Simulation of sensitivity in an optical-access type piezoelectric sensor array

We have proposed two optical-access methods for use with a piezoelectric sensor array, and have compared their sensitivity through simulation results. AT-cut quartz resonators used as sensor elements were constructed on an artificial twin quartz plate using monolithic integration. A photovoltaic element was also installed on the quartz plate. An optical-pulse beam was shone onto the photovoltaic element and an electric pulse wave was obtained. The pulse voltage was applied to resonators to induce piezoelectric vibration. The resonance characteristic of each resonator was optically measured through the photo-elastic effect. This configuration thus enables optical access to the sensor element from a distance. Two major issues must be resolved to make this sensor configuration practical; one is the optical to electric conversion technique and the other is the optical measurement method applied to the piezoelectric resonance. Unlike a conventional solar cell, the photovoltaic element for this configuration must operate in the VHF range. The frequency characteristic of the photoelectric conversion efficiency will limits the upper limit of the operation frequency. The ordinary acousto-optic method cannot be used for the resonance measurement, because a diffraction grating is not formed in the resonator. However, the refractive index deviation caused by stress can be detected through the light interference phenomenon. As the index deviation reaches its maximum value at resonance, the resonance frequency can be measured by sweeping across the excitation light pulse frequency.