DESIGN AND IMPLEMENTATION OF MICROWAVE BASED … · DESIGN AND IMPLEMENTATION OF MICROWAVE BASED ETHANOL SENSOR Rapuru Srinithya1, Velkani E.2, Dr. M. Gulam Nabi Alsath3, Dr. Kirubaveni

DESIGN AND IMPLEMENTATIONOF MICROWAVE BASED ETHANOL

SENSOR

Rapuru Srinithya1, Velkani E.2,Dr. M. Gulam Nabi Alsath3,Dr. Kirubaveni Savarimuthu4

Sri Sivasubramaniya NadarCollege of Engineering, [email protected]

June 25, 2018

Abstract

This paper presents a microwave based ethanol gassensor based on triangular split ring resonator. TiO2nanorods is used as sensitive layers and sensitivity of thesensor towards ethanol gas is analyzed. The nanorods aresynthesized and coated on a glass substrate and are placedon the designed two port resonator to make it as a sensingdevice. An electromagnetic wave is given as input to thesensing device by VNA. On absorption of ethanol, changein resonant frequency of the sensor is observed andanalysis of scattering parameters and sensitivity of sensoris measured. It is observed that there is an increase infrequency shift with increase in concentration of ethanolexposed to the sensor.Sensing device with TiO2 nanorodsshows sensitivity of 1.29.

Keywords: microwave gas sensors, TiO2, Ethanol.

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International Journal of Pure and Applied MathematicsVolume 120 No. 6 2018, 1197-1208ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/

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1 INTRODUCTION

Human activities lead to number of gases that are released intothe atmosphere. Some of the main sources of gases are emissionsfrom vehicles ,manufacturing of pharmaceuticals ,dry cleaning andactivities of industries using organic solvents . Many gases areused in various industrial applications. Some of these gases likeVOCs are directly harmful to humans and environment.Methanol, ethanol, benzene, propane, formaldehyde are some ofthe examples for volatile organic compounds. They are harmful tothe environment and can contribute to respiratory illnesses andreproduction problems. So, detection of volatile organiccompounds (VOCs) has gained enormous attention during thepast few decades. As part of a safety system the presence of gasesin an area can be detected by a gas sensor.

This paper presents a gas sensing process based on microwavetransduction. It is based on measurement of frequency evolutionof the sensitive material’s permittivity consecutive to theadsorption of molecules on the surface of the sensitive layer atroom temperature [1]. It allows estimation of changes in thedielectric characteristics of a sensor, consecutive to the adsorptionof molecules on the sensor at microwave frequency range [2]. In [3]they have reported a grounded coplanar waveguide withphthalocyanine as sensitive material for ammonia. Their work isbased on the variation of real and imaginary parts of reflectioncoefficient upon exposing to ammonia. Advantages ofmicrowave-based gas sensors include portability and operatingtemperature. Materials which are used as sensitive layers in thistechnique can be polymers, metal oxides or carbon nanotubes(SWNT or MWNT) and zeolites. Mostly used sensitive materialsare metal oxides which are selected based on the adsorption of gasmolecules and the reaction between the surface of the sensitivematerials and the gas molecules. Sensitivity to a particular gasvaries with variations in thickness and characterization of thesensing film [4]. In [5] the authors have reported a sensor using apatch antenna with PABS-SWNT as sensing material. In [6] theauthors have demonstrated a microwave resonator coated withPDMS layer which act as acetone sensor. The variation in the

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microwave resonance frequency of the resonator is because of theinduced change in permittivity of the sensitive layer due toadsorption of gas molecules. In [7] authors presented a microwavebased sensing technique for the detection of NH3 using titaniumdioxide nanorods. Numerous variables like real and imaginarypart of reflection coefficient, resonant frequency, amplitudevariations can be tracked using the microwave transductiontechnique, which improves the sensor differentiation capabilitiesthrough data crossing. Among all detection mechanisms, themethod which is based on the shift of the resonant frequency isthe most effective for remote sensing because the amplitude issusceptible to interference and noise, while the frequency shift isrelatively insensitive to those factors [5].

