The Absorption Mechanism And Design Strategy Research Of Broadband Metamaterial Absorber With Magnetic Substrates

Microwave-absorbing materials(MAM),which can help weapons evade radar searches,are of great significance in modern warfare.With the development of modern equipment,stealth weapons need to face a more severe environment,which leads the MAM has to have a broad absorbing band covering different types of radar ranges.However,so far,any kind of traditional MAM,including the magnetic material with the widest absorption bandwidth available,cannot meet such demanding requirements alone.Metasurface,a subwavelength artificial periodic metal array,can control the intensity,phase,and propagation direction of incident electromagnetic waves.If the metasurface is combined with a traditional magnetic absorber,it is expected to greatly expand the absorption bandwidth to prepare an ultra-wide metamaterial absorber.In this thesis,the broadband absorption mechanism of traditional magnetic absorbers and metamaterial absorbers is firstly studied,and the physical mechanism of metasurface expanding the absorption bandwidth is clarified.Based on this,the substrate selection basis of broadband metamaterial absorbers is given.Finally,a metasurface design scheme that can maximize the broadband potential of the substrate is proposed.The main contents and innovations of this paper are as follows:1.A "symmetric model" analysis method is proposed,by which the correctness of the "quarter-wave model" is verified.The interference cancellation mechanism is generalized from the absorption peak to all frequencies;2.Metamaterial absorber was investigated by "symmetric model".It is found that its absorbing performance is also equal to the interference results of the waves reflected from different interfaces of the absorber;The equivalent electromagnetic parameters of the metamaterial absorber are reconstructed,which solves the problem that the previous equivalent electromagnetic parameters do not match the wave's propagation process in metamaterial absorber.It makes the metamaterial absorber and the traditional absorber unified in the form of electromagnetic parameters;We also investigated a sandwichstructured metamaterial absorber.Based on the “symmetric model”,the wave reflected from the backed metal plate was separated first,and the reflected waves of all different interfaces in the sandwich-structured metamaterial absorber were further quantitatively separated.The expansion mechanism of the absorption bandwidth was determined by comparing the changes of the separated reflected waves before and after loading the metasurface;3.Based on the broadening mechanism,the basis for the choice of substrate material is given.A genetic algorithm program is written to pick the potential broadband metamaterial absorber from our material database;4.A set of general metasurface pattern design strategies are proposed.By encoding metasurface patterns,combined with genetic algorithm and deep learning,the automatic generation of specific functional metasurfaces is realized.The broadband absorption metasurface is designed with this program,and its broadband absorption performance is verified from both simulation and experiment.Except that,it is also found that produced metamaterial absorber has a good oblique incidence broadband absorption stability;5.The variation law of the reflection loss with the thickness,the incident angle and the polarization mode is studied.The multiple reflection model is used to explain the underlying physical process,and two formulas are given for prediction: 1).The maximum effective absorption angle of the absorber for the transverse electric wave;2).The required conditions that the absorber can efficiently absorb the transverse magnetic wave at a large incident angle.