Broadband Absorber Design Based On Electromagnetic Metamaterials

New artificial engineering materials—metamaterials have many novel physical properties,including negative phase velocity,inverse Doppler effect,etc.,which are not available in traditional materials.Using metamaterials to absorb electromagnetic waves—metamaterial absorbers,which have important applications in military and civil fields,have been widely paid attention by researchers.Compared with traditional absorbers,metamaterial absorbers have better performance,such as small size,adjustable working frequency,and higher absorption rates.At present,there are more and more applications working in the low-frequency band,and the demand for low-frequency absorbing materials is also increasing.However,achieving broadband absorption in the low frequency is still a challenge;besides,some special occasions have put forward new requirements for its characteristics,for example,the cockpit glass of stealth fighter aircraft,the glass of electromagnetic shielding room and other scenes require the metamaterial absorber to be optically transparent,which is a property that most current absorbers do not have.In this context,this thesis starts from the principle of metamaterial absorbers and studies the metamaterial absorbers around the characteristics of ultra-wideband,low-frequency absorption and transparency,and designs three metamaterial absorbers.To a certain extent,the performance of the metamaterial absorber is improved.The main research results of this article are as follows:First,a lightweight microwave metamaterial absorber was designed based on the resistive film material.The metamaterial unit structure consists of a vertically stacked multilayer structure,the simulation results show that the absorption rate is consistently higher than 90% in the 4.7-39 GHz frequency band,and its relative bandwidth reaches 156%.Besides,the absorber also has incident angle stability and can maintain a stable absorption efficiency when the incident angle changes from 0°to 45°.To figure out the performance of the designed metamaterial absorber,its absorption mechanism was analyzed using impedance matching theory and equivalent circuit model;Finally,the sample was prepared by screen printing with high resistance conductive ink on the substrate and tested in a microwave chamber.The experimental results and simulation results are consistent with the theoretical calculation results,verifying the good performance of the metamaterial absorber.Secondly,to meet the needs of low-frequency applications for absorbing materials,a low-frequency and ultra-wideband metamaterial absorber based on a double ring and cross hollow structure is designed.The metamaterial absorber is composed of a multilayer structure,and the absorption rate is more than 90% in the1.82-18.5GHz band,realizing broadband absorption,and improving the relative bandwidth to 164.2%.Since the structures in the metamaterial unit are all symmetrical patterns,the absorber also has the characteristic of polarization insensitivity,and can still maintain a high absorption efficiency under a large incident angle.Besides,changing the resistance value of the resistance film in a certain range has little effect on the performance of the metamaterial,which indicates that the vibration absorber has strong robustness.Finally,the impedance of the metamaterial absorber is calculated by the parameter inversion method,and the absorption mechanism is explained by the impedance matching theory.Finally,in order to solve the problem of optical opacity of the metamaterial absorber,a broadband,high-absorption metamaterial absorber was designed based on indium tin oxide(ITO)material.The transparent medium and transparent conductive material are used to make the absorber has a certain light transmittance.By observing the energy loss and surface current distribution of the metamaterial absorber,the physical mechanism of its absorption is analyzed.In addition,the absorption efficiency of the designed absorber in the 13.5-18.9GHz frequency band can reach99%,which is close to full absorption.In summary,the metamaterial absorber will have good applications in some special scenes.