A novel gas flow sensing application using

Sensors and Actuators A 187 (2012) 194–200

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A novel gas flow sensing application using piezoelectric ZnO thin films deposited on Phynox alloy Sudeep Joshi, Mitesh Parmar, K. Rajanna ∗ Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore 560012, India

a r t i c l e

i n f o

Article history: Received 3 January 2012 Received in revised form 3 May 2012 Accepted 23 August 2012 Available online 31 August 2012 Keywords: ZnO thin films Piezoelectricity X-ray diffraction Sensing

a b s t r a c t We report on the novel flow sensing application of piezoelectric ZnO thin film deposited on Phynox alloy sensing element. Characterization of piezoelectric ZnO films deposited on Phynox (Elgiloy) substrate at different RF powers is discussed. ZnO films deposited at RF power of 100 W were found to have fine c-axis orientation, possesses excellent surface morphology with lower rms surface roughness of 1.87 nm and maximum d31 coefficient value 4.7 pm V−1 . The thin cantilever strip of Phynox alloy with ZnO film as a sensing layer for flow sensing has been tested for flow rates ranging from 2 to 18 L min−1 . A detailed theoretical analysis of the experimental set-up showing the relationship between output voltage and force at a particular flow rate has been discussed. The sensitivity of flow sensing element is ∼18 mV/(L min−1 ) and typical response time is of the order of 20 m s. The sensing element is calibrated using in-house developed testing set-up. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Numerous applications in several industries and plants often require the accurate measurement of fluid flow rates in the order of L min−1 . A number of techniques are available for the measurement of fluid flow rate. Most of these techniques are based on either microchannel – based – calorimetric method or fiber optic technique [1–3]. Recently, few investigators have also reported on the microcantilever based flow sensors [4–6]. In general, microcantilevers are fabricated by MEMS technology in which the releasing of cantilever beam is a difficult process due to the fundamental problem of stiction, which often results in the failure of the structure. These above mentioned techniques are widely employed and are suitable for the measurement of very low flow rates in the range of nl min−1 to ␮l min−1 . There is still a great challenge ahead to measure the flow rates in the range of L min−1 by using smart thin film materials and micro-sensor technology. In our present work, we have chosen ZnO as a sensing film due to its ease of deposition on wide variety of substrates. Also, ZnO is a compositionally simple material and is examined to a greater extent because of its excellent piezoelectric and mechanical properties. Moreover, unlike PZT and PVDF, ZnO film does not require any poling process because of its self poling ability [3]. The hexagonal wurtzite crystal structure of ZnO, which is one of the most stable forms and lacks the inversion symmetry due to

∗ Corresponding author. Tel.: +91 80 22933188; fax: +91 80 23600135. E-mail addresses: [email protected], [email protected] (K. Rajanna). 0924-4247/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.sna.2012.08.032

which it possess piezoelectric property. ZnO films possessing good piezoelectric property are known to have high degree of c-axis orientation perpendicular to the substrate [7] and lower value of full width at half maxima (FWHM) which increases the grain size of ZnO films resulting in better piezoelectric property [8]. The evaluation of piezoelectric coefficient values of ZnO films is an essential requirement for assessing their suitability in sensing applications. In this paper, we are reporting the use of cantilever sensing element made of Phynox (elgiloy) strips with piezoelectric ZnO film as a sensing layer, to measure the fluid flow rate in the range of L min−1 . The calibration of sensing element was performed by using the in-house developed testing set-up. It is to be noted that, the deposition, characterization and application of piezoelectric ZnO film on Phynox substrate is reported for the first time. 2. Experimental 2.1. Substrate used for ZnO thin film deposition In our present experimental study, ZnO films were deposited on Phynox (Elgiloy) (Lamineries, MATTHEY SA) substrate, which is austenitic cobalt based alloy. The thickness of the Phynox strips employed is 40 ␮m. The Phynox strips served as both, the substrate and as the bottom electrode of sensing element. Phynox has many ideal properties, for its use as a sensing element. It has high ultimate tensile strength (UTS) of 2600 N mm−2 , high Young’s modulus of 220 kN mm−2 , good fatigue strength, low hysteresis and extremely resistant to corrosion. It also has exceptional spring properties and high yield strength of 2200 N mm−2 . It can be used over a very

