Design and realization of sensors and sensor based systems

Abstract

The sensor is a transducing device that converts the change in physical conditions such as temperature, pressure etc. into the measurable electrical responses. Now-a-days sensors are becoming part of our daily lives. At present with the speedy progress in technology, sensors gain its popularity day by day. Semiconducting Metal-Oxides show potential as an attractive sensing material to detect different hazardous gases like ethanol, hydrogen, methane etc. The important characteristics of these gas sensors are photo-catalytic properties, high reliability and low cost. In the present work, fabrication of ethanol sensor with WO3 material by Pt and Pd modulation is carried out to achieve low power, high sensitivity, low temperature sensor. The sensitivity is measured from the gas concentration variation to sensor resistance variation. The sensing performances of two different ethanol sensors (Pd modulated and Pt modulated WO3) are investigated. The effects of noble metal like Pd, Pt on the sensing properties are also studied using Scanning Electron Microscopy and X-Ray Diffraction methods. Present analysis shows that Pt modulated WO3 sensor gives enhanced performance than other sensors. Further to study the enhancing methods of the sensors’ sensitivity, the effects of annealing temperature and the effects of hetero junction structure on gas sensor are investigated. The ZnO and WO3 type materials are chosen for the application of sensing H2 gas for this study. The formation of heterostructure structure sensor is done by using these two materials. On the other hand the study of annealing temperature is carried out during the fabrication process of the sensor. The direct effect of annealing temperature on the grain size of fabricated sensor is studied using Scanning Electron Microscopy and X Ray Diffraction methods. The detection of toxic as well as inflammable gases is necessary for improving the quality of the environment. Generally sensor with the signal conditioning unit is essential to detect different inflammable gases. Hence the voltage to time conversion circuit with fabricated sensor to detect hydrogen (H2) and methane (CH4) gas is proposed based on a bridge circuit, an instrumentation amplifier and a timer circuit. Normally in real time applications if the sensor’s output data i.e. the analog form of sensing data is send without proper signal conditioning then there may be huge degradation in quality and quantity of the signal. Hence in the present work a signal conditioning circuit is tested with fabricated gas sensor and the result is studied thoroughly. Further a proposal using RFID based system for early leakage detection of ethanol with RFID tags as sensors is presented. Now-a-days the RFID technology which is better than available bar code technology is gaining more attention because of its attractive features like low cost, reusability, and stability. Hence in the present work the main RFID component which is RFID tag is used as sensing device to detect leakage of ethanol gas % from 0.15% to 0.5%.