An air medium-based ultra-wideband high-performance wave-absorbing structure and a preparation method thereof

Abstract

The application relates to an air medium-based ultra-wideband high-performance wave-absorbing structure and a preparation method thereof. The wave-absorbing structure is composed of, from top to bottom, an upper metasurface layer, an upper air medium layer, an intermediate metasurface layer, an intermediate air medium layer, a lower metasurface layer, a lower air medium layer and a metal bottom plate. A plurality of fixing holes are arranged in the metasurface layers and the metal bottom plate in a one-to-one correspondence manner. The air medium layers are supported by a plurality of nylon gaskets, the nylon gaskets correspond to the fixing holes in a one-to-one manner, each nylon gasket is provided with a through hole for a nylon fastener, and the metasurface layers, the metal bottom plate and the nylon gaskets are connected through the nylon fastener penetrating the fixing holes and the through holes. The wave-absorbing structure has a reflection coefficient of less than or equal to -15 dB in a super-large bandwidth of 27.2 GHz, exhibits an ultra-wideband absorption performance, and has a lighter and thinner structure and a simpler forming method.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing structure technology, and particularly relates to an ultra-wideband high-performance microwave absorbing structure based on air medium and its preparation method. Background Technology

[0002] With the widespread application of electronic devices, the development of wireless communication systems, and the increasing demand for low-detectability technologies, electromagnetic pollution caused by excessive electromagnetic radiation, such as interference with normal equipment operation, threats to human health, and radar detection threats, has become a key challenge. High-performance absorbing structures, which efficiently absorb and attenuate electromagnetic waves, are urgently needed in the fields of electromagnetic interference and electromagnetic shielding, and must simultaneously meet core requirements such as strong absorption, wide bandwidth, and lightweight design.

[0003] To achieve ultra-wideband high-performance absorption design, a matching design scheme based on multilayer resonant layers and multilayer dielectric layers is usually required. However, adhesive films are needed to bond the multilayer materials together. This technical solution has the following problems: First, during simulation calculations, the material parameters of the adhesive film, dielectric layer, and resonant layer all deviate from the actual materials. The superposition of multiple uncertainties makes the deviation between the simulation calculation results and the measured results of the absorption structure even greater, affecting the reliability of the design. Second, the presence of the adhesive film and dielectric layer increases the thickness and weight of the sample, and the adhesive film and dielectric layer themselves have high dielectric loss, resulting in a decrease in absorption performance and a narrowing of bandwidth. Third, the adhesive film bonding of multilayer materials usually requires a lamination process, which requires high operational precision and has a long curing cycle, making it unsuitable for mass production.

[0004] Therefore, in view of the shortcomings of current multilayer absorbing structures and the future development needs of absorbing structures, it is very necessary to propose a lightweight, ultra-wideband, high-performance absorbing structure with no adhesive film required and its preparation method. Summary of the Invention

[0005] To address one or more technical problems existing in the prior art, this invention provides an ultra-wideband high-performance absorbing structure based on air dielectric and its fabrication method, solving one or more technical problems of previous absorbing structures, such as being heavy, having poor absorption performance, narrow bandwidth, complex structure, and poor reliability of simulation calculations. The absorbing structure proposed in this invention exhibits a reflection coefficient ≤-15dB within a 27.2GHz ultra-wideband bandwidth, demonstrating ultra-wideband high-performance absorption performance. Furthermore, the structure is thinner and lighter, eliminating the need for high-loss materials (films and dielectric plates) that affect absorption performance, and the molding method is simpler.

[0006] The present invention provides, in a first aspect, an ultra-wideband high-performance absorbing structure based on an air medium, comprising, from top to bottom: an upper metasurface layer, including an upper resonant layer and an upper substrate layer; an upper air medium layer; an intermediate metasurface layer, including an intermediate resonant layer and an intermediate substrate layer; an intermediate air medium layer; a lower metasurface layer, including a lower resonant layer and a lower substrate layer; a lower air medium layer; and a metal base plate; wherein the upper metasurface layer, the intermediate metasurface layer, the lower metasurface layer, and the metal base plate are provided with a plurality of fixing holes in corresponding positions; the upper air medium layer, the intermediate air medium layer, and the lower air medium layer are each supported by a plurality of nylon gaskets, wherein the nylon gaskets correspond one-to-one with the fixing holes, and each nylon gasket is provided with a through hole for nylon fasteners to pass through; the upper metasurface layer, the intermediate metasurface layer, the lower metasurface layer, the metal base plate, and each nylon gasket are connected by nylon fasteners passing through the fixing holes and the through holes.

[0007] Preferably, the upper metasurface layer, the middle metasurface layer, the lower metasurface layer, and the metal base plate are uniformly provided with the fixing holes around their perimeter.

[0008] Preferably, the upper substrate layer, the middle substrate layer, and the lower substrate layer are FR4 substrates; the upper resonant layer, the middle resonant layer, and the lower resonant layer each include a plurality of periodically arranged basic units, the basic unit being a square annular carbon black film region, and the plurality of basic units are arrayed in the x and y directions with the same arrangement period.

