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Sensors and Actuators A 216 (2014) 196–201

Contents lists available at ScienceDirect

Sensors and Actuators A: Physical

j ourna l ho me page: www.elsev ier .com/ locate /sna

esoporous surface control of PVDF thin films for enhancediezoelectric energy generation

ajing Chen, Tushar Sharma, John X.J. Zhang ∗

epartment of Biomedical Engineering, University of Texas, Austin 78712, USA

r t i c l e i n f o

rticle history:eceived 1 October 2013eceived in revised form 30 April 2014ccepted 27 May 2014vailable online 2 June 2014

a b s t r a c t

We demonstrate that nanostructured thin films play a significant role in compact energy harvestingpolyvinylidene fluoride (PVDF) nanogenerators. In this work, we introduced a surface control techniquefor preparing mesoporous PVDF thin films toward high piezoelectric output. We demonstrated that themorphology of the film could be controlled by varying the solvent evaporation rate. The material crys-

eywords:VDFesoporousenerator

tallinity was experimentally confirmed by X-ray diffraction (XRD) and differential scanning calorimeter(DSC) measurement. The multilayer PVDF structure with porous surface significantly increased the com-pressibility and charge collecting area which contributes to the significant output enhancement. Thepiezoelectric output increased 100% with the modified mesoporous layer. The charging capacity increased107% compared with the same thickness solid PVDF film.

© 2014 Elsevier B.V. All rights reserved.

. Introduction

Miniature piezoelectric generators are one of the most promis-ng power sources for various portable and implantable devices

ith the potential of in situ recharging process through mechanicalo electrical conversion [1]. For such applications, the energy-arvesting devices need to have comparably small dimensions,ood biocompatibility, as well as specific designs that canespond well to different excitations. The recently developedicro/nanoscale piezoelectric materials have shown great promise

or energy scavenging in biomedical devices [2,3]. Among theseiezoelectric materials, polyvinylidene fluoride (PVDF) as a soft,iocompatible and light-weight polymer material is most capa-le for uses in biomedical devices. PVDF polymer can also beolution processed due to its solubility in common polar solventsN-methyl-2-pyrrolidone (NMP), methyl ethyl ketone (MEK) andimethylformamide (DMF) for example). PVDF based materials areapable of large deformation whereas the brittleness makes ceram-cs prone to fracture and crack propagation even under very smalltrain. Besides, the mass density and processing costs of piezo-

lectric polymers are relatively low per unit volume. The mostuccessful body motion power generators have been demonstratedsing conventional PVDF film based devices designed to fit within

∗ Corresponding author at: BME5.202O, 107 W Dean Keeton St. Austin, TX 78712,SA. Tel.: +1 512 475 6872.

E-mail address: john.zhang@engr.utexas.edu (J.X.J. Zhang).

ttp://dx.doi.org/10.1016/j.sna.2014.05.027924-4247/© 2014 Elsevier B.V. All rights reserved.

shoes and backpack straps [4,5]. The size and power density of thesegenerators is insufficient for current implantable and miniaturedevices due to the limited volume.

In order to achieve high performances of piezoelectric devices,a high content of � phase in PVDF material is desired [6]. PVDF-TrFE copolymer has a high piezoelectric coefficient. Copolymerslike TrFE can create artificial defects to decrease the energy to crys-tallize into the all-trans form. PVDF-TrFE generally exhibits goodpiezoelectric behavior and a single all-trans polar crystalline phase(�-phase) that is stable at room temperature [7].

Current PVDF devices are limited to conventional one-dimension (fiber) and two-dimension (film) structure [8,9].Micro/nano structure can further achieve large surface area tovolume ratio for higher piezoelectric efficiency. But most nanofab-rication methods for piezoelectric materials are only available forinorganic materials like ZnO and PZT [10,11]. Previous efforts havebeen made to fabricate three-dimension PVDF nanostructure, butthe fabrication flow is based on template assisted approach. Thefabrication method is complex and unpractical for large scale depo-sition [12,13].

Multiple approaches including higher � phase content, largercharge collecting area and better strain effect can be employed toenhance the PVDF piezoelectric output. In this paper, we devel-oped a novel and facile method to increase piezoelectric output of

PVDF films by utilizing porous surface on the top of conventionalfilms. Fig. 1a and b shows the concept of the mesoporous PVDF filmdevice, mechanical and material characterization are discussed inthis paper. The piezoelectric output is shown to be doubled with a

D. Chen et al. / Sensors and Actuators A 216 (2014) 196–201 197

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ig. 1. Schematic of mesoporous surface based PVDF nanogenerator. (a) 2-D crossection schematic of the device. (b) The variation of compressibility and piezoelectricharge output for structures of just solid PVDF film and the hybrid film.

ell controllable porous film on the surface. This technology pro-ides an alternative design for efficient film-based generators.

