Abstract
MEMS gas sensors have the advantage of low power operation, fast response time, and have attracted a lot of interest because of their potential low cost. There is a need for monitoring of changes in the environment, in particular for carbon dioxide and methane. These gases can be detected using electro-thermal method based upon thermal conductivity changes. MEMS based micro-TCD which are ultra-low power, requiring less than 6 uJ per measurement and have a response time 100uS or less [1]. Because of their rapid response time they are also very suitable for MEMS-GC systems [2]. We have investigated different modes of pulsed operation for these sensors using constant current, constant resistance, constant power and constant energy. The detection of helium and hydrogen in nitrogen indicated a low level of detection less than 500ppm or better. A comparison of thermal time constants and resistance response for micro-thermal conductivity sensors with different aspect ratio, surface area to volume, operated at constant power density or at similar average temperatures will be discussed. Fitting a model based upon kinetic theory of gases to temperature dependent sensor response of gas mixtures has potential for evaluation of multi component mixtures.
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