Pattern recognition of a gas sensor array using impedance

The response of a semiconductor gas: sensor usually shows variation of resi stance when the sensing material reacts with a gas, but it carl also show a variation of impedance. The variation of impedance represents a variation of capacitance and resistance. The capacitance depends on the types and the concentrations of gases. The variations of the rise and fall times is dete rmined by the capacitance, and the response characteristics can be applied to pattern recognition. The problems of sensing drift and low selectivity i n semiconductor gas sensors are improved by the high selectivity of gas con centration when using sensor array structure and pattern recognition techni que.