Research On The Characteristic Of Broadband Terahertz Antireflection Based On Resonant Electromagnetic Surface

At present,terahertz technology is widely used in various frontier fields such as wireless communication and medical diagnosis.Silicon,as an important material in terahertz devices,usually has high Fresnel reflection loss due to its high dielectric constant,so reducing the reflectivity of the silicon surface is necessary to improve the system performance of terahertz devices.As a new type of sub-wavelength artificial materials,metamaterials have peculiar physical properties that conventional materials in nature do not possess,which has become the focus of research in the field of terahertz antireflection.Now,the common research of terahertz anti-reflection structures mainly achieves the effect of a single band.On the base of these studies,this article cleverly uses the electromagnetic resonance characteristic in the sub-wavelength structure to achieve multi-band and broadband anti-reflection effects on the silicon surface.The main research contents are as follows:(1)A multi-band antireflection metallic metamaterial structure composed of multiple metal resonators is designed.Two or more metal resonance rings with close resonance frequencies are placed above the dielectric layer,so that the metamaterial structure has dual-band and multi-band antireflection characteristics in the range of 0-2THz.The transmission peaks of the dual-band AR coating at 0.94THz and 1.71THz are 96%and 98%,and the bandwidth of the transmission rate above 90%is 0.25THz and 0.12THz respectively.The transmission peaks of the three-band antireflection structure at 0.99THz,1.57THz,and 1.885THz are 95.2%,96.8%and 93.3%,and the bandwidths with transmission above 90%are 0.33THz,0.15THz and 0.045THz respectively.When the size of the two metal resonators changes within a certain range,it only affects the specific resonance frequency in the transmission curve of the dual band.The dual-band transmission effect of the designed metamaterial structure is the superposition of two U-ring metal resonator structures with their respective resonance frequencies.This conclusion is also applicable to the multi-band antireflection structure.The designed structure uses a single-layer metal resonator,the structure is simpler,avoiding the problem of reduced transmittance caused by the multi-layer metal resonator superimposed for dual-band anti-reflection,and obviously has higher transmittance at the resonance position,And it has flexibility to adjust the resonance frequency position.(2)A metal metamaterial structure with angle-insensitive properties is designed.In this structure,the dielectric layer and the metal resonator above have the same shape,both in the shape of"Tian",and the material of the dielectric layer and the base material are both silicon.The transmittance curve reaches the highest peak at 0.893THz,the highest transmittance is 99.2%,almost completely transmitted,and the bandwidth with the transmittance above 90%is 0.34THz.In the 40~o incident range,for TE polarization,the transmission peak is always above 97%,and for TM polarization,the transmission peak is always around 99%.In addition,changes in the structure size will affect the transmittance.(3)A broadband all-dielectric metamaterial structure is designed.Unlike the previous two structures,which use metal resonators,this metamaterial structure is composed of a circular truncated silicon array.The superposition of the two electromagnetic resonance characteristics of Mie resonance and FP resonance makes it have a wider transmission in the terahertz band Bandwidth and maintain a higher transmission level.From 0.699THz to 1.45THz,the transmittance is always higher than90%,and the normalized bandwidth above 90%is as high as 69.5%.The transmission peaks at 0.978 and 1.396 THz are 99.4%and 98%,respectively.Changes in the height and inclination of the silicon circular table have an effect on both resonance states,causing overlap and broadening of the transmission peaks.This structure shows excellent broadband antireflection effect in the terahertz range.In short,our work is mainly to achieve high transmission rate and large bandwidth transmission effect in the terahertz band by designing,analyzing and optimizing three metamaterial structures.The first structure uses a combination of multiple metal resonators to achieve multi-band antireflection in the range of 0-2THz.The second structure uses the"Tian"type metal resonator and the"Tian"type silicon dielectric layer to achieve large-angle insensitivity and broadband anti-reflection.The third structure uses a circular truncated-silicon array to exhibit better broadband antireflection effects.The normalized bandwidth of transmittance above 90%is as high as 69.5%.