Research Article Determining the Optimum Exposure...

Research ArticleDetermining the Optimum Exposure and RecoveryPeriods for Efficient Operation of a QCM Based ElementalMercury Vapor Sensor

K. M. Mohibul Kabir,1 Samuel J. Ippolito,1,2 Glenn I. Matthews,2

S. Bee Abd Hamid,3 Ylias M. Sabri,1 and Suresh K. Bhargava1

1Centre for Advanced Materials & Industrial Chemistry (CAMIC), School of Applied Sciences, RMIT University,Melbourne, VIC 3001, Australia2School of Electrical and Computer Engineering, RMIT University, Melbourne, VIC 3001, Australia3Nanotechnology & Catalysis Research Center (NANOCAT), Institute of Postgraduate Studies (IPS),University of Malaya, 3rd Floor, Block A, 50603 Kuala Lumpur, Malaysia

Correspondence should be addressed to Ylias M. Sabri; [email protected] Suresh K. Bhargava; [email protected]

Received 6 May 2015; Revised 16 July 2015; Accepted 21 July 2015

Academic Editor: Nick Chaniotakis

Copyright © 2015 K. M. Mohibul Kabir et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

In recent years, mass based transducers such as quartz crystal microbalance (QCM) have gained huge interest as potential sensorsfor online detection of elemental mercury (Hg0) vapor from anthropogenic sources due to their high portability and robust natureenabling them to withstand harsh industrial environments. In this study, we determined the optimal Hg0 exposure and recoverytimes of a QCM based sensor for ensuring its efficient operation while monitoring low concentrations of Hg0 vapor (<400 ppbv).The developed sensor was based on an AT-cut quartz substrate and utilized two gold (Au) films on either side of the substrate whichfunctions as the electrodes and selective layer simultaneously. Given the temporal responsemechanisms associated withmass basedmercury sensors, the experiments involved the variation of Hg0 vapor exposure periods while keeping the recovery time constantfollowing each exposure and vice versa.The results indicated that an optimum exposure and recovery periods of 30 and 90minutes,respectively, can be utilized to acquire the highest response magnitudes and recovery rate towards a certain concentration of Hg0vapor whilst keeping the time it takes to report an accurate reading by the sensor to a minimum level as required in real-worldapplications.

1. Introduction

The rapid growth of industrialization in the last century hasincreased the emission of toxic metal species such as elemen-tal mercury in the atmosphere [1–7]. It is of high importanceto control the emission of these metal species from commonindustrial sources in order to reduce the advert effect theyare having on the environment as well as human health.Recently, new andmore stringent rules have been introducedby government and environmental bodies worldwide to limitthe amount ofmercury emitted from industrial processes. Forexample, the average daily mercury emission from cement

kilns in Germany is proposed to be limited to 3.5 ppbv [8].In order to comply with these regulations, efficient removaltechnologies need to be implemented on targeted industrysites. Furthermore, in order to evaluate the efficiency of theseremoval technologies, highly accurate and sensitive onlinemercury vapor sensor is required.

In recent years, it has been shown that the mass basedtransducer such as quartz crystal microbalance (QCM) pos-sesses several major advantages over other commonly usedelemental mercury (Hg0) vapor measurement techniques,which are typically based on atomic absorption spectroscopy(AAS) and atomic fluorescence spectrometry (AFS), and

Hindawi Publishing CorporationJournal of SensorsVolume 2015, Article ID 727432, 7 pageshttp://dx.doi.org/10.1155/2015/727432

2 Journal of Sensors

so forth [9–20]. The QCM based Hg0 vapor sensors werefound to be highly portable and selective and they donot require sample pretreatment which make them highlysuitable for online monitoring of Hg0 vapor within industrialapplications [10]. Moreover, the design and the selective layerof QCM based sensors can be altered to achieve even highersensitivity and selectivity towards low concentrations of Hg0vapor. We recently reported that a QCM sensor based ongold nanospikes [21] can detect Hg0 vapor concentrationsdown to∼2.5 ppbv, which is lower than the thresholdmercuryexposure limit of 5.6 ppbv set by world health organization[22]. Due to their potential to be used as online or hand-heldsensors, it is very important to study QCM based Hg0 vaporsensors extensively in order to achieve the best performancefor Hg0 vapor detection.

