ratios of 119871119867 of pyramidthe better the sensitivity but the nonlinear error will increaseWhen the ratio of 119871119867 of pyramid is aboutradic2 the sensitivityand the linearity could reach a balance pointThismethod canbe used as theoretical guidance for the e-skin processing

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work is supported by the National University StudentInnovation Program (201510613009) of China SichuanProvince Science and Technology Plan Project (no2015JQ0013) and the Fundamental Research Funds forthe Central Universities (A0920502051408-10)

References

[1] M L Hammock A Chortos B C-K Tee J B-H Tok andZ Bao ldquo25th Anniversary article the evolution of electronicskin (E-Skin) a brief history design considerations and recentprogressrdquo Advanced Materials vol 25 no 42 pp 5997ndash60382013

[2] T W Tombler C Zhou L Alexseyev et al ldquoReversible elec-tromechanical characteristics of carbon nanotubes under local-probe manipulationrdquo Nature vol 405 no 6788 pp 769ndash7722000

[3] B Zhu Z Niu H Wang et al ldquoMicrostructured graphenearrays for highly sensitive flexible tactile sensorsrdquo Small vol 10no 18 pp 3625ndash3631 2014

[4] D J Cohen D Mitra K Peterson and M M MaharbizldquoA highly elastic capacitive strain gauge based on percolatingnanotube networksrdquo Nano Letters vol 12 no 4 pp 1821ndash18252012

[5] S C BMannsfeld B C-K Tee RM Stoltenberg et al ldquoHighlysensitive flexible pressure sensors with microstructured rubberdielectric layersrdquo Nature Materials vol 9 no 10 pp 859ndash8642010

[6] W Zhang and R-G Xiong ldquoFerroelectricmetal-organic frame-worksrdquo Chemical Reviews vol 112 no 2 pp 1163ndash1195 2012

[7] L Persano C Dagdeviren Y Su et al ldquoHigh performancepiezoelectric devices based on aligned arrays of nanofibersof poly(vinylidenefluoride-co-trifluoroethylene)rdquo Nature Com-munications vol 4 article 1633 2013

[8] M Ramuz B C-K Tee J B-H Tok and Z Bao ldquoTransparentoptical pressure-sensitive artificial skin for large-area stretch-able electronicsrdquo Advanced Materials vol 24 no 24 pp 3223ndash3227 2012

[9] R Koeppe P Bartu S Bauer and N S Saricifici ldquoLight-and touch-point localization using flexible large area organicphotodiodes and elastomer waveguidesrdquo Advanced Materialsvol 21 no 34 pp 3510ndash3514 2009

[10] R Puers ldquoCapacitive sensors when and how to use themrdquoSensors and Actuators A Physical vol 37-38 pp 93ndash105 1993

[11] J A Dobrzynska and M A M Gijs ldquoFlexible polyimide-basedforce sensorrdquo Sensors and Actuators A Physical vol 173 no 1pp 127ndash135 2012

[12] H BMuhammad C Recchiuto CMOddo et al ldquoA capacitivetactile sensor array for surface texture discriminationrdquo Micro-electronic Engineering vol 88 no 8 pp 1811ndash1813 2011

[13] C S Sander J W Knutti and J D Meindl ldquoA monolithiccapacitive pressure sensor with pulse-period outputrdquo IEEETransactions on Electron Devices vol 27 no 5 pp 927ndash9301980

[14] H-L Chau and K DWise ldquoAn ultraminiature solid-state pres-sure sensor for a cardiovascular catheterrdquo IEEE Transactions onElectron Devices vol 35 no 12 pp 2355ndash2362 1988

[15] S S Kumar and B D Pant ldquoPolysilicon thin film piezoresistivepressuremicrosensor design fabrication and characterizationrdquoMicrosystem Technologies vol 21 no 9 pp 1949ndash1958 2015

[16] K Takahata Y B Gianchandani and K D Wise ldquoMicroma-chined antenna stents and cuffs for monitoring intraluminalpressure and flowrdquo Journal of Microelectromechanical Systemsvol 15 no 5 pp 1289ndash1298 2006

