CN110794492A

CN110794492A - Graphene adjustable broadband terahertz absorber

Info

Publication number: CN110794492A
Application number: CN201911264817.9A
Authority: CN
Inventors: 胡丹; 王红燕; 张进峰
Original assignee: Anyang Normal University
Current assignee: Anyang Normal University
Priority date: 2019-11-29
Filing date: 2019-11-29
Publication date: 2020-02-14

Abstract

The invention discloses a graphene adjustable broadband terahertz absorber. The absorber is composed of a plurality of absorber units, wherein the absorber units are sequentially provided with an all-metal film (1), a medium film (2), a patterned single-layer graphene (3) and three-layer structures which are mutually attached from bottom to top. And the reflection spectrum of the structure is observed through calculation of a finite element method, and perfect absorption in a terahertz broadband is realized. The terahertz wave absorption modulator has the advantages of strong absorption, insensitivity to polarization, simple structure, convenience in processing and the like, and due to the unique electrical characteristics of graphene, the chemical potential and the surface conductivity of the graphene can be changed through the change of external bias voltage, so that the broadband strong absorption of incident terahertz waves can be adjusted in a large range, and the requirements on application in the aspect of terahertz absorption can be met.

Description

Graphene adjustable broadband terahertz absorber

Technical Field

The invention relates to the technical field of terahertz, in particular to a graphene adjustable broadband terahertz absorber. The absorber structure can realize broadband absorption, and the characteristics of adjustable broadband terahertz wave absorption rate and polarization insensitivity can be used for terahertz detection, imaging, stealth and the like.

Background

The broadband metamaterial perfect absorber has important application prospects in the aspects of biosensing, military stealth, photoelectric detectors, photo-thermal conversion and the like, so that people attract extensive attention, and various types of broadband metamaterial perfect absorbers are proposed. One of the most focused research directions in this field is to realize tunable broadband metamaterial perfect absorbers because they have great flexibility in practical applications. At present, two methods are mainly used for designing tunable broadband metamaterial perfect absorbers. One approach is to combine two or more resonators of different sizes to form a super large unit. Another approach is to stack multiple layer resonators with different geometries separated by dielectric layers with appropriate thickness. While broadband and tunable absorption behavior are very desirable, they also face several problems: the size of the structural unit is large, and the device preparation process is complex. These problems greatly hinder their practical application.

The novel metamaterial absorber has the advantages of strong broadband absorption, insensitivity to polarization, thin thickness, single structure, simple structure, convenience in processing and the like. In addition, due to the adjustability of the Fermi level of the graphene, the performance of dynamically adjusting the strength of the absorber can be realized, and the requirements on application in the aspect of terahertz absorption can be met.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a graphene adjustable broadband terahertz absorber.

In order to achieve the purpose, the invention adopts the technical scheme that:

the utility model provides a graphite alkene adjustable broadband terahertz absorber which characterized in that: the metal is used as a reflecting substrate, and the structure of the reflecting substrate is upwards sequentially provided with a dielectric layer and a graphene layer of a pattern. The metal substrate is gold, copper, silver or aluminum, the graphene is of a single-layer atom arrangement structure and is set to be a square resonance structure with four symmetrical rectangular grooves.

The beneficial effects of the invention are as follows:

1. the graphene layer is symmetrical about an x axis and a y axis, the same absorption curve can be obtained for TE and TM waves, and polarization insensitivity of the structure is guaranteed.

2. The broadband absorber disclosed by the invention is simple in structure, the broadband absorption effect can be realized only by using single-layer graphene, and the absorption rate is not lower than 90% in a specific frequency band range.

3. When the incidence angle is increased, good absorption effect can still be maintained.

4. The absorber adopts a two-dimensional periodic structure, has a simple and compact structure and is convenient for large-scale integration.

5. The invention utilizes the electrical adjustability of the graphene to realize the dynamic adjustable characteristic of the strength of the absorber.

Drawings

FIG. 1: the unit structure of the embodiment of the invention is schematically shown.

FIG. 2: the top graphene layer of the embodiments of the present invention is a top view.

FIG. 3: the absorption curve of the absorber under normal incidence of electromagnetic waves.

FIG. 4: changing the absorption curve when the chemical potential is 0-0.9 eV.

In fig. 1, 1: a metal layer; 2: a dielectric layer; 3: a graphene layer. The metal layer has a length and width p of 35 microns, a thickness t2 of 0.2 microns, and a dielectric layer thickness t1 of 16 microns.

