2370 IEEE SENSORS JOURNAL, VOL. 15, NO. 4, APRIL 2015

A Novel Sol–Gel Thin-Film Constant PhaseSensor for High Humidity Measurement

in the Range of 50%–100% RHTarikul Islam, Zia Ur Rahman, and Subhas Chandra Mukhopadhyay, Fellow, IEEE

Abstract— This paper proposes a new type constant phasesensor (CPS) for solving the problem of high humidity mea-surement. It is based on change in phase angle of the CPSwith variation of humidity. The CPS is having interdigi-tated electrode sandwiched between two identical thin films ofγ -Al2O3 fabricated by sol–gel dipcoating method. In the presenceof relative humidity, the device shows a fairly constant phasebehavior over wide signal frequency and its fractional exponentreduces to nearly 0.7 value at 90% RH from the initial valueof 1 at dry humidity. Results show that the CPS is effective inmeasuring humidity in the range of 50%–100% RH at the signalfrequency of 1–5 MHz. Finally, the device has been interfacedwith a simple fractional-order differentiator circuit to measurethe phase angle change with change in relative humidity.

Index Terms— Constant phase sensor, sol-gel method, γ-Al2O3,fractional order differentiator, high humidity measurement.

I. INTRODUCTION

ACONSTANT phase sensor (CPS) is a fractional orderelement whose impedance response shows constant

phase (CP) behavior over wide range of signal frequencies [1].Most of the real objects behave as fractional order systemexcept in some cases the order of the system is close tointeger value. The basic passive circuit elements such as anideal resistance, capacitor and inductor are the examples ofCP device at 0°, −90° and 90° phase angle respectively.The CP behavior has been observed by many researchersworking in the area of electrochemistry, electrical powertransmission, communication, and many other engineeringapplications [2]–[5]. This behavior has been observed at themetal-insulator-solution interface. This occurs due to diffu-sions of ions in the interface of different phases. It is explainedby researchers as the frequency dispersion of capacitance by

Manuscript received September 19, 2014; revised November 12, 2014;accepted November 19, 2014. Date of publication December 12, 2014; dateof current version February 10, 2015. This work was supported by theDepartment of Science and Technology, Government of India, under GrantSR/S2/CMP-11. The associate editor coordinating the review of this paperand approving it for publication was Prof. Gotan H. Jain.

T. Islam is with the Department of Electrical Engineering, Faculty ofEngineering and Technology, Jamia Millia Islamia Central University,New Delhi 110025, India (e-mail; tislam@jmi.ac.in).

Z. U. Rahman is with the Department of Electrical Engineering, JamiaMillia Islamia Central University, New Delhi 110025, India (e-mail:ziaur.678@gmail.com).

S. C. Mukhopadhyay is with the School of Engineering and AdvancedTechnology, Massey University, Palmerston North 4442, New Zealand(e-mail: s.c.mukhopadhyay@massey.ac.nz).

Color versions of one or more of the figures in this paper are availableonline at http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/JSEN.2014.2377242