S. Joshi et al. / Sensors and Actuators A 187 (2012) 194–200

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wide range of temperatures from −268.8 ◦ C (liquid helium) to about 500 ◦ C [9]. It is also known that Phynox is a biocompatible alloy, and hence is widely used as electrode in pacemakers and for implant components. It is used as membranes for pressure sensors and in relays and switches for the automotive industries. Phynox is also used widely in products related to telecommunication and aerospace industries [9]. 2.2. Deposition of ZnO thin films We have used RF reactive magnetron sputtering technique for the deposition of ZnO thin films. The target employed was a sintered stoichiometric ZnO circular target of purity 99.9% (VIN Karola instruments, Norcross, USA). Prior to loading the Phynox substrates for deposition, these were cleaned ultrasonically with soap solution to remove stains of oil and grease, properly rinsed with organic solvent (Isopropyl alcohol/acetone) to remove any remaining dust particles trapped at the surface and subsequently dried in the flowing nitrogen gas. The chamber was evacuated to an ultimate vacuum of ∼1 × 10−6 mbar. Initially, inert argon gas (99.9% pure) was admitted and subsequently reactive oxygen gas (99.9% pure) was introduced and flow rates of both the gases were controlled by using digital mass flow controllers (MKS PR-4000, USA). Prior to deposition, pre-sputtering was carried out in order to remove impurities from the target surface and to make plasma stable. ZnO films were deposited at different RF powers (ranging from 50 to 200 W) by maintaining all other parameters (Ar–O2 ratio 90%–10%, target–substrate distance 55 mm and working pressure 0.035 mbar) constant. The X-ray diffraction studies were performed by using Bruker D8 Advance X-ray diffractometer with Ni-filtered Cu K␣ ( = 0.1542 nm) radiation. The surface roughness was measured using AFM (ESPM 3D AFM, Novascan technologies, USA). The d31 coefficient values of ZnO piezoelectric films were measured by 4point bending method (aixACCT 4-point bending system, model: aix4PB). 2.3. Measurement of the gas flow rate The sensing element employed for the measurement of gas flow rate is a metal–insulator–metal (M–I–M) type structure. It consists of Phynox strips cantilever (dimensions – length: 50 mm, width: 5 mm and thickness: 40 ␮m), which acts as a bottom electrode for sensing element and as a substrate for ZnO sensing film. Thickness of the sensing film was 720 nm and on to which a top silver electrode film (thickness: 100 nm) was deposited. The various optimized sputtering process parameters maintained for the deposition of good quality piezoelectric ZnO sensing film and top silver electrode film are shown in Table 1. The measurement set-up along with ZnO deposited cantilever sensing element used for gas flow rate measurement is shown in Fig. 1. The Phynox cantilever coated with ZnO sensing film itself was very delicate to handle. Therefore, the flow sensing element was Table 1 Various sputtering process parameters optimized for deposition of ZnO sensing film and top silver electrode film. Process parameters Ultimate pressure (mbar) Working pressure (mbar) Target to substrate distance (mm) Ar–O2 ratio (%) Substrate temperature (◦ C) Applied RF power (W)

ZnO

Ag −6

1 × 10 0.035 55 90–10 250 100

4 × 10−6 0.035 52 – R.T. 40

Fig. 1. Measurement set-up along with ZnO deposited cantilever sensing element for gas flow rate measurement.

properly packaged and fixed within the aluminum fixture having the surface roughness less than (ra = 0.04 ␮m) and tightened with the brass screws. As the nozzle was an integral part of our flow system, all the flow rate measurements were performed by using the same nozzle (outlet diameter 0.1 mm and length 50 mm). The position of the nozzle was firmly fixed by using the brass clamps as shown in Fig. 1. A gap of 5 mm was accurately maintained between the nozzle and the cantilever tip for all flow rate measurements. In order to measure the gas flow rate using ZnO deposited cantilever sensing element, the flow rate of test gas was properly controlled using the flow regulator (MESSER, Germany). In our present experiment, argon was used as a test gas due to its easy availability. A solenoid valve was employed to generate the quasistatic pressure pulses, and then these jets of pressure pulses were made to impinge on the tip of cantilever sensing element resulting in the bending of cantilever. Gas flow from the nozzle exerts a concentrated tip force on the cantilever. When the gas flow was suddenly stopped by switching off the solenoid valve the cantilever sets into vibration, resulting in the generation of output voltage signal due to bending stress–induced piezoelectric effect. As the cantilever vibration decays with time, it generates an output voltage waveform of sine wave in nature with decaying amplitude. The amplitude of the first peak of output voltage gives the direct measure of gas flow rate. Larger is the amplitude of first peak, higher is the gas flow rate. Flow rate of argon gas was varied from 2 L min−1 to a maximum of 18 L min−1 . The extent of tip deflection of cantilever sensing element at different flow rates was determined from the images captured by high-speed digital camera (1000 frames per second). 2.4. Calibration method ZnO deposited cantilever sensing element was calibrated using the in-house developed testing set-up. Fig. 2 shows the calibration arrangement consisting of charge amplifier, power supply for electromagnet and digital oscilloscope. The Phynox alloy substrate is non-magnetic, so a small iron filing is glued at the tip of cantilever for the purpose of subjecting the cantilever to deflect using an electromagnet. An electromagnet was brought close to the tip of cantilever sensing element and energized to attract the cantilever. Further the electromagnet was moved vertically downwards in order to bend the cantilever to the desired extent. Subsequently the electromagnet was de-energized, resulting in the release of cantilever and hence setting the cantilever to vibrate.

