Research On The Application Of Metamaterial Periodical Structures In Absorption

The metamaterial?MTM?has some exotic electromagnetic characteristics,which are widely used in the design of a number of high-performance components in the microwave frequency range,such as filters,antennas,absorber,and so on.The metamaterial absorbers?MMAs?play an important role in the designs of metamaterial.Due to its compact structure,light weight,ultra-thin thickness and easy integration with electronic devices as compared with the conventional absorbers,these MMAs have become research hotspot in the field of radar stealth and communication system with high application value.The absorption mechanism and the influence of the structural parameters of the novel metamaterial structures are analyzed in this paper.Meanwhile,the electromagnetic properties,numerical simulation and experimental methods of the metamaterial absorbing structures are discussed.For the different physical properties of the absorbing structures,the equivalent circuit model?ECM?and the surface current distributions are systematically studied.Based on this,a variety of different metamaterial absorbers are optimized and designed.The main contents of this dissertation are organized as follows:1.The miniaturized and multi-band metamaterial absorbers are studied.Three novel types of metamaterial absorbing structures are designed and their absorption mechanisms are analyzed by surface current distributions at the resonant frequencies.The influences of the structural parameters on the absorption performances are studied.Based on the integrations of meandered lines and interdigital structure and fractal structures,the composite structures achieve a better miniaturization.At the same time,the sextuple-band MMA is designed based on triangular spiral-shaped complementary structure,which has good properties of the ultra-thin,miniaturization.2.The concept of active absorption frequency selection surface?AFSS?is proposed,and its transmissive/absorptive mechanism is analyzed in detail.Then the AFSS transmission and reflection characteristic equations are carried out.An active AFSS structure is designed with switchable transmission and adjustable absorption.Changing the operating state of PIN diode by different bias voltages,the switchable lossless transmission band is obtained and a broad tunable absorption property is achieved.3.A novel active AFSS structure with adjustable transmissive/absorptive property is proposed.Based on equivalent circuit model,the physical mechanism of adjustable transmission and absorption is analyzed in depth through the perspective of impedance-matched.Based on the different working states of PIN diode and varactor,the dynamic modulation effect of transmission and absorption is realized.Compared with the passive AFSS designs,this proposed structure has electronically tunable transmissive/absorptive characteristic,which greatly expands the application research of AFSS.4.The active devices in the THz regime are investigated.Firstly,the relation between the pump beam illumination and conductivity of photoconductive silicon?Si?semiconductor materials is studied.Based on this feature,a photoexcited switchable metamaterial polarization convertor/absorber based on the orthogonal double split-ring resonators?ODSRs?structure is designed.The polarization states of the THz reflected wave are modulated through the external pump beam,and the working state between polarization convertor and the absorber is switched.Secondly,the thermally controlled metamaterial broadband polarization conversion modulator is proposed utilizing insulator-metal phase transition of vanadium dioxide?VO₂?thin film.The effects of the phase transition property of VO2 on the polarization conversion rate with different temperatures are analyzed.Through varying temperature,the dynamic cross-polarization modulation of THz reflected wave is obtained.Finally,a novel thermally controlled THz modulator is designed based on VO₂ thin film.It obtains the modulations on the amplitude and center frequency of the transmission band.Compared to the current modulated means of light,electricity and magnetic,thermally controlled method is more convenient and easy to realize.The work of this paper shows that the designs of the metamaterial absorbing structure have good electromagnetic performances,not only overcome some of the shortcomings of the current existing absorbers,but also further improve the research and design theory of the metamaterial absorber,and also provide technical source for application in the field of stealth technology for futher study.