Chemical sensing based on the informational source of nonlinear dynamics

We propose a new method to detect and quantitate various chemical species based on the abundant information of the nonlinear dynamical response, mimicking the essence of chemical sensing in living organisms. Our method is based on the idea to monitor the nonlinear response with the application of periodic forced-oscillations. As an example, we show the experimental result when a sinusoidal voltage is applied to a heater inserted into an SnO₂ gas sensor. The resulting output resistance of the gas sensor is analyzed by the fast Fourier transformation (FFT). It is found that the intensities of the higher harmonics show characteristic changes depending on the concentration and chemical structure of various gas, such as alkane, alkene, and their mixture. The intensity of each harmonics is discussed in relation to the kinetics of adsorption, desorption, and oxidation of gas molecules on the ceramic surface. From a theoretical consideration, it is indicated that the higher harmonics of FFT are originated from the nonlinear property of the response.