R. C. Aiyer

Grain size effects on H2 gas sensitivity of thick film resistor using SnO2 nanoparticles

The effect of ppm level H2 on the d.c. resistance of SnO2 thick film planar resistor with SnO2 particle size variation (∼ 20 to 50 nm) is reported. SnO2 nanoparticles were synthesized using the sol-gel method. The films were prepared using standard screen printing technology. The SnO2 crystallite size, D, is varied in the range of 20–50 nm and sensitivity for H2 is found to increase steeply as D decreases.

Formulation and characterization of ZnO:Sb thick-film gas sensors

ZnO:Sb based screen printed thick-film H2, CO and CH4 gas sensors were fabricated. Films were realized on an alumina substrate by mixing ZnO with lead borosilicate glass frits as a binder and Sb as a catalyst. It was observed that the ZnO:Sb based sensors were more sensitive to these gases than the pure ZnO sensors. The conductance of the sensor increased linearly with the square root of the gas concentration. The dependence of the sensitivity on the amount of the additive (Sb) is discussed. The sensors have a response time of 10 s. Material characterization was carried out by using bulk X-ray diffraction (XRD) and surface morphology by scanning electron microscopy (SEM).

Effect of particle size variation of Ag nanoparticles in Polyaniline composite on humidity sensing

The results of synthesis of Ag-Polyaniline nanocomposite along with an investigation of optical fiber based humidity sensor using evanescent wave absorption spectroscopy are discussed. The sensor was fabricated using Ag-Polyaniline nanocomposite deposited on an optical fiber clad and tested in the range of 5-95% relative humidity (RH). Optimization of clad length (2-8mm) was done and then particle size (15-30 nm) variation of silver nanoparticles in Polyaniline composite was studied for better performance of sensor. The effect of particle size on sensing humidity was investigated. The reduction of particle size, leads to a dramatic improvement in sensitivity and speed of response. The optimized clad length of 6mm exhibits the better results for 15 nm particle size of Ag nanoparticles dispersed in Polyaniline. The sensor response is fully reversible having almost 1% of standard deviation. Response time of the sensor is 30s with a slow recovery of 90 s.

Characterization of SnO2-based H2 gas sensors fabricated by different deposition techniques

Thick and thin films of SnO2 are extensively used for resistive gas sensors. Characteristics are compared for films produced by four different techniques – chemical vapour deposition (CVD), spray pyrolysis, vacuum evaporation and screen printing. The films are characterized for H2 sensing only, using a static measurement system to investigate their temperature selectivity. The samples are tested at a concentration of 300 p.p.m. H2 gas, a typical value for comparison. No selective peak is observed for CVD and spray deposited samples, and the selective peak for vacuum evaporated samples has a low sensitivity. But the selective peak for screen printed samples has a sensitivity of 55% (δR/Rair). And what is more, the screen printed samples have a repeatable response.

A microwave microstrip ring resonator as a moisture sensor for biomaterials: application to wheat grains

A miniaturized, non-destructive sensor employing a microwave microstrip ring resonator (MRR, GHz, mean diameter 3.69 mm) was developed for estimating the moisture content of a single wheat ( Triticum aestivum L) grain. A single wheat grain with a known amount of moisture was placed on the MRR at two different orientations ( and ) with respect to the feedline. The resonance frequency , bandwidth (B) and quality factor of the MRR were calibrated against the moisture content. The measurements were made with a scalar network analyser. The sensor was studied in the normal useful moisture range of 11-32% (on a wet-weight basis), the actual moisture values being obtained by an oven-drying method. The orientation was more sensitive to moisture than was the orientation. The total changes in for a 21% change in moisture content for and 90 orientations were 235 and 150 MHz, respectively. The errors in moisture estimation with for and were % and %, respectively. The corresponding values with B and for orientation were % and %, respectively. The proposed sensor is more sensitive than a reported waveguide resonator and is easy to operate, for the microstrip offers an open structure, thereby facilitating easy loading and unloading of the samples.

Evaluation of co-polyaniline nanocomposite thin films as humidity sensor.