. Principle and design

The power density of PVDF generator remains under.5 �W/cm3 at human motion frequency [14,15]. For com-act piezoelectric generator application, the gap between outputnd practical power requirement is large. In order to producenough energy within a compact volume, a more efficient PVDFlm structure is needed. Meanwhile, bulk PVDF film fabrication isassive producible at low cost, where dip coating and spin-coating

ave been conventionally used for large surface area depositionf PVDF films. It is a great challenge to increase the piezoelec-ric efficiency through nanostructuring while maintaining massroducibility.

One major method to enhance piezoelectric efficiency is increas-ng piezoelectric charge coefficient (d). The piezoelectric chargeoefficient is the polarization generated per unit of mechanicaltress (T) applied to a piezoelectric material. It can be defined as,

ij = ∂Di

∂Tj(1)

where D is the electric charge density displacement.

i = Qi

A= �i

V(2)

where Q is surface charge, A is surface area, � is the total dipoleoment, and V is the volume of the porous film. According to the

elationship (1) and (2), the piezoelectric constant can be writtenn the following form:

ij = ∂

∂Tj= ∂�i

∂Tj

(1V

)− �i

V2

(∂V

∂Tj

)(3)

j = − 1V

∂V

∂Tj(4)

Considering second term of Eqs. (3) and (4), the piezoelectriconstant is proportional to the film compressibility (c). High com-ressibility can be achieved with the larger deformation at the

dentical pressure compared to conventional film form.We developed a novel and facile method to increase piezoelec-

ric output of PVDF films simply by utilizing porous surface on theop of conventional films. The porous PVDF layer and the solid PVDF

olymer were placed in between two electrodes and played the roleor mechanical energy conversion. The bottom Kapton film serveds a supporting substrate to deliver a uniform mechanical stress onhe active layer.

Fig. 2. Fabrication process of mesoporous PVDF film.

Porous polymer film can be achieved by multiple approachesincluding: metal salt additive [17], particle templates [18], mixedsolvents [19]. The salt additive and particle templates methods mayhave particles remain inside the PVDF film which will interfere withpoling procedures. So mixed solvent method is employed in theexperiment. By controlling the volume ratio of two organic sol-vents, different evaporation rate can be achieved. It allows for thecontrolled pore formation and conversion of a polymer from liquidto solid state.

3. Experiments

The solvent evaporation rates during spin coating film formationcan influence the final morphology and distribution of polymer.PVDF-TrFE powder (0.48 g, PVDF to TrFE molar ratio: 75/25) wasdissolved in MEK-Acetone mixed solvent (5 mL) under magneticstirring to form a transparent solution. Acetone and MEK solventratio (volume: volume) was controlled at 0:5, 1:4, 2:3 and 3:2.Patterned copper bottom electrodes were deposited on Kapton filmwith thickness of 200 nm. 0:5 (v/v) solution was first spin coated(1000 rpm, 30 s) on bottom electrodes to form the solid layer, thenfour different ratio solutions were spin coated as subsequent layer.The environment temperature was kept at 25 ◦C with humidity ofRH = 60%.

After each spin coating, to ensure complete removal of thesolvent, the samples were simultaneously dried and annealed at130 ◦C for 30 min. After all layers were deposited, 200 nm thick-ness top copper electrodes were deposited by E-Beam. The finalfilm thickness was measured by using a surface profilometer (Dek-tak 6M). The thickness of each spin coating layer was found to bearound 3 �m and the total film thickness is 6 �m.

The electrical polling process over the porous film was per-formed at 90 ◦C with a 240 V (40 V/�m) electrical field applied for30 min and allowed to cool to room temperature before the appliedvoltage was removed. The process flow of porous PVDF film deviceis schematically shown in Fig. 2.

The morphology of porous surface of samples was observedbefore top electrode deposition with scanning electron microscope(Quanta 650). They were coated with a thin layer of gold prior toSEM observation. Porosity (ε) of PVDF-TrFE porous surface filmswas determined by gravimetric method as follows: dry film wasweighed first (w1), the film was then immersed in DI water. The wetfilm was weighed again and recorded as w2. Porosity was calculatedusing the following equation [20]:

ε = (w1 − w2)/dw

(w1 − w2)/dw + w2/dp× 100% (5)

Where dw was the DI water density (0.998 g/cm3) and dp wasthe PVDF-TrFE copolymer density (1879 g/cm3).

