Middle and far infrared broadband metamaterial absorber and design method thereof

Abstract

The invention provides a middle and far infrared broadband metamaterial absorber and a design method thereof. The middle and far infrared broadband metamaterial absorber comprises metamaterial absorption units which are arranged in a periodic array mode. The whole metamaterial absorption unit is square and comprises a top metal layer, a dielectric layer and a bottom metal layer from top to bottom in sequence. The top metal layer is attached to the upper surface of the dielectric layer and is formed by arranging eight metal sheets according to a certain arrangement mode, namely a circular metal sheet which is arranged at the central position of the upper surface of the dielectric layer, and the center of the circular metal sheet is aligned with the center of the upper surface of the dielectric layer; three annular metal sheets concentric with the circular metal sheet surround the periphery of the circular metal sheet, and gaps exist between the circular metal sheet and the annular metal sheet on the innermost layer and between the annular metal sheets on the adjacent layers from inside to outside. And the four metal square sheets with the same size are respectively arranged at four corners of the upper surface of the dielectric layer. The absorption bandwidth is greatly prolonged, and perfect absorption of a target wave band can be infinitely approached by adjusting geometric parameters of the absorber.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of optical metamaterials, and in particular to a mid-to-far infrared broadband metamaterial absorber and a design method thereof. Background Art

[0002] Metamaterials are artificial synthetic materials that can achieve special electromagnetic properties that are difficult for natural materials to have through artificial design and regulation of their microstructures. Since the concept of metamaterials was proposed, it has attracted widespread attention in many fields such as optics, communications, and sensing, especially its application in electromagnetic wave absorption technology. As an important branch of this field, metamaterial absorbers can achieve perfect absorption of electromagnetic waves at a smaller thickness than traditional absorbers through precise manipulation of incident electromagnetic waves, and are widely used in infrared detection, thermal emitters, optical imaging, sensors and other fields.

[0003] The design of metamaterial absorbers is usually based on a specific resonance mode, which can achieve extremely high absorption efficiency at a specific frequency. However, the resonance characteristics of a single mode mean that its absorption efficiency at other frequencies will drop significantly, which makes it impossible for the absorber to maintain efficient absorption performance over a wide band. Summary of the invention

[0004] In view of the technical problems existing in the prior art, the present invention proposes a mid- and far-infrared broadband metamaterial absorber and a design method thereof.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows: In one aspect, the present invention provides a mid-to-far infrared broadband metamaterial absorber, comprising metamaterial absorption units arranged in a periodic array; The metamaterial absorption unit is square in shape as a whole, and comprises a top metal layer, a dielectric layer and a bottom metal layer from top to bottom; The top metal layer is attached to the upper surface of the dielectric layer and consists of 8 metal sheets arranged in a certain way, namely: A circular metal sheet is located at the center of the upper surface of the dielectric layer, and the center of the circle is aligned with the center of the upper surface of the first dielectric layer; The outer periphery of the circular metal sheet is surrounded by three circular ring-shaped metal sheets with the same center as the circular metal sheet, and there is a spacing between the circular metal sheet and the innermost circular ring-shaped metal sheet and between the adjacent circular ring-shaped metal sheets from the inside to the outside; Four metal square pieces of the same size are respectively arranged at the four corners of the upper surface of the dielectric layer.

[0006] Furthermore, the thickness of each metal sheet in the top metal layer is the same, that is, the thickness of the top metal layer .

[0007] Furthermore, the bottom metal layer is a metal plate attached to the bottom surface of the dielectric layer, and the thickness of the bottom metal layer is Greater than the thickness of the top metal layer .

[0008] Furthermore, the metal material used for the top metal layer and the bottom metal layer is titanium which has high loss.

[0009] Furthermore, the dielectric layer is a composite dielectric layer, which includes a first dielectric layer and a second dielectric layer from top to bottom, the first dielectric layer is a Si layer, the second dielectric layer is a Si3N4 layer, and both Si3N4 and Si are lossy dielectrics.