[0009] Preferably, the outer side length of the square annular carbon black film region in the upper resonant layer is 4.5~5.1mm, the width of the square ring is 0.2~0.5mm, and the surface sheet resistance of the carbon black film is 110~140Ω / sq; the outer side length of the square annular carbon black film region in the middle resonant layer is 6.5~7.3mm, the width of the square ring is 0.8~1.3mm, and the surface sheet resistance of the carbon black film is 70~100Ω / sq; the outer side length of the square annular carbon black film region in the lower resonant layer is 8.5~8.9mm, the width of the square ring is 2.0~2.5mm, and the surface sheet resistance of the carbon black film is 140~170Ω / sq.

[0010] Preferably, the thickness of the upper air medium layer is 0.7~1.2mm, the thickness of the middle air medium layer is 0.7~1.2mm, and the thickness of the lower air medium layer is 1.5~2.0mm.

[0011] Preferably, the fixing holes are twelve M5 size holes; and / or the nylon fasteners include nylon bolts and nylon nuts.

[0012] In a second aspect, the present invention provides a method for fabricating an ultra-wideband high-performance microwave absorbing structure based on air medium according to the first aspect of the present invention, the method comprising the following steps: (1) Prepare the upper metasurface layer, the middle metasurface layer and the lower metasurface layer; (2) Laser drilling is performed at the preset positions of the upper metasurface layer, the middle metasurface layer, the lower metasurface layer and the metal base plate to form multiple fixing holes with one-to-one correspondence. (3) Provide multiple nylon gaskets, each of which has through holes; (4) Stack the layers in the following order from top to bottom: upper metasurface layer, multiple nylon gaskets, middle metasurface layer, multiple nylon gaskets, lower metasurface layer, multiple nylon gaskets, and metal base plate, aligning each through hole with each fixing hole to obtain a stacked body; (5) Pass the nylon fasteners through the corresponding fixing holes and through holes of each layer of the stack and lock them in sequence, so that each nylon gasket is pressed between two adjacent layers to form an upper air medium layer, a middle air medium layer and a lower air medium layer, thus obtaining an ultra-wideband high-performance absorbing structure based on air medium.

[0013] Preferably, step (1) is as follows: three FR4 substrates are provided as the upper substrate layer, the middle substrate layer and the lower substrate layer respectively. Multiple periodically arranged square annular carbon black film regions are formed on the upper substrate layer, the middle substrate layer and the lower substrate layer by screen printing process. Then, the upper resonant layer, the middle resonant layer and the lower resonant layer are obtained by laser trimming. The upper resonant layer and the upper substrate layer constitute the upper metasurface layer, the middle resonant layer and the middle substrate layer constitute the middle metasurface layer, and the lower resonant layer and the lower substrate layer constitute the lower metasurface layer.

[0014] Preferably, the positions of the nylon gaskets correspond one-to-one with the fixing holes; and / or the thickness of each nylon gasket located between the upper metasurface layer and the intermediate metasurface layer corresponds to the thickness of the upper air medium layer, the thickness of each nylon gasket located between the intermediate metasurface layer and the lower metasurface layer corresponds to the thickness of the intermediate air medium layer, and the thickness of each nylon gasket located between the lower metasurface layer and the metal base plate corresponds to the thickness of the lower air medium layer.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The ultra-wideband high-performance absorbing structure based on air medium proposed in this invention solves the problems of heavy absorbing materials, poor absorbing performance, narrow bandwidth and complex structure in the past. At the same time, it avoids the use of adhesive film and medium, and adopts nut forming method instead of conventional adhesive film pasting. The forming method is simpler. In simulation experiments, it can reduce the inaccuracy of material parameters during the simulation process and improve the reliability of simulation data. The improvement of simulation reliability can enable the research and development of absorbing structures to shift from "trial and error iteration" to "precise design", which can significantly shorten the research and development cycle, reduce costs, and support the rapid development and application of high-performance absorbing structures in high-frequency bands and complex scenarios. The absorbing structure of this invention exhibits better absorbing performance and larger absorbing bandwidth with a smaller thickness.

[0016] (2) The three-layer resonant layer of this invention adopts a symmetrical square ring structure design, which enables the absorbing structure to have consistent and excellent absorption performance under both horizontal and vertical polarization conditions. It is insensitive to the polarization angle of electromagnetic waves and has stronger environmental adaptability. Furthermore, through the precise matching of the square ring structure of the three-layer resonant layer with the three-layer air dielectric layer, and the optimized combination of the area size and surface sheet resistance of each layer of square annular carbon black film, the total thickness of the absorbing structure can achieve an ultra-wideband high-performance absorption with a reflection coefficient ≤-15dB in the range of 12.8GHz~40GHz (bandwidth 27.2GHz) with a total thickness of ≤4.5mm. Compared with the existing multi-layer absorbing structure using adhesive film bonding, this invention achieves a wider absorption bandwidth and stronger absorption performance with a thinner thickness.

