Study On The Magnetic Field Modulation Of Surface Acoustic Wave In Magnetoelectric Laminate Composites

The laminate composite magnetoelectric?ME?sensors have the properties of high sensitivity,high resolution,simple structure and preparation process,making it great potentials in the magnetic field detection.However,for such devices based on the interaction of magnetostrictive and piezoelectric effect,the output response sharply increases at the resonant frequency and sharply decreases at the non-resonant frequency.The resonance frequency of the bulk device usually occurs in the frequency ranges of several kHz or even MHz.Even in the case of thin-film structure,the lowest resonance frequency is also around200 Hz,and there are some problems to further reducing the resonance frequency.For the detection of geomagnetic field,magnetocardiography,magnetoencephalography,etc.,these not only require the high sensitivity,but also a wide range of frequency response,from DC to low-frequency.Therefore,how to realize the high-sensitivity,high-resolution detection of low-frequency and DC magnetic fields,has great value in academic research and practical application.The multilayer composite ME devices,based on the interaction of Delta-E effect and surface acoustic wave?SAW?,can realize the frequency response from DC to low-frequency continuously with high sensitivity and resolution.Additionally,it is always working at the mechanical-resonance-enhancement state,and is also a research hotspot in the magnetic field detection.In this work,amorphous FeCoSiB thin films are used as magnetostrictive materials,to study on the magnetic field modulation of surface acoustic wave in ME laminate composites.The single crystal ST-cut 90^oX quartz/FeCoSiB multilayer composite structure was used,and the dependence of devices'sensitivity on the thickness of the magnetic layer,annealing under magnetic fields,the doping modification of the magnetic layer and so on is investigated.Based on the above investigation,a comprehensive analysis of the influences of the delta-E effect on the properties of a SAW resonator is performed.The conclusions can be drawn as follows:Initially,the four-layer-structure device of ST-cut 90^oX single crystal quartz/Ta electrodes/SiO₂ insulating layer/FeCoSiB magnetostrictive layer was fabricated with the magnetron sputtering,revealing the dependence of devices'sensitivity on the thickness of the magnetic layer,annealing under magnetic fields,the doping modification of the magnetic layer,and also realizing the modification of the measurement range,sensitivity,and magnetic square wave response.When the magnetic layer is thin and also not annealed in magnetic fields,the sensitivity of the longitudinal direction?L-direction?of the device is larger than that of the width direction?W-direction?.However,when annealed in the magnetic field along the L-direction,the properties are changed,and the maximum sensitivity in the W-direction is larger than that of the L-direction.When the magnetic layer is thick and still not annealed in the magnetic fields,the sensitivity of the W-direction is also much greater than that of the L-direction.For the non-annealed and thickness of magnetic layer 300 nm sample,the resonance frequency sensitivity?RFS?of the sensor resulting from the delta-E effect in the W-direction is 364.28 Hz/?T and is almost 4.79 times greater than that in the L-direction,which is only 76.06 Hz/?T;and the maximum RFS achieved by this magnetic sensor in the non-linear region is 663.98 Hz/?T.Additionally,when the FeCoSiB film is doped with Terfenol-D,the sensitivity is decreased,but the linear response range is significantly increased.Then,based on the previous sensitivity response tested under the DC magnetic fields,the sensitive response of the low-frequency AC magnetic field was also tested and analyzed.The results have shown that:first,the device can maintain a stable output under a sinusoidal alternating magnetic field;second,fixed the amplitude of the AC magnetic field,when the AC frequency is increased from 0.001Hz to 1Hz,the deviation of the resonance frequency response is much smaller,and it is also the same with the DC response.Therefore,the multi-layer composite ME sensor based on the delta-E effect and SAW indeed can achieve a non-dispersion stability response from DC to low-frequency range.Finally,through the analysis of the dynamic magneto-elastic coupling,electro-elastic coupling and loss,the variations of electrical and acoustic characteristics of the SAW device under the external magnetic field were investigated,and the interaction mechanism between the delta-E effect and SAW was also explored.With the increase of the external magnetic field,the change trends of the parameters followed the delta-E effect,except for the FWHM?full-width-at-half-maximum?which exhibited an opposite trend.The reason is that the magneto-elastic-coupling efficiency of the magnetic layer varied with the change of the external magnetic field,which led to the variation in the efficiency of the SAW parameters.Additionally,when the magnetic layer is thin,the variation of the parameters along with the change of EMF are smaller.When the magnetic layer is thicker,the parameters are slowly varied at first,and then sharply varied,finally slowly varied again with the EMF increase along the W-direction?hard axis?;but it is always slowly varied along the L-direction?easy axis?.