Full-wave-band perfect absorber covering millimeter waves to intermediate infrared rays and preparation method of full-wave-band perfect absorber

Abstract

The invention relates to the technical field of perfect absorbers, in particular to a full-wave-band perfect absorber covering millimeter waves to intermediate infrared rays and a preparation method of the full-wave-band perfect absorber. The absorber comprises a plurality of absorber unit structures, and each absorber unit structure comprises a conformal substrate supporting layer, a metal reflecting layer deposited on the lower surface of the conformal substrate supporting structure and a three-dimensional gradient structure conductive film covering the upper surface of the conformal substrate supporting structure. The full-bandwidth perfect absorber has full-bandwidth absorption covering millimeter waves to mid-infrared rays, and the average absorption rate is as high as 99.999% especially in the range of 0.5-20 THz. In addition, the material has a good incident angle insensitive characteristic, and 90% of efficient absorption can still be kept in a wide incident angle range of-75 degrees to 75 degrees. Besides, the full-bandwidth perfect absorber adopts a three-dimensional gradient structure which is symmetrical in the x direction and the y direction, has the characteristic of polarization independence, and has excellent absorption characteristics for millimeter waves to intermediate infrared waves which are incident in different polarization directions.

Description

Technical Field

[0001] This invention relates to the field of perfect absorber technology, specifically a full-band perfect absorber covering millimeter waves to mid-infrared and its preparation method. Background Technology

[0002] Electromagnetic wave absorbing materials have crucial application value in fields such as radar stealth, electromagnetic compatibility, infrared thermal management, and photoelectric detection. In recent years, with the rapid expansion of electromagnetic spectrum applications into millimeter-wave, terahertz, and mid-infrared bands, developing functional materials capable of achieving efficient and stable electromagnetic energy absorption in these frequency bands has become a critical technological need requiring breakthroughs. Such absorbers not only need to achieve high absorption rates across a wide frequency band to cope with complex electromagnetic applications such as frequency-agile radar, ultra-wideband electromagnetic compatibility, and broadband infrared imaging, but also need to possess performance stability at wide incident angles and electromagnetic wave polarization insensitivity to adapt to the complex and varied incident conditions in practical applications. Currently, research on ultra-wideband absorbers mainly focuses on two major technological directions: composite materials and metamaterial absorbers.

[0003] Traditional composite absorbing materials typically combine absorbers such as ferrites, carbon-based materials, or conductive polymers with a polymer matrix. Their absorption mechanism mainly relies on the dielectric or magnetic losses of the material itself. However, the intrinsic impedance and free-space impedance of bulk materials are difficult to match well over ultra-wideband frequencies, causing most incident electromagnetic waves to be reflected at the surface and unable to penetrate the material for dissipation. Furthermore, improving the absorption performance often requires complex modification processes, such as surface coating, doping, or core-shell structure construction of absorber particles, which significantly increases process complexity and cost. Simultaneously, the uniformity of modification is difficult to control precisely, and the uniformity of absorber dispersion in the matrix, interfacial bonding, and microstructure consistency are hard to guarantee, resulting in large fluctuations in the material's macroscopic electromagnetic parameters and absorption performance that often falls short of theoretical design expectations.

[0004] In 2008, Landy and his research team made a breakthrough in the microwave frequency range, successfully achieving complete absorption of metamaterials. This absorption effect can be applied to multiple frequencies, extending from microwaves to terahertz, visible light, and even the ultraviolet band. Metamaterials can provide many unconventional optical properties, and their electromagnetic properties are easily controlled. Metamaterial absorbers, by designing the geometry of subwavelength units, can achieve free manipulation of the amplitude, phase, and polarization state of electromagnetic waves, thus achieving near-perfect absorption effects at specific frequencies or within narrow bands. However, the strong absorption peaks of such absorbers are highly dependent on the resonance effect of the structure, and the resonance bandwidth is usually narrow, making it difficult to cover the ultra-wide spectral range from millimeter waves to mid-infrared. Although bandwidth extension can be achieved through multilayer stacking or coupling of multiple resonant units, this drastically increases the complexity of design and fabrication. Furthermore, most metamaterial absorbers are highly dependent on the incident angle and polarization state of electromagnetic waves, exhibiting excellent absorption performance only under normal incidence or specific polarization states. When electromagnetic waves are obliquely incident or the polarization state changes, the resonance condition is disrupted, and the absorption rate drops sharply, which severely limits their practicality in real-world environments.