X-ray diffraction (XRD) measurement (Cu X-ray, Philips) wasdone to examine the crystalline phase changes in porous surfacesample and bulk samples. The XRD data was collected for angular

position 2� in the interval of 15–55◦, in steps of 0.03◦. Thermal prop-erties of the polymer films were measured by using a differentialscanning calorimeter (Mettler Toledo Thermal Analysis) at heat-ing rates of 10 ◦C/min from 40 to 200 ◦C under N2 atmosphere. To

198 D. Chen et al. / Sensors and Actuators A 216 (2014) 196–201

Fig. 3. Top view SEM of spin coated porous PVDF-TrFE film in mixed solvent of acetone and MEK. The volume ratio of acetone and MEK was controlled at: (a) 0:5, (b) 1:4, (c)2

mo0r(

4

et(

fopo

:3 and (d) 3:2. Cross section SEM of (e) solid film and (f) surface porous film.

easure the performance of the generator, the film was installedn the bending machine with a step motor. Repeatable strain of.103% was applied on the film. The output voltage and output cur-ent density were measured by oscilloscope and a picoammeterKeithley 6487), respectively.

. Results and discussion

The films from 0:5 (v/v) acetone/MEK solutions were transpar-nt with a smooth surface. When the volume of acetone increased,he film surface appeared rougher. The membranes spin from 3:2v/v) acetone/MEK solutions were opaque and white.

Fig. 3 shows the typical SEM photographs of PVDF films obtained

rom different acetone/MEK mixture ratio solutions. The additionf acetone into a PVDF solution has great effect on the film mor-hology. The size and density of the pores increased as the contentf acetone increased. In Fig. 3a, the film is relatively smooth and

flat with pores below 1 �m diameter. When 20% v/v acetone wasadded into the solution, small pores with diameter were generatedas showed in Fig. 3b. The average pore diameter in Fig. 3c is 1.6 �m.In Fig. 3d, the average diameter of pores became 2.4 �m. TheseSEM data suggests that the membrane mean pore size increasedin proportion to the increase in the amount of acetone presencein the polymer solution. When the acetone volume ratio was over60%, the solution evaporation rate becomes too high for smoothlyspin coating. Table 1 shows the addition of acetone results in theincrease of PVDF-TrFE film porosity. The porosity of film increaseddramatically from 48% to 73% when the volume ratio of acetonechanged from 20% to 40%. This trend agrees well with the changeof pore configuration observed from SEM images.

XRD patterns can provide information on the long-range order

and the crystal structure of PVDF-TrFE films. The strong character-istic peak at 19.9◦ in Fig. 4 corresponds to the (1 1 0) and (2 0 0)reflections of the � phase in all samples. � phase with features

D. Chen et al. / Sensors and Actuators A 216 (2014) 196–201 199

Table 1Material properties of PVDF-TrFE films.

Sample number Acetone volume ratio (volume%) Porosity ε (%) Average pore size (�m) Crystallinity Xc (%)

1 0 37 0.2 85.12 20 48 0.5 83.93 40 73 1.6 82.74 60 79 2.4 82.1

Ff

azhTm0

ccmpmptmaac

Fa

ig. 4. XRD patterns of PVDF-TrFE films. Embedded: zoom-in view of XRD spectrarom 18◦ to 21◦ .

round 18◦ and 35◦ are not observed from the patterns[21]. Inoom-in view of Fig. 4, the diffraction peak at 19.9◦ intensity and thealf-diffraction width increased as the volume of acetone increased.he intensity increase indicated that the overall crystallinity of theaterial in the 2:3 (v/v) acetone/MEK films is slightly higher than

:5 (v/v) acetone/MEK film samples.Similar results were reflected by the differential scanning

alorimeter (DSC) measurements of the films in Fig. 5. In theurve for the pristine sample it is possible to see two endother-ic peaks, the lower temperature one related to ferro-paraelectric

hase transition and the other at higher temperature related to theelting phase transition. The area under the melting peak is pro-

ortional to the latent heat necessary to undergo the melting ofhe crystallites. 0/5 (v/v) acetone/MEK sample shows an endother-

ic peak between at 146 ◦C, attributable to its melting. 3:2 (v/v)cetone/MEK samples present a higher melting peak than 0:5 (v/v)cetone/MEK samples by about 7 ◦C, reflecting a higher degree ofrystallinity (64.5%), in agreement with XRD results. The same trend

ig. 6. Electrical characteristics of PVDF-TrFE films. (a) Output voltage and output currencetone/MEK films.