The schematic of a typical QCM based gas sensor isshown in Figure 1.The sensor is usually fabricated by deposit-ing two electrodes on both sides of a suitable piezoelectricsubstrate (i.e., AT cut quartz). A bulk acoustic wave isgenerated upon the application of an electric potential on oneof the electrodes [23–26]. The sensing film can be depositedon the electrode or the electrodes themselves can bemade of amaterial which is selective to target analytes. Crystallographiccharacteristics and the thickness of the substrate and theelectrodes determine the resonant frequency (𝑓

0) of the

sensor. Any perturbation on the sensing film (which typicallyoccurs through mass loading of targeted analytes on thesensing film) results in a shift of the resonant frequency (𝑓

0)

of the sensor. This shift in 𝑓0is highly dependent on the

amount of analyte that interacts with the sensing film and canbe related by the Sauerbrey equation (1) [27]:

Δ𝑓 = −

2𝑓0

2

𝐴√𝜌𝜇

Δ𝑚, (1)

where Δ𝑓 represents the shift in the resonant frequency, Δ𝑚is the change in the mass of the sensing surface, 𝐴 is theactive area of the QCM electrodes, and 𝜌 and 𝜇 are thecrystal density and shearmodulus of the piezoelectric crystal,respectively. It can be observed from (1) that the shift in 𝑓

0

increases as the mass loading on the sensing film increases,which indicates that the shift in 𝑓

0is proportional to the

concentration of the species being detected.In the current study, we focused on the Hg0 vapor

detection application of a QCM based sensor. Therefore,extensive experimental and analytical approach was taken todetermine the optimum exposure and recovery period to beused in order to efficiently monitor low concentration of Hg0vapor using QCM based sensors.

2. Experimental

2.1. Sensor Fabrication and Quality Factor Determination.The QCM based sensor was fabricated on an AT cut quartzsubstrate having a diameter and thickness of 7.5mm and166 𝜇m, respectively. 100 nm of Au layer on a 10 nm Titanium(Ti) adhesion layer was deposited on both sides of the quartzsubstrate to function as electrodes as well as the sensing

Analytes Electrodes with sensing film

Piezoelectric substrate

Figure 1: Schematic diagram of a typical QCM based gas sensor.

layer simultaneously. The deposition was performed usinga Balzers e-beam (BAK 600) evaporator operating at 22∘C.Both of the electrodes were circular shaped which werepatterned by using a shadow mask. The diameter of theelectrodes was 4.5mm.A photograph of the fabricated sensoris shown in Figure 2(a).

A network analyzer (Agilent E5100A) was used to mea-sure the frequency response and determine the quality factorof the fabricated sensor. Figure 2(b) shows the frequencyresponse of the sensor at 2 kHz span around the centerfrequency (9.99909MHz). The quality factor of the sensorcan be calculated using [28]

𝑄 = 𝜔

energy storedpower loss

, (2)

where 𝜔 = 2𝜋𝑓. The quality factor of the fabricated sensorwas calculated as 6410 (i.e., >2500), indicating the sensor issuitable for gas phase analysis.

2.2. Mercury Testing Setup. The Hg0 vapor concentrationused in different experiments of this study was 365 ppbv.This particular concentration of Hg0 vapor was generatedby setting the temperature of a NIST certified permeationtube (VICI) to 80∘C. The Hg0 delivery system was alsocalibrated on site using a potassium permanganate (KMnO

4)

trapping method. This involved capturing the generatedHg0 vapor steam within a train of impingers containingH2SO4/KMnO

4and analyzing the solution by inductively

coupled mass spectroscopy (ICP-MS) afterwards. This wasdone in order to ensure the concentration of Hg0 vapor wascorrect. The chamber which housed the QCM sensor hadvolume of 100mL and was made of Teflon and stainless steel.The sensor recovery was a one-step process involving theexposure of the sensor toward dry nitrogen (N

2). A constant

flow rate of 200 sccm and an operating temperature of 30∘Cwere maintained throughout the whole study. The operatingtemperature of the sensor chamber was kept constant usingan active PID controller. Temperature fluctuations within±0.5∘Cwere observed; however, this did not affect the sensing

Journal of Sensors 3

Au electrode

Quartz substrate

Electrical Connection

(a)

9.998 9.999 10.000−7

−6

−5

−4

−3

Mag

nitu

de (d

B)Frequency (MHz)

Q = 6410

3dB

9.99909MHz

9.99823MHz 9.99979MHz

(b)

Figure 2: (a) Photograph of the developed QCM based sensor and (b) network analyzer response of the sensor at 2 kHz span around thecenter frequency.