dielectric relaxation, where the electric current density phaselags the changing electric field [6]. Constant phase behavioris not well understood, some researchers in the analyticalchemistry have reported that this phenomenon is observedat metal-insulator interface in polarizing medium such aswater [7], [8]. The CP behavior of CPS arises due to porousnature of the insulating film and the pore morphology ofthe film has significant effect on the parameters such as thefractional exponent and the amplitude [9]. CP behavior hasalso been reported due to nonuniformity and porous nature ofthe interface electrode [7]. Construction of the constant phasesensor is very simple and its response shows fairly constantphase angle within 0 to −90° over significant frequency rangein an ionized medium. The phase angle change depends on thearea of the contact electrode with the electrolyte, thickness ofthe insulating layer and the ionic conductivity of the polarizingmedium [6], [7]. The CP device has been employed success-fully in several sensing applications by some researchers suchas to monitor the microbial growth in yeast and raw milk, liq-uid level sensing and conductivity measurement etc. [6]–[10].Interface electronic circuit to convert the phase angle changeinto voltage output for such type of device is also very sim-ple [10]. The experimental results of the CPS in measurementapplications lead us to develop a new kind of CP device tomeasure high relative humidity. Humidity and temperature arewidely needed physical parameters which are to be measuredfor different industrial and home appliances [11]. Althoughthe temperature can be measured accurately with presenttransducers but measurement of humidity is complex since itis having extremely wide dynamic range. Such wide range cannot covered by a single sensor [11], [12]. Also measurementof humidity in trace level below 1000 ppm as well as highlevel above 95% RH is still a challenge [13]. There are severalimportant applications where high level of humidity measure-ment is needed and its importance is gradually increasing dayby day [14]. The most important problem in high humiditymeasurement above 95% RH is the water condensation inthe pores which causes difficulty in desorption [14]. Alsoin some cases, due to water adsorption, the sensing filmgets damaged [15]. Nanostructured ceramic humidity sensorsare widely used to fulfill the application needs in differentranges due to their chemical inertness, mechanical strength andlarge working temperature [12], [13], [15]. Relative humiditysensor is conventionally fabricated by porous ceramic, poroussilicon, polymer or electrolytic type materials [9], [10], [12].

1530-437X © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.

ISLAM et al.: NOVEL Sol–Gel THIN-FILM CPS 2371

Conventional polymer based RH sensor is not suitable forthe measurement of humidity above 95% RH [15]. The mostwidely used capacitive sensors have interdigitated electrode forrelative humidity sensing [11]. When a capacitive humiditysensor is exposed to the humidity there is a possibility forthe formation of double layer capacitance at the interface ofmetal (electrode) and electrolyte (water vapor) [1], [7], [16],[17]. The effect of the double layer capacitance is significantat low signal frequency [7]. Formation of double layer capac-itance depends on the pore morphology like pore dimension,distribution of pores, thickness, nonuniformity of the porousinsulating film and the concentration of the humidity [6], [7].Due to lack of unanimity, different equivalent circuits havebeen proposed to represent the interface phenomenon such asHelmholtz model for the formation of double layer capacitanceat the interface or the Gouy-Chapman-Stern model havingtwo capacitors in series [7] or more exact model utilizingconstant phase element [1]. Although this behavior has beenobserved for almost all type of capacitive humidity sensors, itis mostly overlooked in the equivalent circuit of the sensor formany work reported in the literature [18], [19]. Selection ofsignal frequency is very crucial for sensing relative humiditybecause of the formation of double layer capacitance at lowfrequency [19].

Present work studies the behavior of a CP element in pres-ence of humidity thus proposes a new type device for sensinghigh humidity. The CPS consists of an interdigitated electrodesandwiched between two identical thin film layers of γ-Al2O3.The film is prepared by the sol-gel method [13], [20], [21].The construction of the device is very simple and it is bulkproducible at low cost. In the sol-gel method materials aremixed at molecular level resulting a solution having colloidalgel. Once the solvent is removed during heating, a pure solidthin film with high degree of fine porosity is produced. Thesolid film is then subsequently sintered to produce a more fullydense nanostructured layer [20], [21]. γ-Al2O3 film preparedby this method is hydrophilic to water vapor condensation andthe film does not damage even if there is water condensationas observed to the polymer based RH sensor [11], [15]. Alsothe effective surface area of the film is very large whichis desirable for high sensitivity and the film can withstandhigh working temperature. Fabrication of the device has beendescribed. The parameters of the constant phase sensor havebeen studied under different % RH over wide frequency rangeof 100 Hz to 5 MHz. An equivalent circuit has been proposedto explain the behavior of the device. Finally a simple circuithas been developed to measure the phase angle of the CPSwith change in relative humidity.

II. THIN FILM CONSTANT PHASE SENSOR

A. Fabrication of the Sol-Gel Thin Film CPS Sensor

The CPS has been fabricated slightly in different waysas reported in the literature [1], [6], [9]. Instead ofusing polymythayl metha accrylate (PMMA) insulating film,aluminum oxide film because of its chemical inertness andthermal stability has been used [6]. An alumina substrateof dimension 19 mm × 9 mm and thickness of 0.65 mm

Fig. 1. Schematic of the constant phase sensor (CPS) for humiditymeasurement.

