Abstract
In order to enhance the sensitivity of a Fabry–Perot (F-P) acoustic sensor without the need of fabricating complicated structures of the acoustic-sensitive diaphragm, a mini-type external sound pressure amplification structure (SPAS) with double 10 μm thickness E-shaped diaphragms of different sizes interconnected with a 5 mm length tapered circular rod was developed based on the acoustic sensitive mechanism of the ossicular chain in the human middle ear. The influence of thickness and Young’s modulus of the two diaphragms with the diameters of 15 mm and 3 mm, respectively, on the amplification ratio and frequency response were investigated via COMSOL acoustic field simulation, thereby confirming the dominated effect. Then, three kinds of dual-diaphragm schemes relating to steel and thermoplastic polyurethanes (TPU) materials were introduced to fabricate the corresponding SPASs. The acoustic test showed that the first scheme achieved a high resonant response frequency with lower acoustic amplification due to strong equivalent stiffness; in contrast, the second scheme offered a high acoustic amplification but reduced frequency range. As a result of sensitivity enhancement, adapted with the steel/TPU diaphragm structure, an optical fiber Fabry–Perot sensor using a multilayer graphene diaphragm with a diameter of 125 μm demonstrated a remarkable sensitivity of 565.3 mV/Pa @1.2 kHz due to the amplification ratio of up to ~29.9 in the range of 0.2–2.3 kHz, which can be further improved by miniaturizing structure dimension, along with the use of microstructure packaging technology.
Highlights
Academic Editors: Jihoon Lee and School of Instrumentation Science and Opto-Electronics Engineering, Beihang University, Beijing 100191, Research Institute of Beihang University in Shenzhen, Shenzhen 518055, China
In order to enhance the acoustic sensitivity for an F-P acoustic sensor via an amplification structure, a human ear-inspired cylindrical sound pressure amplification structure (SPAS), whose outer diameter and height were 18 mm 9 mm, was designed by means of two circular diaphragms interconnected with a conical round rod
The COMSOL-based sound field simulation of the amplification structure demonstrated the dominating influence of structural parameters of the diaphragm on the amplification ratio and resonant frequency response
Summary
Referring to the structural illustration of a human middle ear, external air pressure is strengthened via large TM vibration and lever amplification offered by malleus and incus In this case, the amplified acoustic pressure is passed to the following inner ear by the use of the stapes. Radius of the upper endface of the connecting rod; E1 and μ1 are Young’s modulus a Poisson’s ratio of the diaphragm material. The deflection ω2(r) of diaphragm under the uniform dynamic load p2 and the central load pc can be obtained by: where R2 and H2 are the radius and the thickness of diaphragm 1, respectively; r radius of the lower endface of the connecting rod; E2 and μ2 are Young’s. The structural parameters of SPAS could be optimized by the mechanical amplification responsivity on basis of Equation (8)
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