Study On Low Frequency Mechanical Antennas Based On Magnetoelectric Composite Heterostructures

Antenna is the core component of wireless communication system.One of the key challenges facing low frequency antennas today is how to reduce their size significantly while essentially maintaining their radiative performance.This thesis mainly studies the low-frequency mechanical magnetoelectric antenna based on magnetoelectric heterostructure.This mechanical magnetoelectric antenna converts the mechanical energy generated by material vibration into electromagnetic energy by means of magnetomechanical-electrical coupling to generate radiation field.Under the premise of not changing the working frequency of the antenna,according to the principle that the acoustic wave is less than the wavelength of electromagnetic wave in the long run,Antennas can be reduced to one-tenth or even one-hundredth the size of conventional antennas.The main vibration mode of magnetoelectric composite with cantilever beam structure is bending vibration.Because bending vibration is the one with the lowest resonant frequency among all vibration modes,it also means that the cantilever beam structure design can further reduce the size of mechanical magnetoelectric antenna compared with the longitudinal stretching vibration mode.In this thesis,the magnetoelectric performance of magnetoelectric heterostructures based on these two resonant modes and the radiation performance of low-frequency magnetoelectric antennas are studied.Specific work is as follows:Theoretically,based on the equivalent circuit method,the equivalent magnetomechanical-electrical equations of magneto electrical heterojunction were derived and established,the complex magneto electrical coupling problem was transformed into a simple circuit problem,and the general expressions of resonance frequency and positive(inverse)magneto electrical coupling coefficient of magneto electrical heterojunction were calculated.At the same time,the effective electromechanical/mechano-magnetic coupling coefficient was introduced.The peak magnetoelectric coupling coefficient of the magnetoelectric heterojunction is deduced according to the characteristic that the reactance is zero when the circuit is resonant in series.Furthermore,based on the magnetic dipole model,the near-field radiation performance expression of the mechanical magnetoelectric antenna is derived.In the aspect of simulation,the finite element software COMSOL Multiphysics was used to establish the simulation model of magnetoelectric heterojunction.The two-ended free structure and cantilever beam structure were differentiated by whether a fixed constraint was set on one end boundary of the magnetoelectric heterojunction along the length direction.The positive(inverse)magnetoelectric coupling coefficient of PZT-5H/Fe Ga heterojunction under longitudinal stretching vibration and transverse bending vibration is studied.In terms of experiments,a low-frequency mechanical magnetoelectric antenna element based on the magnetoelectric heterostructure of PZT-5H/Fe Ga was prepared,and a positive(inverse)magnetoelectric coupling coefficient test platform was built.The optimal bias magnetic field of the magnetoelectric antenna element was obtained through the dynamic sweep frequency test method,and the positive magnetoelectric voltage coupling coefficient and inverse magnetoelectric coupling coefficient under the optimal bias magnetic field were measured as well as the frequency variation curves of the positive magnetoelectric voltage coupling coefficient and the inverse magnetoelectric coupling coefficient under the optimal bias magnetic field.On the one hand,it is verified with the results of theoretical calculation and finite element simulation.On the other hand,the near field radiation ability of magnetoelectric antenna element at different distances is calculated,which lays a foundation for the realization of the array mechanical magnetoelectric antenna.