Gas sensing based on a nonlinear response: Discrimination between hydrocarbons and quantification of individual components in a gas mixture

A novel sensing system is proposed based on the multi-dimensional information contained in a dynamic nonlinear response. A sinusoidal temperature change was applied to a SnO2 semiconductor gas sensor, and the resulting output conductance of the sensor was analyzed by fast Fourier transformation (FFT). The higher harmonics of the FFT characterized the nonlinear properties of the response. The amplitudes of the higher harmonics of the FFT exhibit characteristic changes which depend on the chemical structure, concentration, and the kinetics of adsorption and the reaction of hydrocarbon gases and aromatic vapors on the sensor surface. In addition, it is possible to distinguish between gases in a gaseous mixture with a single detector using this dynamic nonlinear response. Nonlinear responses are discussed in relation to the kinetics of the reaction at the sensor surface and the temperature-dependent barrier potential of the semiconductor.