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 (AlN) based piezoelectric sensing. The d33 mode is incorporated with a prime focus on sensitivity enhancement which leads to signal-to-noise ratio (SNR) 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.

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.

Conventional manual ultrasound (US) imaging is a physically demanding procedure for sonographers. A robotic US system (RUSS) has the potential to overcome this limitation by automating and standardizing the imaging procedure. It also extends ultrasound accessibility in resource-limited environments with the shortage of human operators by enabling remote diagnosis. During imaging, keeping the US probe normal to the skin surface largely benefits the US image quality. However, an autonomous, real-time, low-cost method to align the probe towards the direction orthogonal to the skin surface without pre-operative information is absent in RUSS. We propose a novel end-effector design to achieve self-normal-positioning of the US probe. The end-effector embeds four laser distance sensors to estimate the desired rotation towards the normal direction. We then integrate the proposed end-effector with a RUSS system which allows the probe to be automatically and dynamically kept to normal direction during US imaging. We evaluated the normal positioning accuracy and the US image quality using a flat surface phantom, an upper torso mannequin, and a lung ultrasound phantom. Results show that the normal positioning accuracy is 4.17 $\pm$ 2.24 degrees on the flat surface and 14.67 $\pm$ 8.46 degrees on the mannequin. The quality of the RUSS collected US images from the lung ultrasound phantom was equivalent to that of the manually collected ones.