[0010] Furthermore, the thickness of the first dielectric layer is Less than the thickness of the second dielectric layer .

[0011] On the other hand, the present invention provides a design method of the above-mentioned mid- and far-infrared broadband metamaterial absorber, comprising: Determine the target band; Determine the optimized structural parameters, including: the radius of the circular metal piece in the top metal layer , the radius of the three circular metal sheets from the inside to the outside , , And width , , , the distance between the circular metal sheet and the innermost circular metal sheet, and between the adjacent layers of circular metal sheets from the inside to the outside , , , the width of the metal square , metamaterial absorption unit period length The dielectric layer is a composite dielectric layer, which includes a first dielectric layer and a second dielectric layer from top to bottom. The thickness of the top metal layer, the first dielectric layer, the second dielectric layer, and the bottom metal layer is , , , ; Determine that the metal material used for the top metal layer and the bottom metal layer is titanium with high loss; Determine the materials of the first dielectric layer and the second dielectric layer: the first dielectric layer is Si layer, and the second dielectric layer is Si 3 N 4 layer; Initialize the structural parameters of the mid-infrared broadband metamaterial absorber, use the finite-difference time-domain method to simulate the mid-infrared broadband metamaterial absorber, and analyze the influence of different structural parameters on the absorptivity of the target band; by comparing the absorptivity curves under different structural parameter designs, verify the absorption performance of the design, and optimize the structural parameters to achieve the best absorption effect.

[0012] Compared with the prior art, the technical effects of the present invention are: The present invention provides a mid-to-far infrared broadband metamaterial absorber, which is a design of a mid-to-far infrared broadband absorber based on a metalloid-dielectric-metal structure. The absorber adopts a four-layer structure of high-loss metal and composite dielectric layer, and realizes broadband and efficient absorption in the mid-to-far infrared band by optimizing the top metal pattern design and selecting electromagnetic high-loss materials. The invention has the characteristics of simple structure and easy manufacturing process, and is suitable for various optical systems such as infrared detectors, optical filters, thermal emitters, imaging equipment and sensors, and is widely used in military, scientific and civilian fields.

[0013] Compared with the traditional electromagnetic absorption structure, the metamaterial absorber usually adopts a metal-dielectric-metal three-layer structure, which shows excellent characteristics in wave absorption performance. Specifically, the present invention designs a top metal layer pattern structure, which is specifically arranged in a certain arrangement of 8 metal sheets, namely: a circular metal sheet, located at the center of the upper surface of the dielectric layer, and its center is aligned with the center of the upper surface of the first dielectric layer; the outer periphery of the circular metal sheet is surrounded by three circular ring metal sheets with the same center as the circular metal sheet, and there is a spacing between the circular metal sheet and the innermost circular ring metal sheet, and between the adjacent layers of circular ring metal sheets from the inside to the outside; four metal square sheets of the same size are respectively arranged at the four corners of the upper surface of the dielectric layer. The top metal layer pattern design of the present invention can excite surface plasmon resonance, and different surface plasmon resonance modes can be excited at multiple frequencies by adjusting the structural parameters. These modes are coupled with each other to form multiple absorption peaks, thereby effectively broadening the absorption bandwidth, and can achieve strong absorption of incident electromagnetic waves in a specific frequency band.

[0014] Furthermore, the dielectric layer is a composite dielectric layer, including a first dielectric layer and a second dielectric layer from top to bottom, the first dielectric layer is a Si layer, the second dielectric layer is a Si3N4 layer, and both Si3N4 and Si are lossy dielectrics. In this way, the dielectric layer acts as a resonant cavity, which can effectively enhance the localization effect of electromagnetic waves. The bottom metal layer acts as a reflective layer to prevent electromagnetic waves from penetrating, thereby achieving efficient absorption of incident light by the absorber.

