Acoustic radiation-free surface phononic crystal resonator for in-liquid low-noise gravimetric detection

TL;DR

This paper introduces a novel surface phononic crystal resonator that significantly reduces acoustic radiation in liquid, leading to higher quality factors and improved gravimetric biosensing performance.

Contribution

The paper presents a locally-resonant surface phononic crystal design that confines acoustic energy near the surface, preventing radiation into the liquid and enhancing sensor quality.

Findings

Quality factor 15 times higher than conventional resonators

Numerical and experimental validation of the SPC resonator

Potential application to various acoustic biosensors

Abstract

Acoustic wave resonators are promising for gravimetric biosensing. However, they generally suffer from strong acoustic radiation in liquid, which limits their quality factor and increases their frequency noise. This article presents an acoustic-radiation-free gravimetric biosensor based on a locally-resonant surface phononic crystal (SPC) consisting of periodic high aspect ratio electrodes to ad-dress the above issue. The acoustic wave generated in the SPC is slower than the sound wave in water, hence preventing acoustic propagation in the fluid and resulting in energy confinement near the electrode surface. This energy confinement results in a significant quality factor improvement and thus reduces the frequency noise. The proposed SPC resonator is numerically studied by finite element analysis and experimentally implemented by an electroplating based fabrication process. Experimental results show that the SPC resonator exhibits an in-liquid quality factor 15 times higher than a conventional Rayleigh wave resonator with a similar operating frequency. The proposed radiation suppression method using SPC can also be applied in other types of acoustic wave resonators. It can thus serve as a general technique for boosting the in-liquid quality factor and the sensing performance of many acoustic biosensors.