0 600 1200 1800 2400 3000Time (min)

Dry N2

Hg exposure

(a)

0 600 1200 1800 2400 3000

−100−50

0

Resp

onse

(Hz)

Time (min)

(b)

Figure 3: (a) Structure of the test performed to determine the optimum Hg0 exposure time; (b) sensor’s dynamic response during the fulltest. Each exposure/recovery event’s cycle was repeated 3 times before the next event started.

result due to the high temperature stability of AT-cut quartz.A Maxtek RQCM was used for oscillation as well as tomonitor resonant frequency of the sensor.

3. Results and Discussion

3.1. OptimumHg0 Vapor Exposure Time. The performance ofthe developed Hg0 vapor sensor for different exposure timeswas investigated by exposing the sensor towards 365 ppbv ofHg0 vapor for a range of exposure period ranging from 10 to120minutes whilst keeping the recovery period constant at 60minutes.The structure of the full test is shown in Figure 3(a).It can be seen that after every Hg0 vapor exposure perioddry N

2was flushed to the sensor for a period of 60 minutes.

This process was performed in order to desorb the Hg0 vapormolecules from the Au surface and thus allow the sensorto recover to its baseline frequency. Figure 3(b) shows thedynamic response of the sensor for the entire test. It can beobserved that the Hg0 exposure resulted in a negative shiftin the resonant frequency while the sensor was observed toreturn it to its baseline frequency during the recovery time.

Figure 4(a) shows the sensor’s response towardHg0 vaporconcentration of 365 ppbv for an exposure time of 30 and120 minutes while the recovery period was kept constantat 60 minutes. The pulses shown were extracted from a setof continuous pulses which were measured using a fixedexposure and recovery time for at least 3 cycles.Thiswas donein order to obtain stable performance of the sensors in thefinal cycle. It can be observed fromFigure 4(a) that the sensorresponse profile between the two exposure periods is differentwhen considering the first 30-minute exposure period. Thiswas mainly due to the different initial state between thetwo conditions presented (i.e., see Figure 3(b)). This can befurther justified from Figures 4(b) and 4(c). That is, it canbe observed from Figure 4(b) that the last pulse of 30-minuteexposure and 60-minute recovery period cycles has the sameadsorption response profile as the first pulse of 40-minuteexposure and 60-minute recovery period cycle due to thesame initial state of the sensor. This is further confirmed inFigure 4(c) where it can be observed that the last pulse of 90-minute exposure and 60-minute recovery period respondssimilarly as 120-minute exposure and 60-minute recoveryperiod. Figure 4(d) shows the response magnitudes of the


0 1 2 3

−20

−10

0

Time (hrs)

Sens

or re

spon

se (H

z)

120min exposure-60 min recoverymin recovery30min exposure-60

(a)

0.0 0.4 0.8 1.2 1.6−25

−20

−15

−10

−5

0

Time (hrs)

Sens

or re

spon

se (H

z)30min exposure-60min recovery40min exposure-60min recovery

(b)

0 1 2 3

−25

−20

−15

−10

−5

0

Time (hrs)

Sens

or re

spon

se (H

z)

120min exposure-60min recovery90min exposure-60min recovery

(c)

0 30 60 90 120

15

18

21

24

Exposure time (min)

Resp

onse

mag

nitu

de (H

z)

(d)

Figure 4: (a) Sensor’s dynamic response toward Hg0 vapor concentration of 365 ppbv exposed for 30 and 120 minutes; (b) 30 and 40minutes;and (c) 90 minutes and 120 minutes, all having a constant recovery time of 60 minutes. (d) Sensor’s response magnitude towards 365 ppbv ofHg0 exposed for 10 to 120 minutes with a recovery time of 60 minutes.

sensor toward the same Hg0 vapor concentration (365 ppbv)for different exposure periods ranging from 10 to 120minutesand a constant recovery period of 60 minutes. The responsemagnitudes of the last pulses for eachHg0 vapor exposure andrecovery cycle were considered for analysis.The final pulse ofeach cycle was chosen as it allowed for the sensor to reachstability thereby resulting in desorption of the adsorbed Hg0

molecules from the Au surface and thus reducing the impactof a preceding pulse on the characterization of the followingHg0 exposure cycle. It can be observed from Figure 4(d) thatthe sensor’s response magnitude increased rapidly when theHg0 vapor exposure time was increased up to 30 minutes.However, it can also be observed that the sensor’s responsemagnitudes did not vary significantly when the Hg0 vapor


0 600 1200 1800Time (min)

Dry N2

Hg exposure

(a)

Resp

onse

(Hz)

0 600 1200 1800−40

−20

0

Time (min)

(b)

Figure 5: (a) Structure of the test performed to determine the optimum Hg0 recovery time; (b) sensor’s dynamic response during the fulltest. Each exposure/recovery event’s cycle was repeated 3 times before the next event started.

