Flexible and wearable sensors are highly desired for health monitoring, agriculture, sport, and indoor positioning systems applications. However, the currently developed wireless wearable sensors, which are communicated through radio signals, can only provide limited positioning accuracy and are often ineffective in underwater conditions. In this paper, a wireless platform based on flexible piezoelectric acoustics is developed with multiple functions of sensing, communication, and positioning. Under a high frequency (≈13 MHz) stimulation, Lamb waves are generated for respiratory monitoring. Whereas under low‐frequency stimulation (≈20 kHz), this device is agitated as a vibrating membrane, which can be implemented for communication and positioning applications. Indoor communication is demonstrated within 2.8 m at 200 bps or 4.2 m at 25 bps. In combination with the sensing function, real‐time respiratory monitoring and wireless communication are achieved simultaneously. The distance measurement is achieved based on the phase differences of transmitted and received acoustic signals within a range of 100 cm, with a maximum error of 3 cm. This study offers new insights into the communication and positioning applications using flexible acoustic wave devices, which are promising for wireless and wearable sensor networks.

In this paper, we explore the acoustofluidic performance of zinc oxide (ZnO) thin-film surface acoustic wave (SAW) devices fabricated on flexible and bendable thin aluminum (Al) foils/sheets with thicknesses from 50 to 1500 μm. Directional transport of fluids along these flexible/bendable surfaces offers potential applications for the next generation of microfluidic systems, wearable biosensors and soft robotic control. Theoretical calculations indicate that bending under strain levels up to 3000 με causes a small frequency shift and amplitude change (<0.3%) without degrading the acoustofluidic performance. Through systematic investigation of the effects of the Al sheet thickness on the microfluidic actuation performance for the bent devices, we identify the optimum thickness range to both maintain efficient microfluidic actuation and enable significant deformation of the substrate, providing a guide to design such devices. Finally, we demonstrate efficient liquid transportation across a wide range of substrate geometries including inclined, curved, vertical, inverted, and lateral positioned surfaces using a 200 μm thick Al sheet SAW device.

We propose a flexible virtual sensor array (FVSA) based on MXene and LIG-IDEs for selective detection of VOCs and validate the capability of the FVSA to identify alcohol content in human breath.

Flexible human–machine interfaces show broad prospects for next-generation flexible or wearable electronics compared with their currently available bulky and rigid counterparts. However, compared to their rigid counterparts, most reported flexible devices (e.g., flexible loudspeakers and microphones) show inferior performance, mainly due to the nature of their flexibility. Therefore, it is of great significance to improve their performance by developing and optimizing new materials, structures and design methodologies. In this paper, a flexible acoustic platform based on a zinc oxide (ZnO) thin film on an aluminum foil substrate is developed and optimized; this platform can be applied as a loudspeaker, a microphone, or an ambient sensor depending on the selection of its excitation frequencies. When used as a speaker, the proposed structure shows a high sound pressure level (SPL) of ~90 dB (with a standard deviation of ~3.6 dB), a low total harmonic distortion of ~1.41%, and a uniform directivity (with a standard deviation of ~4 dB). Its normalized SPL is higher than those of similar devices reported in the recent literature. When used as a microphone, the proposed device shows a precision of 98% for speech recognition, and the measured audio signals show a strong similarity to the original audio signals, demonstrating its equivalent performance compared to a rigid commercial microphone. As a flexible sensor, this device shows a high temperature coefficient of frequency of −289 ppm/K and good performance for respiratory monitoring.

In this work, ZnO/Al thin film based flexible acoustic wave devices are demonstrated for their applications in gas flow rate measurements based on the changes in temperature of the devices. A good sensitivity of gas flow rate can be achieved, mainly because thin film based device has a large temperature coefficient of frequency of ∼280 ppm K ⁻¹ , owing to the large coefficient of thermal expansion of aluminum foil. A heat source is used to enhance the sensitivity of the thin film device by introducing a temperature offset. The flexible acoustic wave device shows a high sensitivity, fast response times, and a good repeatability for measurement of the flow rate of nitrogen. When the flexible acoustic wave device is bent and attached onto the inner wall of a pipe, the device exhibits good performance for monitoring the gas flow rate, demonstrating its applications of flow rate measurement on curved or randomly shaped surfaces.