Research On Wideband Reconfigurable Metamaterial Rasorber

Metamaterials have electromagnetic properties that do not exist in natural materials,also known as artificial electromagnetic materials,which can achieve many novel electromagnetic phenomena,such as negative refractive index,electromagnetic invisibility and Doppler effect,etc.Applications based on electromagnetic metamaterials have become a research hotspot,especially in the design field of absorber and rasorber.Compared with traditional absorber materials,metamaterial absorbers have excellent properties such as ultra-thin,perfect absorption,and angle stability.Based on metamaterials,the rasorber with in-band transmission and out-of-band absorption can improve the out-of-band antenna stealth ability while ensuring antenna transmission performance.It has potential application value in electromagnetic invisibility,electromagnetic shielding,and reducing radar cross section(RCS).Starting from the basic theory of metamaterials,this thesis focuses on the research of characteristics such as ultra-wideband,angle stability,and tunable absorptivity.The main research contents are the design of ultra-wideband high absorption metamaterial absorber and the tunable absorptive and wideband transmission metamaterial rasorber.(1)Working mechanism of broadband high absorption achieved by multilayer resonant coupling was studied,and a high-performance metamaterial absorber with ultra-wideband and large angle stability was designed.The metamaterial absorber adopts a double-layer coupling structure,consisting of electrically conductive films with different shapes and sheet resistances,dielectric layers,and a metal plate.This structure achieves broadband absorption and angle stability,with an absorption bandwidth of 4.3-24.5GHz,a relative bandwidth of 140.3%,and a relative thickness of0.119λ.It can still achieve relatively stable broadband absorption at incident angles from 0° to 60°.An equivalent circuit model was established based on the transmission line theory to analyze the working mechanism of achieving broadband absorption performance.The reason for the absorption peak was also analyzed from the perspective of surface current,and the absorber’s near-limit thickness was calculated based on the theory of limit thickness.The metamaterial absorber sample was fabricated by cascading a resistive film,PMI foam,and metal patches,where the resistive film was made of conductive ink with different conductivity printed on a PET substrate.The performance of oblique incidence and single-station RCS was tested in a microwave anechoic chamber,and the results were consistent with the simulation,proving the angle stability and potential application for RCS reduction of the absorber.(2)The principles of broadband transmission and active absorption were studied,and a reconfigurable metamaterial rasorber loaded with PIN diodes was designed.The reconfigurable metamaterial rasorber consists of a loss layer and a partially reflective layer.The loss layer is composed of metal patches and FR-4 dielectric substrate,and the PIN diode is loaded on the metal patch to achieve adjustable absorptivity.The partially reflective layer consists of three layers of metal square rings and two layers of Trconic dielectric substrate,achieving high-performance transmission.The loss layer and the partially reflective layer are cascaded to achieve impedance matching between ports within the target bandwidth,which can realize the in-band transmission and outof-band absorption characteristics of electromagnetic waves.The designed reconfigurable metamaterial rasorber can achieve adjustable absorptivity within 3.5GHz-10.5 GHz(relative bandwidth of 100%)and less than 2d B insertion loss within12.5GHz-18GHz(with a relative bandwidth of 36%).Based on the transmission line theory,an equivalent circuit model of the metamaterial was established to analyze the mechanism of the broadband adjustable absorptivity of the loss layer,that is,the absorptivity adjustment is achieved by changing the voltage of the PIN diode to control the change of resistance.At the same time,the mechanism of broadband highperformance transmission of the partially reflective layer was analyzed,that is,the coupling between layers was used to improve the transmission efficiency.Sample processing was carried out using Printed Circuit Board technology,and PIN diodes were soldered for measurement in a darkroom.The adjustable absorption trend and transmission effect were consistent with expectations,proving the feasibility of the design scheme.