0.0 0.5 1.0 1.5 2.0

−20

−15

−10

−5

0

Sens

or re

spon

se (H

z)

Time (hrs)

70min recovery

90min recovery

120min recovery

30min exposure

(a)

0 30 60 90 120 150

12

15

18

Adsorption magnitude

Recovery time (min)

Desorption magnitude

Resp

onse

mag

nitu

de (H

z)

(b)

Figure 6: (a) Sensor’s dynamic response towards 365 ppbv of Hg0 vapor exposed for 30 minutes with desorption time of 70, 90, and 120

minutes and (b) sensor’s adsorption and desorption magnitude towards 30 minutes of Hg0 vapor exposure while the desorption period wasvaried between 10 and 120 minutes. The response magnitudes of the final cycle of each event are plotted.

exposure time was increased beyond 30 minutes. This obser-vation indicates that the processes of Hg-Au amalgamationand diffusion of Hg atoms into the Au surface are relativelyhigh up to a period of 30 minutes; however, they are reducedsignificantly beyond the exposure period of 30minutes due tothe Au surface reaching saturation. Therefore, no significantincrease in response magnitudes was observed when the Hg0vapor was exposed for more than 30 minutes. The initialHg0 sorption kinetics (Figure 4(a)) is also observed to havechanged (slowed) at the exposure time of 120 minutes dueto the higher content of the mercury that was already onthe surface from the preceding two cycles of the same pulse(i.e., having 120-minute exposure and 60-minute recoveryperiods).

3.2. Optimum Hg0 Vapor Recovery Time. In order to deter-mine the optimum recovery time of the QCMbasedHg0 sen-sor, the sensor was exposed towards Hg0 vapor concentrationof 365 ppbv for a period of 30 minutes while the recovery

periodwas variedwithin a range of 10 to 90minutes. A periodof 30 minutes was chosen as the Hg0 vapor exposure time asit was determined to be the optimum time from the previoustest (Section 3.1) at which the saturated response magnitudewas achieved at a low turnaround time. The test structure fordetermining optimum recovery period for QCM based Hg0vapor sensor is shown in Figure 5(a).

The dynamic response of the sensor throughout the testcan be observed from Figure 5(b). It can be observed thateach exposure and recovery cycle was repeated 3 times beforethe next cycle started. The sensor’s dynamic response for30 minutes exposure toward Hg0 vapor concentration of365 ppbv employing three different recovery periods of 70, 90,and 120minutes can be seen in Figure 6(a). It can be observedthat the sensor exhibited a response magnitude of ∼17.5Hzwhen Hg0 exposure and recovery periods were 30 and 70minutes, respectively. It can also be observed that the sensor’sresponsemagnitude rose to ∼19Hz when the recovery periodwas increased to ∼90 minutes while keeping the same Hg0


vapor exposure period. Interestingly, the sensor’s responsemagnitudes did not vary significantly when the recoveryperiod was further increased to 120 minutes.

A clearer view of sensor’s adsorption and desorptionmagnitudes for the different recovery periods ranging from10 to 120 minutes can be observed from Figure 6(b). Here,it should be noted that the sensor’s desorption magnitudeswere taken from the end of the recovery periods. It wasinteresting to observe that a ∼23Hz response magnitude wasobserved for a 30-minute exposure and 60-minute recoveryperiods pulse (Figure 4(d)) while in Figure 6(b) a ∼18Hzresponse was observed for the same exposure and recoveryconditions. However, the difference arises from the precedingpulse cycles that were run for each condition. That is, thereduction in response magnitude for recovery period testwas observed because the preceding recovery periods (i.e., 50minutes) were not efficient enough for the sensor to releasethe adsorbed Hg0 molecules from Au surface as opposedto the longer recovery period (60 minutes) used in all thepulses of the exposure test (Figure 3(a)). It can be seen fromFigure 6(b) that the sensor’s adsorption and desorption mag-nitudes increased significantly up to 90 minutes even thoughthe Hg0 exposure period was kept constant at 30 minutes. Itcan also be observed from Figure 6(b) that while the sensorhas high recovery efficiency for most of the recovery timestested the 90-minute recovery period showed to have morethan 90% recovery efficiency while exhibiting maximumresponse magnitude towards Hg0 vapor. Overall, the resultsindicate that at least 90 minutes of recovery period is neededto acquire the highest possible responsemagnitudes as well asthe recovery efficiency from the sensor while detecting lowconcentrations of Hg0 vapor without jeopardizing sensor’sresponse time. Getting a higher response magnitude and therecovery efficiency is particularly important as it will enablethe sensor to have high sensitivity and thereby result in theefficient detection of low concentrations of Hg0 vapor inindustrial processes.