196


2.5. Theoretical analysis The aim of this section is to derive an analytical expression to establish the relationship between the force exerted by test gas at a particular flow rate and the output voltage. First part of this section, deals with the analysis of nozzle wherein the extent of force exerted at a particular flow rate of test gas is discussed. The later part deals with the magnitude of output voltage generated due to the mechanical bending of the cantilever sensing element by the force exerted at a particular flow rate. 2.5.1. Analysis of the gas flow from the nozzle Fig. 4 shows the schematic diagram of nozzle and cantilever sensing element. The velocity of test gas at section “1” is denoted by V1 . As the flow rate of test gas, Q is known, we can find out V1 from continuity equation: Q = A1 V1

(2)

4Q

Fig. 2. In-house developed calibration set-up for ZnO deposited cantilever sensing element.

V1 =

The cantilever sensing element was released from different heights and corresponding output voltage waveforms obtained were recorded. As the vertical distance moved by the electromagnet increases, the deflection also increases resulting in higher concentrated tip force at free end of the cantilever. The amplitude of first peak of output voltage waveform gives a measure of the concentrated point force applied at the tip of cantilever. The amplitude of first peak obtained serves as a signature for the magnitude of point force at the cantilever tip. The extent of force to which the cantilever was subjected at different tip deflection was calculated from the Euler–Bernoulli beam theory as:

where A1 and D1 are the area and diameter of the nozzle at section “1” respectively. In order to find out the expression for velocity of test gas coming out of the nozzle at section “2”, denoted by V2 , we apply the Bernoulli’s equation:

F=

3EIı L3

(1)

where ı = deflection of the tip, F = force applied, L = length of the cantilever, E = modulus of elasticity, I = moment of inertia. The in-house developed calibration process gave us the relationship between, the point force applied at the tip of cantilever and amplitude of first peak of output voltage waveform. In order to achieve higher accuracy during calibration process, measurements were repeated for 5 times at a particular deflection of the cantilever sensing element. Fig. 3 shows the variation of output voltage (mV) versus force (mN) at the tip of cantilever sensing element. It is clearly evident that, the variation exhibits linearity.

Fig. 3. Variation of output voltage (mV) with respect to force (mN).

V12 2

(3)

˘D12

+ gZ1 +

V2 P1 P2 = 2 + gZ2 + 1 2 2

(4)

where P1 and P2 are the pressure at section “1” and “2” respectively, g is the acceleration due to gravity, Z1 and Z2 are the respective elevation of section “1” and “2” with respect to reference level, i.e. section “3”. In order to make the analysis simpler, friction losses are neglected and the density of test gas is assumed to be same, Hence we have 1 = 2 = . V22 2

=

V2 =

V12 2

+ gZ1 +

P1 P2 − gZ2 − 1 2

V12 + 2g(Z1 − Z2 ) +

(5)

2 (P1 − P2 )

(6)

The jet of test gas is coming out in the atmosphere, so the pressure at section “2”, i.e. P2 becomes equal to the atmospheric pressure. As the density, of test gas used is known, hence we can

Fig. 4. Schematic diagram of the nozzle and the cantilever sensing element.