[0015] The simulation results show that the top metal layer, bottom metal layer and dielectric layer are all made of high-loss materials, combined with a special top metal pattern design, which simultaneously excites propagating surface plasmons and localized surface plasmons, thereby ensuring a high absorption rate while forming a large absorption broadband. The absorber has a significant absorption effect in the mid- and far-infrared band of 16.3-29.3μm, with an average absorption rate of 95%; in the 15-35μm band, the average absorption rate reaches 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0017] Figure 1 A schematic structural diagram of a mid- and far-infrared broadband metamaterial absorber provided by an embodiment; Figure 2 A schematic diagram of a top metal layer of a metamaterial absorption unit in one embodiment; Figure 3 A diagram showing a layered structure of a metamaterial absorption unit in one embodiment; Figure 4 is a comparison diagram of absorption curves of several metamaterial absorbers with different metal sheet arrangements in a comparative embodiment; Figure 5 The diagram is an electromagnetic field distribution diagram of the top layer of the absorber along the XY coordinate axis when the infrared wavelengths are 18.1 μm, 22.2 μm and 26.3 μm respectively in one embodiment, wherein (a) is the electric field distribution diagram of the top layer of the absorber at 18.1 μm; (b) is the electric field distribution diagram of the top layer of the absorber at 22.2 μm; (c) is the electric field distribution diagram of the top layer of the absorber at 26.3 μm; (d) is the magnetic field distribution diagram of the top layer of the absorber at 18.1 μm; (e) is the magnetic field distribution diagram of the top layer of the absorber at 22.2 μm; (f) is the magnetic field distribution diagram of the top layer of the absorber at 26.3 μm, wherein 18.1 μm and 26.3 μm are the wavelengths corresponding to the two absorption peaks, and 22.2 μm is the wavelength corresponding to the middle absorption valley.

[0018] Numbers in the figure: 1 is a metamaterial absorption unit; 1-1 is a top metal layer; 1-2 is a first dielectric layer; 1-3 is a second dielectric layer; 1-4 is a bottom metal layer; 1-1-1 is a circular metal sheet; 1-1-2 is an innermost circular metal sheet; 1-1-3 is an intermediate circular metal sheet; 1-1-4 is an outermost circular metal sheet; 1-1-5 is a metal square sheet. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] In one embodiment of the present invention, referring to Figure 1 , Figure 2 and Figure 3 , providing a mid-to-far infrared broadband metamaterial absorber, comprising metamaterial absorption units 1 arranged in a periodic array.

[0021] The metamaterial absorption unit 1 is square in shape as a whole, and comprises a top metal layer 1-1, a dielectric layer and a bottom metal layer 1-4 from top to bottom. The dielectric layer is a composite dielectric layer, and comprises a first dielectric layer 1-2 and a second dielectric layer 1-3 from top to bottom.

[0022] Surface plasmon resonance is the core absorption mechanism of metamaterial absorbers. When an incident electromagnetic wave hits the metal surface, the free electrons in the metal oscillate collectively at a specific frequency and resonate with the electromagnetic field of the incident wave. This phenomenon is called surface plasmon resonance. By designing the geometric structure of the top metal pattern, plasmons of specific frequencies can be selectively excited, thereby achieving efficient absorption of electromagnetic wave energy. Surface plasmon resonance theory is the basis of metamaterial absorber design, and the absorption frequency can be precisely controlled by adjusting the pattern size. In this embodiment, the top metal layer 1-1 is attached to the upper surface of the first dielectric layer and is composed of 8 metal sheets arranged in a certain arrangement, namely: A circular metal sheet 1-1-1 is located at the center of the upper surface of the first dielectric layer 1-2, and the center of the circle is aligned with the center of the upper surface of the first dielectric layer 1-1; The circular metal sheet 1-1-1 is surrounded by three circular metal sheets with the same center as the circular metal sheet. There are spacings between the circular metal sheet 1-1-1 and the innermost circular metal sheet 1-1-2, between the innermost circular metal sheet 1-1-2 and the middle circular metal sheet 1-1-3, and between the middle circular metal sheet 1-1-3 and the outermost circular metal sheet 1-1-4, respectively. , , .

