Isolation of bulk acoustic waves in a sensor array with phononic crystals

In recent years, multiple bulk acoustic wave sensors have been fabricated on a single piezoelectric substrate to develop a sensor array for the detection of multiple analyte parameters. However, such an array may induce acoustic interference between adjacent sensors. Phononic crystals are synthetic structures with periodic variation of elastic property. A phononic crystal with band gaps forbids acoustic waves within the frequency ranges of band gaps to propagate through the structure. In this paper, we propose a sensor array consisting of multiple quartz crystal microbalances surrounded by phononic crystals. Phononic crystals are utilized for isolating acoustic energy of individual bulk acoustic wave sensor and suppressing the interference. A theoretical investigation on a sensor array consisting of multiple quartz crystal microbalances (QCMs) surrounded by phononic crystals is presented. The resonance responses of a QCM were calculated by finite element analysis. A square-lattice phononic crystal structure was designed to have an complete band gap covering the QCM's resonance frequency. Finally, QCM sensor arrays with and without phononic crystals were analyzed to evaluate the isolation performance of the phononic crystals. Results show that the QCM's resonance frequency is around 10.06 MHz when the thickness of the AT-cut quartz substrate is 165 μm. The designed phononic crystal structure, whose lattice constant and filling ratio are 220 μm and 0.475, has a complete band gap from 9.66 to 10.08 MHz. The sensor array with the designed phononic crystals has a centralized mode shape, indicating that the phononic crystals indeed contribute to a confinement of acoustic energy of individual QCM. Accordingly, phononic crystals are verified to be capable of suppressing the crosstalk between adjacent bulk acoustic wave sensors in a sensor array.