In fig. 2, the length and width of the square single-layer graphene are a 1-4 micrometers, and the length of the square single-layer graphene is b 1-11 micrometers.

Detailed Description

The following description will be made with reference to the accompanying drawings.

The invention designs a graphene adjustable broadband terahertz absorber, which comprises the following specific implementation modes:

fig. 1 is a schematic diagram of a graphene-based broadband absorber. A metal layer (1) with the period of p and the thickness of t2 is used as a reflection substrate, a middle medium layer (2) is made of silicon dioxide, and a top graphene layer (3) is of a single-layer structure. The metal layer can be made of gold, copper, silver or aluminum, wherein the thickness of the metal is far larger than the skin depth of the metal in the terahertz wave band, and t 2-0.2 micrometer is selected as the thickness of the metal.

FIG. 2 is a top graphene pattern, square graphene having a length and width of 30 microns, rectangular recesses of 4 microns in width and 11 microns in length, the four rectangular recesses being disposed on the positive and negative axes of the x and y axes and having coordinate centers at (9.5 microns, 0), (-9.5 microns, 0), (0, 9.5 microns), (0, -9.5 microns), respectively. The invention relates to a reflective absorber at 0.4-4.5THz, whereby the period p of the structuring element is chosen to be 35 μm.

The chemical potential of the graphene is 0.9eV, and an absorption curve of the terahertz absorber obtained through electromagnetic simulation is shown in FIG. 3.

One of the most important properties of graphene is electrical tunability, and therefore, when the chemical potential of graphene is analyzed to change from 0eV to 0.9eV, the absorption efficiency of a wide frequency band is shown in fig. 4, and it can be seen that dynamic tuning of an absorption rate of 15% -100% can be achieved between 0eV and 0.9 eV.

Regarding the calculation of the absorption rate, when the incident electromagnetic wave is incident from the free space to the surface of the structure, a part of the incident electromagnetic wave is directly reflected to the free space to form a reflected wave, the rest part of the incident electromagnetic wave is incident to the inside of the structure in the form of a transmitted wave, a part of the incident electromagnetic wave is converted into heat energy or energy in other forms in the form of ohmic loss, and a part of the incident electromagnetic wave continues to propagate forward in the form of a transmitted wave. Therefore, the electromagnetic wave absorption rate expression is: a (ω) ═ 1-R (ω) -T (ω) ═ 1-S₁₁|²-|S₂₁|²(1)

Wherein R (omega) and T (omega) are respectively reflectivity and transmissivity, S₁₁、S₂₁Respectively the reflection coefficient and the transmission coefficient of the absorber.

For a reflective absorber, the function of the 0.2 micron thick metal plate is to block the transmission of electromagnetic waves into the structure, so S₂₁0. The electromagnetic wave at this time only needs to calculate the reflectivity and the absorptivity, and the reflectivity is:

R(ω)＝|S₁₁|²(2)

i.e. the absorption rate can be simplified to:

A(ω)＝1-R(ω)＝1-|S₁₁|²。(3) 。

Claims

1. the utility model provides a graphite alkene adjustable broadband terahertz absorber, adjustable absorber include all metal film (1), dielectric film (2), patterned monolayer graphite alkene (3), laminate each other between the three-layer structure.

2. The graphene tunable broadband terahertz absorber of claim 1, wherein: its individual structure period was 35 microns.

3. The graphene-based broadband tunable terahertz wave absorber according to claim 1, characterized in that: the dielectric film (2) is made of silicon dioxide and has the thickness of 16 microns.

4. The graphene-based broadband tunable terahertz wave absorber according to claim 1, characterized in that: the single-layer graphene structure is patterned, and four symmetrical rectangular grooves are dug on the square single-layer graphene.

5. The graphene-based broadband tunable terahertz wave absorber according to claim 4, characterized in that: the length and the width of the square graphene are both 30 micrometers, the width of the dug rectangular groove is 4 micrometers, and the length of the dug rectangular groove is 11 micrometers.

6. The graphene-based broadband tunable terahertz wave absorber according to claim 1, characterized in that: the graphene is in a single-layer atomic arrangement structure.

7. The graphene-based broadband tunable terahertz wave absorber according to claim 1, characterized in that: the all-metal film (1) is made of a high-conductivity metal material and has a thickness of 0.2 micrometer.

8. The graphene-based broadband tunable terahertz wave absorber according to claim 1, characterized in that: the all-metal film (1) is gold, copper, silver or aluminum.