The wireless and passive surface acoustic wave (SAW) sensing system comprises SAW sensors and a SAW reader. In dynamic application scenarios such as strain, torque, and vibration measurements, there is a critical need for high sensing speeds. However, existing high-speed readers encounter challenges related to limited sensing range and reduced demodulation accuracy, which impede the broader adoption of SAW wireless passive sensing technology. This paper presents a time-domain simulation model for SAW echo signals and explores the amplitude-frequency response characteristics of the reader to optimize its excitation time. Additionally, a noise model is developed based on actual data to assess the sensor bandwidth coverage provided by a single reader excitation, thereby optimizing the reader’s interrogation frequency. Experimental platforms for wireless temperature and strain sensing are also constructed. Experimental results indicate that the developed high-speed reader achieves a measurement speed of 13 kHz while maintaining practical measurement accuracy and distance for the SAW sensor.

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.

A surface acoustic wave (SAW) device is proposed for sensing current by employing the patterned FeGa thin film as the sensitive interface. The layered media structure of FeGa/SiO₂/LiNbO₃ was established to reveal the working principle of the sensors, and an SAW chip patterned by delay-line and operating at 150 MHz was fabricated photolithographically on 128° YX LiNbO₃ substrate. The FeGa thin film with a larger magnetostrictive coefficient was sputtered onto the acoustic propagation path of the SAW chip to build the sensing device. The prepared device was connected into the differential oscillation loop to construct the current sensor. The FeGa thin film produces magnetostrictive strain and so-called ΔE effect at the magnetic field generated by the applied current, which modulates the SAW propagation velocity accordingly. The differential frequency signal was collected to characterize the measurand. Larger sensitivity of 37.9 kHz/A, low hysteresis error of 0.81%, excellent repeatability and stability were achieved in the experiments from the developed sensing device.

Wide-range and high-sensitivity hydrogen sensors are critically important for hydrogen safety in aerospace and advanced transportation sectors. This work demonstrates a thermal-conductivity surface acoustic wave (SAW) based sensor to achieve high sensitivity hydrogen sensing. By integrating thermal balance and acoustic wave equations, a precise mechanistic model elucidating the structure-activity relationships among gas flow rate, operating temperature, and MEMS architecture in determining sensing sensitivity is constructed. Guided by this model, the SAW hydrogen sensor with on-chip microheater integration was developed. Furthermore, a highly integrated SAW hydrogen sensing system with ultra-low baseline noise (<30 µV) was constructed for performance evaluation. Leveraging the exceptional thermal sensitivity of the SAW device and system stability, the optimized sensor achieves wide detection range (up to 100% vol), low detection limit (~6 ppm), rapid response and recovery time (T₉₀/T₁₀: ~15 s), excellent repeatability (error<2.4%) at a relatively low operating temperature (120 °C). The prepared SAW sensor provides an effective solution for hydrogen leakage monitoring across unprecedented concentrations (ppm-100% vol), establishing a new paradigm for hydrogen safety applications.

This work illustrates a new pressure sensing method by measuring the surface acoustic wave (SAW) propagation attenuation. The quality value (Q-value) of the sensing chip decreases with the external pressure because of the energy radiation of the Rayleigh wave. This method abandons the traditional pressure-sensing structure, which can expand the measurement range and eliminate the negative effects such as hysteresis and creep arising from the sealant layer. The sensing chip is developed by the standard photolithographic technique. A high Q-value of over 9000 is achieved from the developed sensing chip operating at approximately 430MHz. Then, the pressure sensing experiment is conducted using the developed sensing chip, which demonstrates excellent performance in the 0.1–4MPa range, with low hysteresis of −2.02%, excellent nonlinearity of −0.44%, low-temperature drift coefficient of 0.01068 ppm/°C, and the maximum relative error of −2.453%. Excellent stability and consistency in several rounds of experiments are also obtained.