˙ At section “3” due to the stagnation find out the mass flow rate, m. condition, we assume that at tip of cantilever the velocity, V3 = 0. Assuming the total momentum transfer from nozzle’s end to the tip of cantilever, the amount of force exerted by jet of test gas coming out of the nozzle at the tip of cantilever can be given by rate of change of momentum: ˙ × V2 F =m

(7)

2.5.2. Analysis of the ZnO deposited cantilever sensing element Fig. 5 shows the schematic diagram of ZnO deposited cantilever sensing element. The substrate material is Phynox alloy, which is a non-piezoelectric material and ZnO sensing film is a piezoelectric material. Hence, the present sensing element is a unimorph cantilever structure. The equation for the amount of charge, Q developed for an external tip force, F acting on the unimorph sensing cantilever element has been derived by Wang et al. [10] Q =

3d31 L2 2 tsen

AB(B + 1) F 1 + 4AB + 6AB2 + 4AB3 + A2 B4

sen S11 sub S11

=

Esub t and B = sub Esen tsen

C=

LwεX33 tsen

2 1 − k31

AB(1 + AB3 ) 1 + 4AB + 6AB2 + 4AB3 + A2 B4

(10)

2 is transverse piezoelectric coupling coefficient, εX is where k31 33 dielectric constant of ZnO piezoelectric film. Since, we know the values of charge, Q and capacitance, C then the voltage, V can be obtained by the relation:

Q = CV

Hence we can have,

V=

Q C

(11)

Putting values from Eqs. (8) and (10), we have the output voltage, V as follows [10]: V =

3d31 L X ε33 wtsen AB(B + 1) 2 AB(1 + AB3 ) 1 + 4AB + 6AB2 + 4AB3 + A2 B4 − k31

F

(12)

Hence, Eq. (12) shows the relationship between the force, F exerted by test gas at a particular flow rate, Q and the output voltage, V generated from ZnO deposited cantilever sensing element.

In the above equation, A and B denotes: A=

The value of capacitance, C for unimorph cantilever sensing element is given by following relation [10].

× (8)

197

(9)

where d31 is the transverse piezoelectric coefficient, L is the length of cantilever element, tsen is the thickness of ZnO sensing layer, sen is the elastsub is the thickness of flexible Phynox substrate, S11 sub is the elastic tic compliance of ZnO piezoelectric sensing layer, S11 compliance of flexible Phynox substrate, Esen is the Young’s modulus of ZnO piezoelectric sensing layer, Esub is the Young’s modulus of flexible Phynox substrate.

Fig. 5. (a) Schematic diagram of ZnO deposited cantilever sensing element and (b) Bending of the cantilever element due to the force (F) exerted by the flow of test gas at a particular flow rate on the tip of cantilever sensing element.

3. Results and discussion 3.1. Crystallographic characteristics The X-ray diffraction patterns of ZnO films deposited at different RF powers are shown in Fig. 6. The ZnO film thickness (720 nm) for all the deposited samples was maintained almost constant to allow comparison. The peak at about 34.4◦ corresponds to the diffraction from (0 0 2) plane of ZnO, the presence of (0 0 2) peak indicates that, the films have a strong c-axis orientation which is perpendicular to the substrate surface. This high degree of c-axis orientation or high degree of (0 0 2) preferred polycrystalline structure enhances the piezoelectric properties of ZnO films [7]. The lattice parameters of these films were found to be, a = 3.35 A˚ and c = 5.22 A˚ as denoted by ICDD (International center for diffraction data), PDF No. 751533, which were comparable to the values reported for good piezoelectric ZnO films [11]. As can be seen in Fig. 6, the peaks corresponding to bare Phynox substrate (without ZnO deposition) at 43.5◦ and 74.6◦ are present in all deposited samples. These peaks corresponds to (1 1 1) and (1 1 0) planes of chromium and cobalt respectively (ICDD, PDF No. 882323 and 011278 respectively), which are the major constituents of Phynox alloy. The intensity of (0 0 2) peak obtained for ZnO films deposited at RF power of 50 W was too low which indicates poorly crystalline

Fig. 6. X-ray diffraction patterns of ZnO films deposited at different RF powers.