[0005] A perfect absorber (PA) is a device that can achieve near 100% absorption within a specific frequency band. Due to limitations in intrinsic impedance and loss mechanisms, composite materials in existing technologies cannot achieve efficient and stable absorption over an ultra-wide spectrum. While metamaterial absorbers can theoretically achieve perfect absorption, their narrow band, angle and polarization sensitivity, and complex and difficult-to-fabricate structures also fail to meet the practical requirements of full-band coverage from millimeter waves to mid-infrared, ultra-wide oblique incidence angles, polarization insensitivity, and ease of fabrication.

[0006] Therefore, there is an urgent need to develop a perfect absorber that combines ultra-wideband high-efficiency absorption, excellent angle and polarization stability, and has a simplified structure and flexible fabrication capabilities across the entire wavelength range. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a full-band perfect absorber to achieve perfect absorption of at least the ultrawide spectrum from millimeter waves to mid-infrared.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A full-band perfect absorber covering millimeter waves to mid-infrared includes several absorber unit structures. Each absorber unit structure includes a conformal substrate support structure, a metal reflective layer deposited on the lower surface of the conformal substrate support structure, and a three-dimensional gradient conductive film covering the upper surface of the conformal substrate support structure.

[0010] In some embodiments, the conformal base support structure is a composite geometry, including a columnar support layer in the lower half and a three-dimensional gradient layer in the upper half that is conical; the cone includes a pyramid, a frustum, a cone, and a frustum of a circle.

[0011] In some examples, the three-dimensional gradient layer is a quadrangular frustum structure, with a bottom side length of 0.05~100 mm and a top side length of 0~50 mm; preferably, the bottom side length is 0.1~5 mm and the top side length is 0~10 mm. In some examples, the thickness of the three-dimensional gradient layer is 0.05~100 mm and the refractive index of the material is 1.01~10; preferably, the thickness is 1.5~10 mm and the refractive index of the material is 1.1~5.

[0012] In some examples, the support layer is a prism structure with a thickness of 0.1 to 30 mm and a refractive index of 1.01 to 10; preferably, the thickness is 0.5 to 10 mm.

[0013] In some examples, the conformal substrate support structure is made of materials including photosensitive resin, epoxy resin, ABS plastic, polypropylene, polytetrafluoroethylene, polycarbonate, SiO2, Si, and Si3N4; wherein the support layer and the three-dimensional gradient layer are made of the same or different materials.

[0014] In some examples, the three-dimensional gradient structure conductive film is a plurality of MXene films conformally to the upper surface of the three-dimensional gradient structure, with a surface conductivity of 0.01 to 1000 mS; preferably, the surface conductivity is 4 to 6 mS.

[0015] In some embodiments, the thickness of the bottom metal reflective layer is greater than 100 nm, and the conductivity is 1×10⁻⁶. 5 ~1×10 8 S / m; preferably, the thickness of the metal reflective layer is 0.2~10 µm, and the conductivity is 1×10 7 ~8×10 7 S / m.

[0016] In some examples, the material of the metal reflective layer includes gold, silver, copper, etc.

[0017] In some embodiments, the structural period of the absorber unit structure is 0.05~1000 mm; preferably, the structural period is 0.5~20 mm.

[0018] The method for fabricating the full-band perfect absorber includes the following steps: S1: Select the material of the conformal substrate support layer, and select a molding process for preparation based on the material's processability; S2: Hydrophilic modification is performed on the upper surface of the conformal substrate support structure, and an MXene film is dipped onto the upper surface to form a conformal film. Then, it is dried and cured to form the three-dimensional gradient structure conductive film. S3: A metal layer is deposited at the bottom of the conformal substrate support structure to form the metal reflective layer.

