MEMS Directional Microphone Research Articles

Design and characterizations of a multi–sound receiver using fly Ormia ochracea's ears–inspired MEMS directional microphone array

Fly Ormia ochracea ears–inspired MEMS directional microphones show directionality at a reduced size. The progress within this area is limited to prototype development and feasibility studies, which leaves a limited choice of using it in practical applications. Here, we presented how this trend of directional microphones reacts to multiple incoming sound sources and what we can hear after converting the sensing sound. A multi-sound receiver is developed that receives multiple incoming sounds, and an analog logic is added to differentiate them. When the intensity, frequency, and propagation angle are unknown, the developed device is evaluated in an anechoic chamber using numerous sound sources. The results are promising and enable the advances of using fly Ormia ochracea's ears-inspired MEMS directional microphone in various acoustic applications.

Real-Time Sound Source Localization in Robots Using Fly Ormia Ochracea Inspired MEMS Directional Microphone

Sound localization is an integral part of robots for safe interaction with the environment. However, the constraints like high computational time, multiple microphones, and low accuracy require the researcher to focus on innovative solutions. Herein, we have presented a unique and easy-to-implement approach for sound source localization (SSL) by taking the advantage of the “figure-of-eight” response of the fly-inspired MEMS directional microphone (DM). The complete SSL task is performed using a single microphone. Initially, the servo motor-controlled rotational stage comprising DM is placed at an angle where the DM has a maximum response. Afterward, the system performs lateralization based on the intensity information. This step narrows down the search from 360 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> to 90 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> with some ambiguities. Finally, for localization, the system tracks the “figure-of-eight” response by calculating the intensity differences and stops the servo motor when the maximum response position of DM faces the sound. For better visualization, the system is also equipped with a laser diode to pinpoint the sound source. The results indicate that the system is capable of localizing the sound with an accuracy of nearly <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm 5^{\circ }$</tex-math></inline-formula> . The proposed system opens a path for SSL in several situations, particularly in human–robot interactions using a single microphone with less complexity and high accuracy.

Sound source localization by Ormia ochracea inspired low\u2013noise piezoelectric MEMS directional microphone

The single-tone sound source localization (SSL) by majority of fly Ormia ochracea’s ears–inspired directional microphones leaves a limited choice when an application like hearing aid (HA) demands broadband SSL. Here, a piezoelectric MEMS directional microphone using a modified mechanical model of fly’s ear has been presented with primary focus to achieve SSL in most sensitive audio bands to mitigate the constraints of traditional SSL works. In the modified model, two optimized rectangular diaphragms have been pivoted by four optimized torsional beams; while the backside of the whole structure has been etched. As a result, the SSL relative to angular rotation of the incoming sound depicts the cosine dependency as an ideal pressure–gradient sensor. At the same time, the mechanical coupling leads the magnitude difference between two diaphragms which has been accounted as SSL in frequency domain. The idea behind this work has been analytical simulated first, and with the convincing mechanical results, the designed bio–inspired directional microphone (BDM) has been fabricated using commercially available MEMSCAP based on PiezoMUMPS processes. In an anechoic chamber, the fabricated device has been excited in free-field sound, and the SSL at 1 kHz frequency, rocking frequency, bending frequency, and in-between rocking and bending frequencies has been found in full compliance with the given angle of incidence of sound. With the measured inter-aural sensitivity difference (mISD) and directionality, the developed BDM has been demonstrated as a practical SSL device, and the results have been found in a perfect match with the given angle of incidence of sound. Furthermore, to facilitate the SSL in noisy environment, the noise has been optimized in all scopes, like the geometry of the diaphragm, supportive torsional beam, and sensing. As a result, the A-weighted noise of this work has been found less than 23 dBA across the audio bands, and the equivalent-input noise (EIN) has been found to be 25.52 dB SPL at 1 kHz frequency which are the lowest ever reported by a similar device. With the developed SSL in broadband–in addition to the lowest noise–the developed device can be extended in some audio applications like an HA device.

Effect of squeeze air film damping on diffraction grating based bio-inspired MEMS directional microphone

A thin air film between two closely oscillating micro structures plays vital role in modifying the system dynamics. The thin air film brings damping and spring effects. Here, we designed a properly perforated MEMS directional microphone to mitigate the squeeze air film damping effects by taking inspiration from fly Ormia ochracea ear response, where damping helps it to produce distinct interaural differences in response to an external acoustic pressure. The coupled and perforated diaphragms are pivoted to a central hinge, and are designed to fit into a multi-user fabrication process. A nano-scale metrology is incorporated to accurately capture the motion of the diaphragms. The characterization of the directional microphone is performed with electrostatic actuation having the same magnitude and different phase difference replicating the scenario of a directional acoustic signal in real world. The experimental results demonstrate a significant vibration magnitude difference, and show a great potential of the fabricated microphone to enhance the directional cues by mitigating the squeeze air film damping.

Effect of Torsional Beam Length on Acoustic Functionalities of Bio-Inspired Piezoelectric MEMS Directional Microphone

In MEMS, the vibrations of torsionally supported diaphragms largely depend on the torsional beam specifications. An amiss selection of the beam parameters can lead to significant imperfection in the microphone functionalities, such as modal frequency, sensitivity, directionality, signal-to-noise ratio (SNR), and input-referred noise floor. Here, we present two piezoelectric MEMS directional microphones inspired by the ear anatomy of fly Ormia ochracea, with a prime focus to identify the effect of torsional beam dimensions on their acoustic functionalities. The dimensions of both diaphragms and the width & thickness of the torsional beams are identical for both microphones, the only difference between these two microphones lies in the torsional beam length. The microphones are fabricated by a commercially available micromachining process; PiezoMUMPs. To convert the mechanical vibrations into the electronic signal, a unique piezoelectric sensing scheme is developed comprising of aluminium nitride (AlN) and D33 transducer mode. The performances of both microphones are carried out by the theoretical analysis and simulation and further verified with the experimental measurements. It is found from all analyses that the microphone having a shorter length of the torsional beam is better in terms of sensitivity, noise floor, and SNR regarding its low propagation delay.

