Capacitive Gas Sensor Using Polymer Fill-In

This paper presents the measuring technique of CO2 gas molecule present significantly in the atmosphere and its alarming rate of increase creates a cause of concern to protect the public and environment from chemical threats, by detecting at an earlier stage accurately and taking the needed action. The development of a MEMS sensor system to detect compounds from a mixture has paved way to the development of small scaled reliable detection systems. The paper provides a novel idea of incorporating a MEMS chemical capacitive sensor element with a monolithically integrated signal conditioning circuit. CO2 gas molecules are sensed using a parallel plate chemical capacitor which uses the adsorption principle. The adsorbed CO2 molecules will form the dielectric media of the sensor thereby changing the overall capacitance of the sensor. This change would in turn provide the quantity of CO2 molecule present. The change in capacitance could be known to us by using a suitable signal conditioning circuit, here a modified schering bridge is considered and the corresponding voltage output gives us the quantity of CO2. This paper provides an overview of the design of the sensor element and the sensing circuit.