Acoustic impedance enables many interesting acoustic applications. However, acoustic impedance for gas sensing is rare and difficult. Here we introduce a micro-nano surface acoustic wave (SAW) chip based on the acoustic impedance effect to achieve ultra-fast and wide-range gas sensing. We theoretically established the relationship between surface load acoustic impedance and SAW attenuation, and analyzed the influence of acoustic impedance on acoustic propagation loss under different gas/humidity media. Experimental measurements reveal that the differences in acoustic impedance generated by different gases trigger different acoustic attenuation, and can achieve wide-range (0–100 v/v%) gas monitoring, with ultra-fast response and recovery speeds reaching sub-second levels (t₉₀ < 1 s, t₁₀ < 0.5 s) and detection limit of ~1 v/v%. This capability can also be perfectly utilized for human respiratory monitoring, accurately reflecting respiratory status, frequency, and intensity. Consequently, the SAW chip based on the acoustic impedance effect provides a new solution for in-situ detection of gas leaks and precise monitoring of human respiration.

Currently, the surface acoustic wave (SAW) magnetic field sensing technique utilises the SAW velocity/frequency mechanism of magnetoacoustic interaction as an indicator of the magnetic sensitivity mechanism. However, this method has low sensitivity and poor stability. To address this problem, a dynamic magnetoelastic coupling theoretical model is constructed to theoretically simulate the influence of the ΔE effect of magnetically sensitive thin films on SAW propagation attenuation. This study describes a high-sensitivity SAW magnetic field sensing mechanism based on magnetoacoustic attenuation. The simulation results show a clear relationship between the acoustic propagation loss and external magnetic field, indicating a structure-property relationship. An amorphous soft magnetic material (Fe₉₀Co₁₀)₇₈Si₁₂B₁₀ was used as a magnetically sensitive thin film due to its high permeability, low coercivity (Hc), low hysteresis, ease of magnetisation and demagnetisation. SAW magnetosensitive device operating on a frequency of 200 MHz has been experimentally developed using a standard semiconductor photolithography process. A SiO₂ layer was deposited on a 36° YX-LiTaO₃ substrate as a waveguide, and a (Fe₉₀Co₁₀)₇₈Si₁₂B₁₀ layer was on the top of the propagation area as a magnetosensitive film. The experimental results showed that the acoustic loss change due to the magnetic field variation was 4.63 dB within a magnetic field range of 0 Oe to ±10 Oe, which agreed with the theoretical results. The sensor had a sensitivity of 0.7546 dB Oe⁻¹ within the range of 0–4 Oe and the lower detection limit of magnetic fields was 0.272 Oe, low hysteresis error of 0.54%, multiple repeatability error of 0.13%, excellent repeatability and stability were achieved in the experiments from the developed sensing device.

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.

To prevent the potential failure of the surface acoustic wave (SAW) atomizer caused by the concentration of thermal stresses, this study investigates the thermal elevation process inherent to the operation of the surface wave atomizer. Subsequently, a method for temperature regulation is proposed. By collecting the temperature rise data of SAW atomizers with water, olive oil, and glycerol at 5/6/7 Watts (W) of power, the temperature curves of the atomizer surface under different conditions are obtained, and the stress changes in the working process are simulated additionally. The results indicate that although the stress generated by surface acoustic wave atomizers varies for different media, there is always a problem of rapid heating during the initial working stage in all cases. To address the above issues, this study analyzed the time when the maximum stress occurred and proposed control methods based on experimental data. The simulation results show that by controlling the driving power within 4 s after the start of atomization, the problem of excessive stress during the heating stage can be avoided. Finally, the feasibility of the control method was verified through a simple power control method (limiting the driving power to 3 W in the first 2 s), proving that this method can effectively reduce the thermal stress during the working process of the atomizer and prevent the atomizer from cracking.

This work achieves the regulation of acoustic modes by metal modification on the surface of piezoelectric crystals, and successfully designs a low loss surface acoustic wave (SAW) device for liquid-phase sensing. The wave equations in piezoelectric crystals and metal modified piezoelectric crystals were solved using the effective dielectric constant method, and the main acoustic modes propagated in the piezoelectric crystals before and after metal modification were obtained. By calculating the transmission depth, it was found that the energy dissipation decreased after metal modification, thereby reducing device losses. Meanwhile, the optimized device structure design parameters were extracted employing finite element method and coupled of mode theory. On this basis, a delay-line patterned SAW device using LiTaO ₃ /SiO ₂ structure and operating at 80 MHz was photolithographically developed, and the measured insertion loss was around 10.5 dB. Then, a 500 nm Aluminum is sputtered onto the acoustic propagation path between the interdigital transducers prior to SiO2 deposition to perform surface metal modification on the device. The measured results show that after aluminum metal modification, the insertion loss of the SAW device is reduced to 6.9 dB. Interestingly, after metal modification, the sensitivity of SAW devices to liquid-phase environments decreased by about 83%. After fully immersing in the liquid-phase environment, the device loss only increased by 3.7 dB, which is much lower than the loss generated by unmodified devices in the liquid-phase environment. The low-loss SAW device obtained through modal analysis and structural optimization in this article has great potential for application in liquid-phase sensing.