198


Fig. 7. Variation of d31 coefficient values (pm V−1 ) and X-ray diffraction intensity of (0 0 2) peak of ZnO films as a function of RF power (W) variation.

films. The c-axis of the ZnO film deposited was almost parallel to the substrate surface, which is an indication of poor quality piezoelectric films [12]. This is attributed to the inadequate supply of kinetic energy to the atoms which is required for surface mobility resulting in proper diffusion. The intensity of (0 0 2) peak for the film deposited at 100 W was maximum with lowest FWHM value of 0.28◦ , due to better crystalline films with larger grain size. This in turn indicates that, the c-axis of hexagonal phase of the ZnO is perpendicular to substrate surface, which is an indication of good quality piezoelectric films [12]. The probable reason is increased kinetic energy of the sputtered atoms arriving at substrate surface resulting in the exact surface diffusion in the vacancies to yield a homogenous and crystalline film [13]. At 150 W and 200 W, the decreasing trend in (0 0 2) peak intensity was observed whereas FWHM value was found to be increased. This shows that, higher RF power deteriorates the quality of ZnO films, which resembles the observation made by Yamamoto et al. [14]. The variation of d31 coefficient values and X-ray diffraction intensity of (0 0 2) peak of ZnO films as a function of RF power variation is shown in Fig. 7. As the RF power was increased to 100 W, the maximum (0 0 2) peak intensity was obtained, resulting in lower FWHM value and higher d31 coefficient value of 4.7 pm V−1 . The reason for the above observation is attributed to the better c-axis orientation and increased grain size of deposited films. However at much higher RF powers of about 150 W and 200 W, the (0 0 2) peak intensity and the d31 coefficient value shows a decreasing trend. This decrease in d31 coefficient value was due to deterioration in the degree of c-axis orientation and increased FWHM value, which also indicates smaller grain size of ZnO films. The d31 coefficient value observed at 150 W and 200 W were 2.5 pm V−1 and 1.1 pm V−1 respectively.

Fig. 8. The 3-dimensional AFM images of ZnO films deposited at different RF powers. (a) 50 W, (b) 100 W and (c) 150 W.

3.2. Evaluation of ZnO films by AFM Fig. 8 shows the 3-dimensional AFM images of ZnO films deposited at different RF powers. The rms surface roughness of ZnO film deposited at 50 W was found to be 1.27 nm (Fig. 8(a)), which is slightly less than the rms roughness of the film deposited at 100 W (1.87 nm) which is seen in Fig. 8(b). This observation was believed to be due to the higher energy of the molecules arriving at surface and having larger surface diffusion coefficient at higher RF powers [15]. ZnO films deposited at 50 W were having lower d31 coefficient value of 3.5 pm V−1 as they were less dense, when compared to films deposited at 100 W. The highest value of d31 coefficient of about 4.7 pm V−1 was obtained at the RF power of 100 W, which was

believed to be due to the combined effects of high density, lower rms surface roughness, and improvement in the grain size (as discussed in Section 3.1). When the RF power was further increased to 150 W and 200 W, the value of rms surface roughness of deposited ZnO films was increased to about 3.28 nm and 5.27 nm respectively. This may be attributed to the presence of non–uniform and irregular grains at higher RF power. The increase in surface roughness at higher RF powers of 150 W and 200 W results in lower d31 coefficient values of 2.5 pm V−1 and 1.1 pm V−1 respectively. This was an indication of poor piezoelectric property of deposited films at such higher RF powers.


199

Table 2 Specifications of the MEMS pressure sensor (SCL-517, ISRO, Chandigarh, made in India). Characteristics

Values

Nominal pressure range Excitation voltage Sensitivity Error Temperature range Full scale output

0–1 bar 3 V DC (Nominal), 5 V DC (Maximum) 0.0616 mV/mm of Hg at 3 V excitation ±0.5% of full scale output 0 ◦ C to 50 ◦ C 50 ± 4 mV at 3 V excitation

3.3. Flow rate measurement Fig. 9 shows the experimental and theoretical values of force (mN) with respect to different flow rates (L min−1 ). The force exerted by gas jet was measured experimentally by using a MEMS pressure sensor (SCL-517, ISRO, Chandigarh, made in India). The specifications of MEMS pressure sensor used are listed in Table 2. As can be seen, there is a strong agreement between experimental and theoretical values of force at lower flow rates (≤8 L min−1 ) and the values tend to deviate at higher flow rates. The observed discrepancy between experimental and theoretical values of force at higher flow rates was attributed to the increased flow velocities. At flow rates higher than 8 L min−1 , the high gas jet velocity results into Mach number greater than 0.7. Therefore, the Bernoulli’s equation does not hold well. The experimentally obtained output voltage responses of ZnO deposited cantilever sensing element for different flow rates are shown in Fig. 10. The output voltage waveforms were recorded by a digital oscilloscope (Yokogawa, DLM 2022) and were filtered by using LabVIEW software. The amplitude of first peak can be correlated to the magnitude of point force experienced at the tip of cantilever at a particular flow rate. Hence the amplitude of first peak of output voltage gives a direct measure of the gas flow rate. Fig. 10(a–c) indicates the amplitude of first peak of output waveforms – 305 mV, 270 mV and 230 mV corresponding to the flow rates of 18 L min−1 , 16 L min−1 and 14 L min−1 respectively. It is clearly evident from Fig. 10 that higher flow rate results in larger amplitude of first peak of output waveform due to higher magnitude of point force at the tip of sensing element.

