Modelling of adsorption-desorption noise in gas sensors using Langmuir and Wolkenstein models for adsorption

A comparison between adsorption-desorption (A-D) noise models obtained using Langmuir and Wolkenstein theories is presented. This noise is generated by instantaneous fluctuations in the number of the adsorbed molecules, which cause free electron´s density fluctuations in the sensing layer, and consequently a fluctuation in the conductance of the gas sensor. The numerical results show that the A-D noise spectrum obtained using the Wolkentein adsorption theory has a low frequency magnitude, which is greater than that of the spectrum obtained using the Langmuir theory. The presented models show that the power density spectrum of the fluctuation of the sensor´s conductance has a cut off frequency and low frequency magnitude, which are specifics of the adsorbed gas. This result confirms that conductance (or resistance) noise spectroscopy could be a useful tool for extracting information on the nature of the detected gas.