Fig. 2. FESEM image of the nanoporous γ-Al2O3 thin film.

was initially soaked in boiled acetone for some time thencleaned in running DI water. The substrate was then driedin the nitrogen gas flow [22]. Thin film of γ-Al2O3 ofthickness ∼6 μm has been deposited from the AlO(OH) solby dipcoating method. The sol solution has been prepared byYoldas method [20], [21]. The film was dried initially at 80 °Cfor 5m and then sintered at 450 °C for 1h. The interdigitatedgold electrode of area 10 mm × 7 mm has been printed onthe film by screen printing technique. The finger width of theelectrode is 5 mm and the gap between the fingers is 3 mm.The electrode is then sintered at 900 °C for 1h. Another thinfilm of γ-Al2O3 of same thickness has been formed on theelectrode and sintered at 450 °C for another 1h. Thus thedevice has thin film of Al2O3 on both side of the electrode.Thin insulation of Al2O3 on the top layer of the electrode hasbeen provided to minimize the charge transfer process betweenmetal electrode and water vapor condensed on the electrode.The insulated metal surface also makes the interface behaviormore consistent [1]. Fig. 1 shows the schematic representationof the CPS.

Pore morphology of the thin film plays important role forits CP behavior at different concentration of humidity. Poremorphology of the film is controlled by varying the fabricationparameters such as sintering temperature and sintering time inaddition to the preparation parameters of the sol solution [13].To avoid the pilling off the film from the electrode, the film isheated at small heating rate of 50 °C/h. Pore morphology of thefilm was studied by BET surface area analyzer and FESEM.Detailed studies of the morphology have been reportedelsewhere [13].

Fig. 2 shows FESEM image of the porous Al2O3 film. Theeffective surface area of the film per unit gram of the sample

2372 IEEE SENSORS JOURNAL, VOL. 15, NO. 4, APRIL 2015

as obtained by the BET method is approximately 200 m2/g.The average dimension of the pores is 10.4 Å and themicropore volume is ∼0.20 cc/g. The film has distributionof pores in the range of ∼0.8 to 60 Å.

B. Working of the CPS Device for Humidity Sensing

The impedance Z of CPS is given by [6], [8], [23]

Z(s) = Qs−β (1)

where s is the Laplace operator, Q and β are the parametersof the sensor. Replacing s by jω, (1) can be written as

Z ( jω) = Q ( jω)−β = Qω−β j−β (2)

where ω is the signal frequency, β is the fractional exponent(−1 < β < 1), Q is the coefficient. Magnitude of theimpedance is given by |Z( jω)| = Qω−β and the phase angleis given by θ = −πβ/2. Magnitude of the CPS depends onthe frequency as well as fractional exponent. The phase angledoes not depend on the signal frequency but depends on thevalue of β. For the CPS, β varies from 1 to 0. When β =1,Z(jω) = Q/jω representing a pure capacitor and when β = 0,Z(jω) = Q representing a pure resistance. The phase angle θdepends on different factors as given by

θ = f (A, t, RH ) (3)

where A is the contact area of the electrode in polarizingmedia, t is the thickness of the insulating layer and RH is thepercentage relative humidity. For the present CPS, parametersA (= 44 mm2) and t (∼6μm) are constant and RH variesfrom 4 to 96%. When the sensor is exposed to ambienthumidity the water molecules are initially chemisorbed in theporous layer and subsequently with increase in humidity, watermolecules are physisorbed on the chemisorbed layer [16].At low humidity, monolayer of chemisorbed water is disso-ciated into hydroxyl ion (OH−) and proton (H+). These ionsare remained attached on the oxide surface. At high humidity,water molecules will be physisorbed on chemisorbed layer andsubsequently multilayer water molecules behaving as liquidwater will be formed. The water molecules will condensein the pores of the film having radius less than the Kelvinradius [11], [16]. At high humidity, H+ is the dominantcharge carrier and the condensed physisorbed water layerpossesses high dielectric constant causing large change in bothconductance and capacitance [11], [16], [17].

