1/f and 1/f2 noise spectral densities in sensors made by polymers and SnO2

Noise measurements of conductive sensors made by either polymers and SnO2 materials, have been done at 25°C and around 300 °C respectively, in order to study their ultimate performances in terms of signal to noise ratio and the excess noise implications in multisensor artificial olfaction systems. In all the studied cases, of which only a few are here reported, excess noise spectral densities proportional to l/f were observed in the frequency range of about 1-10 kHz, even in presence of different kinds of adsorption processes. This suggests that the evaluation of the resolution values must be determined after noise characterizations have been done, especially for slow responding sensors. In fact if the time constants fall in the low frequency region where the amplitude of the noise spectral density may not be neglected. Furthermore, in presence of gas flow even l/f2 noise spectral density type (with n between 1 and 4) can be observed in Sn02, while the same kind of noise is also evident in polymer based sensors operating at room temperature at constant volatile compounds gas pressure conditions.