Optimized multi-frequency temperature modulation of microhotplate gas sensors

We demonstrate, for the first time, how it is possible to optimize a multi-frequency signal to be used in the modulation of the operating temperature of an integrated gas sensor microarray. In the first step, a multilevel pseudo-random sequence (MPRS), which allows for modulating the operating temperature of the sensors in a wide frequency range, is used to obtain an estimate of the impulse response of each microsensor-gas system. In the second step, by analyzing the spectral components of the impulse response estimates, the modulating frequencies that better help in discriminating the gases and gas mixtures considered are found. Finally, by selecting a subset of the best modulating frequencies (e.g., up to 5 frequencies), an optimized multi-frequency temperature-modulating signal can be synthesized. The method is illustrated by analyzing different concentrations of NH₃, NO₂ and their mixtures using a microarray of WO₃-based gas sensors.