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This paper introduces a directional MEMS microphone designed for hearing aid applications appropriate to low-frequency hearing impairment, inspired by the hearing mechanism of a fly, the female Ormia ochracea. It uses both piezoelectric and capacitive sensing schemes. In order to obtain a high sensitivity at low frequency bands, the presented micro...
Context in source publication
Context 1
... mechanical vibration model of Ormia ochracea's hear- ing system has previously been reported [5], which assumes that the mass of two tympana are the same as well as the stiffness of the tympana and the damping caused by the air cavity underneath, and thus infers the Eigen-frequencies and mechanical frequency response of the system. These assumptions are also applied in their subsequent symmetric microphone development [18]. In the case of this paper, the mass M of the two diaphragms are different, as well as the distance between the rotation beam and each diaphragm centroid. Fig. 2 shows the two-degree-of-freedom equivalent mechanical vibration model of the design. Leaving the air damping between the comb fingers out of consideration, the equations of motion in the frequency domain can be expressed ...
Citations
... Considering the fact that signals below 1 kHz are crucial for speech applications and environmental noise localization [71]. As illustrated in Figure 12, Zhang et al. [72] achieved low-frequency applications at 500 Hz and 2 kHz by adjusting the central axis position of the device to modify resonant frequencies, and they utilized piezoelectric detection and capacitive auxiliary detection. Ren et al. further optimized Zhang's work by tuning the two modal frequencies to 395 Hz and 739 Hz therefore leveraging the high vibration sensitivity of the fiber-optic Fabry-Perot interferometer (FPI) at the diaphragm's distal edge [73]. ...
... Figure 12. SEM images of the asymmetric microphone (Reprinted with permission from Ref. [72]). ...
... SEM images of the asymmetric microphone (Reprinted with permission from Ref.[72]). ...
The MEMS microphone is a representative device among the MEMS family, which has attracted substantial research interest, and those tailored for human voice have earned distinct success in commercialization. Although sustained development persists, challenges such as residual stress, environmental noise, and structural innovation are posed. To collect and summarize the recent advances in this subject, this paper presents a concise review concerning the transduction mechanism, diverse mechanical structure topologies, and effective methods of noise reduction for high-performance MEMS microphones with a dynamic range akin to the audible spectrum, aiming to provide a comprehensive and adequate analysis of this scope.
... Later experiments successfully determined that O. ochracea has a sound localization precision in the azimuthal plane of 2 • [23,24], comparable to that of humans. This high precision, together with the relative simplicity of the model and the easily reproducible structure of the hearing mechanism used by O. ochracea, led to a new stream of research in O. ochracea-inspired designs for directional microphones and hearing aids [25][26][27][28][29][30][31]. Despite its utility, the model contains a number of simplifications that limit its biological accuracy. ...
... O. ochracea's hearing system has repeatedly been a source of inspiration for bio-inspired designs for directional microphones and hearing aids [25][26][27][28][29][30][31]40]. Including the angle-dependent behavior of the expanded q2D model in future Ormia-inspired device designs may also provide significant avenues for improvement in device performance or may expand the functionality of devices like acoustic sensors through miniaturization and tunable frequency sensitivities. ...
Although most binaural organisms locate sound sources using neurological structures to amplify the sounds they hear, some animals use mechanically coupled hearing organs instead. One of these animals, the parasitoid flyOrmia ochracea, has astoundingly accurate sound localization abilities. It can locate objects in the azimuthal plane with a precision of 2°, equal to that of humans, despite an intertympanal distance of only 0.5 mm, which is less than 1/100th of the wavelength of the sound emitted by the crickets that it parasitizes.O. ochraceaaccomplishes this feat via mechanically coupled tympana that interact with incoming acoustic pressure waves to amplify differences in the signals received at the two ears. In 1995, Mileset al.developed a model of hearing mechanics inO. ochraceathat represents the tympana as flat, front-facing prosternal membranes, though they lie on a convex surface at an angle from the flies' frontal and transverse planes. The model works well for incoming sound angles less than ±30°, but suffers from reduced accuracy (up to 60% error) at higher angles when compared to response data acquired fromO. ochraceaspecimens. Despite this limitation, it has been the basis for bio-inspired microphone designs for decades. Here, we present critical improvements to the classicO. ochraceahearing model based on information from three-dimensional reconstructions ofO. ochracea's tympanal organ. We identified the orientation of the tympana with respect to a frontal plane and the azimuthal angle segment between the tympana as morphological features essential to the flies' auditory acuity, and hypothesized a differentiated mechanical response to incoming sound on the ipsi- and contralateral sides that depends on these features. To explore this, we incorporated spatially-varying model coefficients that represent this asymmetric response, making a new quasi-two-dimensional (q2D) model. The q2D model has high accuracy (average errors of under 10%) for all incoming sound angles. This improved biomechanical model may inform the design of new microscale directional microphones and other small-scale acoustic sensor systems.

