Abstract
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.
Highlights
The sound source localization (SSL) is one of the fundamental requirements of some free–field and far–field acoustic applications, such as mobile robot, noise activated cameras in surveillance system, and HA1
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 kHz4,5,15,16
Because the cosine dependency works for the SSL relative to the angular rotation of incoming sound; whereas, the magnitude difference followed by the phase difference between two pivoted diaphragms leads the SSL in frequency domain
Summary
The SSL is one of the fundamental requirements of some free–field and far–field acoustic applications, such as mobile robot, noise activated cameras in surveillance system, and HA1. 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 kHz13, low-frequency (below 3 kHz)[14]. Because the cosine dependency works for the SSL relative to the angular rotation of incoming sound; whereas, the magnitude difference followed by the phase difference between two pivoted diaphragms leads the SSL in frequency domain. The outstanding contributions of this work as compared to the similar devices are as follows: (1) the SSL, for the first time, in wide–band was modeled and experimentally presented by an Aluminum Nitride (AlN) & D33 mode based bio-inspired piezoelectric MEMS directional microphone, (2) unlike Kuntzman et al.[13], a modified cosine dependency algorithm was adopted; which in turn, the issue of localizing the “off-axis” was solved in this work, and (3) for the first time, a MEMS directional microphone with less than 23 dBA broadband noise was developed and experimentally presented
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