[0023] Four metal square sheets 1-1-5 of the same size are respectively arranged at the four corners of the upper surface of the first dielectric layer 1-2; The bottom metal layer 1-4 is a metal plate attached to the bottom surface of the second dielectric layer. The bottom metal layer 1-4 serves as a reflection layer to prevent electromagnetic waves from penetrating.

[0024] Furthermore, the thickness of each metal sheet in the top metal layer 1-1 is the same, that is, the thickness of the top metal layer . The thickness of the bottom metal layer 1-4 Greater than the thickness of the top metal layer 1-1 .

[0025] The metal layer of the metamaterial absorber usually selects precious metals with high Q values, such as Au, Cu and Ag, etc. These metals have excellent resonance selectivity. However, for the metal layer of the broadband absorber, metals with high loss are a better choice. The metal material used for the top metal layer and the bottom metal layer of the present invention is titanium with high loss. As a high-loss metal, titanium can not only excite broadband plasma resonance, which helps to broaden the absorption bandwidth, but also has a large imaginary part of its refractive index and a strong absorption effect on light waves, especially in the infrared band, which helps to excite broadband plasmon resonance and significantly improve the absorption efficiency.

[0026] Furthermore, the first dielectric layer and the second dielectric layer are made of the same material, both of which are composite dielectric layers, consisting of a layer of Si and a layer of Si3N4. Both Si3N4 and Si are lossy dielectrics, and their intrinsic absorption can better broaden the absorption bandwidth and improve the absorption efficiency. Furthermore, the thickness of the first dielectric layer is Less than the thickness of the second dielectric layer .

[0027] When infrared light hits the absorber surface, surface plasma resonance is excited at the interface between the top metal layer and the dielectric layer, and the bottom metal layer reflects this resonance, so that the entire absorber can be regarded as a resonator. There are two or more electromagnetic resonance modes inside the resonator, and various resonances interact to form new coupling forms. The equation of coupled mode theory is as follows: (1) (2) In formula (1) is the resonance amplitude, is the resonant frequency, is the attenuation rate caused by the inherent loss of the material itself, is the power loss rate of the resonator itself, in formula (2) and They are respectively expressed as the amplitude of the incident wave and the reflected wave. Formula (1) means the energy change inside the resonator, and formula (2) means that the total reflected wave is the sum of the reflected part of the incident wave and the radiation wave from the resonator. Therefore, combining formula (1) and formula (2), the reflection coefficient of the absorber can be derived as: (3) The absorption coefficient It can be expressed as: (4) Equation (4) shows that when the system is in resonance ( = ), the inherent loss rate and power loss rate are the same ( = ), the reflection coefficient is zero, so perfect absorption can be achieved.

[0028] Metal-dielectric-metal (MIM) structures are widely used in metamaterial absorbers because they can achieve perfect absorption through impedance matching. The top metal layer of the MIM structure is used to excite surface plasmon resonance, and the dielectric layer acts as a resonant cavity for electromagnetic waves. The choice of its thickness and dielectric constant has a significant effect on the resonant frequency and absorption efficiency. The main function of the bottom metal layer is to prevent electromagnetic waves from transmitting, thereby forming an interference effect inside the absorber and further improving the absorption efficiency.

[0029] Furthermore, the present invention forms multiple resonance peaks by adjusting structural parameters and exciting multiple surface plasmon modes, thereby expanding the bandwidth of the absorber. The multi-mode resonance coupling mechanism ensures efficient absorption in a wider band, and is particularly suitable for broadband absorption applications in the mid- and far-infrared bands.

