[2019] [paper notes] tunable THz broadband absorption based on metamaterials——

Preface

type
$Terahertz+Metamaterial$
Periodical
$Journal\; of\; Physics$
author
$Chen\; Jun,Yang\; Maosheng,Li\; Yadi,Chengdengke,Guogengliang,Jiang\; Lin,Zhang\; Haiting,Song\; Xiaoxian,Ye\; Yunxia,Renyunpeng,Ren\; Xudong,Zhang\; Yating,Yaojianquan$
Time
$2019$

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Metamaterial

Metamaterials are artificially designed periodic arrays , It has many strange electromagnetic characteristics , Such as Negative refractive index 、 Asymmetric transmission and cross polarization cone . All these special properties make metamaterials excellent candidates for electromagnetic wave absorbing materials

About metamaterial based absorbers , The research focuses on different bands （ infrared 、 Terahertz 、 microwave ） Range
Most of these metamaterial absorbers are single frequency 、 Dual frequency 、 Multifrequency , This kind of Scattered frequency point Their absorption limits their application

• Passive ： By adjusting the geometric dimension of the absorber , Achieve absorption performance （ Once the preparation is completed ）
• Active ： The tunable electromagnetic metamaterial absorber can change according to the electromagnetic environment , Control the absorption of electromagnetic wave by electromagnetic metamaterial absorber
  Mostly graphene 、 Vanadium dioxide To adjust the absorption spectrum

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Graphene and vanadium dioxide

The absorption rate of graphene in the visible light region is as high as $2.3\%$, Suitable for terahertz full absorption materials

Because the surface conductivity of graphene can be adjusted by changing the chemical potential , So graphene absorbers can work at multiple frequencies

Vanadium dioxide is a phase change material at room temperature , When temperature $\ge$ Phase transition temperature , Show metal properties （ The conductivity of vanadium dioxide increases rapidly during the phase transition ）
When temperature $<$ Phase transition temperature , Display dielectric properties

The absorber with graphene structure often needs to be composed of graphene Complex patterns , This makes production process Become very complex

Vanadium dioxide is temperature sensitive , And the working temperature will be limited to its phase transition temperature , The scope of application is limited

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therefore , Use sheet metal + Electromagnetic material is a new solution
Simple structure 、 Easy to generate , It also solves the problem of passive adjustment of the absorber
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Sheet metal

This paper presents a T Type terahertz + Metamaterial absorber in far infrared frequency range

• Metal layer - Dielectric layer - Metamaterial

Take a sheet metal as the base , With Polyimide as the matching medium layer Placed in metal
Layer above , The top layer is patterned metal - Silicon mixed layer

1. By changing the conductivity , The designed absorber can achieve near perfect absorption in the desired frequency range . When the conductivity of silicon is 1600 S/m when , The absorber is 0.786 THz The absorption peak is reached at the frequency , Its absorption rate is 99.998%, And the absorption rate exceeds 90% The bandwidth of has reached 240 GHz.

2. By adjusting the conductivity of silicon , The presence or absence of the absorption band and the frequency point of the absorption peak can be easily adjusted , The frequency of absorption peak can be at 30 GHz Within the width range of .

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Conclusion

This paper designs T Type structure tunable THz Broadband metamaterial absorber . By removing the square photosensitive silicon chip on the top layer , Convertible THz Multi frequency absorber

They are all three-tier structures ： Metal substrate - Match the dielectric layer - Metamaterial

T Type metamaterials THz The multi frequency absorber has six absorptances over $90\%$ The absorption peak of , The average absorption rate is $96.26\%$

THz Broadband tunable absorber , The conductivity of the silicon wafer in the metamaterial layer is adjusted by the intensity of light radiation , Realize the purpose of adjusting the absorption belt of the absorber

1. When silicon conductivity $\sigma$ achieve $1600S/m$ when , Maximum absorption bandwidth , by $99.998\%$

2. When the conductivity of silicon wafer changes from $1S/m$ Increase to $1000S/m$, The absorption peak is from $2.826THz$ Moved to $0.78THz$. There is $2.046THz$ Frequency redshift phenomenon （ Frequency reduction is redshift ）

3. Continue to increase the conductivity of silicon , The absorption peak is from $0.78THz$ Move oh $0.81THz$, There is $30GHz$ Blue shift （ Frequency increase is blue shift ）

The absorption mechanism of the device comes from the excitation of the magnetic dipole resonance mode of the metamaterial absorber

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problem

The surface structure satisfying what characteristics is metamaterial or hypersurface ？

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