Study Of One-way Spatial Transmission Structure And Absorbing Structure Based On The Broken Time Reversal Symmetry

One-way spatial transmission structure is the one that can transmit the spatial electromagnetic(EM)wave only in one direction while reflect(or absorb)in the opposite direction.One-way spatial transmission structures with backward absorption characteristic can find important application in EM stealth and radomes etc.Most of the traditional one-way spatial transmission structures possess only the characteristics of forward transmission and backward reflection with a narrow backward absorption bandwidth or without backward absorption.Recently,it has been found that the time reversal symmetry of gyromagnetic material can be broken under bias magnetic field(BMF),which results in the occurring of nonreciprocal surface EM mode on the surface of the gyromagnetic material.Because the bandwidth of forward transmission and backward absorption can be adjusted by changing the parameters of BMF and the structure,the nonreciprocal surface EM mode provides a new way for the design of one-way spatial transmission structure.This dissertation focus on the nonreciprocal surface EM mode with broken time inversion symmetry and proposed a one-way spatial transmission structure with forward transmission and backward absorption characteristics.Further,an absorbing structure with nonreciprocal transmission property is proposed,which can transmit spatial EM wave forward while suppress the backward transmission,thereby improve its absorption performance.Firstly,the conditions to generate a nonreciprocal surface EM mode with broken time inversion symmetry are studied;then,a novel one-way spatial transmission structure with forward transmission and backward absorption is proposed,which is constructed of periodic ferrite rods and periodic metal strips.To verify the present design,a prototype operating at 5.9 GHz-8.4 GHz is designed,fabricated and tested.Simulated and measured results show that the structure has excellent forward transmission and backward absorption properties.Based on the above structure,an absorbing structure with nonreciprocal transmission properties for EM wave is proposed,which is constructed of periodic ferrite rods,periodic metal strips and metal plate.Simulation result shows good absorption in 6.1 GHz-8.3 GHz.Theoretical analysis reveal that the absorption bandwidth can be expanded by adjusting the spatial distribution of BMF and the magnetization of the ferrite.Two broadband nonreciprocal absorbing structures with the thickness of 10 mm and absorption band of 4.73 GHz-8.20 GHz and 4.83 GH-9.16 GHz are designed as examples.Finally,by fitting the magnetization curve of the ferrite and using dielectric material with higher relative permittivity,a P-band absorbing structure with the thickness of 0.066 ?max and the band of 0.62 GHz-0.97 GHz is proposed.