[0030] The MIM-like four-layer mid-infrared broadband metamaterial absorber proposed by the present invention perfectly combines the intrinsic absorption of the material with the hybrid plasma resonance, greatly extending the absorption bandwidth. By adjusting the geometric parameters of the absorber, the perfect absorption of the target band can be infinitely close.

[0031] In order to better optimize the structural design of metamaterial absorbers, numerical simulation methods are widely used. Among them, the finite-difference time-domain method (FDTD) is an effective calculation tool that can accurately simulate the propagation behavior of electromagnetic waves in complex structures. Through FDTD simulation, the influence of different geometric parameters and material combinations on the absorption performance can be analyzed, thereby providing theoretical guidance for the design of efficient broadband absorbers. Based on this type of numerical simulation method, designers can achieve optimized absorption of the target band by adjusting structural parameters and material properties.

[0032] In order to prove the effectiveness of the solution proposed by the present invention, a specific comparative example is provided below: The first metamaterial absorber in the comparative example is the one provided by the present invention. Figures 1 to 3 The structure shown, its metamaterial absorption unit is square in shape as a whole, and includes a top metal layer 1-1, a first dielectric layer 1-2, a second dielectric layer 1-3 and a bottom metal layer 1-4 from top to bottom. The top metal layer 1-1 is attached to the upper surface of the first dielectric layer, and is composed of 8 metal sheets arranged in a certain arrangement, namely: a circular metal sheet 1-1-1, located at the center of the upper surface of the first dielectric layer 1-2, and its center is aligned with the center of the upper surface of the first dielectric layer 1-1; the circular metal sheet 1-1-1 is surrounded by three circular metal sheets with the same center as the circular metal sheet, and there is a spacing between the circular metal sheet 1-1-1 and the innermost circular metal sheet 1-1-2, between the innermost circular metal sheet 1-1-2 and the middle circular metal sheet 1-1-3, and between the middle circular metal sheet 1-1-3 and the outermost circular metal sheet 1-1-4, respectively. , , Four metal square pieces 1-1-5 of the same size are respectively arranged at the four corners of the upper surface of the first dielectric layer 1-2; the bottom metal layer 1-4 is a metal plate attached to the bottom surface of the second dielectric layer. The bottom metal layer 1-4 acts as a reflection layer to prevent electromagnetic waves from passing through. The radius of the circular metal piece in the top metal layer is , the radius of the three circular metal sheets from the inside to the outside is , , , the width is , , . Width of the metal square , metamaterial absorption unit period length ; Thickness of top metal layer, first dielectric layer, second dielectric layer, bottom metal layer , , , The metal material used in the top metal layer and the bottom metal layer is titanium with high loss; the first dielectric layer is Si layer, and the second dielectric layer is Si 3 N 4 layer.

[0033] The difference between the second metamaterial absorber in the comparative example and the first metamaterial absorber is that four metal square pieces 1-1-5 are removed from the top metal layer in the second metamaterial absorber, and other settings are exactly the same. The top metal layer of the second metamaterial absorber is referred to as a "ring plus center circle structure".

[0034] The difference between the third metamaterial absorber in the comparative example and the first metamaterial absorber is that the four metal square pieces 1-1-5 and the circular metal piece 1-1-1 are removed from the top metal layer of the third metamaterial absorber, and other settings are exactly the same. The top metal layer of the third metamaterial absorber is referred to as a "ring structure".

[0035] The above three metamaterial absorbers (the three metamaterial absorber structures only have different metal patterns in the top metal layer, and other simulation parameters are exactly the same) are simulated, and the absorption rates of the three metamaterial absorbers are calculated and analyzed by finite-difference time-domain (FDTD) simulation. - Flat The axis is irradiated from top to bottom. and Use periodic boundary conditions in the direction. Perfect matched layers (PML) boundary conditions are used in the direction. The influence of different patterns of the top metal layer on the absorption performance is analyzed by simulation to verify the importance of pattern design for optimizing absorption.

