Evaluating a Human Ear-Inspired Sound Pressure Amplification Structure with Fabry–Perot Acoustic Sensor Using Graphene Diaphragm

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.

Ultrasensitive Acoustic Detection Using an Enlarged Fabry–Perot Cavity with a Graphene Diaphragm

“…According to the small deflection deformation theory, the volume change (Δ V ) of the air cavity due to the uniform pressure ( p ) imposed on the graphene can be approximated as where r , t , E , and μ are the radius, thickness, Young’s modulus, and Poisson’s ratio of the graphene diaphragm, respectively; ω­(ρ) is the deflection of the graphene diaphragm at the position ρ relative to the center of the membrane. Assuming that an equilibrium is reached at any instance, in terms of the ideal gas equation, the pressure change (Δ p ) in the air cavity induced by the volume change (Δ V ) at a constant room temperature can be expressed as …”

“…Unfortunately, this method inevitably increased the thickness of the diaphragm, resulting in a decrease in S M by 25%. Then, in 2021, Li achieved a higher S M with ∼14.8 nm/Pa@1.2 kHz for a graphene-based F–P acoustic sensor via an external sound pressure amplification structure . However, the acoustic pressure amplification structure is remarkably functional in the frequency band ranging from 0.2 to 2 kHz.…”

A high sensitivity fiber optic acoustic sensor based on incident-angle sensing: application to detect snoring signals

“…5(a), the resonant frequency of the sensor is 18KHz. The reason for the unevenness of the response frequency curve may be that the ratio between the diameter and thickness of the quartz film of the sensor is too large [15] , or the surface of the quartz film is rough. Therefore, the subsequent improvement of the sensor can be started from the preparation process of quartz film to pursue a flatter frequency response.…”

2D-Materials-Based Wearable Biosensor Systems

“…Li et al reported an artificial eardrum using an acoustic sensor based on 2D MXene (Ti 3 C 2 T x ), which can enable a two-stage amplification of pressure and acoustic sensing, thus mimicking the function of a human eardrum for realizing voice detection and recognition. As shown in Figure 4 C, the MXene artificial eardrum shows an extremely high sensitivity of 62 kPa −1 and a very low detection limit of 0.1 Pa [ 124 ]. Later, Wang et al designed a graphene throat patch that is capable of recording deformation resistance through weak vibrations even when no sound is emitted subsequently through AI analysis of the signal [ 125 ].…”

“…Copyright 2021, Springer Nature. ( C ): Cochlear sensor resistance change with decibels; inset shows the MXene cochlear sensor [ 124 ]. Copyright 2021, Multidisciplinary Digital Publishing Institute.…”