So, the present work is based on the shift of resonant frequencydue to adsorption of gas molecules by sensitive layer. TiO2 is usedas a sensitive material for detection of ethanol. Ethanol sensingperformance shows a lower operatingtemperature, faster responsebehavior and better selectivity.

2 SYNTHESIS AND

CHARACTERIZATION OF

SENSITIVE MATERIAL

Tetrabutyl orthotitanate(TBT) was mixed with the equimolarratio (1:1) of acetylacetone (ACA) along with water. The formedyellow colour solution was transferred into autoclave. Thenautoclave which contains the precursors is heated to 170◦C andkept for 3 days without any interruption under stirring condition.After 3 days, the autoclave was naturally cooled down to ambienttemperature [8]. Fig.1 and Fig.2 represents FESEM and XRDimages of prepared TiO2 nanorods.

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Fig.1: FESEM image of prepared TiO2

Fig.2:XRD image of prepared TiO2

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3 SYSTEM DESIGN

A. Sensor Design

The proposed sensor structure consists of three triangular doublesplit ring resonators. This structure has been etched on FR-4substrate with relative permittivity of εr=4.3, thickness ofh=1.6mm and width w=3.137mm. Double split ring resonator is aring type of frequency selective structure used to enhance theperformance of the two port resonator designed. To haveminiaturization, triangular split ring resonator is designed as itoccupies less area that is 21% and 42.7% less than that of thecircular and square SRR respectively [9].

Fig.3: Triangular split ring resonator.

This paper presents three different split ring resonators thatresonate at three different frequencies when microwaves are

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propagated to the structure. The three SRR are designed forresonant frequencies 2GHz, 4.5GHz and 6.5GHz. Figure 3 givesthe structure of triangular split ring resonator. The parametersdescribing the triangular split ring resonator are s: side of theouter triangle, w: the width of TSRR strip, d: the gap betweenthe inner and outer triangles and g: metal bridge width inTSRR’s. Table 1 shows the parameters of the three split ringresonators designed. Width of metal bridge in TSRR g=0.3mm.The designed resonator is represented in Figure 4.

Table1: Dimensions of designed SRR

Fig.4: Designed Resonator

B.Sensitive Layer Deposition

The nanorods are deposited on glass substrate of thickness 1mmand the substrate is placed on the designed resonator which makesa sensing device. Figure 5 shows the proposed sensing device.

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Fig. 5:Proposed Sensing Device

C.Experimental Setup

A homemade-setup which is shown in Figure 6 is used to performsensitivity of ethanol gas. The sensing device is placed in a closedchamber at room temperature and atmospheric pressure. The gasis passed into the chamber with the help of a syringe. Vectornetwork analyzer is used to conduct microwave measurements. ASOLT calibration (short-open-load-thru) was performed toeliminate the systematic error terms in s-parametermeasurements.

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Fig.6: Experimental Setup

The sensing device is exposed to several concentrations of ethanolgas increasing from 100ppm to 700ppm using the experimentalsetup.

4 RESULTS AND DISCUSSION

A. Frequency shift:

Experiment is performed by using TiO2 nanorods coated glasssubstrate. The sensing device is made to be exposed to 100ppm ofethanol gas. Measurements from the VNA are collected for every30seconds to observe the response and recovery time. Data iscollected till the sensor reaches to its initial position. From thedata collected frequency shift of 7.5MHz is observed on passingethanol gas. The same experiment is conducted for concentrationsvarying from 100ppm to 700ppm. An increase in frequency shifthas been observed when the concentration of ethanol gas absorbedis increased. Figure 7 shows the frequency shift versus the

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concentration of ethanol gas for three different frequencies f1 =2.157 GHz , f2 = 4.685 GHz and f3 = 6.305 GHz.

Fig.7 : Concentration of ethanol gas Vs Frequency shift by usingTiO2 as sensitive layer.

B. Spectral Analysis

The spectral analysis is performed by using the observedscattering parameters. For the analysis of small changes inducedby the adsorption of molecules on a surface of sensitive materialdifferential treatment is performed. By calculating the differencebetween the spectra collected with and without ethanol exposure,differential spectra ∆S11 and ∆S21 are calculated at eachconcentration (equation 1, example of ∆S11 at 100ppm)

∆S11(100ppm)=S11(100ppm)-S11( vacuum)............ (1)

The result shows that upon gas absorption each resonance has itsown behaviour.