4. Conclusion

The Hg0 vapor sensing performance of a QCM based sensorwas investigated for different Hg0 vapor exposure and recov-ery periods. The developed sensor was based on an AT-cutquartz substrate containing thin Au-film electrodes on bothsides.The sensor was tested towardsHg0 vapor concentrationof 365 ppbv while the Hg0 vapor exposure and recoveryperiods were varied between 10 and 120 minutes. The overallresults indicate that 30-minute Hg0 vapor exposure and 90-minute recovery periods can be utilized to achieve the highestresponse magnitudes and recovery efficiency from the sensorwhile keeping the turnaround time in a minimum level forreal-world applications.

Conflict of Interests

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

Acknowledgments

The authors acknowledge the Microelectronic and MaterialsTechnologyCentre (MMTC) at RMITUniversity for allowingthe use of their facilities. Authors also acknowledge the Aus-tralian Research Council (ARC) for supporting this projectand Samuel J. Ippolito acknowledges the ARC for APDIfellowship (LP100200859).

References

[1] UNEP, Global Mercury Assessment 2013: Sources, Emissions,Releases and Environmental Transport, UNEP ChemicalsBranch, Geneva, Switzerland, 2013.

[2] L. B. Chakraborty, A. Qureshi, C. Vadenbo, and S. Hellweg,“Anthropogenicmercury flows in india and impacts of emissioncontrols,” Environmental Science and Technology, vol. 47, no. 15,pp. 8105–8113, 2013.

[3] L. D. Hylander andM.Meili, “500 years of mercury production:global annual inventory by region until 2000 and associatedemissions,” Science of the Total Environment, vol. 304, no. 1–3,pp. 13–27, 2003.

[4] D. W. Boening, “Ecological effects, transport, and fate ofmercury: a general review,” Chemosphere, vol. 40, no. 12, pp.1335–1351, 2000.

[5] S. Liang, C. Zhang, Y. Wang, M. Xu, andW. Liu, “Virtual atmo-spheric mercury emission network in China,” EnvironmentalScience and Technology, vol. 48, no. 5, pp. 2807–2815, 2014.

[6] D. Jampaiah, K. M. Tur, S. J. Ippolito et al., “Structural charac-terization and catalytic evaluation of transition and rare earthmetal doped ceria-based solid solutions for elemental mercuryoxidation,” RSC Advances, vol. 3, no. 31, pp. 12963–12974, 2013.

[7] C. T. Driscoll, R. P. Mason, H. M. Chan, D. J. Jacob, and N.Pirrone, “Mercury as a global pollutant: sources, pathways, andeffects,” Environmental Science and Technology, vol. 47, no. 10,pp. 4967–4983, 2013.

[8] K.M.Kabir, Y.M. Sabri, G. I.Matthews, L. A. Jones, S. J. Ippolito,and S. K. Bhargava, “Selective detection of elemental mercuryvapor using a surface acoustic wave (SAW) sensor,”TheAnalyst,2015.

[9] K. M. Kabir, Y. M. Sabri, G. I. Matthews, S. J. Ippolito, andS. K. Bhargava, “Cross sensitivity effects of volatile organiccompounds on a SAW-based elemental mercury vapor sensor,”Sensors and Actuators B: Chemical, vol. 212, pp. 235–241, 2015.

[10] Y. M. Sabri, S. J. Ippolito, A. J. Atanacio, V. Bansal, and S.K. Bhargava, “Mercury vapor sensor enhancement by nanos-tructured gold deposited on nickel surfaces using galvanicreplacement reactions,” Journal of Materials Chemistry, vol. 22,no. 40, pp. 21395–21404, 2012.

[11] P. D. Selid, H. Xu, E. M. Collins, M. S. Face-Collins, and J.X. Zhao, “Sensing mercury for biomedical and environmentalmonitoring,” Sensors, vol. 9, no. 7, pp. 5446–5459, 2009.

[12] N. Pirrone, W. Aas, S. Cinnirella et al., “Toward the nextgeneration of air quality monitoring: mercury,” AtmosphericEnvironment, vol. 80, pp. 599–611, 2013.