Fig. 10. Output voltage responses of ZnO deposited cantilever sensing element for different flow rates. (a) 18 L min−1 , (b) 16 L min−1 and (c) 14 L min−1 .

Fig. 9. Variation of experimental and theoretical values of force (mN) with respect to different flow rates (L min−1 ).

200


sensing element and calibration method discussed in this paper are simple and cost-effective. Acknowledgements The authors wish to thank Dr. M.M. Nayak of Centre for Nanoscience and Engineering (CeNSE), Indian Institute of Science, Bangalore for his valuable support in the theoretical analysis and experimental studies of the work presented in this paper. His contributions are gratefully acknowledged. References

Fig. 11. Variation of experimental and theoretical values of output voltage (mV) with respect to gas flow rate (L min−1 ).

Fig. 11 shows the variation of experimental and theoretical values of output voltage (mV) with respect to gas flow rate (L min−1 ). As can be seen, that there is a strong agreement between the experimental and theoretical values for lower range of flow rates, and as the flow rate increases the discrepancy between the experimental and theoretical values increases. This increase in discrepancy between the values is attributed to the error in the force calculation from Bernoulli’s equation. The output voltage calculation was done from Eq. (12) have force (F) term in it, and any error in force calculation will also reflect in calculation of output voltage. Fig. 9 also corroborates the above observation. The equation used to calculate discrepancy (%) between the experimental and theoretical values of output voltages is as follows: Discrepancy (%) =

Vtheoretical − Vexperimental Vtheoretical

× 100%

(13)

In our present case the discrepancy (%) ranged between 2% to 7%. The flow sensing element was having the sensitivity of 18 mV/(L min−1 ). The measurement of flow rates higher than 18 L min−1 results in the large amount of bending of cantilever (40 mm), which was found to be the limiting factor of the sensing element. The larger bending of the cantilever may result in development of cracks in ZnO sensing layer which in turn affects the overall performance of flow sensing element. 4. Conclusion ZnO films were deposited on Phynox alloy substrate by RF reactive magnetron sputtering for flow sensing application. The effect of RF power variation on crystalline orientation, surface roughness and d31 coefficient value has been studied. Films deposited at RF power of 100 W were well oriented having their c-axis perpendicular to substrate, highly crystalline with larger grain size, lower rms surface roughness of 1.87 nm and highest d31 coefficient value of 4.7 pm V−1 . Flow sensing element was calibrated using in-house developed testing set-up. The flow rate measurements were performed. Output voltage waveforms were recorded for different flow rates ranging from 2 to 18 L min−1 and the amplitude of first peak of output waveform gives the measure of flow rate. The flow sensing element offers the advantage that, the flow rate measurement is independent of the nature of the gas. The flow sensing element is suitable for flow rate measurement in the range of L min−1 . The flow

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Biographies Sudeep Joshi received his B.E. (Hons) (2008) in Instrumentation and Control engineering from Rajiv Gandhi Proudyogiki Vishwavidyalaya, Bhopal, Madhya Pradesh, India. Presently he is pursuing his Ph.D. from Department of Instrumentation and Applied Physics, Indian Institute of Science (IISc), Bangalore, India. His research interests are development of sensors and actuators based on piezoelectric principle, deposition and characterization of thin films, MEMS based devices and energy harvesting. Mitesh Parmar received his Ph.D. from Department of Instrumentation and Applied Physics, Indian Institute of Science (IISc), Bangalore, India. Presently, he is a full-time researcher at MEMS and Nanotechnology lab (National lab), School of Mechanical Engineering, Chonnam National University, Gwangju, Korea. His research interests are growth as well as characterization of nano-materials, development of gas sensors (including graphene based sensors), bio-sensors, MEMS and piezo-materials for various applications. K. Rajanna received his Ph.D. (1993) from Department of Instrumentation and Applied Physics, Indian Institute of Science (IISc), Bangalore, India. Presently, he is a Professor and Chairman of the same department. His field of research covers gas sensors, radiation sensor, development of piezo-materials based sensors and MEMS.