Electromagnetic Wave Regulation Method Based On Resonance Characteristics Of THz Metamaterials

Terahertz wave is an electromagnetic wave between infrared and microwave.It has great application potential in communication,imaging,biological sensing and other fields.Metamaterials are a new type of artificial electromagnetic materials,which are generally composed of sub-wavelength array elements,and can produce some special electromagnetic responses that do not exist in nature.In recent years,metamaterials have been widely used in terahertz devices,and have greatly promoted the development of terahertz functional devices.The scattering field of metamaterials is mainly because the external field excites the multipole resonance inside it.Therefore,it is necessary to study and analyze the resonant modes supported by different terahertz metamaterials.This thesis mainly discusses the direct excitation of various dipole resonances in terahertz metamaterials,as well as the adjustment and control of the amplitude,polarization and phase of electromagnetic waves by using various resonance modes.The main research contents and innovative research results are as follows:1.Using electric dipole resonance and magnetic dipole resonance,a dual broadband absorption metamaterial based on metal and vanadium dioxide composite structure was designed.The absorption frequency band of the device can be controlled by controlling the temperature of vanadium dioxide.At T=300K,the designed metal ferrule structure can achieve broadband absorption before VO₂ phase transformation.The results show that the absorption rate can exceed 90%in the wide spectral range of1.375-2.087 THz.In the case of T=350K,VO₂ changes to metal state,and the designed symmetrical open ring can realize ultra-wideband absorption,and the absorption band is transferred to 2.6-7.03 THz.In addition,the structure is insensitive to the polarization angle of the incident wave and can maintain stable absorption performance when the incident angle of the electromagnetic wave is less than 45 degrees.The proposed absorber can be applied in many fields,such as amplitude modulation device,terahertz switch and power acquisition.2.An electromagnetic metamaterial supporting electric toroidal dipole resonance is designed.The resonance response of the electric toroidal dipole can be successfully excited without complicated metal ring structure by using the TM polarized light of normal incidence and by reasonably arranging the thin metal strip and long metal arm of the ring.The results show that the toroidal dipole moment G cannot be ignored at0.61 THz and 0.65 THz frequencies.The influence of the annular dipole on the polarization mode of the electromagnetic wave is analyzed.In addition,the application of toroidal dipole resonance is deeply studied.By rearranging the metamaterial structure that excites the resonance response of the electric toroidal dipole,the circular dichroism and anomalous refraction characteristics of the dual-band are successfully realized.The proposed structure can be applied to many fields,such as research on annular multipole;Design of circular polarization converter;Particle capture and other fields.3.The application of toroidal dipole resonance is further studied.A vector vortex electromagnetic wave antenna is designed based on the method of slotted rectangular waveguides,and the excitation of the equivalent toroidal dipole moment from 55.6 GHz to 56.7 GHz is successfully realized.The results show that the TE₁₀ mode electromagnetic wave transmitted in the rectangular waveguide is converted into vector vortex electromagnetic wave and radiated outward under the action of the toroidal dipole moment.This structure can quickly realize the excitation of toroidal dipole and the generation of vector vortex beam.The method of generating vector vortex beam is universal and can be extended to a higher frequency band.