[0019] In some embodiments, in step S1, the forming process includes 3D printing, laser etching, machining, or photolithography.

[0020] In some embodiments, step S2, the hydrophilic modification method includes soaking in a strong alkali.

[0021] In some embodiments, in step S2, the dip coating and drying curing are repeated several times to ensure that the MXene film is uniformly coated; and by repeating the dip coating and drying curing several times, several layers of MXene film can be formed, thereby adjusting the thickness of the three-dimensional gradient structure conductive film and thus adjusting the surface conductivity; preferably, the process is repeated 4 to 10 times.

[0022] It is worth noting that, through simulation calculations using the Drude-Smith model, when using support structure materials with different refractive indices (n=1.0, 1.5, 2.0, 3.0) and loss tangent values ​​(Df=0, 0.001, 0.01, 0.05, 0.1), the simulation results show that the absorptivity curves of different support materials almost completely overlap (e.g., ...). Figure 7 As shown in the figure, this may indicate that changes in the properties of the supporting structure material have a negligible impact on the overall absorption rate of the absorber, and the absorption performance may mainly depend on the top MXene conductive film. For conductive films with different conductivity properties, the absorption rate exhibits a non-monotonic change with increasing conductivity. In the low-frequency region (0.1-0.4 THz), the performance is optimal when the surface conductivity is 4-6 mS, with an average absorption rate of 0.999. However, in the high-frequency region (>0.4 THz), excessively high conductivity exacerbates impedance mismatch, leading to increased interface reflection and decreased absorption rate. MXene films, due to their precisely controllable thin-layer conductivity, intrinsic ultra-wideband absorption characteristics, and good solution processability, are ideal materials for the three-dimensional gradient structure in this invention. By repeatedly dipping and coating, the surface conductivity can be controlled to 4-6 mS, achieving a high degree of compatibility between its electromagnetic parameters and the structural impedance requirements, thus overcoming the limitations of traditional conductive films that are difficult to efficiently absorb waves due to increased thickness and impedance mismatch.

[0023] In some embodiments, in step S3, the deposition method includes magnetron sputtering, electroless plating, or vapor deposition.

[0024] In some embodiments, the preparation method specifically includes: T1: Construct a 3D model of the full-band perfect absorber composed of several absorber unit structures, pour the material of the conformal substrate support structure into the material tank of the 3D printer, and perform 3D printing to obtain the conformal substrate support structure of the printed part. T2: The conformal substrate support structure is washed with alcohol and then immersed in a strong alkaline solution for activation to obtain an activated conformal substrate support structure; T3: The MXene film is dip-coated onto the surface of the three-dimensional gradient layer of the activated support structure, and then dried and cured. T4: Repeat step S3 several times to uniformly coat several layers of the MXene film onto the upper surface of the conformal substrate support structure (i.e., the upper surface of the three-dimensional gradient layer) to form a three-dimensional gradient structure conductive film. T5: A metal layer is deposited on the lower surface of the conformal substrate support structure (i.e., the lower surface of the support layer) by chemical plating to form the metal emission layer, thus obtaining the full-band perfect absorber.

[0025] Notably, the full-band perfect absorber of this invention utilizes a three-dimensional gradient-structured MXene thin film, which enables impedance matching and reduces surface reflection. When electromagnetic waves are incident on the absorber from different directions and polarization states, the waves are continuously reflected between the MXene thin film and the bottom metal layer, ultimately being absorbed by the MXene thin film, thus achieving ultra-wideband near-perfect absorption. This structure achieves an absorption rate exceeding 90% in an ultra-wideband range from millimeter waves to mid-infrared. Within a wide incident angle range of ±75°, the absorber maintains excellent absorption performance without significant attenuation. Furthermore, thanks to its symmetrical three-dimensional gradient design in the x and y directions, the absorber exhibits polarization-independent characteristics.

