Towards Acoustic Radiation Free Lamb Wave Resonators for High-Resolution Gravimetric Biosensing

A novel Lamb wave resonator with fully suppressed acoustic radiation in water is proposed for high-resolution mass-sensitive detection of biomolecules. The elimination of acoustic radiation is achieved by slowing down the Lamb wave to a velocity lower than the sound speed in water. This enables high-quality-factor resonance in water and reduces the sensing frequency noise. High aspect ratio electrodes (HAREs) are used to slow down the Lamb wave. The elastic resonance and large surface area of the HAREs can also enhance the mass sensitivity of the device. The improved mass sensitivity together with the low frequency noise substantially improves the overall sensing resolution. Although reducing the plate thickness can also slow down the Lamb wave, it makes the device very fragile and not practical to use. In contrast, slowing down the Lamb wave by increasing electrode height allows the use of thick plates which is robust. In this article, the behavior and performance of the proposed high aspect ratio electrode Lamb wave resonator (HARE-LWR) are theoretically analyzed using finite element method simulations. Optimum design parameters were found through the simulations. Reported results show that a significant figure of merit improvement was achieved by the proposed HARE-LWR design.