Optimal Design Of Broad-Band Absorbers Based On Metamaterials

With the development of electronic information technology,electromagnetic absorber has a wide range of applications in the fields of weapon stealth,radiation protection,and terahertz imaging.The improvement of processing technology and the emergence of new material preparation technology,the performance of traditional absorber can not meet the current demand,which has higher requirements on absorber thickness,absorbing ability,bandwidth and preparation difficulty.Metamaterials are artificial composite structures that have some special electromagnetic properties.Since the left-hand material was realized,metamaterials have been widely concerned and applied by scholars.In 2008,Landy used of metamaterials to achieve "perfect absorber".Then there are scholars to design a wide angle of incidence and polarization-insensitive metamaterial absorber,showing that the unique electromagnetic properties of metamaterials can be applied to the field of novel absorber.This thesis first introduces the research background,significance and current situation of traditional microwave absorber and metamaterials,analyzes the absorbing principle of Salisbury screen and Jauman microwave absorber,and then focuses on the research progress of absorber based on metamaterials.In this thesis,we focus on how to realize the broadband absorbing capability of metamaterial absorber and how to optimize the design of metamaterial absorber,especially in the 2-12 GHz frequency band.We work on the equivalent circuit method of metamaterials,and on the basis of summarizing previous work,innovatively propose the equivalent circuit of various shape metamaterials.We calculate the equivalent impedance of the complementary structure using the Babinet principle;then use the neural network technology to calculate the equivalent impedance of the irregular shape metamaterial.Based on the equivalent circuit model of metamaterials,transmission line equivalent circuit modes for single-layer and multi-layer metamaterial supersonic wave absorbing structure are established.We analyze the influence of the selection of metamaterials on the performance of microwave absorbing structures.We propose a multi-layer cascading optimization method based on genetic algorithm for adding dielectric parameters to broadband absorption targets.In this way,a double-layer absorbing structure with a relative bandwidth of up to 125% is obtained.Finally,we develop an absorbing/transparent material optimization software in the App Designer environment of Matlab software.The software has clear and concise human-computer interaction interface,which can input indicators based on wave absorption ability,thickness,frequency band and incident angle.After the selection of the metamaterial,the adaptive algorithm can be used to optimize the corresponding equivalent circuit to obtain an S-parameter curve and an equivalent electromagnetic parameter curve.In addition,the wave-absorbing structure can be directly introduced into commercial software HFSS and CST for co-simulation.Moreover,a method to speed up the joint simulation of Matlab-CST is proposed.In particular,the efficiency and stability of iterative optimization of existing electromagnetic structures are improved.