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... Nevertheless, the presence of a backplate was a design constraint that limited mechanical vibrations. To overcome this problem, in recent studies [19][20][21][22][23][24][25][26][27][28] , the presence of the backplate was less explored. The absence of the backplate brings two additional advantages: as almost zero SFD and cosine-dependent directionality 29,30 . ...
... Figure 6a shows a 3D coordinate, where P is the applied sound pressure located at the azimuth, elevation = α, φ from distance r. The simplifications have been made by assuming that the whole sinusoidal acoustic pressure is converted to force 5,20,29,39 . Then, the summed directionality of the developed array underlying DM1, DM2, and DM3 can be given as 40 , ...
Fly Ormia ochracea ears have been well-studied and mimicked to achieve subwavelength directional sensing, but their efficacy in sound source localization in three dimensions, utilizing sound from the X-, Y-, and Z-axes, has been less explored. This paper focuses on a mm-sized array of three Ormia ochracea ear-inspired piezoelectric MEMS directional microphones, where their in-plane directionality is considered a cue to demonstrate sound source localization in three dimensions. In the array, biomimetic MEMS directional microphones are positioned in a 120° angular rotation; as a result, six diaphragms out of three directional microphones keep a normal-axis relative to the sound source at six different angles in the azimuth plane starting from 0° to 360° in intervals of ±30°. In addition, the cosine-dependent horizontal component of the applied sound gives cues for Z-axis directional sensing. The whole array is first analytically simulated and then experimentally measured in an anechoic chamber. Both results are found to be compliant, and the angular resolution of sound source localization in three dimensions is found to be ±2° at the normal axis. The resolution at the azimuth plane is found to be ±1.28°, and the same array shows a ± 4.28° resolution when sound is varied from the elevation plane. Looking at the scope within this area combined with the presented results, this work provides a clear understanding of sound source localization in three dimensions.
... A popular source of inspiration for such innovative microphones is the natural world, which received the name of bio-inspiration. 5, 15,22,33 Insects are an example of living creature that face the very same challenge we described above. Directional hearing is desirable to find a potential mate or escape a predator, but insects' body size is usually small. ...
The need for small directional microphones is patent in the current market. From smartphones to hearing aids, a small microphone capable of rejecting ambient noise is highly desirable. Most MEMS microphones are omnidirectional and have to resort to arrays to achieve directionality, effectively counteracting the reduced size that they offer in the first place. For this reason, we use bio-inspiration and turn to nature to find examples of solutions to this problem. The female specimens of the moth Achroia grisella are capable of monoaural directional hearing, which they use to track the males’ mating calls. It is believed that they achieve directionality solely due to the morphology of their tympana. To test it, we first produce a multiphysics simulation of the structure that serves as a starting point. For experimental measurements, additive manufacturing is chosen for its ease and cost-efficiency. 3D-printed samples of the same model are examined through micro-CT scanning and then measured using laser-Doppler vibrometry to determine their frequency and directivity responses. The results of both approaches are compared, and it is found that the structure does indeed show directionality and the experimental and simulated results are in good agreement.
... Due to the small size of the MEMS diaphragm, the bio-inspired directional microphones reported to date usually have an operating frequency greater than 1 kHz, which are not suitable for low-frequency environmental noise detection. There are currently few papers reporting on low-frequency bionic directional microphones with MEMS diaphragms except for the recent work by Zhang et al. [13]. ...
... Compared with another type of bionic MEMS diaphragm, which consists of two periphery-fixed circular silicon membranes and an upper SiO 2 /Si 3 N 4 bilayer bridge connecting the centers of the two membranes [21], the structure of the above-mentioned dual-wing diaphragm is simpler and easier to prepare. Zhang and coworkers developed a bionic low-frequency directional microphone by using the MEMS bionic diaphragm based on the piezoelectric and capacitive combined transduction mechanism [13]. Differently, the bionic directional microphone designed herein uses the extrinsic fiber-optic FPI as effective acousto-optic transducer, containing a closed back air cavity. ...