Spin coated films of Co-Polyaniline nanocomposite are evaluated for their transmission properties using He-Ne laser for humidity sensing. The thickness (17-29 microm) of the films is varied by multiple deposition of Co-Polyaniline nanocomposite on a glass substrate. The samples exhibit typically two to three regions in their sensitivity curve when tested in the relative humidity (RH) range of 20-95%. The sensitivity ranges from 0.1 mV/%RH to 12.26 mV/%RH for lower to higher thickness. The sensors show quick response of 8s (20-95%RH), and a recovery time of 1 min (95-20%RH) with good repeatability, reproducibility and low hysteresis effect. The sensitivity of the sensor increases with humidity and thickness. Material characterization is done by X-ray diffraction (XRD), scanning electron micrograph (SEM) and Fourier transform infra-red spectroscopy (FTIR).

Humidity sensor using planar optical waveguides with claddings of various oxide materials

A planar optical waveguide, fabricated using an ion-exchange process in soda glass (Na+ exchanged by K+), is studied as a humidity sensor with screen printed claddings of BaTiO3, SnO2, Al2O3, ZrO2, V2O5 and ZnO as well as sintered ZnO, with cladding thicknesses between 20 and 25 μm. A He-Ne laser beam (0.1 mm dia., λ = 632.8 nm, 0.5 mW) is coupled to the guide using prism film coupling and a silicon photovoltaic detector is used to measure the intensity of transmission. The lengths of the claddings used, which give the maximum TM-polarization because of the relative attenuation, are between 3 and 5 mm. The relative humidity (RH) is varied from 3 to 98%. BaTiO3 offers maximum sensitivity as compared to the other oxides used. SnO2 exhibits a response time of 3 s and a recovery time of 10 min, the fastest amongst all. The maximum hysteresis of 1% is observed, except for V2O5 cladding (8%). The sensitivity curves show 3 regions, which are attributed to different possible dominant processes.

Effect of film thickness and curing temperature on the sensitivity of ZnO:Sb thick-film hydrogen sensor

This paper reports the effect of film thickness and curing temperature on the sensitivity of the screen-printed thick-film ZnO (incorporated with 7 wt%Sb) H2, CO and CH4 sensors. The sensitivity of the sensors increases up to 60 μm and decreases for higher film thickness. Increase in the curing temperature of the films, decreases the sensitivity of the sensors because of the increase in the average grain size, as observed by scanning electron microscopy.

Electrical and humidity characterization of m-NA doped Au/PVA nanocomposites

The Meta-Nitroaniline (m-NA) doped (by varying weight percentage (wt. %)) gold/polyvinyl alcohol (Au/PVA) nanocomposites were synthesized using gold salt and hydrazine hydrate (HH) by in situ process. The composite was coated on ceramic rods having two end electrodes by drop casting method for studying their electrical behavior at different relative humidity (RH) levels, ranging from 4 to 95% RH at room temperature. The optimized wt. % was used to prepare coatings of various thicknesses (20-40 microm) of the films. As the humidity decreases, the resistance increases. The low humidity sensing characteristic can be tailored by varying wt. % of m-NA and thicknesses of the nanocomposite films. The resistive-humidity sensor shows two regions of sensitivity having highest sensitivity for lower RH. The sensor response and recovery time is about 6-10s and 52 s respectively. The dynamic range of variation of the resistance allows a promising use of the films as a humidity sensor. The material was characterized by X-ray diffraction (XRD) and impedance spectroscopy at 60% RH.

Microwave microstrip ring resonator as a paper moisture sensor: study with different grammage

This paper reports use of a nondestructive, miniaturized, microwave microstrip ring resonator for moisture sensing application in papers. Advantages offered by this sensor over the prevailing sensors are room-temperature operation, response time in milliseconds, measurements unaffected by dusty environment and ionic conductivity of samples. Samples of eleven types were tested, with grammage (grams per square metre) and thickness varying from 21 to 70 g m−2 and 24 to 80 µm respectively. The wet basis moisture normalization (with respect to instantaneous moisture content in the sample) was established to remove scatter and to bring out clearly grammage dependence, thus avoiding error in moisture prediction due to density variations, using only scalar measurements. A single equation for fr variations is realized in terms of grammage and normalized percentage moisture (Mww) which is valid for all types of tested paper. A model of the wet paper is suggested mainly based on water–dry paper interaction, also considering parameters like thickness and surface roughness, to explain trends of the sensitivity curves. The estimated %Mww shows an error of ±0.9% in the estimated value as compared to the actual value.