Application of pulsed digital oscillators to volatile organic compounds sensing

Pulsed digital oscillators (PDO) are sampled nonlinear structures that include a resonator device, a one-bit quantifier and a feedback loop with n-delays. PDOs can be used in a wide range of frequency-based sensing applications. This paper describes for the first time the application of PDOs as self-sustained oscillators in gravimetric sensors for volatile organic compounds (VOC) detection and measurement. For this application, the device is a MEMS cantilever with a polymer layer deposited on top of it. The deposited layer is mass-sensitive to the concentration of VOC, so that the concentration of VOC changes the oscillation frequency of the PDO. Two different polymeric materials have been tested: poly-epichlorohydrin (PECH) and poly-dimethylsiloxane (PDMS). Our results show that low concentrations of toluene and octane can be detected successfully. The practical influence of parameters, such as the MEMS damping losses on the sensor performance are also analyzed and experimentally tested. These are the first experimental results showing how PDOs can successfully track changes in the resonant frequency of MEMS resonators.