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C. Sensitivity of sensor

To measure the sensitivity of the sensor and compare responses ofdifferent materials, sensor response defined by equation 2 is used[4].

sensor response= ∆ΓΓ

= Γgas−Γvacuum

Γvacuum................................(2)

Where Γvacuum and Γgas are the reflection coefficients before andafter introduction of the gas, respectively. Sensitivity for thesensor while using TiO2 nanoparticles as sensitive layer iscalculated to be 1.29.

5 CONCLUSION

This work presents design and implementation of microwave basedethanol gas sensor. Triangular split ring resonator structures areused to design a two port resonator. The prepared sensing deviceis developed with sensing material as TiO2 nanorods. Multipleexperiments on passing Concentrations of ethanol gas increasingfrom 100ppm to 700ppm are performed. An increase in frequencyshift with increase in concentration of ethanol gas is observed onabsorption of gas for the sensing device. Spectral analysisperformed on scattering parameters highlights that uponabsorption each resonance has its own behaviour.

References

[1] Rossignol, J., Barochi, G., De Fonseca, B., Brunet, J., Bouvet,M.,Pauly,A. and Markey, L., 2012. Development of gas sensorsby microwave transduction with phthalocyanine film. ProcediaEngineering, 47, pp.1191-1194.

[2] De Fonseca, B., Rossignol, J., Bezverkhyy, I., Bellat, J.P.,Stuerga, D. and Pribetich, P., 2015. Detection of VOCs bymicrowave transduction using dealuminated faujasite DAYzeolites as gas sensitive materials. Sensors and Actuators B:Chemical, 213, pp.558-565

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[3] Barochi, G., Rossignol, J. and Bouvet, M., 2011. Developmentof microwave gas sensors. Sensors and Actuators B: Chemical,157(2), pp.374-379.

[4] Jouhannaud, J., Rossignol, J. and Stuerga, D., 2007.Metal oxidebased gas sensor and microwave broad-bandmeasurements: an innovative approach to gas sensing. InJournal of Physics: Conference Series (Vol. 76, No. 1, p.012043). IOP Publishing.

[5] Lee, H., Shaker, G., Naishadham, K., Song, X., McKinley,M., Wagner, B. and Tentzeris, M., 2011. Carbon-nanotubeloaded antennabased ammonia gas sensor. IEEE Transactionson Microwave Theory and Techniques, 59(10), pp.2665-2673.

[6] Zarifi, M.H., Sohrabi, A., Shaibani, P.M., Daneshmand,M. and Thundat, T., 2015. Detection of volatile organiccompounds using microwave sensors. IEEE Sensors Journal,15(1), pp.248-254.

[7] Bailly, G., Harrabi, A., Rossignol, J., Domenichini, B.,Bellat, J.P., Bezverkhyy, I., Pribetich, P. and Stuerga,D., 2016. Influence of the design in microwave-based gassensors: ammonia detection with titania nanoparticles.Procedia Engineering, 168, pp.264-267.

[8] Rajamanickam, G., Narendhiran, S., Muthu, S.P.,Mukhopadhyay, S. and Perumalsamy, R., 2017.Hydrothermally derived nanoporous titanium dioxidenanorods/nanoparticles and their influence in dyesensitizedsolar cell as a photoanode. Chemical Physics Letters, 689,pp.19-25.

[9] Vidyalakshmi, M.R., Rekha, B. and Rao, P.H., 2011,December. Stopband characteristics of complementarytriangular split ring resonator loaded microstrip line. InApplied Electromagnetics Conference (AEMC),2011 IEEE(pp.1-4). IEEE.

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DESIGN AND IMPLEMENTATION OF MICROWAVE BASED … · DESIGN AND IMPLEMENTATION OF MICROWAVE BASED ETHANOL SENSOR Rapuru Srinithya1, Velkani E.2, Dr. M. Gulam Nabi Alsath3, Dr. Kirubaveni