[0036] The results show that the first metamaterial absorber (i.e. the mid-to-far infrared broadband metamaterial absorber proposed in the present invention) achieved absorption peaks of 99.72% and 96.2% at 18.1μm and 26.3μm respectively, with a broadband absorption region of 15-35μm and an average absorption rate of 95%.

[0037] The above three metamaterial absorbers are simulated, and the simulation structure diagram is as follows: Figure 4 As shown, Figure 4 This is a comparison of absorption curves of several metamaterial absorbers with different metal sheet arrangements in the comparative embodiment; the results show that the third metamaterial absorber with a "ring structure" top metal layer has two absorption peaks at 14.6μm and 23.7μm, respectively, with absorption rates of 98.2% and 99.4%, and the absorption valley drops to 87% at 18.6μm; The second metamaterial absorber with a top metal layer of a "ring plus central disc structure" raised the absorption valley to 89.8% at its lowest point.

[0038] The first type of metamaterial absorber, which has a complete picture of three circular metal sheets, four square metal sheets, and circular metal sheets, significantly improves the overall absorption efficiency. The peak value of the absorption peak increases, the absorption rate of the absorption valley also increases to 92%, and the average absorption rate reaches 95.2%.

[0039] In one embodiment, based on the mid- and far-infrared broadband metamaterial absorber structure proposed by the present invention, Figure 5 The electromagnetic field distribution diagram of the top layer of the absorber on the XY coordinate axis when the infrared wavelength is 18.1μm, 22.2μm, and 26.3μm, respectively. (a) is the electric field distribution diagram of the top layer of the absorber at 18.1μm; (b) is the electric field distribution diagram of the top layer of the absorber at 22.2μm; (c) is the electric field distribution diagram of the top layer of the absorber at 26.3μm; (d) is the magnetic field distribution diagram of the top layer of the absorber at 18.1μm; (e) is the magnetic field distribution diagram of the top layer of the absorber at 22.2μm; (f) is the magnetic field distribution diagram of the top layer of the absorber at 26.3μm, where 18.1μm and 26.3μm are the wavelengths corresponding to the two absorption peaks, and 22.2μm is the wavelength corresponding to the middle absorption valley. By analyzing the electromagnetic field intensity distribution at the absorption peak and absorption valley, we can see the generation of localized surface plasmon resonance. The distribution of electric and magnetic fields on the pattern gradually increases or decreases with the frequency change. Finally, through the optimization of structural parameters, efficient absorption in a broadband range is achieved.

[0040] On the other hand, the present invention provides a design method of the above-mentioned mid- and far-infrared broadband metamaterial absorber, comprising: Determine the target band; Determine the optimized structural parameters, including: the radius of the circular metal piece in the top metal layer , the radius of the three circular metal sheets from the inside to the outside , , And width , , , the distance between the circular metal sheet and the innermost circular metal sheet, and between the adjacent layers of circular metal sheets from the inside to the outside , , , the width of the metal square , metamaterial absorption unit period length The dielectric layer is a composite dielectric layer, which includes a first dielectric layer and a second dielectric layer from top to bottom. The thickness of the top metal layer, the first dielectric layer, the second dielectric layer, and the bottom metal layer is , , , ; Determine that the metal material used for the top metal layer and the bottom metal layer is titanium with high loss; Determine the materials of the first dielectric layer and the second dielectric layer: the first dielectric layer is Si layer, and the second dielectric layer is Si 3 N 4 layer; Initialize the structural parameters of the mid-infrared broadband metamaterial absorber, use the finite-difference time-domain method to simulate the mid-infrared broadband metamaterial absorber, and analyze the influence of different structural parameters on the absorptivity of the target band; by comparing the absorptivity curves under different structural parameter designs, verify the absorption performance of the design, and optimize the structural parameters to achieve the best absorption effect.

