Design and characterization of an acoustic sensor based on fiber segment interferometry
Abstract
This paper presents the design, simulation, and experimental characterization of a distributed acoustic membrane sensor based on fiber segment interferometry (FSI). A custom fiber Bragg grating (FBG) chain was bonded onto a circular Mylar membrane, enabling simultaneous strain measurements at seven spatially separated sensing segments along a single optical fiber. A finite element model implemented in a multiphysics simulation environment was used to analyze membrane deformation, strain distribution, and vibroacoustic modal behavior before fabrication. The prototype was characterized regarding frequency response, pressure linearity, sensitivity, signal-to-noise ratio (SNR), total harmonic distortion (THD), directional behavior, and spatially resolved vibroacoustic mode shape detection. At 300 Hz, the cumulative fiber signal achieved a sensitivity of 5.4nmPa−1 with a linearity error below 1.25 %. At 1 kHz and 106 dB sound pressure level (SPL), an SNR of 55.2 dB, calculated using a spectral peak-to-noise-floor approach commonly reported in optical microphone studies, and a THD of 0.69% were measured. The segment-resolved FSI signals enabled identification of membrane modes up to approximately 1.5 kHz. In addition, the fiber position outside the neutral membrane plane allowed the membrane motion direction to be determined for sufficiently small deflections, while larger deflections led to a rectification effect consistent with Kirchhoff–Love plate theory. The results show that FSI-based membrane sensors can combine acoustic sensing with spatially resolved modal analysis using a single optical fiber.