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Magnetostrictive thin-film coated Surface Acoustic Wave (SAW) devices were promising for sensing magnetic field owing to their superior features as micro-size, fast response, and high sensitivity originated from the magnetostrictive effect. However, the magnetostriction nature in magnetostrictive thin-film causes significantly mechanical fatigue in service, deteriorating the sensor performances. In this work, the fatigue phenomenon in magnetostrictive coating was underlined by characterizing the prepared FeCo thin-film coated magnetic device cyclically. Obvious shedding was observed in FeCo coating after cyclic testing and the magnetic-sensitivity decreases significantly. One of the reasons is the weak adhesion of FeCo thin-film towards the substrate. As an available way allowing enhancement of adhesion, a Cr thin-film was employed as the transition-layer to weaken the mechanical fatigue. However, it accompanied by the issue of the reduced magnetostrictive coefficient and the obstruction in magnetostrain-tranfer to piezoelectric substrate. As a result, the slump in sensitivity was observed. To address such issues, a design of dotted-pattern with Cr transition layer was employed to build the SAW based magnetic-device. High magnetic-sensitivity and excellent long-term stability were achieved because of the release of coercive force in FeCo dots and enhancement of the FeCo adhesion to the substrate.

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.

A surface acoustic wave (SAW) device with an aluminum nitride (AlN) composite structure of Al2O3/IDTs/AlN/Metal/Si was proposed for sensing at extreme high-temperature in this work. Optimization allowing determination of optimal design parameters for SAW devices was conducted using the typical coupling of modes (COM) model. The SAW propagation characteristics in the layered structure were investigated theoretically by employing the finite element method (FEM). Multiple acoustic-wave modes that occurred in the AlN composite structure was analyzed, and the corresponding suppression of spurious mode was proposed. The COM simulation parameters corresponding to the effective acoustic-wave mode were extracted, and the optimized parameters of the one–port SAW resonator with a high-quality factor were determined.

Research has shown that SAW (surface acoustic wave) devices with an LGS/Pt (langasite La3Ga5SiO14/platinum) structure are useful in high-temperature sensor applications. Extreme high temperature brings great acoustic attenuation because of the thermal radiation loss, which requires that the sensing device offer a sufficiently high quality factor (Q) and a low loss. Therefore, it is necessary to improve the performance of the quality factor as much as possible so as to better meet the application of high-temperature sensors. Based on these reasons, the main work of this paper was to extract accurate simulation parameters to optimize the Pt/LGS device and obtain Q-value device parameters. Optimization of SAW devices with LGS/Pt structure for sensing extreme high temperature was addressed by employing a typical coupling of modes (COM) model in this work. Using the short pulse method, the reflection coefficient of Pt electrodes on LGS substrate was extracted accurately by characterizing the prepared SAW device with strategic design. Other relevant parameters for COM simulation were determined by finite element analysis. To determine the optimal design parameters, the COM simulation was conducted on the SAW sensing device with a one-port resonator pattern for sensing extreme temperature, which allows for a larger Q-value and low insertion loss. Experimental results validate the theoretical simulation. In addition, the corresponding high-temperature characteristics of the prepared sensing device were investigated.

This study addresses the theoretical and experimental investigations of grating-patterned magnetostrictive FeCo coated surface acoustic wave (SAW) device for sensing magnetic field. The proposed sensor is composed of a configuration of differential dual-delay-line oscillators, and a magnetostrictive FeCo grating array deposited along the SAW propagation path of the sensing device, which suppresses effectively the hysteresis effect by releasing the internal binding force in FeCo. The magnetostrictive strain and ΔE effect from the FeCo coating modulates the SAW propagation characteristic, and the corresponding shift in differential oscillation frequency was utilized to evaluate the measurant. A theoretical model is performed to investigate the wave propagation in layered structure of FeCo/LiNbO3 in the effect of magnetostrictive, and allowing determining the optimal structure. The experimental results indicate that higher sensitivity, excellent linearity, and lower hysteresis error over the typical FeCo thin-film coated sensor were achieved from the grating-patterned FeCo coated sensor successfully.

A magnetostrictive FeNi-coated surface acoustic wave (SAW)-based current sensor was proposed in this work. The weak remanence and hysteresis effect of the FeNi itself contributes to suppress the asymmetry in sensor response at increasing and decreasing current. The sensor response was simulated by solving the coupled electromechanical field equation in layered structure considering the magnetostrictive effect and an approach of effective dielectric constant. The effects from the aspect ratio and thickness of the FeNi film on sensor response were analyzed to determine the optimal design parameters. Differential oscillation structure was used to form the sensor, in which, the FeNi thin film was deposited along the SAW propagation of the sensor chip by using RF magnetron sputtering. The magnetostrictive effect of the FeNi coating induced by the magnetic loading generates the perturbation in SAW velocity, and corresponding oscillation frequency. High sensitivity of 10.7 KHz/A, good linearity and repeatability, lower hysteresis error of 0.97% were obtained from the developed prototype 150 MHz SAW FeNi coated current sensor.

The magnetostrictive effect in micro-dotted FeCo film coated surface acoustic wave (SAW) devices was demonstrated by solving coupling equations using the specific coupling of modes parameters extracted by FEM analysis. Dotted-pattern on FeCo thin-film proposed in this work contributes well to suppression in hysteresis effect by fully releasing the internal coericivity of the magnetistrictive FeCo thin-film. The theoretical demonstration was confirmed well by characterizing the constructed SAW magnetic devices with FeCo dots depositing along the SAW propagation path. Significantly improvements on suppression of hysteresis phenomenon were observed by characterizing the prepared FeCo dots coated SAW magnetic devices, higher magneto-sensitivity of 21.17 kHz mT−1, and lower hysteresis error of 0.82% were achieved successfully. [ABSTRACT FROM AUTHOR]

A temperature-compensated surface acoustic wave (SAW)-based current sensor was proposed in this contribution, composed of a sensor chip made by SAW delay line patterns on a SiO2/128° YX LiNbO3 piezoelectric substrate, a magnetostrictive FeCo film deposited on the SAW propagation path, and a corresponding differential oscillation configuration. The FeCo coating produced magnetostrictive strain under the magnetic field generated by the applied current, leading to linearity changes in the SAW propagation in the form of velocity change. The corresponding differential oscillation frequency shift was used to evaluate the tested current. By solving the coupled electromechanical field equation in a layered structure while considering the magnetostrictive effect, the optimal FeCo film thickness, and sensor operation frequency yielding high current sensitivity, were determined, and then confirmed experimentally by evaluating the developed SAW current sensor system utilizing a Helmholtz coil. A high sensitivity of 16.6 KHz A−1 (8.3 KHz m−1 T−1), excellent linearity, and lower detection limit (∼0.2 mA) were achieved with our 300 MHz SAW sensor with a 500 nm FeCo coating and aspect ratio of 2:1. [ABSTRACT FROM AUTHOR]