III. TESTING OF THE SENSOR

Experiment has been performed using Agilent 4294Aimpedance analyzer with sinusoidal ac voltage of500 mV (rms) in (Z,θ), and (R,X) modes. The frequency ofthe input signal is varied from 100 Hz to 5 MHz. Effect ofvariation of signal amplitude to the phase angle change hasalso been studied. The schematic of the experimental set upfor testing the sensor is shown in Fig. 3. Percentage relativehumidity has been varied by mixing dry N2 gas with watervapor created using a bubbler. The concentration of humidityin the N2 gas is varied from 4 to 96% RH. The humidity levelin the chamber has been measured with a commercial RH

Fig. 3. Schematic of the experimental set up for testing the CPSwith % relative humidity.

Fig. 4. Variation of impedance of the sensor with humidity (%) at differentsignal frequency.

meter (Honeywell). The accuracy of the meter is ±3.5% RH.The sensor is placed inside a stainless steel sample chamberof volume ∼100 cc. The leads of the sensor are connectedto the impedance analyzer which is interfaced to a desktopPC with a data acquisition card. Experiments are performedat room temperature of 25 °C to determine the deviceparameters such as: (i) impedance response, (ii) phase angleshift, (iii) variation of CPS parameters (β, Q), (iv) variationof phase with amplitude of ac signal, (v) transient responsefor response and recovery time and (vi) repeatability of thesensor output.

A. Determination of the Electrical Characteristicsof the Sensor

Initially, the sensor is refreshed by dry N2 gas at 4% RHand it is then exposed to different percentage humidity. Theimpedance response with humidity at different signal fre-quency is shown in Fig. 4.

Initially at low humidity, the impedance change is smalland above 40% RH, the impedance of the sensor decreasessignificantly with increase in humidity. Impedance value alsodecreases with increase in signal frequency. Fig. 5 shows thevariation of phase angle with signal frequency for differenthumidity. It is observed that at constant RH, the phase angleis fairly constant over wide range of frequencies (1 to 5MHz)but as the humidity level increases, the constant phase angle isshifted from initial value. At 3 MHz signal frequency when thesensor is exposed to 4% RH, the phase angle is close to −90°but at 96% RH, the phase angle is −63°. From the experimen-tal data in Z, θ mode for different RH, the parameters of CPSsuch as Q and β have been determined. Values of β and Qat different signal frequency with the variation of humidity

ISLAM et al.: NOVEL Sol–Gel THIN-FILM CPS 2373

Fig. 5. Variation of phase angle of the sensor with humidity at differentsignal frequency.

Fig. 6. Variation of fractional exponent (β) with humidity (%) at differentsignal frequency.

Fig. 7. Variation of Q with humidity (%) at different signal frequency.

are shown in Fig. 6 and Fig. 7 respectively. At 4% RH,parameter β is close to unity behaving as a capacitor but asRH level increase, β decreases and at 96% RH, it reducesto nearly 0.70 (f = 3 MHz). Thus, the value β decreases byalmost 30% due to nearly 92% change in RH. The responseof the CPS for varying signal amplitude at constant RH isshown in Fig. 8 and it has been observed that the phase angleis nearly constant with signal amplitude. CP behavior does notchange due to change in signal amplitude [6].

IV. RESULTS AND DISCUSSION

The constant phase behavior of the sensor is due to theporous nature of the γ-Al2O3 film deposited on the electrode.At low humidity the device shows CP behavior over widesignal frequency but at humidity above 40% RH, it is shiftedto higher frequency range. When the sensor is exposed to

Fig. 8. Variation of phase angle with change in signal amplitude at 50% RH.

