Acoustic detection is of great significance because of its wide applications. This paper reports a Micro-Electro-Mechanical System (MEMS) acoustic sensor based on grating interferometer. In the MEMS structure, a diaphragm and a micro-grating made up the interference cavity. A short-cavity structure was designed and fabricated to reduce the impact of temperature on the cavity length in order to improve its stability against environment temperature variations. Besides this, through holes were designed in the substrate of the grating to reduce the air damping of the short-cavity structure. A silicon diaphragm with a 16.919 µm deep cavity and 2.4 µm period grating were fabricated by an improved MEMS process. The fabricated sensor chip was packaged on a conditioning circuit with a laser diode and a photodetector for acoustic detection. The output voltage signal in response to an acoustic wave is of high quality. The sensitivity of the acoustic sensor is up to −15.14 dB re 1 V/Pa @ 1 kHz. The output signal of the high-stability acoustic sensor almost unchanged as the environment temperature ranged from 5 °C to 55 °C.

This paper reports on a fiber-optic directional microphone with a bionic MEMS diaphragm for low-frequency sound source localization. The diaphragm consists of two 3 mm $\times3$ mm wings connected by a 1 mm $\times1$ mm bridge, and two 0.2 mm $\times0.1$ mm torsion beams anchor the diaphragm to the Silicon-On-Insulator (SOI) frame along the bridge’s central axis. The bridge causes the mechanical coupling between the two wings, resulting in rocking and bending vibration modes of the diaphragm. The designed microphone contains a closed back cavity and works by measuring vibration at one of the diaphragm’s distal edges by a fiber-optic Fabry-Perrot interferometer (FPI). Simulation and experimental results demonstrated that the microphone can make a significant directional response in a wide low-frequency band centered on the rocking-mode eigenfrequency, giving a typical bi-directional polar pattern, but its directionality disappears at the bending-mode eigenfrequency. The directional sensitivity of the microphone was determined to be 1.86 mV/° at 300 Hz based on the measured linear response to the incident angle in an angular range from $\theta =0$ to 60°. The minimum detectable pressure (MDP) of the microphone relies on both the incident angle and sound frequency, and MDP was measured to be $12.68\mu $ Pa/ $\surd $ Hz at 300 Hz and $\theta = 100^{\circ }$ . The fiber-optic FPI serving as the acousto-optic transducer offers the directional microphone high sensitivity and strong immunity to electromagnetic interference, rendering it suitable for low-frequency sound source localization in harsh environments, especially for tracing the environmental noise sources.

Optical interferometric sensors have been widely used for highly sensitive detection of various physical quantities, and most of them operate in simple intensity interrogation mode. The deviation between the sensor's operating point and its quadrature point (Q-point) can cause signal distortion and sensitivity reduction. In this work, a new method for judging and compensating the above-mentioned deviation is proposed for improving sensor performance. Judgment of the degree of deviation is performed using the amplitude of the second harmonic (SH) component derived from the sensor's output signal, and the deviation compensation is achieved through wavelength tuning. The wavelength tuning direction is determined by the relationship between the two phases of fundamental frequency (FF) and SH components, which eliminates the ambiguity of the sign of wavelength change and expedites the tuning speed. The method was fully verified by simulation and experiment based on a Fabry-Perot interferometer (FPI) based fiber-optic microphone with a tunable laser. Experimental results show that the FF and SH amplitudes oppositely changes with changing the ambient temperature after fixing the laser wavelength and fast tuning of the laser wavelength minimizes the SH amplitude close to zero and simultaneously maximizes the FF amplitude, consequently maintaining the operating point of the microphone at its Q-point. Moreover, the proposed method shows high precision and strong robustness to the laser power fluctuation. According to the criterion that the total harmonic distortion allowed is less than 3%, the phase deviation between the microphone's operating point and its Q-point should be smaller than 0.004°, which can be easily satisfied by the method proposed in this work.

