Time-gated technique for contactless electromagnetic interrogation of MEMS resonators

A novel technique for contactless interrogation of entirely passive micromechanical resonator sensors has been investigated. The technique is based on the separation in time of the excitation and detection phases, exploiting the transient response of the resonator. An interrogation external primary coil is electromagnetically air-coupled to a secondary coil connected to a conductive path running along the edges of the resonator. Firstly the resonator is driven into vibrations during the excitation phase, and then in the detection phase the excitation signal is turned off and the decaying oscillations are contactless sensed. The principle has been modeled by a lumped-element equivalent circuit and then tested on a MEMS SOI microcantilever resonator. The obtained experimental results agree with the predictions of the developed equivalent model and demonstrate a working distance of up to 1 cm. The proposed principle can be exploited for the measurement of physical or chemical quantities affecting the resonant frequency and quality factor of the microresonator.