Abstract
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.
Highlights
The surface acoustic wave (SAW) sensors employing magnetostrictive thin film as sensitive interface supply a new approach of exploiting magnetic field sensing, favours some superior features as fast response, high sensitivity, low cost, small size, robust, and possible wireless and passive measurement
Elhosni et al proposed a similar SAW magnetic sensor with a magnetostrictivepiezoelectric layered structure of Ni/ZnO/interdigital transducers (IDTs)/LiNbO3.4,5 Utilizing the magneto-sensitive Galfenol thin film, a SAW magnetic field sensor was developed by Li et al, a maximum change of 0.64% in SAW velocity was calculated theoretically with a 500nm Galfenol thick film.[6]
The SAW devices for magnetic field sensing is developed by using the overlay photolithographic technique, which is composed of a delay line pattern on 128o YX LiNbO3 substrate with high velocity of 3961 m/s and larger electromechanical factor of 5.5%, and a FeCo grating array deposited along the SAW propagation path between the two photolithographically defined 300nm Al transducers separated by a path length of 2.5mm
Summary
Proposed for sensing current/magnetic field, obtained sensitivity was up to 8.3KHz/mT based on the theoretical optimization.[9] the strong hysteresis effect in magnetostrictive thin-film induces significant hysteresis error, degrading significantly the sensor performance. A grating-patterned design is proposed for the FeCo coated SAW magnetic field sensor configuration to suppress the strong hysteresis effect of the magnetostrictive coating. The magnetostrictive effect in the FeCo stimulated by the magnetic field to be tested modulates the SAW propagation, and the corresponding shift in oscillation frequency was collected to evaluate the measurant. FeCo grating weakens the hysteresis effect, and contributes well to fully release the magnetostrictive strain; high sensitivity, excellent linearity, and low hysteresis error are expected
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