... The diaphragm has the rocking and bending modes with different resonance frequencies, and the closed back cavity allows the microphone to work around the rocking-mode eigenfrequency for low-frequency SSL function. Compared with the electrical low-frequency directional microphone reported by Zhang et al. [13], the fiber-optic FPI based low-frequency directional microphone developed in this work has higher sensitivity, lower signal transmission loss and stronger immunity to electromagnetic interference, thereby more suitable for deployment in harsh electromagnetic environment for localizing the low-frequency noise pollution source. Simulation, fabrication, and performance characterization of the fiber-optic FPI based bionic low-frequency directional microphone are described in detail in the following sections. ...
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.
... Beyond this, sensing modification has drawn significant attention regarding the improvement of the microphone's functionalities at a reduced size. Of the reported sensings, which include optical [9][10][11][12], capacitive [13] and piezoelectric sensing [14][15][16], piezoelectric sensing with optimally selected materials and transducer modes has shown good performance, such as a high signal-to-noise ratio (SNR) made of low noise and moderate sensitivity. As previously mentioned, the acoustic sensitivity is the multiplied outcome of the mechanical sensitivity and electrical sensitivity [14]. ...
... As the device dimensions are limited in MEMS technology, the enhancement of the acoustic sensitivity does not allow the microphone's dimensions to be increased. As a result, the improvement of the acoustic sensitivity has been regularly reported on using various piezoelectric sensing techniques, such as lead zirconate titanate (PZT) with D31 mode/top-to-bottom electrodes [14], aluminum nitride (AlN) with D31 mode [16] and AlN with D33 mode/inter-digitated electrode (IDTs) [15]. Among them, the thickness of the piezoelectric film limits the performance of the D31 mode regarding its vertical polarization [19][20][21]. ...
Microelectromechanical system (MEMS) directional microphones have been identified as having use in multi-projected virtual reality applications such as virtual meetings for projecting cameras. In these applications, the acoustic sensitivity plays a vital role as it biases the directional sensing, signal-to-noise ratio (SNR) and self-noise. The acoustic sensitivity is the multiplied outcome of the mechanical sensitivity and the electrical sensitivity. As the dimensions are limited in MEMS technology, the improvement of the acoustic sensitivity by reflecting the mechanical as well as electrical domains is a challenge. This paper reports on a new formation of the D33 mode, the coupled D33 mode, based on piezoelectric sensing to improve the acoustic functionalities. The unique advancement of the proposed D33 mode is that it allows multiple spans of the regular D33 mode to perform together, despite this increasing the diaphragm’s dimensions. At a reduced diaphragm size, the orientation of the coupled D33 mode realizes the maximum conversion of the mechanical deflection into electrical sensitivity. The significance of the proposed D33 mode in comparison to the regular D33 mode is simulated using COMSOL Multiphysics. Then, for a proof–of–concept, the experimental validation is carried out using a piezoelectric MEMS directional microphone inspired by the ears of the fly Ormia ochracea. In both ways, the results are found to be substantially improved in comparison with the regular approach of the D33 mode, showing the novelty of this work.
... As a result, the inter-modal distance was improved by ∼2 kHz frequency as compared to the previous study [11]. However, the further improvements of inter-modal distance can be carried out by increasing the torsional beam length/serpentine torsional beam [9]. But, the higher length of torsional beam shows a negative impact on the sensitivity and noise [5]. ...
The majority of fly
Ormia ochracea
inspired sound source localization (SSL) works are limited to 1D, and therefore SSL in 2D can include a new vision for ambiguous acoustic applications. This article reports on an analytical and experimental work on SSL in 2D using a pair of fly
O. ochracea
inspired MEMS directional microphones. The reported directional microphones were designed identically in circular shape and operated using piezoelectric sensing in 3–3 transducer mode. In X–Y plane, they were canted in a 90° phase difference, i.e., one microphone was in X–axis and another one was in Y–axis. As a result, their directionality results from the X–axis (cosine) and Y–axis (sine) formulated the tangent dependent 2D SSL in the X–Y plane. The highest accuracy of the SSL in 2D was found to be ±2.92° at bending frequency (11.9 kHz) followed by a ±3.25° accuracy at rocking frequency (6.4 kHz), a ±4.68° accuracy at 1 kHz frequency, and a ±6.91° accuracy at 18 kHz frequency. The subjected frequencies were selected based on the measured inter-aural sensitivity difference (mISD) which showed a proportional impact on the cue of 2D SSL, i.e., the directionality. Besides, the basic acoustic functionalities, such as sensitivity, SNR, and self–noise were found to be 20.86 mV/Pa, 66.4 dB, and 27.6 dB SPL, respectively at 1 kHz frequency and 1 Pa sound pressure. Considering this trend of microphones, the outstanding contribution of this work is the SSL in 2D with higher accuracy using a pair of high performing bio–inspired directional microphones.
