The Research Of Electromagnetic Absorptive Structures Based On Permeability-near-zero And Spoof Surface Plasmon

Metamaterials are artificial composite structural materials formed by periodic arrangement of unit cell structures.These structures are typically artificially designed,and far smaller than their working wavelengths.By proper design,metamaterials are able to deliver exotic electromagnetic(EM)properties non-existent amongst natural materials.In recent years,a wide range of research has been conducted on metamaterial-based manipulation of EM wave propagation.The research on metamaterial-based absorptive structures has especially become the hotspot,and new types of absorbers continue to rise.Compared with traditional absorptive structures,structures based on metamaterials are thinner and lighter and often have an edge on absorption bandwidth.In this paper,two types of absorbers based on metamaterials are designed.First,a switchable absorber working at P band is designed based on permeability-near-zero(MNZ)theory.Currently,research on absorbers working at P band is scarce,as most metamaterial-based absorbers work at higher frequency bands.Hence,considering that MNZ-based structures can absorb incident EM wave effectively even though their thickness may be very small,a dielectric unit cell structure with Swiss-roll-like metallic structures printed on both sides is designed.The structure absorbs EM wave near 0.69 GHz.By loading PIN diodes on Swiss-roll-like metallic structures and controlling their on/off state by controlling their voltage feed,the effective length of Swiss-roll-like metallic structures can be controlled.Therefore,the absorption peak can be switched between 0.69 GHz and 0.80 GHz.Effective dual-polarization absorption is realized by orthogonally placing single-polarization structures.In addition,a way to widen the absorption bands of MNZ-based structures is also studied in this paper.It mainly combines Swiss-roll-like metallic structures of different lengths,which introduces multiple resonance that joins nearby absorption peaks.The feasibility of the proposal is verified by both numerical simulation and experiment.Next,several wideband absorbers based on spoof surface plasmon(SPP)are designed in this paper.Being tightly bound,the SPP can excite at the cut-off frequency a slow-wave mode,which absorbs incident EM wave.Using this mechanism,a cross-shaped rectangular metal-dielectric superimposed structure is designed.The structure is placed together with ferromagnetic materials to provide an absorption rate over 90%across 1 GHz-9.7 GHz.Besides,a cross-shaped dielectric structure covered by gradient metallic gratings is also designed.Such structures of different sizes are combined to realize absorption across even wider bands,thus proving that combining differently sized SPP-based unit cell structures enlarges absorption bands even more.Moreover,a pyramid-like metal-dielectric composite structure is investigated.A new unit cell structure is formed by combining such pyramid-like structures of different sizes to provide an absorption rate over 90%across 6 GHz-20 GHz.At last,a rectangular loop slot is introduced to the composite pyramid-like unit cell structures,achieving integration of absorption and transmission.