Fig. 9. Nyquist plot of the impedance data of the sensor: (a) 30–60% RHand (b) 70%–96% RH.

higher humidity, water is diffused inside the pores. Somepores are deep enough that water comes in contact withthe electrode. The origin of the CP behavior is attributed tothe capacitance dispersion of double layer at metal electrodeand water interface. There is a surface distribution of timeconstant (RC) due to inhomogeneous nature of the thin film.This distribution of time constant also causes CP behaviorof the sensor [24]–[29]. The complex impedance plot wherenegative of imaginary component of the impedance (X) isplotted against real component (R) is shown in Fig. 9.

Fig. 9(a) shows the plot between X v/s R for variationof humidity from 30–60% and Fig. 9(b) shows the plot forthe variation of humidity from 70–96%. The data for theplot have been obtained by performing an experiment usingimpedance analyzer in R, X mode. At lower humidity, theresponse is a curved line but at higher humidity, the responsehas two distinct parts (i) a semicircle at higher frequencyand (ii) curved straight line at lower frequency. The radiusof the semicircle is different for different humidity level. Thecurved line in the complex impedance plots can be explainedby diffusion mechanism. Diffusion gives rise to CP behaviordue to inhomogeneities in the shape and the size of the pores ofthe film as well as electrode. A constant phase element can beused to model this behavior of the sensor [8], [16], [17], [23].The semicircular part of the complex impedance plot shrinksas the humidity level increases. H+ ion is the dominantcharge carrier at high humidity. The concentration of thecarrier increases with increase in humidity. These H+ ionscan move more freely through the physisorbed water layers.This increases the electrical conductivity of the sensor. Thesensor also possesses high effective dielectric constant as thewater molecules form dipoles and condense in the pores of thefilm. Hence at high humidity, both conductance and dielectricconstant of the film change significantly. The semicircularnature of the plot can be modeled by a parallel RC circuit.

2374 IEEE SENSORS JOURNAL, VOL. 15, NO. 4, APRIL 2015

Fig. 10. Proposed equivalent circuit of the sensor.

At low frequency, the dipoles can orient-reorient freely underac field causing large change in capacitance. Impedance of theparallel RC circuit is given by

Z R‖C = R1

1 + ω2C21 R2

1

− jωC1 R2

1

1 + ω2C21 R2

1

(4)

where, ω is the angular frequency. If the negative of imaginarypart of the above impedance is plotted against the real part,the resulting plot will be a semicircle with diameter equalto R [16], [27]. As humidity increases, resistance of thefilm decreases and the diameter of the semicircle reduces.The slightly curve straight line reflecting CP behavior canbe represented by (2) [16]. Based on the experimental datashown in Fig. 9, the approximate equivalent circuit is shownin Fig. 10.

Parallel (C1, R1) represents the semicircle part of theresponse curve, (CPpore, Cpore) indicates water diffusionoccurring inside the nano order pores of the sensor and(CPelec, Celec) represents interface between water and electrode(electrode charge transfer). CPpore and CPelec are the two CPelements formed at the pores and the interface of electrodeand ionic medium. Cpore and Celec are the capacitance formedat the pores and the interface. These four elements representthe straight line part of the complex impedance plot. Thecapacitance Cc depends on the geometries of the electrode.It is possible to detect the humidity level above 96% RHby the sensor. Testing of the device above 96% RH usingreference meter has been avoided to protect the reference RHsensor from water condensation which may cause failure ofthe RH meter. At saturation vapor pressure, when the RH levelreaches 100%, the water molecules do not remain in vaporform rather these become liquid and there will be condensationof water in the sensing film. The reference RH sensor utilizespolymer sensing film which is spoiled sometimes due to watercondensation [15]. However, to obtain the reponse of the CPSabove 96% RH, the experiment has been conducted by dippingthe sensor in liquid water and its impedance change withsignal frequency from 100 Hz to 5 MHz has been determined.The response has been noted at different dipping length. Theresponse curve of the sensor in liquid water is plotted inFig. 11. It has been observed that the phase angle is shiftedfrom almost −90° at 4% RH to −25° at almost 100% RHat 2.75 MHz frequency (1cm dip). Since, the sensing film ofCPS is of Al2O3, it is not damaged even though it is dipped inliquid water. Fig. 12. shows the constant phase angle responseof the sensor with different RH at 2.75 MHz frequency.

