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In this work, the major methods for implementing flexible sensing technology—flexible surface acoustic wave (SAW) sensors—are summarized; the working principles and device characteristics of the flexible SAW sensors are introduced; and the latest achievements of the flexible SAW sensors in the selection of the substrate materials, the development of the piezoelectric thin films, and the structural design of the interdigital transducers are discussed. This paper focuses on analyzing the research status of physical flexible SAW sensors such as temperature, humidity, and ultraviolet radiation, including the sensing mechanism, bending strain performance, device performance parameters, advantages and disadvantages, etc. It also looks forward to the development of future chemical flexible SAW sensors for gases, the optimization of the direction of the overall device design, and systematic research on acoustic sensing theory under strain. This will enable the manufacturing of multifunctional and diverse sensors that better meet human needs.

A Pd/Ni nanowire (NW) film coated surface acoustic wave (SAW) sensor exhibited super-fast response as 2 s to 1 ∼ 3 v/v % hydrogen at room temperature (25 ℃). By using anode aluminum oxide (AAO) template-confined electrodeposition, the Pd/Ni NWs were prepared, and then deposited on the surface of the SAW device to build the SAW hydrogen sensor. The developed SAW sensor was integrated in a phase discriminating circuit, and experimentally characterized. The larger specific surface of Pd/Ni NW contributes well to improvement of the response time.

A surface acoustic wave (SAW) temperature sensor with high accuracy was developed and wirelessly characterized in this work. The sensing chip with reflective delay line pattern was simulated using typical coupling of modes (COM) model and prepared by the standard photolithographic technique. Sharp reflection peaks with high signal-to-noise (SNR) were observed from the developed sensing chip operating at 433 MHz. Referring to the frequency-stepped continuous wave (FSCW)-based transceiver, planar antennas, and the developed SAW chip, the wireless and passive temperature sensor system was built. Adaptive Least Mean Square (LMS) algorithm was used for the first time in the SAW sensor signal processing to significantly improve the system SNR, and the corresponding phase fluctuation is down to only 3°. High temperature sensitivity of 36.5 °C and very high accuracy of ±0.2 °C in the range of −30 °C∼100 °C were achieved successfully by wireless measurement.