[13] D. Martın-Yerga, M. B. Gonzalez-Garcıa, and A. Costa-Garcıa,“Electrochemical determination of mercury: a review,” Talanta,vol. 116, pp. 1091–1104, 2013.

[14] S. K. Pandey, K.-H. Kim, and R. J. C. Brown, “Measurementtechniques for mercury species in ambient air,” Trends inAnalytical Chemistry, vol. 30, no. 6, pp. 899–917, 2011.


[15] M. Rex, F. E. Hernandez, and A. D. Campiglia, “Pushingthe limits of mercury sensors with gold nanorods,” AnalyticalChemistry, vol. 78, no. 2, pp. 445–451, 2006.

[16] B. Mazzolai, V. Mattoli, V. Raffa et al., “A microfabricatedphysical sensor for atmospheric mercury monitoring,” Sensorsand Actuators A: Physical, vol. 113, no. 3, pp. 282–287, 2004.

[17] D. P. Ruys, J. F. Andrade, and O. M. Guimaraes, “Mercurydetection in air using a coated piezoelectric sensor,” AnalyticaChimica Acta, vol. 404, no. 1, pp. 95–100, 2000.

[18] T. Thundat, E. A. Wachter, S. L. Sharp, and R. J. Warmack,“Detection of mercury vapor using resonating microcan-tilevers,” Applied Physics Letters, vol. 66, pp. 1695–1697, 1995.

[19] E. P. Scheide and J. K. Taylor, “Piezoelectric sensor for mercuryin air,” Environmental Science and Technology, vol. 8, no. 13, pp.1097–1099, 1974.

[20] K. M. Kabir, Y. M. Sabri, A. E. Kandjani et al., “Mercurysorption and desorption on gold: a comparative analysis ofsurface acoustic wave and quartz crystal microbalance-basedsensors,” Langmuir, 2015.

[21] Y. M. Sabri, S. J. Ippolito, J. Tardio, V. Bansal, A. P. O’Mullane,and S. K. Bhargava, “Gold nanospikes based microsensoras a highly accurate mercury emission monitoring system,”Scientific Reports, vol. 4, article 6741, 2014.

[22] T. P. McNicholas, K. Zhao, C. Yang et al., “Sensitive detectionof elemental mercury vapor by gold-nanoparticle-decoratedcarbon nanotube sensors,” Journal of Physical Chemistry C, vol.115, no. 28, pp. 13927–13931, 2011.

[23] S. K. Vashist and P. Vashist, “Recent advances in quartz crystalmicrobalance-based sensors,” Journal of Sensors, vol. 2011,Article ID 571405, 13 pages, 2011.

[24] K. Kanazawa and N.-J. Cho, “Quartz crystal microbalance asa sensor to characterize macromolecular assembly dynamics,”Journal of Sensors, vol. 2009, Article ID 824947, 17 pages, 2009.

[25] M. Hoummady, A. Campitelli, and W. Wlodarski, “Acousticwave sensors: design, sensing mechanisms and applications,”Smart Materials and Structures, vol. 6, no. 6, pp. 647–657, 1997.

[26] D. Jr. Ballantine, R. M. White, S. J. Martin et al., AcousticWave Sensors: Theory, Design,& Physico-Chemical Applications,Academic Press, 1996.

[27] G. Sauerbrey, “Use of quartz vibration for weighing thin filmson a microbalance,” Zeitschrift fur Physik, vol. 155, pp. 206–212,1959.

[28] M. D.Ward and D. A. Buttry, “In situ interfacial mass detectionwith piezoelectric transducers,” Science, vol. 249, no. 4972, pp.1000–1007, 1990.

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttp://www.hindawi.com Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttp://www.hindawi.com Volume 2014


Active and Passive Electronic Components

Control Scienceand Engineering

Journal of



RotatingMachinery


Hindawi Publishing Corporation http://www.hindawi.com

Journal ofEngineeringVolume 2014

Submit your manuscripts athttp://www.hindawi.com

VLSI Design



Shock and Vibration


Civil EngineeringAdvances in

Acoustics and VibrationAdvances in



Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation http://www.hindawi.com

Volume 2014

The Scientific World JournalHindawi Publishing Corporation http://www.hindawi.com Volume 2014

SensorsJournal of


Modelling & Simulation in EngineeringHindawi Publishing Corporation http://www.hindawi.com Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks


Research Article Determining the Optimum Exposure...

Documents

Transcript of Research Article Determining the Optimum Exposure...