Fig. 11. Phase angle change of the sensor when dipped in liquid water.

Fig. 12. Phase angle response of the sensor with humidity at 2.75 MHz.

This response has been plotted to observe the total shiftin phase angle of CPS for change in humidity from4% to 96% RH. Phase angle change starts at 40% RH andabove 50% RH it is significant.

However phase angle change below 50% RH is not signif-icant. At lower RH, due to the lower concentration of waterinside the pores, phase angle of the impedance response ofthe sensor is close to −90°. As humidity increases, amount ofwater diffused inside the pores increases causing the sensor toshow CP behavior and phase angle deviates from −90°. Porousnature of the electrode surface and the pore morphology ofthe insulating film may play an important role in enhanc-ing the sensitivity and lowering the frequency range of theCP device [27], [30]. In the present case, the pore sizeis less than 50 nm and the constant phase is observed athigher frequency. It is expected that by optimizing the poremorphology, both sensing range of humidity and frequencyband of CP can be improved. Response time and repeatabilityof the output are other important characteristics of the sensor.The repeatability of the sensor has been determined from thetransient response curve for 10 to 90% step change of relativehumidity for several cycles at signal frequency of 1 MHz.The reproducibility of the sensor is shown for three identicalhumidity cycles. The sensor output for phase angle shift ishighly repeatable as shown in Fig. 13. The response time ofthe device is ∼80s and recovery time is ∼53s respectively. Thestability of the thin film of Al2O3 for developing capacitivetrace moisture sensor due to variation of ambient temperaturewas studied and the sensor showed negligible change in theoutput [13].

ISLAM et al.: NOVEL Sol–Gel THIN-FILM CPS 2375

Fig. 13. Reproducibility of the sensor output for 10% to 90% step changein humidity.

Fig. 14. Schematic of the phase angle measuring circuit at different RH.

Fig. 15. Photograph of the digital oscilloscope (DSO) screen showing phasedshift at 90% RH.

V. INTERFACING THE CPS WITH SIGNAL

CONDITIONING CIRCUIT

Sensor was interfaced with a fractional order differentiatorcircuit to measure the phase shift with humidity. Fig. 14 showsthe schematic of the circuit. Sinusoidal excitation voltage of2.6 V and frequency of 1 MHz was applied as input to thecircuit. 1 MHz signal frequency has been selected as theCPS has shown fairly constant phase behavior above 1 MHzfrequency. A simple circuit has been used to produce two180° out of phase signals using conventional low cost OpampsLF-356 at 1 MHz frequency. The sensor is connected to theinput of the differentiator circuit and a resistor of suitable valueis connected to the feedback path [6].

The device is exposed to different humidity and the phaseshift between input and output wave forms is measured bya digital oscilloscope (Agilent technologies DSO 1002A).Fig. 15 shows the photograph of the DSO screen at 90% RHshowing phase shift from reference input.

Fig. 16 shows the phase shift at different humidity measuredfrom DSO output. The behavior of the curve is similar to thatof CP response obtained using the impedance analyzer. At low

Fig. 16. Change in phase angle of output signal of the electronic circuit withrelative humidity.

humidity, the phase shift is close to zero. With increase inhumidity beyond 50% RH, the phase shift increases and itbecomes ∼−50o at 96% RH. The shift in phase angle can beconverted into voltage signal by using phase detection circuitshown in the Fig. 14.

VI. CONCLUSION

Present work deals with the development of a novel constantphase humidity sensor using thin porous film of metal oxideof Al2O3. Film is deposited by sol-gel dip coating method.Sensor behaves as CP device when it is exposed to humiditydue to the porous nature of the film. Experimental result showsthat there is a significant change in the fractional order of theCPS with humidity. The sensor was finally interfaced witha fractional order differentiator to measure phase shift withhumidity at 1 MHz frequency. The phase shift versus RH plotwas similar to the phase angle response of the sensor obtainedfrom impedance analyzer. From the results and discussionsit is apparent that the proposed CP device can be used forhumidity measurement above 50 % RH even the humiditylevel at saturation vapor pressure. The fabrication as well asdetection electronics circuit for phase angle measurement isvery simple. The device is suitable for large scale productionand it has the potential for industrial application. Future workrequires improving the detection range of the sensor to lowerhumidity by optimizing the pore morphology and electrodestructure.

