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 novel wireless and passive surface acoustic wave (SAW) based temperature-compensated vibration sensor utilizing a flexible Y-cut quartz cantilever beam with a relatively substantial proof mass and two one-port resonators is developed. One resonator acts as the sensing device adjacent to the clamped end for maximum strain sensitivity, and the other one is used as the reference located on clamped end for temperature compensation for vibration sensor through the differential approach. Vibration directed to the proof mass flex the cantilever, inducing relative changes in the acoustic propagation characteristics of the SAW travelling along the sensing device, and generated output signal varies in frequency as a function of vibration. A theoretical mode using the Rayleigh method was established to determine the optimal dimensions of the cantilever beam. Coupling of Modes (COM) model was used to extract the optimal design parameters of the SAW devices prior to fabrication. The performance of the developed SAW sensor attached to an antenna towards applied vibration was evaluated wirelessly by using the precise vibration table, programmable incubator chamber, and reader unit. High vibration sensitivity of ~10.4 kHz/g, good temperature stability, and excellent linearity were observed in the wireless measurements.

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 new wireless and passive surface acoustic wave (SAW)-based chemical sensor for organophosphorous compound (OC) detection is presented. A 434 MHz reflective delay line configuration composed by single phase unidirectional transducers (SPUDTs) and three shorted reflectors was fabricated on YZ LiNbO₃ piezoelectric substrate as the sensor element. A thin fluoroalcoholpolysiloxane (SXFA) film acted as the sensitive interface deposited onto the SAW propagation path between the second and last reflectors of the SAW device. The first reflector was used for the temperature compensation utilizing the difference method. The adsorption between the SXFA and OC molecules modulates the SAW propagation, especially for the time delay of the SAW, hence, the phase shifts of the reflection peaks from the corresponding reflectors can be used to characterize the target OC. Prior to the sensor fabrication, the coupling of modes (COM) and perturbation theory were utilized to predict the SAW device performance and the gas adsorption. Referring to a frequency-modulated continuous wave (FMCW)-based reader unit, the developed SAW chemical sensor was wirelessly characterized in gas exposure experiments for dimethylmethylphosphonate (DMMP) detection. Sensor performance parameters such as phase sensitivity, repeatability, linearity, and temperature compensation were evaluated experimentally.

Because echo signal energy of the resonant wireless and passive surface acoustic wave (SAW) sensor is weak and exponentially decays over time, the frequency resolution of the traditional FFT-based demodulation algorithm is relatively low. Additionally, SAW echo signals are susceptible to environmental noise interference during wireless transmission, significantly impacting the accuracy of traditional demodulation algorithms. To improve demodulation resolution and accuracy of sensor, this study proposes a novel signal processing algorithm based on the PRONY algorithm. The algorithm successfully transforms the high-order difference equations of PRONY algorithm into first-order matrix difference equations, avoiding the potential ill-conditioning problem and round-off error associated with high-order polynomial root-finding. Simulation and experimental results demonstrate that the proposed algorithm achieves high-resolution and high-precision demodulation of SAW echo signals compared to traditional methods. The proposed algorithm is integrated with the developed SAW temperature measurement hard system, the experimental results reveal that within the temperature range of -20~100°C, the system can achieve high-precision temperature measurement of ±0.3°C,while maintaining excellent temperature resolution below 0.0566°C, and achieve maximum distance is up to 2m.

This study proposes a directivity model for surface acoustic wave (SAW) vector magnetic field sensing based on dynamic magnetoelastic coupling. The model, derived by combining magnetoelastic mechanics and the SAW propagation theory, was experimentally validated. The relationship between the ${\Delta } {E}/{\Delta } {G}$ effect of the magnetic film in a 2-D magnetic field and the sensing response was elucidated through the dynamic magnetoelastic coupling model. Additionally, the angular distribution of the magnetic field in space was quantitatively calibrated to construct a directivity model for SAW-based magnetic field sensing. A 200 nm aluminum electrode layer, 600 nm silicon dioxide waveguide layer, and 300 nm (Fe₉₀Co₁₀)₇₈Si₁₂B₁₀ magnetic film were deposited successively on an ST-90°X piezoelectric quartz substrate using photolithography and magnetron sputtering. The developed sensing device was integrated with a discriminative circuit to create a 200 MHz SAW vector magnetic field sensor. A test platform using a Helmholtz coil was constructed to evaluate the sensor performance. The sensor exhibited a maximum sensitivity of, lower detection limit of ${1.3905} \times {10}^{-{3}}$ Oe, response error of less than 0.139%FS, and directivity mode error of less than 2.16% FS. These results demonstrate that the developed sensor features excellent sensitivity, directivity, stability, and repeatability.