[0026] The beneficial effects of this invention are: 1. The full-bandwidth perfect absorber of the present invention exhibits absorption across the entire bandwidth from millimeter waves to mid-infrared, particularly with an average absorptivity of up to 99.999% in the 0.5-20 THz range. Furthermore, this full-bandwidth perfect absorber also possesses excellent incident angle insensitivity, maintaining a high absorption efficiency of 90% over a wide incident angle range of -75° to 75°. In addition, this full-bandwidth perfect absorber employs a symmetrical three-dimensional gradient structure in both the x and y directions, exhibiting polarization-independent characteristics and excellent absorption properties for millimeter waves to mid-infrared waves incident from different polarization directions.

[0027] 2. The core three-dimensional structure of the full-bandwidth perfect absorber of the present invention can be processed by a variety of mature processes such as 3D printing, laser etching, machining or photolithography, and is compatible with different material systems. The preparation scheme can be flexibly selected according to cost, precision and mass production requirements, and has broad industrial application prospects. Attached Figure Description

[0028] Figure 1 This is a three-dimensional structural schematic diagram of the full-band perfect absorber in this invention; Figure 2 This is a three-dimensional structural schematic diagram of the absorber unit in this invention; Figure 3 This is a cross-sectional view of the absorber unit in this invention; Figure 4 This is a three-dimensional SEM image of the full-band perfect absorber in Embodiment 1 of the present invention; Figure 5 This is a top SEM view of the full-band perfect absorber in Embodiment 1 of the present invention; Figure 6 This is a front view of the full-band perfect absorber in Embodiment 1 of the present invention via SEM. Figure 7 To simulate and calculate the effect of support materials with different refractive indices and loss tangents on absorption performance, the simulation results are as follows: Figure 7 a represents the effect of support materials with different refractive indices on absorption performance. Figure 7 b represents the effect of support materials with different loss tangent values ​​on absorption performance; Figure 8 The absorption rate of the three-dimensional gradient structure conductive films with different conductivity in the embodiments of the present invention is in the range of 0.1~0.4THZ.

[0029] Figure 9 The absorption spectrum of the absorber in the experimental example of this invention; Figure 10 This is the absorption performance of the absorber in the experimental example of the present invention under TE and TM polarization and different incident angles.

[0030] Reference numerals: 1-Three-dimensional gradient structure conductive thin film, 2-Conformal substrate support structure, 3-Metallic reflective layer. Detailed Implementation

[0031] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the following description.

[0032] Example 1 This embodiment uses 3D printing, chemical plating, and other methods to prepare a full-band perfect absorber covering the millimeter wave to mid-infrared range. The specific methods are as follows: A schematic diagram of the absorber structure is shown below. Figure 1 As shown, the structure of a single absorber unit is designed as follows: the metal reflective layer 3 has a thickness of 2µm, is made of silver, and has an electrical conductivity of 6.3×10⁻⁶. 7 The spacer layer has a thickness of 2 mm and is made of epoxy photosensitive resin (purchased from Beijing Yihexin Technology Co., Ltd.) with a refractive index of 1.68. The three-dimensional gradient layer has a frustum structure with a height of 3 mm, is made of the same material as the spacer layer, has a bottom side length of 0.5 mm, and a top side length of 0.1 mm. The surface conductivity of the three-dimensional gradient conductive film 1 is 4 mS. The period of the absorber unit structure is 0.5 mm. The specific fabrication method is as follows: 1) Create a 3D model of the absorber according to the design structure and export it as an STL file, then import it into the CHITUBOX software. Set the printing parameters: bottom layer exposure time is 80 seconds, normal exposure time is 3 seconds, and add support strips with a support density of around 80%. After completing the settings, perform slicing and import the sliced ​​file into the 3D printer. Pour epoxy photosensitive resin into the feed tank and start printing. After printing, remove the printed part and rinse it five times with anhydrous ethanol to ensure the surface is clean. After it dries, remove the bottom support strips and polish the bottom to maintain a smooth surface.