Miniature microphones inspired by the ears of the parasitic fly Ormia Ochracea are an important means to overcome the fundamental size constraint of microphone arrays for sound source localization (SSL). However, the signal demodulation performance and the SSL range of the biomimetic microphones need to be improved. This study aims to develop a miniature biomimetic microphone with good signal demodulation capability and wide SSL range. Specifically, in this paper, an optical beam deflection (OBD) demodulation system was designed and combined with a micro-electro-mechanical system omimetic diaphragm to form a miniature microphone for SSL. The OBD-based biomimetic microphone shows many merits in signal demodulation, including low noise floor (⩽−110 dB), high repeatability of sound pressure measurement, and linear temperature response. The theoretical and experimental results demonstrated that the two wings of the biomimetic microphone have the bi-directional polar patterns with different sizes of lobes at the rocking-mode eigenfrequency, and have omnidirectional response at the bending-mode eigenfrequency. Furthermore, a new SSL method was proposed, which effectively extends the SSL range of the biomimetic microphone at the rocking-mode eigenfrequency to ±90° by combining the interaural intensity difference between the two wings. The proposed OBD-based biomimetic microphone not only has the advantages of small volume and low power consumption, but also has the stable and wide-range SSL capability, which shows that it has a great prospect in the practical applications of SSL, such as wearable devices and rescue robots, etc.

MEMS microphones inspired by the coupled ears of the fly Ormia ochracea have been extensively studied to achieve miniaturization of sound source localization (SSL). However, the SSL of all current biomimetic microphones relies on the electrical signals converted from the directional vibration of the biomimetic diaphragms. Consequently, only the electrical performance of the biomimetic microphones under sound pressure excitation (i.e., electrical sensitivity mV/Pa) has been characterized, whereas the mechanical performance (i.e., mechanical sensitivity nm/Pa) has not. Characterizing the mechanical sensitivity can not only directly represent the acoustic response magnitude of the biomimetic microphones, but also directly verify the corresponding theoretical models. Therefore, in this paper, we designed and fabricated a MEMS biomimetic microphone with a fiber-optic Fabry-Pérot interferometer, based on which we successfully measured the mechanical sensitivity of the biomimetic microphone by the fast demodulated white-light interferometry for the first time. Additionally, an improved theoretical model with exact expressions was first derived to better describe the acoustic response of the biomimetic microphone, and the theoretical and measurement results can be corroborated each other in terms of the mechanical sensitivity. Therefore, this study verifies a feasible solution to directly measure the acoustic response of the biomimetic microphone and constructs a more effective and detailed theoretical model to describe this acoustic response. The results in this paper can not only provide a numerical reference for designing future demodulation systems regarding the dynamic range and the linear demodulation interval, but also promote a deeper understanding of the working mechanism of the biomimetic microphones.

MEMS microphones inspired by the coupled ears of the fly Ormia ochracea have been extensively investigated for miniature, high-accuracy, and low-noise-floor sound source localization (SSL). However, most studies focus on the rocking-mode-dominated bidirectional polar response for SSL while neglecting the omnidirectional response of the bending mode, leaving other directional responses arising from the dual-mode superposition largely unexplored. Therefore, in this paper, based on a low-damping optical beam deflection (OBD) biomimetic microphone with a pronounced bending-mode omnidirectional response, various directional responses arising from the dual-mode superposition are identified and characterized. Both simulation and experimental results demonstrate that, under the dual-mode superposition, the directional responses of the OBD biomimetic microphone transition from the bidirectional polar pattern with asymmetric lobes to the two gradually overlapping circular patterns and eventually to the two nearly completely overlapping circular patterns, and this process is well described by the developed theoretical model. Moreover, we explore the SSL performance of the modal superposition-induced directional responses and demonstrate for the first time that the non-overlapping circular patterns have the same sinusoidal SSL potential as the bidirectional polar responses. This paper advances the understanding of modal superposition-induced directional responses and expands the variety of directional responses available for SSL in biomimetic microphones.