[0041] By analyzing the absorption curve and the electromagnetic field intensity distribution diagram, the geometric structure of the absorber is further optimized. The focus is on improving the electric and magnetic field intensities at the absorption peak and smoothing the absorption curve to improve the overall absorption efficiency in the broadband range.

[0042] The optimized structure has been verified under laboratory conditions to test its absorption performance in the mid- and far-infrared bands. The verified structure can achieve a near-perfect absorption rate and is suitable for a variety of optical systems such as infrared detectors, optical filters, and thermal emitters.

[0043] Matters not covered by the present invention are known technologies.

[0044] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0045] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A mid-to-far infrared broadband metamaterial absorber, characterized in that: It includes metamaterial absorption units arranged in a periodic array; The metamaterial absorption unit is square in shape as a whole, and comprises a top metal layer, a dielectric layer and a bottom metal layer from top to bottom; The top metal layer is attached to the upper surface of the dielectric layer and consists of 8 metal sheets arranged in a certain way, namely: A circular metal sheet is located at the center of the upper surface of the dielectric layer, and the center of the circle is aligned with the center of the upper surface of the dielectric layer; The outer periphery of the circular metal sheet is surrounded by three circular ring-shaped metal sheets with the same center as the circular metal sheet, and there is a spacing between the circular metal sheet and the innermost circular ring-shaped metal sheet and between the adjacent circular ring-shaped metal sheets from the inside to the outside; Four metal square pieces of the same size are respectively arranged at the four corners of the upper surface of the dielectric layer.

2. The mid-to-far infrared broadband metamaterial absorber according to claim 1, characterized in that: The thickness of each metal sheet in the top metal layer is the same, that is, the thickness of the top metal layer .

3. The mid-to-far infrared broadband metamaterial absorber according to claim 2, characterized in that: The bottom metal layer is a metal plate attached to the bottom of the dielectric layer. The thickness of the bottom metal layer is Greater than the thickness of the top metal layer .

4. The mid-to-far infrared broadband metamaterial absorber according to claim 1, 2 or 3, characterized in that: The metal material used for the top metal layer and the bottom metal layer is metal titanium with high loss.

5. The mid-to-far infrared broadband metamaterial absorber according to claim 4, characterized in that: The dielectric layer is a composite dielectric layer, and comprises a first dielectric layer and a second dielectric layer from top to bottom.

6. The mid-to-far infrared broadband metamaterial absorber according to claim 5, characterized in that: The first dielectric layer is a Si layer, and the second dielectric layer is a Si3N4 layer.

7. The mid-to-far infrared broadband metamaterial absorber according to claim 5 or 6, characterized in that: The thickness of the first dielectric layer Less than the thickness of the second dielectric layer .

8. The design method of the mid-to-far infrared broadband metamaterial absorber as claimed in claim 1, characterized in that: include: Determine the target band; Determine the optimized structural parameters, including: the radius of the circular metal piece in the top metal layer , the radius of the three circular metal sheets from the inside to the outside , , And width , , , the distance between the circular metal sheet and the innermost circular metal sheet, and between the adjacent layers of circular metal sheets from the inside to the outside , , , the width of the metal square , metamaterial absorption unit period length The dielectric layer is a composite dielectric layer, which includes a first dielectric layer and a second dielectric layer from top to bottom. The thickness of the top metal layer, the first dielectric layer, the second dielectric layer, and the bottom metal layer is , , , ; Determine that the metal material used for the top metal layer and the bottom metal layer is titanium with high loss; Determine the materials of the first dielectric layer and the second dielectric layer: the first dielectric layer is a Si layer, and the second dielectric layer is a Si3N4 layer; Initialize the structural parameters of the mid-infrared broadband metamaterial absorber, simulate the mid-infrared broadband metamaterial absorber using the finite-difference time-domain method, and analyze the influence of different structural parameters on the absorption rate of the target band; By comparing the absorption rate curves under different structural parameter designs, the absorption performance of the design is verified, and the structural parameters are optimized to achieve the best absorption effect.

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