Research On Electromagnetic Antenna Technology In Seawater Medium

Due to the unique conductivity of seawater,coupled with the demand for undersea communication,people have put forward more and more higher requirements for underwater antennas: miniaturization,high radiation efficiency,long-distance communication,and mechanical antenna is a new type of low-frequency transmitting antenna that generates electromagnetic radiation through the mechanical movement of electric charge or magnetic dipole,and the new radiation mechanism enables it to break the traditional antenna wavelength constraint on physical size,so that it Therefore,this thesis conducts a simulation study on the laminated magnetoelectric low frequency mechanical antenna based on the magnetoelectric conversion capability of the composite structure of magnetostrictive and piezoelectric materials,in which the inverse magnetoelectric effect can convert the electric signal to magnetic signal as a unique effect.The details of the study are as follows:Firstly,the development status of underwater antennas and mechanical antennas is introduced,secondly,the propagation characteristics of underwater electromagnetic waves are discussed,the surface wave effect which is beneficial to underwater communication is analyzed,the performance of two types of basic oscillators underwater is compared,and the selection of underwater antennas is given,after that,the mechanical antenna with composite structure of magnetoelectric material is introduced through the miniaturization of low-frequency antennas,and after analyzing its radiation mechanism and radiation model,it is explained that the performance of the antenna with the composite material compared to the conventional antenna for underwater applications is explained after analyzing its radiation mechanism and radiation model;Secondly,to study the magnetoelectric mechanical antenna,the finite element model of the magnetoelectric mechanical antenna is constructed and verified by using the nonlinear instantonal equation of magnetostrictive materials and the linear instantonal equation of piezoelectric materials for the multi-physical field coupling contained in the magnetoelectric composite;Then,the inverse magnetoelectric coefficients under small signal excitation are solved by establishing the equivalent circuit model of the magnetoelectric mechanical antenna.For the strong nonlinearity of the magnetoelectric mechanical antenna,the inverse magnetoelectric coefficients at different magnetic field bias,pre-stress,temperature,material and thickness ratios are investigated by simulation using the established nonlinear finite element model.The mechanical antenna has a length of 40 mm,the antenna resonates at 12.67 k Hz,and the inverse magnetoelectric coefficient reaches 65 Oe cm/V.The radiation model of the magnetoelectric mechanical antenna is verified by comparing the near field,and the radiation efficiency of the magnetoelectric mechanical antenna is found to be four orders of magnitude higher when compared with that of the loop antenna at the same size;Finally,the frequency window of the magneto-electric mechanical antenna is extended by introducing the bending vibration mode through the asymmetric structure;the narrow-band characteristics of the magneto-electric mechanical antenna are improved by the parallel magneto-electric composite structure,and the simulation shows that the excitation phase has a great influence on the parallel magneto-electric composite structure,and the inverse band coefficient is improved by adjusting the excitation phase of each magneto-electric composite block to match the vibration phase of the neighboring magneto-electric blocks.The depression of the magnetic band coefficient in the frequency band is successfully obtained a wide and flat inverse magnetoelectric coefficient curve(the fractional bandwidth is widened from 1% to 11.2%),which corresponds to a broadband magnetoelectric low frequency mechanical antenna.