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Tarikul Islam received the B.Sc.Eng. degree inelectrical engineering and the M.Sc.Eng. degree ininstrumentation and control systems from AligarhMuslim University, Aligarh, India, in 1994 and1997, respectively, and the Ph.D. (Eng.) degree fromthe Department of Electronics and Telecommuni-cation Engineering, Jadavpur University, Kolkata,India, in 2007. He is currently a Professor withthe Department of Electrical Engineering, Faculty ofEngineering and Technology, Jamia Millia IslamiaCentral University, New Delhi, India. He has

authored 36 papers in peer-reviewed journals and 45 papers in the internationaland national conferences. He received a grant from the Department of Scienceand Technology and the Department of Atomic Energy, India, over 161 000on different research projects. His research interests include thin-film sensor,sensor and electronic instrumentation, and soft computing techniques forsignal conditioning.

Zia Ur Rahman received the M.Tech. degree ininstrumentation and control systems from AligarhMuslim University, Aligarh, India. He is currentlya Ph.D. Research Scholar with the Department ofElectrical Engineering, Faculty of Engineering andTechnology, Jamia Millia Islamia Central University,New Delhi, India. His research interest is in instru-mentation and measurement.

Subhas Chandra Mukhopadhyay (M’97–SM’02–F’11) received the (Hons.) degree from the Depart-ment of Electrical Engineering, Jadavpur University,Kolkata, India, the master’s degree in electricalengineering from the Indian Institute of Science,Bangalore, India, the Ph.D. (Eng.) degree fromJadavpur University, and the Dr.Ing. degree fromKanazawa University, Kanazawa, Japan. He is cur-rently a Professor of Sensing Technology with theSchool of Engineering and Advanced Technology,Massey University, Palmerston North, New Zealand.

He has over 25 years of teaching and research experience. His fields ofinterest include sensors and sensing technology, instrumentation, wirelesssensor networks, electromagnetics, control, electrical machines, and numericalfield calculation. He has authored or co-authored three books and over300 papers in different international journals, conferences, and book chapter.He has edited 12 conference proceedings. He has also edited 11 specialissues in international journals as a lead Guest Editor and 19 books out ofwhich 17 books are with Springer-Verlag. He has delivered 216 seminars askeynote, invited, tutorial, and special lectures in 24 countries. He receivednumerous awards throughout his career and attracted over NZ 3.6 M ondifferent research projects. He is a Fellow of the Institution of Engineering andTechnology (U.K.) and the Institution of Electronics and TelecommunicationEngineers (India). He is a Topical Editor of the IEEE SENSORS JOURNAL,an Associate Editor of the IEEE TRANSACTIONS ON INSTRUMENTATIONAND MEASUREMENTS, a Technical Editor of the IEEE TRANSACTIONS ON

MECHATRONICS, and a Co-Editor-in-Chief of the International Journal onSmart Sensing and Intelligent Systems. He was the Technical Program Chairof ICARA 2004, ICARA 2006, and ICARA 2009. He was the General Chair/Co-Chair of ICST 2005, ICST 2007, the IEEE ROSE 2007, the IEEE EPSA2008, ICST 2008, the IEEE Sensors 2008, ICST 2010, the IEEE Sensors 2010,ICST 2011, ICST 2012, ICST 2013, and ICST 2014. He has organized theIEEE Sensors Conference 2009 at Christchurch, New Zealand, as the GeneralChair. He is planning to organize the Ninth ICST in Auckland, New Zealand,in 2015. He is the Founding and Ex-Chair of the IEEE Instrumentation andMeasurement Society New Zealand Chapter, and the Chair of the IEEE IMSTechnical Committee 18 on Environmental Measurement.