Fig. 5. DSC patterns of PVDF-TrFE films spin coated with different Acetone to MEKvolume ratio solvents.

is found in the Curie point. The integrated areas under the curveswere examined to show that the blends exhibit larger overall heatflow for the same mass. This suggests that �-phase increase withincreasing content of acetone in the solvent.

Electrical behavior was observed by dynamic bending experi-ments performed using porous PVDF-TrFE samples on Kapton filmswith thicknesses of 50 �m. A flexural endurance tester subjectedthe samples to cycling bending tests at 1 Hz. Fig. 6 shows varia-tions of periodic alternation of positive and negative voltage andcurrent output peaks with respect to time. When the strain was

applied on the films, charge was generated which build up thepotential difference across the piezo film, and the correspond-ing peak was observed in the positive direction. The peak in thenegative direction was observed when the strain was released.

t of 3:2 (v/v) acetone/MEK films. (b) Output voltage and output current of 0:5 (v/v)

200 D. Chen et al. / Sensors and Actua

Fig. 7. Characterization of piezoelectric nanogenerator based on mesoporous PVDFfilms. (a) Schematic diagram of layer-by-layer structured porous PVDF film and therfi

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Acknowledgments

ectifying circuit and charge storage devices. (b) Experimental setup for the PVDFlm generator. (c) Charging capabilities of various mesoporous PVDF thin films.

he positive and negative peaks in the voltage thus correspondo the compression and tension in the porous film respectively.witched polarity test was showed in Fig. S1 to confirm the elec-rical output originated from piezoelectric response. The peaks ofurrent and voltage outputs of 0:5 (v/v) acetone/MEK film reached60 nA and 0.8 V, respectively. The peaks of current and voltageutputs of 3:2 (v/v) acetone/MEK film reached 300 nA and 2 V,espectively.

Many biomedical electronics require a regulated DC powerupply voltage while piezoelectric harvesters generate time-arying voltages; therefore, rectification is essential. The simplestopologies to achieve rectification are full-wave rectifier circuitsonsisting of four diodes or transistor switch as showed in Fig. 7a.he PVDF generator test setup is showed in Fig. 7b. The PVDF filmttaches on a flexible substrate and undergoes 1 Hz cyclic strainsy a rotating motor. The generated electrical signal will be drainedff the electrodes into a rectifier and then into a capacitor. The

harging feature of the capacitor via rectifier is shown in Fig. 7c.he output voltage was measured on 1 �F charge storage capaci-or. Under the same impact frequency (1 Hz), the charging capacityor different samples varied. The voltage of the capacitor reached

tors A 216 (2014) 196–201

1700 mV at 360 bending cycles of 2:3 (v/v) Acetone/MEK sample.The voltage of capacitors connected to 0:5 (v/v) Acetone/MEK filmreached 820 mV after 360 cycles under same force. The Acetone-MEK device showed a significant enhancement in generated charge.When switch was turned on, the charge stored in capacitor wassufficient enough to light up a LED. After the same bending cycles(360 times), the 1 �F capacitor reached 1700 mV, equal to 1.7 �Cstored in capacitor. Compared with 820 mV (0.82 �C) chargingcapacity, the charging capacity increased 107% compared with thesame thickness solid PVDF film. Considering the film surface area(2 cm × 0.4 cm), the power density of porous PVDF film reaches8.36 � W/cm3.

The boiling points of acetone and MEK are 56 ◦C, 79 ◦C, respec-tively. The different boiling points lead to different evaporationrates during film formation, which can influence the morphologyand distribution of polymer in the final films. The driving force forthe pore formation in the presence of acetone is related to surfacetension change and water vapor droplets formed at the film sur-face. After complete evaporation of the solvent and water, tracesof water droplets in the polymer film become pores with varieddiameters.

