Molding The Propagation Of Electromagnetic Waves Based On Magnetic Metamaterials

Metamaterial(MM)is a kind of artificial electromagnetic(EM)materials composed of subwavelength resonating unit structure,which possesses many amazing physical properties and potential applications compared with traditional materials,such as subwavelength EM waveguide,invisible cloak,perfect lens,negative refraction,and zero-index material.Therefore,MMs attain great advantage in information communication,EM wave radar,medical research,and the applications in the field of national defense science and technology and other related research fields.As a result,an intensive investigation on MMs is of great importance and necessary.At the same time,to facilitate the possible applications the MMs with flexibly controlling properties attract considerable attention and become a research hotspot.This can be achieved by some critical parameters such as temperature,voltage,magnetic field,and so on.In this paper,the propagating behavior of EM waves in magnetic MM consisting of an array of ferrite rods are thoroughly investigated,which can be easily controlled by a bias magnetic field in the microwave region.The zero-index MM and the gradient index MM are implemented and they are used to manipulate the wave propagation.This dissertation consists of five chapters,among which the first chapter introduces the basic physical concepts,the unique physical properties,and the applications of MMs and metasurfaces.In chapter two,we introduce the theoretical approaches and the configuration under consideration.In our work,the operating wavelength of the EM wave is about 9 times the lattice constant of the structure,satisfying long-wavelength limit.Therefore,the magnetic MM can be approximately regarded as a homogeneous medium with the effective permittivity,permeability and refractive index,which can be obtained by the effective medium theory.Furthermore,the scattering coefficients of a single rod and multiple ferrite rods can be calculated by the Mie scattering theory and the multiple scattering theory,in this way,the electric field and magnetic field at any position can be obtained,and then the pointing vectors can be obtained.In chapter three,the tunable asymmetric transmission of EM wave based on the zero-index heterojunction is introduced.The heterojunction is a magnetic system with two parts,among which one part of the structure is the zero-index MM,and the other part is not zero-index MM.The EM wave incident normally the structure from two opposite directions exhibits asymmetric behavior,producing a one-way transmission phenomenon.In addition,because the magnetic permeability of ferrite rods is dependent on the bias magnetic field the effective permittivity and permeability can be magnetically controlled.Based on this,by tuning the bias magnetic field,the non-zero refractive index MM can be transformed into a zero refractive index medium,and the zero refractive index MM becomes a non-zero refractive index medium.At this point,the one-way transmission behavior can be reversed by reversing the bias magnetic field,adding additional degree of freedom.In chapter four,inspired by the gradient EM metasurfaces,the propagating behavior of EM waves in the gradient-index magnetic MM will be discussed.In this work,the effective refractive index of the system is linearly dependent on the bias magnetic field within a particular range,so the gradient index can be introduced in the slab structure by setting the gradient bias magnetic field.Thereby,the phase compensation of EM wave along the interface is achieved so that the transmission phase of EM wave also controlled.In this way,the tunable EM wave transmission can be realized just by changing the gradient of bias magnetic field.In the final chapter,we have summarize the results and present the conclusion,meanwhile,the outlook on controllable asymmetric propagation based on gradient-index configuration is put forward.