Design And Verification Of Acoustic Resonant Electrically Small Antenna Based On Magnetoelectric Composite Materials And Preparation Of Thin Film Materials

Acoustic resonance electrically small antenna overturns the transmission/reception mode of the traditional electrically small antennas based on electromagnetic wave resonance.It uses acoustic wave resonance to radiate or receive electromagnetic signals.Because the acoustic wave wavelength is much smaller than the electromagnetic wave,the theoretical size of the acoustic wave resonant electrically small antenna is a millionth of that of the electromagnetic one,which is of great significance for antenna miniaturization.Acoustic resonant electrically small antennas mainly use the electric-acoustic(resonance)-magnetic coupling characteristics of magnetoelectric materials working at the acoustic resonant frequency.The multiphase magnetoelectric composite materials have high magnetoelectric coupling coefficient at the resonance frequency of acoustic wave and are ideal materials for application.In the past ten years,most of the research on acoustic resonant electrically small antennas has focused on the theoretical level,and only a few work reported the experiment results.In order to deeply understand the basic principles of acoustic resonant electrically small antennas and verify its feasibility,this work carried out the model analysis of acoustic resonant electrically small antennas working at k Hz/MHz/GHz frequencies from the perspective of material selection and structural design of composite magnetoelectric materials.The small antenna samples were experimentally prepared and their principles were verified by performance test.The main research contents and results of this thesis work are as follows.Firstly,the horizontal acoustic resonant electrically small antennas(k Hz band)based on Fe-Si-B/PIMNT((110)cut type)composites was designed and prepared,including the horizontally resonant L(longitudinal)-T(transverse)type,in which the magnetic field is along the longitudinal direction and the electric field along the transverse direction,and M(multiple)-L-L type,in which the magnetic field and electric field are both along the longitudinal direction.The Fe-Si-B amorphous magnetostrictive ribbon and the PIMNT piezoelectric single crystal are bonded and hot-pressed to form acoustic resonant electrically small antennas with different structures and sizes.The transmission and reception performance are characterized.By optimizing the bias magnetic field of the horizontally resonant L-T acoustic resonant electrically small antenna,the transmission and reception excitation response is realized in its acoustic primary(half-wave)resonance mode,which can be equivalent to a magnetic dipole antenna.By optimizing the antenna sample width to 2-6mm,the transceiver performance can be improved.By adjusting the antenna sample length to50-200 mm,the frequency characteristics from 10 k Hz to 45 k Hz can be realized.Both experiment and theory show that narrower and longer sample required smaller bias magnetic field,while the resonant frequency and sample length show an inverse relationship.At the working frequency of ?25k Hz,the optimized antenna sample size is 6 mm*80 mm,and its direct magnetoelectric coupling coefficient is as high as ?1771 V/cm·Oe(49.59 V/Oe),The near-field reception pattern of the antenna sample is obtained through testing.Secondly,a vertical acoustic resonant electrically small antenna(MHz/k Hz band)based on Fe-Ga/PIMNT((001)cut type)composite was designed and prepared.Using multi-physics field simulation,the radiation frequency and efficiency of the vertical resonant L-T type three-layer structured and the two-layer structured acoustic resonant electrically small antenna are analyzed,and the feasibility of the design is proved.According to the designed model,the directionally solidified Fe-Ga alloy sheet and PIMNT piezoelectric single crystal are bonded and hot-pressed to form acoustic resonant electrically small antennas with different structures.Because the epoxy resin weakens the vertical non-shear sound wave conduction,the antenna was not working at the design frequency(MHz band).However,a flexural resonance mode was obtained at low frequencies(k Hz band).Compared with the horizontally resonant L-T type acoustic resonant electrically small antenna,the acoustic resonant electrically small antenna with the low-frequency flexural vibration mode shows lower reception performance.The direct magnetoelectric coupling coefficient of the former is ?27.7 V/cm·Oe(0.69 V/Oe),but that for the latter is ?1771 V/cm·Oe(49.59 V/Oe).Further investigation showed that the two-layer structure has better performance than the three-layer structure in low-frequency flexural vibration mode.Finally,a vertical acoustic resonant thin-film electrically small antenna(GHz band)based on Fe-Ga/AlN thin-film composite was designed.The preparation of the piezoelectric and magnetostrictive thin films for such small antennas has been studied.DC magnetron sputtering was employed to fabricate the AlN films with out-of-plane(002)preferred orientation and Fe-Ga alloy films with out-of-plane(110)orientation at room temperature.The relationship between the structure and magnetic properties of the film and the preparation process is analyzed,which lays the foundation for the realization of the thin film acoustic resonant electrically small antenna in the future.Overall,this work verifies the theoretical feasibility of acoustic resonant electrically small antennas based on magnetoelectric composites and provides an important reference for the design of acoustic resonant electrically small antennas working at different frequencies.