[0033] 2) Immerse the printed parts in a strong alkaline solution for 30 minutes to remove surface oil. Simultaneously, this process introduces hydrophilic functional groups such as hydroxyl groups onto the surface of the printed parts, enabling them to form hydrogen bonds with water molecules, thereby achieving a hydrophilic effect on the absorber surface.

[0034] 3) Dip-coating MXene film (liquid-liquid interface self-assembly): The MXene film is transferred to the upper surface of the absorber after step 2) by dip coating, and then dried and cured in a drying oven at 45°C.

[0035] 4) Repeat step 3) 5 times to ensure that the absorber surface is uniformly coated with a multilayer MXene film with a surface conductivity of 4 mS.

[0036] 5) A 0.5 µm silver layer is deposited at the bottom of the absorber by chemical plating.

[0037] Example 2 This embodiment uses 3D printing and chemical plating to prepare a full-band perfect absorber covering the millimeter wave to mid-infrared range. The method is the same as in Example 1, except that some preparation parameters are adjusted, as follows: A schematic diagram of the absorber structure is shown below. Figure 1 As shown, the structure of a single absorber unit is designed as follows: the metal reflective layer 3 has a thickness of 1.5µm, is made of copper, and has a conductivity of 4.5×10⁻⁶. 7The spacer layer has a thickness of 1.2 mm, is made of ABS plastic, and has a refractive index of 1.54. The three-dimensional gradient layer has a frustum structure, is made of the same material as the spacer layer, and has a height of 2.5 mm, a bottom side length of 0.6 mm, and a top side length of 0.05 mm. The surface conductivity of the three-dimensional gradient conductive film 1 is 6 mS. The period of the absorber unit structure is 0.6 mm. The specific fabrication method is as follows: 1) First, create a 3D model of the absorber according to the design and export it as an STL file, then import it into the CHITUBOX software. Set the printing parameters: bottom layer exposure time is 100 seconds, normal exposure time is 5 seconds, and add support strips with a support density of 60%. After completing the settings, perform slicing and import the sliced ​​file into the 3D printer. Pour ABS plastic into the feed hopper and start printing. After printing, remove the printed part and rinse it five times with anhydrous ethanol to ensure the surface is clean. After it dries, remove the bottom support strips and polish the bottom to maintain a smooth surface.

[0038] 2) Immerse the printed parts in a strong alkaline solution for 40 minutes to remove surface oil. Simultaneously, this process introduces hydrophilic functional groups such as hydroxyl groups onto the surface of the printed parts, enabling them to form hydrogen bonds with water molecules, thereby achieving a hydrophilic effect on the absorber surface.

[0039] 3) Dip-coating MXene film: The MXene film is transferred to the upper surface of the absorber after step 2) by dip coating, and then dried and cured in a drying oven at 50°C.

[0040] 4) Repeat step 3) 6 times to ensure that the absorber surface is uniformly coated with a multilayer MXene film with a surface conductivity of 6 mS.

[0041] 5) A 2 µm copper layer is deposited at the bottom of the absorber by chemical plating.

[0042] Example 3 This embodiment uses 3D printing and chemical plating to prepare a perfect absorber covering the entire wavelength range from millimeter waves to mid-infrared. The method is the same as in Embodiment 1, except that the material used to prepare the conformal substrate support structure 2 is different. Instead, an epoxy resin material with a refractive index n=1.64 and a loss tangent Df=0.02 (purchased from Beijing Yihexin Technology Co., Ltd.) is used. The preparation is repeated multiple times to obtain multiple sets of absorber samples.

[0043] Experimental Example 1) Absorption spectrum of a full-bandwidth perfect absorber: A set of absorber samples prepared in Example 3 were used, and the absorbance of the samples in different bands was detected by a vector network analyzer (VNA), a terahertz time-domain spectroscopy system (THz-TDS), and a Fourier transform infrared spectrometer (FTIR). The VNA was used to test the absorbance in the millimeter wave band (50–110 GHz), the THz-TDS was used to test the absorbance in the terahertz low-frequency band (0.1–1.6 THz), and the FTIR was used to test the absorbance in the mid-infrared high-frequency band (1.6–20 THz).

