Vibration enhancement for fiber-optic acoustic sensors via Helmholtz resonator-membrane synergy

Abstract

The vibration-responsive membrane enables effective and sensitive sound wave capture, and enhancing membrane vibration is essential for optimizing sensor performance. Typically housed within an acoustic chamber to protect against external disturbances, the membrane's interaction with a carefully engineered chamber provides a promising pathway to improve sound-induced vibration. Here, we propose a design paradigm that effectively enhances membrane vibration by exploiting the synergy between the Helmholtz resonator and membrane dynamics. The complex modal analysis incorporating acoustic impedance and mass corrections is developed to characterize the synergistic vibration behavior of the Helmholtz resonator-coupled membrane, validated through finite element analysis and experimental testing. We apply the Helmholtz resonator-membrane synergy into a fiber-optic acoustic sensor prototype with a 50 μm-thick flexible polymer membrane, achieving a maximum sensitivity of 654 nm/Pa (-104.05 dB re rad/μPa), together with a minimum detectable sound pressure down to 7.7 μPa/$\sqrt{\text{Hz}}$. This synergy-enabled vibration enhancement provides a straightforward and efficient method for optimizing sensitivity and extending bandwidth, demonstrating strong potential for advanced acoustic detection applications.