Lei Shi

In this work, we reported a theoretical model for a novel piezoelectric micromachined ultrasonic transducer (PMUT). The sensing cells with hexagonal transduction diaphragms in the PMUT array are designed and arranged in a bioinspired honeycomb structure. Based on the classical piece-wise approach commonly used for PMUT with circular diaphragm, an enhanced theoretical model is developed. In this model, the deflection of the honeycomb diaphragm is analytically determined by the volume deflection, rather than the path deflection commonly used in the previous models. The hexagonal diaphragm is converted as a circular one, whose radius is derived by correcting the characteristic size of the hexagonal diaphragm multiplied by a correction factor. The calculated parameters by the reported theoretical model of a transduction cell in the PMUT array, such as resonant frequency and static deflection, matched well with the data obtained by finite element analysis and experiment. Special investigations are made on the effects of top electrode coverage and transduction layer thickness towards PMUT’s performance. The reported theoretical model in this work is suitable not only for PMUTs with circular and hexagonal transduction cells, but also for square and other arbitrary shape diaphragms. This enhanced theoretical model provides an interesting insight on design optimizations of PMUT with various transduction cell geometries.2022-0093

A miniaturized ultrasonic sugar concentration detection system based on piezoelectric micromachined ultrasonic transducers (PMUTs) is presented in this work. An $8\times 9$ PMUT array together with a TDC1000 ultrasonic sensing analog front end is used to alternately transmit and receive ultrasonic signals. A PT1000 temperature sensor is employed for real-time monitoring the solution temperatures. The acquired and processed signals are sequentially subjected to ultrasonic time-of-flight (TOF), ultrasonic velocity, and sugar concentration calculations, followed by a temperature compensation by a microcontroller unit (MCU). A feasibility evaluation of the designed ultrasonic sugar concentration detection system is conducted. A sucrose solution is selected as the measurement sample. Measurement results show that the reported system can be used to determine sugar concentration in solutions well and can perform automatic temperature compensation. The reported ultrasonic sugar concentration system has a fast response of less than 1 s, an accuracy of 1.4%, and a high resolution of 0.6%, which is comparable to the classical optical saccharimeter. Furthermore, the reported system can be designed as a small catheter-based test probe with high portability for portable sugar concentration detections in food industry because of the compact size of the PMUT sensor.

A piezoelectric micromachined ultrasonic transducer (PMUT) array-based smart electronic stethoscope is presented for Internet of Medical Things (IoMT). For the first time, an electronic stethoscope based on a high-performance PMUT array is demonstrated to record mechanoacoustic cardiopulmonary signals from the body. This electronic stethoscope can continuously capture the cardiopulmonary signals and enable the telemedicine as well as the digital smart medical becoming a reality. The measured cardiopulmonary signals are collected using the PMUT array and transmitted to a mobile terminal via Bluetooth. Then, primary diagnosis can be implemented in real time using a customized APP in the terminal. The PMUT array was designed with high acoustic pressure sensitivity, high noise resolution, and wide operation bandwidth. These crucial parameters enabled simultaneous monitoring of multiple health parameters associated with the cardiopulmonary system, namely, respiratory rate, heart rate, lung sounds, and heart sounds. A feasibility test was implemented on patients with preexisting medical condition, in order to detect weak mechanoacoustic signals related to tachyarrhythmia and asthma. This article demonstrates the potential use of smart electronic stethoscope in healthcare applications, such as the assessment of heart and lung diseases, which provides an innovative auscultation technology and brings great benefits to IoMT.

In this paper, a low noise amplification circuit is designed for aluminum nitride-based piezoelectric micromachined ultrasonic transducers (PMUTs) with three different sensing configurations. The acoustic pressure sensitivity and noise resolution of PMUTs corresponding to different readout configurations are analyzed and characterized. With the differential readout configuration, the acoustic pressure sensitivity of the PMUTs is improved by 5.76 dB (re: 1 V µ Pa ⁻¹ ) on average, and the noise resolution is reduced by about 8 dB at 500 Hz (re: 1 µ Pa (Hz 1 / 2 ) ⁻¹ ). Compared to the conventional readout configuration, both theoretical analysis and measurement results show that the output voltage of PMUTs is doubled with the differential readout configuration and thus the acoustic pressure sensitivity is improved. Moreover, the noise resolution of PMUTs is reduced and thus the signal-to-noise is improved. This work offers new insight on improving the receiving performance of PMUTs.

In this article, we present a high-performance aluminum nitride (AlN)-based microelectromechanical system (MEMS) hydrophone sensor, in which the sensing cells are designed and arranged as an innovative honeycomb architecture for achieving large acoustic pressure sensitivity and high fill-factor. An 8×9 array of 360 μm in characteristic size, 0.92-MHz MEMS hydrophone sensor is developed based on an AlN-on-cavity silicon-on-insulator (CSOI) platform. The size of the MEMS hydrophone sensor is 3.2 mm ×3.2 mm. The MEMS hydrophone sensor and its preamplification circuit are integrated on a printed circuit board and packaged together with an acoustically transparent material, in order to meet the stringent requirements of underwater applications. The packaged MEMS hydrophone is fully characterized through using an industry-standard hydrophone calibration instrument. The MEMS hydrophone achieves an acoustic pressure sensitivity of -178 dB (re: 1 V/ μ Pa), with a maximum nonlinearity of 0.1%, and a noise resolution of 58.7 dB (re: 1 μPa/Hz). The measurement results show that the reported MEMS hydrophone sensor with bioinspired honeycomb structure is compared favorable with advanced commercially available bulky hydrophones.

This article investigates the dependence of transmitting sensitivity on the top electrode design of piezoelectric micromachined ultrasonic transducers (PMUTs). Two typical top electrodes, namely inner electrode (IE) and outer electrode (OE), are designed and fabricated. The measured transmitting velocities of the fabricated PMUTs at resonance under a drive voltage of 5 $\text{V}_{\mathrm {p-p}}$ (peak-to-peak) are 15.36 mm/s for the IE design and 20.67 mm/s for the OE design with a circular diaphragm and 16.62 mm/s for the IE design and 22.18 mm/s for the OE design with a hexagonal diaphragm. The OE design demonstrates a transmitting velocity improvement of 34.57% for the circular diaphragm and 33.45% for the hexagonal diaphragm. The improvement is due to the fact that the OE design shows higher quality factor ( ${Q}$ ) than the IE counterpart. Moreover, the resonant frequency of the OE design is higher than that of the IE design, which results in a larger acoustic pressure output and hence higher transmitting sensitivity. This work highlights an effective and simple approach for PMUTs to achieve high transmitting sensitivity, which is an important parameter in the applications that require large sound pressures, such as fingerprint imaging, gesture recognition, and ranging.