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Eye blinking is closely related to human physiology and psychology. It is an effective method of communication among people and can be used in human–machine interactions. Existing blink monitoring methods include video-oculography, electro-oculograms and infrared oculography. However, these methods suffer from uncomfortable use, safety risks, limited reliability in strong light or dark environments, and infringed informational security. In this paper, we propose an ultrasound-based portable approach for eye-blinking activity monitoring. Low-power pulse-echo ultrasound featuring biosafety is transmitted and received by microelectromechanical system (MEMS) ultrasonic transducers seamlessly integrated on glasses. The size, weight and power consumption of the transducers are 2.5 mm by 2.5 mm, 23.3 mg and 71 μW, respectively, which provides better portability than conventional methods using wearable devices. Eye-blinking activities were characterized by open and closed eye states and validated by experiments on different volunteers. Finally, real-time eye-blinking monitoring was successfully demonstrated with a response time less than 1 ms. The proposed solution paves the way for ultrasound-based wearable eye-blinking monitoring and offers miniaturization, light weight, low power consumption, high informational security and biosafety. [ABSTRACT FROM AUTHOR]

Cardiac auscultation is an orthodox method to prevent and diagnose cardiovascular diseases. Traditional stethoscopes cannot offer a highly reliable diagnosis, and electronic stethoscopes suffer from low signal-to-noise ratio (SNR) and high cost. This paper reports an electronic stethoscope based on piezoelectric bimorph MEMS transducers for cardiac sound monitoring. The stethoscope prototype, measuring 37 $\times 28\times12$ mm3, contains a preamplifier, holders and polydimethylsiloxane (PDMS) packaging. The transducer is designed using a lumped element model, fabricated by MEMS process, packaged, and assembled for final use. A triangular cantilever is chosen as a basic element for the transducer, with analytical analysis showing high sensitivity per unit area as a figure of merit (FoM). Performance parameters such as sensitivity and noise are experimentally characterized and consistent with simulation results. Owing to the outstanding receiving performance of the aluminum nitride (AlN) material and bimorph triangular cantilever structure of the transducer, compared with the commercial electronic stethoscopes, the proposed stethoscope demonstrates real-time phonocardiogram (PCG) with higher SNR. With its small size, high performance and low cost, the stethoscope is developed for portable and wearable cardiac sound monitoring. [2022-0007] [ABSTRACT FROM AUTHOR]

The development of Internet of Things (IoT) requires demanding accurate and low-power indoor localization. In this article, a high-precision 3-D ultrasonic indoor localization system with ultralow power is proposed. A new piezoelectric micromachined ultrasonic transducer (PMUT) chip with a slotted membrane is designed and fabricated as a receiver, breaking the dilemma of low resonant frequency and wide field of view required for indoor localization. The system works based on the time difference of arrival (TDoA), and an improved quantum genetic algorithm (QGA) is used to estimate the location. The results show that the system achieves centimeter-level positioning precision, which is among the best solutions nowadays. Due to the high performance and small size endowed by the PMUT, the receiver footprint reaches as small as 0.25 cm2 and power consumption could reach as low as 0.1 mW, which are far better than that of current indoor localization systems. [ABSTRACT FROM AUTHOR]

Implantable medical devices are increasingly being used to perform electrophysiological stimulation, thus calling for wireless implantable neural stimulators for which wireless power transfer is needed. Compared with radio frequency and inductive coupling wireless power transfer methods, acoustic wireless power transfer features lower attenuation, a smaller size and a higher safe power threshold. This paper demonstrates the design, fabrication, assembly and characterization of a mm-sized acoustic wireless implantable neural stimulator based on a piezoelectric micromachined ultrasound transducer. Ex vivo experiments in water are conducted to characterize the power transfer link, showing improvement of the power transfer efficiency by more than two times with a matching circuit. Following FDA guidelines, the wireless implantable neural stimulator achieves a 3.24 μW output power in tissue. The feasibility for rat sciatic nerve stimulation is successfully demonstrated in vivo by the implantable prototype with a size of 5 × 5.5 × 2.5 mm3. The proposed solution has the potential to shrink the entire implanted system to a monolithic transducer-IC chip, paving the way toward an acoustic wireless implantable neural stimulator with higher levels of biocompatibility, integration and miniaturization. • The acoustic wireless implantable neural stimulator is tiny in size and biocompatible. • The stimulator is based on piezoelectric micromachined ultrasound transducers. • In vivo test shows successful and repeatable sciatic nerve stimulation of rats. • Sciatic nerve stimulation is confirmed by leg twitch and electromyography feedback. • The solution has the potential to shrink the entire system to a monolithic chip. [ABSTRACT FROM AUTHOR]