Bioinspired low noise circular-shaped MEMS directional microphone

The traditional state-of-the-art miniature directional microphones suffer from a higher noise level mainly due to size constraints. Herein, a miniature directional microphone mimicking the fly Ormia ochracea’s ear anatomy is presented with the prime focus on achieving higher signal-to-noise ratio at reduced size. The microphone has circular shape with aluminum nitride (AlN)-based piezoelectric readout scheme deposited at the center of the diaphragm. The 3-3 transduction mode is adopted for sensitivity enhancement. The microphone testing is performed in an anechoic chamber. Besides the bidirectional response, the A-weighted noise under broadband excitation is ∼29 dBA, which is lower than the optical directional microphone of Miles et al., which is the most prominent noise analysis work in the area of fly inspired MEMS directional microphone.

Bio-Inspired Rectangular Shaped Piezoelectric MEMS Directional Microphone

The noise floor of a piezoelectric MEMS directional microphone largely depends on piezoelectric materials and transducer modes. A careful choice of these parameters (piezoelectric materials and transducer modes) can help to significantly improve the difficulties of noise floor. Here, we present a unique diaphragm-based biomimetic MEMS directional microphone having multiple-port sensing schemes. The diaphragm is separated into two wings and supported by two torsional beams, which are hinged to a fixed support as to imitate the unique inter-tympanal feature of the fly Ormia ochracea . In this microphone, the thermal-mechanical noise (Johnson noise) is minimized by adopting aluminium nitride-based piezoelectric sensing. The d33 mode is incorporated with a prime focus on sensitivity enhancement which leads to signal-to-noise ratio improvement. Measured directivity patterns of both wings show a strong agreement with the direction of applied acoustic pressure as expected for an ideal bi-directional microphone. The measured noise floor at 1-kHz frequency and overall A-weighted noise floor across the audio frequency are 31.35 dB SPL and 32.5 dBA, respectively, which are quite less than some notable works on directional microphones. The experimental results verify the uniqueness of this work.

Fly &lt;italic&gt;Ormia Ochracea&lt;/italic&gt; Inspired MEMS Directional Microphone: A Review

Since the discovery of the ears of Ormia ochracea , a parasitic fly, a significant work in designing a microelectromechanical (MEMS)-based directional microphone and its potential applications in medical device, hearing aids, has been carried out. In this paper, we first report the anatomical and behavioral studies of the fly’s ear system and fly’s quest for host finding, respectively. We then give a brief history of the microphones inspired from the fly’s ear anatomy, starting from the beginning when the first time biomechanics of the fly’s ear was reported by Miles group in 1995. Finally, the most demanded application of the MEMS directional microphone, hearing aids, is also reported along with the insight of current challenges and future perspective of the directional microphones.

Squeeze film damping analysis of biomimetic micromachined microphone for sound source localization

The trapped air between two closely oscillating MEMS devices introduces significant damping in the system. These damping effects can be modeled by designing a suitable perforation ratio in the system. Here, we design a perforated MEMS directional microphone inspired from the fly Ormia ochracea’s ear anatomy. The designed microphone is circular in shape and regularly perforated with circular holes to mitigate the squeeze film damping (SFD) effects. The mathematical modeling of the fly's model demonstrates the significance of the rocking mode’s critical damping in improving the cues for the directional sensitivity. To grasp the in-depth dynamics of the system damping, an analytical modeling of the SFD of both rocking and bending modes is performed by utilizing the modified Reynolds equation. The required damping formulas are extracted by using the Green’s function. The derived analytical modeling results are utilized to configure the microphone parameters as to bring the damping ratio of the rocking mode in the vicinity of the critical damping. The final deduced values of the parameters are utilized to fabricate the microphone by the PolyMUMPs micromachining process. The testing of the microphone is performed in an anechoic chamber by considering a sound source having 45° incidence angle. The figured results show a substantial vibration magnitude difference and validate the significance of modeling the SFD in the dynamic response of the fly’s inspired MEMS directional microphone.

Analytical modeling of squeeze air film damping of biomimetic MEMS directional microphone

Squeeze air film damping is introduced in microelectromechanical systems due to the motion of the fluid between two closely spaced oscillating micro-structures. The literature is abundant with different analytical models to address the squeeze air film damping effects, however, there is a lack of work in modeling the practical sensors like directional microphones. Here, we derive an analytical model of squeeze air film damping of first two fundamental vibration modes, namely, rocking and bending modes, of a directional microphone inspired from the fly Ormia ochracea׳s ear anatomy. A modified Reynolds equation that includes compressibility and rarefaction effects is used in the analysis. Pressure distribution under the vibrating diaphragm is derived by using Green׳s function. From mathematical modeling of the fly׳s inspired mechanical model, we infer that bringing the damping ratios of both modes in the critical damping range enhance the directional sensitivity cues. The microphone parameters are varied in derived damping formulas to bring the damping ratios in the vicinity of critical damping, and to show the usefulness of the analytical model in tuning the damping ratios of both modes. The accuracy of analytical damping results are also verified by finite element method (FEM) using ANSYS. The FEM results are in full compliance with the analytical results.