Flexible Acoustic Wave Devices Research Articles

Multifunctional and Wearable Patches Based on Flexible Piezoelectric Acoustics for Integrated Sensing, Localization, and Underwater Communication

AbstractFlexible 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.

Bending behaviors of flexible acoustic wave devices under non-uniform elasto-plastic deformation

Flexible acoustic wave devices (FAWDs) have been explored in various applications where bending is inevitable. However, theoretical investigations of bending behavior of FAWDs hitherto are mostly done in the linear deformation regime. Herein, we develop a multi-sublayer model based on a stiffness matrix method for analysis of frequency shifts of surface acoustic waves and Lamb waves under elasto-plastic deformations. Using this model, we calculate the frequency shifts for the cases of both an elastic bending and an elasto-plastic bending. Experimental frequency shifts of ZnO/Al flexible devices show good agreement with the theoretical results in the elastic bending tests (with a relative error of strain sensitivity < 3%) and also show relatively good agreement with the qualitative theoretical predictions in the nonlinearly elasto-plastic bending. For three successive bending and recovery processes, the experimentally obtained frequency shifts show good repeatability in the elastic and elasto-plastic bending, demonstrating maximum relative errors of strain sensitivities less than 6.1% and 18.2%.

Flexible ZnO thin film acoustic wave device for gas flow rate measurement

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.

Flexible and bendable acoustofluidics based on ZnO film coated aluminium foil

ZnO coated Al foil of 50μm thick was used to fabricate flexible and bendable acoustofluidic devices with various wavelengths (from 64 to 800μm). Different acoustic wave modes (including Lamb waves and Rayleigh waves) were obtained experimentally and verified from theoretical analysis. Flexibility and deformability of the ZnO/Al foil acoustic wave devices were demonstrated by (1) deformation testing by bending the acoustic wave devices with strain values up to 1.375%; (2) fatigue testing by bending the devices for 2000 cycles. Using Lamb waves and Rayleigh waves generated from the ZnO/Al foil acoustofluidic devices, functions of droplet streaming and pumping were demonstrated using the flexible acoustic wave devices under different bending and twisting positions.