Acoustic interference suppression of QCM sensor arrays utilizing phononic crystals

In this paper, we propose a sensor array consisting of multiple quartz crystal microbalances (QCMs) surrounded by phononic crystals. Phononic crystals are utilized for isolating acoustic energy of individual bulk acoustic wave sensor and suppressing the interference. The resonance response of a QCM was calculated by finite element analysis. A -square-lattice phononic crystal structure was designed to have a complete band gap covering the QCM's resonance frequency. Finally, the monolithic QCM sensor arrays with/without phononic crystals were fabricated by micromachining processes and measured to evaluate the isolation performance of the phononic crystals. As a result, the QCM has a resonance frequency of around 20.8 MHz when the AT-cut quartz plate is 80 μm thic . The designed phononic crystal structure, whose lattice constant and filling ratio are 100 μm and 0.475, has a complete band gap from 1944 to 23.1 MHz. Besides, the QCM sensor arrays with phononic crystals were successfully fabricated by deep reactive ion etching. Measurement results show the phononic crystal with band gap indeed forbids effectively acoustic waves excited by QCMs and reduces spurious modes in the frequency response of the sensor array. Accordingly, the phononic crystal is verified to be capable of suppressing the acoustic interference between adjacent QCMs in a sensor array.