High �-phase crystalline, mechanical compressibility and elec-trodes area all contributed to the increase of device piezoelectricoutput. We investigated the mesoporous surface induced mate-rial characterization change in PVDF thin film by XRD and DSC.Since conventional PVDF-TrFE solid film could also achieve highcrystallinity after annealing, the material enhancement is notdomain in piezoelectric output enhancement. Compared with otherporous PVDF film with through-holes, multilayer porous struc-ture promised full charge colleting area. The output increase wasmainly contributed by the porous polymer structure. As describedin Eqs. (1)–(4), the piezoelectric charge coefficient is proportionalto the compressibility of piezo-material. One of the vital advan-tages of the porous film generator is that the expected piezoelectriceffect became much higher because of the empty pore space. Dis-continuities in film morphology cause piezoelectric material toexperience a local increase in the intensity of a stress field. Anotheradvantage of porous film is the ultra-large electrode surface. Athree-dimension structure allows the rough electrode collectscharge not only from surface and also from the inner part of PVDF-TrFE film.

5. Conclusions

In summary, we have introduced a new, facile techniquefor preparing high piezoelectric output porous PVDF films. Wedemonstrated that the morphology of the film could be con-trolled by varying the concentration of acetone in solvent. Theoutput enhancement could be contributed by high PVDF mate-rial crystallinity, compressibility and charge collecting area. Thematerial crystallinity was experimentally confirmed by XRD andDSC measurement. The mesoporous PVDF film maintained thehigh crystallinity. In this work higher compressibility and stressconcentration contributed most to the output enhancement. Thepiezoelectric voltage and current output increased over 100%with the addition of mesoporous layer. The charging capacityincreased 107% compared with the same thickness solid PVDF film.The nanostructured PVDF thin films show great potential towarddeveloping high performance piezoelectric generators and bio-compatible self-powered systems.

This work was supported by National Science Foundation grants(ECCS 1128677, ECCS 1309686). We gratefully acknowledge the

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quently China-America Frontiers of Engineering Symposium (CAFOE) program in

D. Chen et al. / Sensors and

iscussions with Dr. Marc Feldman and Dr. Christopher Ellison, andhe support from the Center for Nano and Molecular Science (CNM)t University of Texas at Austin.

ppendix A. Supplementary data

Supplementary material related to this article can be found, inhe online version, at http://dx.doi.org/10.1016/j.sna.2014.05.027.

eferences

[1] Y. Hu, Y. Zhang, C. Xu, L. Lin, R.L. Snyder, Z.L. Wang, Self-poweredsystem with wireless data transmission, Nano Lett. 11 (2011) 2572–2577.

[2] Z.L. Wang, J. Song, Piezoelectric nanogenerators based on zinc oxide nanowirearrays, Science 312 (2006) 242–246.

[3] X. Chen, S. Xu, N. Yao, Y. Shi, 1.6 V nanogenerator for mechanical energy har-vesting using PZT nanofibers, Nano Lett. 10 (2010) 2133–2137.

[4] D. Fourie, Shoe mounted PVDF piezoelectric transducer for energy harvesting,MIT Undergraduate Res. J. 19 (2010) 66–70.

[5] J. Granstrom, J. Feenstra, H.A. Sodano, K. Farinholt, Energy harvesting from abackpack instrumented with piezoelectric shoulder straps, Smart Mater. Struct.16 (2007) 1810.

[6] A.J. Lovinger, Ferroelectric polymers, Science 220 (1983) 1115–1121.[7] Y. Higashihata, J. Sako, T. Yagi, Piezoelectricity of vinylidene fluoride-

trifluoroethylene copolymers, Ferroelectrics 32 (1981) 85–92.[8] C. Chang, V.H. Tran, J. Wang, Y.-K. Fuh, L. Lin, Direct-write piezoelectric poly-

meric nanogenerator with high energy conversion efficiency, Nano Lett. 10(2010) 726–731.

[9] M. Lee, C.Y. Chen, S. Wang, S.N. Cha, Y.J. Park, J.M. Kim, L.J. Chou, Z.L. Wang,A hybrid piezoelectric structure for wearable nanogenerators, Adv. Mater. 24(2012) 1759–1764.

10] G. Zhu, R. Yang, S. Wang, Z.L. Wang, Flexible high-output nanogen-erator based on lateral ZnO nanowire array, Nano Lett. 10 (2010)3151–3155.

11] F. Morrison, Y. Luo, I. Szafraniak, V. Nagarajan, R. Wehrspohn, M. Steinhart, J.Wendroff, N. Zakharov, E. Mishina, K. Vorotilov, Ferroelectric Nanotubes, Rev.Adv. Mat. Sci. 4 (2) (2003) 114–122.

12] S. Cha, S.M. Kim, H. Kim, J. Ku, J.I. Sohn, Y.J. Park, B.G. Song, M.H. Jung, E.K. Lee,B.L. Choi, Porous PVDF as effective sonic wave driven nanogenerators, NanoLett. 11 (2011) 5142–5147.