... The cues are amplified from 1.5 μs to 50 μs and 1 dB to 12 dB, respectively for ITD, and IID near at the rocking mode which leads a SSL in range of ±30° with ±2° accuracy 6,[8][9][10] . By inspiring these astonishing abilities of the fly Ormia ochracea, a number of SSL works have been reported, such as SSL at bending mode (1.69 kHz) 9 , rocking mode 6,8,[10][11][12] , at 2 kHz 13 , low-frequency (below 3 kHz) 14 . Moreover, the majority of aforementioned works are fully replicated the ears of fly Ormia ochracea; as a result, they showed best performance at a single frequency like-wise the fly Ormia ochracea-best performance is at 5 kHz 4,5,15,16 . ...
... In addition, c r , c b , k r , k b , d, and θ are the damping coefficient at rocking mode, damping coefficient at bending mode, torsional stiffness, bending stiffness, distance between two force points, and angular rotation of the diaphragm, respectively. To give an insight of the coupling, the equations of motion of the mechanical model by assuming small angular bending can be given as 4,14,18 , ...
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.
... The torsional beam performs two functions-one is it acts as a pivot to facilitate the model to perform a see-saw rocking mode and the other one is to divide the plate into two diaphragms with the same surface area so that they represent the two identical tympana of the fly Ormia. This facilitates the bending mode operation [250]. Kuntzman et al. [251] developed a PZT sensing microphone with the first resonance frequencies at 13 kHz. ...
This paper discusses piezoelectric acoustic devices based on widely used piezoelectric materials.Commonly used piezoelectric thin film deposition techniques and the influence of process parameters on the growth, texture and orientation of the films are discussed. Etching techniques are also outlined. A comparative study of different devices developed previously is given. Also, applications of developed devices in aero-acoustic and medical fields have been briefly discussed. Flow charts of various techniques of deposition along with a combined one for full acoustic device fabrication are given.Various techniques, frequently used for thin film characterization have been discussed. The
testing and measurement techniques to determine the responses of acoustic devices such as sensitivity, resonance frequency, frequency response, piezoelectric co-efficient etc. have been briefly illustrated.This paper discusses common failure modes with respect to the field of use of acoustic devices. It also concisely discusses various reliability tests done in industries to assess the quality of the developed devices.This review has also suggested directions for future development of thin film acoustic sensors.
... Furthermore, an optimization design was reported by Ishfaque et al. with a circular diaphragm [70]. To improve its acoustic electrical response, Zhang et al. introduced a combination of the piezoelectric and the capacitive sensing mechanisms for acoustic sensing as shown in Figure 4d [71]. It claimed that the asymmetric structure broadened its frequency response range and the later an improved cross design has achieved spatial sound detection capability [72]. ...
... (d) Hybrid-mode microphone with a piezoelectric and a capacitive mechanism. Adapted with permission from Zhang et al. [71]. (e) Schematics of two optical microphones. ...
With the fast development of the fifth-generation cellular network technology (5G), the future sensors and microelectromechanical systems (MEMS)/nanoelectromechanical systems (NEMS) are presenting a more and more critical role to provide information in our daily life. This review paper introduces the development trends and perspectives of the future sensors and MEMS/NEMS. Starting from the issues of the MEMS fabrication, we introduced typical MEMS sensors for their applications in the Internet of Things (IoTs), such as MEMS physical sensor, MEMS acoustic sensor, and MEMS gas sensor. Toward the trends in intelligence and less power consumption, MEMS components including MEMS/NEMS switch, piezoelectric micromachined ultrasonic transducer (PMUT), and MEMS energy harvesting were investigated to assist the future sensors, such as event-based or almost zero-power. Furthermore, MEMS rigid substrate toward NEMS flexible-based for flexibility and interface was discussed as another important development trend for next-generation wearable or multi-functional sensors. Around the issues about the big data and human-machine realization for human beings’ manipulation, artificial intelligence (AI) and virtual reality (VR) technologies were finally realized using sensor nodes and its wave identification as future trends for various scenarios.
