Research On The Structure Of Terahertz Metamaterial Absorber And Dielectric Detection Methods Of Insulating Materials

Terahertz wave has important application prospects in biomedicine,aerospace,food and drug testing due to its fingerprint quality,high security,high temporal-spatial resolution and strong penetrability.However,it is difficult to find natural materials that respond strongly to terahertz wave.Metamaterials,as a kind of artificially designed periodic structure,can absorb,block or bend the incident waves by arbitrarily designing their own structures and unit cell arrangements.The terahertz wave has received much attention due to its free and efficient manipulation.Metamaterial based absorbers have the advantages of ultra-thin,near-perfect absorption rate,adjustable operating frequency than traditional absorbers,and have great application prospects in the fields of imaging,sensing,solar energy collection,etc.But the metamaterial absorbers still have problems that the absorption band is not wide enough,the dynamic regulation mode is small,the design method and the working mechanism are not clear enough,and needs to be studied in detail.Based on the basic principle of terahertz wave detection and metamaterial absorber,this thesis studied the terahertz metamaterial absorbers including narrow-band,ultra-wideband,dynamic regulation and analyzes the working mechanism of these absorbers.The dielectric properties detection method of insulating materials based on metamaterial absorbers is further studied,which provided a new idea for the detection of insulating materials.Finally,the lithographic processing of the proposed metamaterial absorbers is carried out,and the terahertz time domain spectrum system was built.The effectiveness of the metamaterial absorber and detection method were proved through experiments.The main contents and results of the thesis are as follows:(1)Research and construction of a narrow-band terahertz metamaterial absorber based on MDM architecture.Firstly,a double "L" type metamaterial absorber based on split resonant ring was proposed.The equivalent LC circuit model of the absorber structure was established and the qualitative analysis of the resonant frequency was carried out.The effective circuit was effective for the structural characterization of the metamaterial absorber,and the working mechanism of the absorber structure was explained by the electromagnetic field distribution and surface current distribution.Second,a three-band absorber based on a three-ring resonant unit was constructed.Through the comparison and analysis of the corresponding single-resonance unit absorber,the effectiveness of the multi-band metamaterial absorber method using multi-resonance unit was demonstrated,this method is instructive for the design and optimization of the multi-band absorber and broadband absorber in the future.(2)A barium titanate based metamaterial absorber with resonant frequency independently tunable was constructed and studied.Based on the analysis of the characteristics of barium titanate material,the equivalent characterization model of barium titanate material in the terahertz band was established.Combined with the "sandwich" classic metamaterial absorber structure,the dynamics of the absorption frequency of the metamaterial absorber was implemented.The results showed that the dynamic frequency regulation of the absorber reaches 770 GHz with the peak absorption rate 99% or more by changing the external temperature from 400 K to 200 K without changing the geometry size of the structure.This study enriches the current means of regulation of the absorber.(3)Research and construction of graphene-based ultra-wideband terahertz metamaterial absorbers.By studying the electromagnetic parameters of graphene materials and performing equivalent characterization in the terahertz regime,the two-dimensional equivalent surface impedance was used to model graphene,and then the multi-resonant unit design thoery and gradient modulation method are utilized to design the graphen pattern.Ultra-wideband property was implement in the absorber.The results show that the structure of the absorber is in the range of 0.1~3.5 THz,and the bandwidth of the absorption rate above 90% reached 1.57 THz,and the dynamic regulation of the absorption peak is 19% to 100% through the change of the chemical potential of graphene.(4)Research on the dielectric properties detection method of the insulation materials based on terahertz metamaterial absorber.Our designed metamaterial absorber was fabricated and used as a sensor,where the insulating material was placed on the surface of the metamaterial absorber.The influence of different analyte thickness on the sensitivity of the absorber and the sensitivity of the absorber to different insulating materials(with different dielectric constants)were both discussed in detail;the numerical fitting calculation shows that the two cases exhibit a double exponential decay function and a positive linear function.By studying the electric field and energy distribution in the sensor application,the mechanism of the sensing detection was further analyzed.Finally,the effectiveness of the absorber structure itself and the sensing method based on the absorber was verified by experiments.