[0044] The results are as follows Figure 9 As shown, the absorption rate of this structure exceeds 96% in the ultra-wideband of 50 GHz-20 THz, especially in the range of 0.5-20 THz, where the average absorption rate is as high as 99.999%.

[0045] 2) Absorption spectra of the full-bandwidth perfect absorber for TE and TM polarization at different oblique incidence angles: A set of absorber samples prepared in Example 3 were used to test the absorption performance of the samples under different incident angles and polarization states using a terahertz time-domain spectroscopy (THz-TDS) system. The specific steps were as follows: First, in TE polarization mode, the sample was fixed and the incident angle was adjusted to 15°, 30°, 45°, 60° and 75° for testing; then, the sample was rotated 90°, switched to TM polarization mode, and the above tests were repeated at the same series of incident angles.

[0046] The results are as follows Figure 10 As shown, the absorber is insensitive to both TE and TM polarization states, exhibiting excellent polarization-independent characteristics. Furthermore, its absorption performance remains stable with increasing incident angle, without significant attenuation. Even under a large oblique incidence angle of 75°, the absorptivity remains as high as 90% at a frequency of 0.1 THz, demonstrating that this structure possesses excellent wide-angle incident stability and angle tolerance.

[0047] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A full-band perfect absorber covering millimeter waves to mid-infrared, comprising several absorber unit structures, characterized in that: The absorber unit structure includes a conformal substrate support structure (2), a metal reflective layer (3) deposited on the lower surface of the conformal substrate support structure (2), and a three-dimensional gradient structure conductive film (1) covering the upper surface of the conformal substrate support structure (2).

2. The full-band perfect absorber according to claim 1, characterized in that: The conformal base support structure (2) is a composite geometry, including a columnar support layer in the lower half and a three-dimensional gradient layer in the upper half that is conical; the cone includes a pyramid, a frustum, a cone and a frustum.

3. The full-band perfect absorber according to claim 2, characterized in that: The three-dimensional gradient layer is a quadrangular frustum structure, with a bottom side length of 0.05~100 mm and a top side length of 0~50 mm.

4. The full-band perfect absorber according to claim 2, characterized in that: The thickness of the three-dimensional gradient layer is 0.05~100 mm, and the refractive index of the material is 1.01~10.

5. The full-band perfect absorber according to claim 2, characterized in that: The three-dimensional gradient structure conductive film (1) consists of several layers of MXene film conforming to the upper surface of the three-dimensional gradient structure, with a surface conductivity of 0.01~1000mS.

6. The full-band perfect absorber according to claim 1, characterized in that: The thickness of the bottom metal reflective layer (3) is greater than 100 nm, and the conductivity is 1×10⁻⁶. 5 ~1×10 8 S / m.

7. The full-band perfect absorber according to any one of claims 1-6, characterized in that: The structural period of the absorber unit is 0.05~1000 mm.

8. The method for fabricating a full-band perfect absorber as described in any one of claims 1-7, characterized in that, Includes the following steps: S1: Select the material of the conformal substrate support layer, and select a molding process for preparation based on the material's processability; S2: Hydrophilic modification is performed on the upper surface of the conformal substrate support structure, and an MXene film is dipped onto the upper surface to form a conformal film. Then, it is dried and cured to form the three-dimensional gradient structure conductive film. S3: A metal layer is deposited at the bottom of the conformal substrate support structure to form the metal reflective layer.

9. The preparation method according to claim 8, characterized in that: In step S1, the molding process includes 3D printing, laser etching, machining, or photolithography.

10. The preparation method according to claim 8, characterized in that: In step S3, the deposition method includes magnetron sputtering, chemical plating, or vapor deposition.

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