[17] T G S M Rijks P G Steeneken J T M van Beek et alldquoMicroelectromechanical tunable capacitors for reconfigurableRF architecturesrdquo Journal of Micromechanics and Microengi-neering vol 16 no 3 pp 601ndash611 2006

[18] K I Arshak DMorris A Arshak O Korostynska and E JaferldquoDevelopment of a wireless pressuremeasurement systemusinginterdigitated capacitorsrdquo IEEE Sensors Journal vol 7 no 1 pp122ndash129 2007

[19] J Ji S T Cho Y Zhang K Najafi and K D Wise ldquoAnultraminiature CMOS pressure sensor for amultiplexed cardio-vascular catheterrdquo IEEE Transactions on Electron Devices vol39 no 10 pp 2260ndash2267 1992

[20] H Tian Y Shu X Wang et al ldquoA graphene-based resistivepressure sensor with record-high sensitivity in a wide pressurerangerdquo Scientific Reports vol 5 article 8603 pp 1ndash6 2015

[21] C Tao Z Zhaohua R Tianling et al ldquoA novel dual-functionalMEMS sensor integrating both pressure and temperature unitsrdquoJournal of Semiconductors vol 31 no 7 Article ID 074013 2010

[22] X Huang and D Zhang ldquoA high sensitivity and high linearitypressure sensor based on a peninsula-structured diaphragm forlow-pressure rangesrdquo Sensors andActuators A Physical vol 216pp 176ndash189 2014

[23] N J Madduri G Lakkoju B L Kasturi S Sravanam andT Satyanarayana ldquoDesign and deformation analysis of MEMSbased piezoresistive pressure sensorrdquo International Journal ofAutomotive Engineering and Technologies vol 7 pp 521ndash5312014

[24] B A Ganji and M Shahiri-Tabarestani ldquoA novel high sensitiveMEMS intraocular capacitive pressure sensorrdquo MicrosystemTechnologies vol 19 no 2 pp 187ndash194 2013

8 Journal of Sensors

[25] K Hosoda Y Tada and M Asada ldquoAnthropomorphic roboticsoftfingertipwith randomly distributed receptorsrdquoRobotics andAutonomous Systems vol 54 no 2 pp 104ndash109 2006

[26] J CHelton J D JohnsonC J Sallaberry andC B Storlie ldquoSur-vey of sampling-based methods for uncertainty and sensitivityanalysisrdquo Reliability Engineering and System Safety vol 91 no10-11 pp 1175ndash1209 2006

[27] J Y ZhaoDetection and Sensing Technology Southwest JiaotongUniversity Press Chengdu China 2007

[28] L Lin H-C Chu and Y-W Lu ldquoSimulation program forthe sensitivity and linearity of piezoresistive pressure sensorsrdquoJournal of Microelectromechanical Systems vol 8 no 4 pp 514ndash522 1999

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Page 8: Research Article Microstructure-Based Interfacial …downloads.hindawi.com/journals/js/2016/2428305.pdfResearch Article Microstructure-Based Interfacial Tuning Mechanism of Capacitive

8 Journal of Sensors

[25] K Hosoda Y Tada and M Asada ldquoAnthropomorphic roboticsoftfingertipwith randomly distributed receptorsrdquoRobotics andAutonomous Systems vol 54 no 2 pp 104ndash109 2006

[26] J CHelton J D JohnsonC J Sallaberry andC B Storlie ldquoSur-vey of sampling-based methods for uncertainty and sensitivityanalysisrdquo Reliability Engineering and System Safety vol 91 no10-11 pp 1175ndash1209 2006

[27] J Y ZhaoDetection and Sensing Technology Southwest JiaotongUniversity Press Chengdu China 2007

[28] L Lin H-C Chu and Y-W Lu ldquoSimulation program forthe sensitivity and linearity of piezoresistive pressure sensorsrdquoJournal of Microelectromechanical Systems vol 8 no 4 pp 514ndash522 1999

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Page 9: Research Article Microstructure-Based Interfacial …downloads.hindawi.com/journals/js/2016/2428305.pdfResearch Article Microstructure-Based Interfacial Tuning Mechanism of Capacitive

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of