13] K. Choi, S.C. Lee, Y. Liang, K.J. Kim, H.S. Lee, Transition from nanorod to nanotubeof poly (vinylidene trifluoroethylene) ferroelectric nanofiber, Macromolecules46 (8) (2013) 3067–3073.

14] S.-H. Bae, Kahya o, B.K. Sharma, J. Kwon, H.J. Cho, B. Ozyilmaz, J.-H. Ahn,Graphene-P (VDF-TrFE) multilayer film for flexible applications, ACS nano 7(4) (2013) 3130–3138.

15] M. Ma, L. Guo, D.G. Anderson, R. Langer, Bio-inspired polymer compos-ite actuator and generator driven by water gradients, Science 339 (2013)186–189.

17] E. Fontananova, J.C. Jansen, A. Cristiano, E. Curcio, E. Drioli, Effect of additivesin the casting solution on the formation of PVDF membranes, Desalination 192(2006) 190–197.

18] J. Li, J. Fu, Y. Cong, Y. Wu, L. Xue, Y. Han, Macroporous fluoropolymeric films

templated by silica colloidal assembly: a possible route to super-hydrophobicsurfaces, Appl. Surf. Sci. 252 (2006) 2229–2234.

19] M.S. Park, W. Joo, J.K. Kim, Porous structures of polymer films prepared byspin coating with mixed solvents under humid condition, Langmuir 22 (2006)4594–4598.

tors A 216 (2014) 196–201 201

20] J. Xi, X. Qiu, J. Li, X. Tang, W. Zhu, L. Chen, PVDF–PEO blends based micro-porous polymer electrolyte: Effect of PEO on pore configurations and ionicconductivity, J. Power Sources 157 (2006) 501–506.

21] B. Newman, C. Yoon, K. Pae, J. Scheinbeim, Piezoelectric activity and field-induced crystal structure transitions in poled poly (vinylidene fluoride) films,J. Appl. Phys. 50 (1979) 6095–6100.

Biographies

Dajing Chen received his PhD degree in Biomedical Engi-neering from Zhejiang University (China) in 2011. From2012 to 2013, he was a post-doctor in University ofTexas, Austin. Currently he works as a research associatein Dartmouth College. His research interesting includesnanostructure materials and piezoelectric material forenergy harvesting and sensing applications.

Dr. John X.J. Zhang is currently an Associate Professorat the University of Texas of Austin (UT Austin), USA.He received his PhD from Stanford University, California,and was a Research Scientist at Massachusetts Institute ofTechnology (MIT), Cambridge, before joining the facultyat UT Austin.

Zhang’s research focuses on exploring bio-inspirednanomaterials, scale-dependent biophysics, and nanofab-rication technology, towards developing new diagnosticdevices and methods on probing complex cellular pro-cesses and biological networks critical to developmentand diseases. Both multi-scale experimental and theoret-ical approaches are combined to investigate fundamental

force, flow and energy processes at the interface of engineering and biomedicine.In particular, his laboratory is leading the development of integrated photonicmicrosystems (MEMS, micro-electro-mechanical systems), semiconductor chipsand nanotechnologies critical to healthcare, defense and environmental applica-tions. He has published over 120 peer reviewed papers and proceedings, presentedover 45 invited seminars worldwide, and filed over 15 US patents (5 patents issued).His research findings have been highlighted in many public media, and were licensedto two companies: CardioSpectra, Inc. (acquired by Volcano, Nasdaq: VOLC) andNanoLite Systems, Inc. He has co-organized many major conferences in the area ofMEMS/BioMEMS, nanotechnologies and biomedical engineering.

In addition to being the Principle Investigator of many major grants from U.S.federal agencies such as NIH, NSF and DARPA, Dr. Zhang was also recipient ofmany prestigious awards, including: the Wallace H. Coulter Foundation Early CareerAward for Translational Research in Biomedical Engineering, the British CouncilEarly Career RXP Award, NSF Faculty Early Career Development Program (NSFCAREER) Award, DARPA Young Faculty Award, and an invitee to attend U.S. NationalAcademy of Engineering, Frontiers of Engineering (NAE-FOE) program in 2011, theNAE Frontiers of Engineering Education (NAE FOEE) program in 2012, and subse-

2013. He is currently an Associate Editor for Biomedical Microdevices, IEEE/ASMEJournal of Microelectromechanical Systems, and has published a textbook titled“Molecular Sensors and Nanodevices: Principles, Designs and Applications in BiomedicalEngineering”.