A real-time intelligent gas sensor system using a nonlinear dynamic response

We developed an intelligent gas sensor system for discrimination and quantification of gases by a single semiconductor gas sensor in real-time. This system is based on the information embedded in a nonlinear dynamic response. By applying a sinusoidal voltage to a heater attached to a sensing material, a characteristic time-dependent trace of the sensor resistance is obtained as a response to environmental gases. In order to evaluate the characteristic response in a quantitative manner, fast Fourier transformation (FFT) was performed for the dynamic response. Higher harmonics, obtained by performing FFT, were processed by using a discrimination method and a multiple regression. It is possible for the system to respond in the time order of several seconds. The physico-chemical meaning of the response was also discussed.