[0017] (3) The present invention uses air as the medium layer, eliminating the need for heavy adhesive film and dielectric plate. The overall thickness is ≤4.5mm, and the weight is significantly reduced. In the preparation process, the high-precision mass production of the resonant layer is achieved through a combination of screen printing and laser trimming. The traditional adhesive film lamination is replaced by nylon mechanical fixing, eliminating the need for complex curing processes. Assembly is simple and quick, making it suitable for large-scale production. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. The drawings of the present invention are provided for illustrative purposes only, and the proportions, sizes, and quantities of the parts in the drawings may not be consistent with the actual product.

[0019] Figure 1 This is a schematic diagram of the ultra-wideband high-performance absorbing structure based on air medium of the present invention; Figure 2This is a schematic diagram showing that, in some specific embodiments of the present invention, multiple basic units in the upper resonant layer are arranged in an array with the same arrangement period in the x and y directions. Figure 3 This is a schematic diagram showing the relationship between the basic units and the arrangement period of the upper resonant layer in some specific embodiments of the present invention; Figure 4 This is a schematic diagram showing the relationship between the basic units and the arrangement period of the middle resonant layer in some specific embodiments of the present invention; Figure 5 This is a schematic diagram showing the relationship between the basic units and the arrangement period of the lower resonant layer in some specific embodiments of the present invention; Figure 6 This is a reflection coefficient curve of the absorbing structure in Embodiment 1 of the present invention under horizontal polarization; Figure 7 This is a reflection coefficient curve of the absorbing structure in Embodiment 1 of the present invention under vertical polarization.

[0020] In the figure, 1: metal base plate; 2: substrate layer; 3: air dielectric layer; 4: upper resonant layer; 5: middle resonant layer; 6: lower resonant layer; 7: basic unit; In this invention, the upper substrate layer, middle substrate layer and lower substrate layer are collectively referred to as substrate layer; the upper air dielectric layer, middle air dielectric layer and lower air dielectric layer are collectively referred to as air dielectric layer. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0022] In its first aspect, this invention provides an ultra-wideband high-performance microwave absorbing structure (abbreviated as microwave absorbing structure) based on an air medium, for example, such as Figure 1As shown, from top to bottom, it includes: an upper metasurface layer, including an upper resonant layer 4 and an upper substrate layer; an upper air dielectric layer; an intermediate metasurface layer, including an intermediate resonant layer 5 and an intermediate substrate layer; an intermediate air dielectric layer; a lower metasurface layer, including a lower resonant layer 6 and a lower substrate layer; a lower air dielectric layer; and a metal base plate 1. The upper, intermediate, and lower metasurface layers, as well as the metal base plate, are provided with multiple fixing holes in corresponding positions. The upper, intermediate, and lower air dielectric layers are each supported by multiple nylon gaskets (not shown in the figure). The nylon gaskets correspond one-to-one with the fixing holes, meaning the positions of the nylon gaskets and the fixing holes are one-to-one. Each nylon gasket has a through hole for the nylon fastener to pass through. Each nylon gasket is respectively disposed between the upper metasurface layer and the middle metasurface layer, between the middle metasurface layer and the lower metasurface layer, and between the lower metasurface layer and the metal base plate, and the through holes of each nylon gasket are aligned with the fixing holes of the corresponding layers. The upper metasurface layer, the middle metasurface layer, the lower metasurface layer, the metal base plate, and each nylon gasket are connected by nylon fasteners passing through the fixing holes and the through holes.

[0023] In this invention, each of the upper, middle, and lower air medium layers is supported by a plurality of nylon gaskets with a thickness equal to the preset thickness of the corresponding air medium layer. The upper, middle, and lower metasurface layers, the metal base plate, and each nylon gasket are connected by nylon fasteners passing through the fixing holes and the through holes, so that the nylon gaskets are pressed between adjacent layers, thereby precisely maintaining the thickness of each air medium layer, thus forming the upper, middle, and lower air medium layers.

[0024] The microwave absorbing structure in this invention can be used to solve the problems of poor microwave absorbing performance, narrow bandwidth, heavy weight, and complex molding scheme caused by the thick adhesive film layer, high dielectric loss, and high material parameter loss of the dielectric layer in previous microwave absorbing structure designs. Specifically, the microwave absorbing structure consists of three metasurface layers based on a hard substrate material and three air dielectric layers. The resonant units (basic units) in the resonant layer of the metasurface are square annular carbon black film regions (square annular carbon black structure) with a certain surface sheet resistance. The three metasurface layers and the air dielectric layers form a typical "sandwich" structure. The fabrication method of the flat plate sample based on the absorbing structure of the present invention can be as follows: Multiple basic units of the absorbing structure of the present invention are arranged in the horizontal and vertical directions and processed into a flat plate sample to obtain each metasurface layer. Each metasurface layer has twelve M5 holes pre-reserved in its substrate. Multiple nylon gaskets with corresponding air dielectric layer thicknesses are used to isolate each metasurface layer, thus leaving an air dielectric layer. Nylon bolts are passed through the fixing holes and the through holes of the nylon gaskets, and finally, nylon nuts are used for fixing. This fixes the multi-layer structure of the present invention while simultaneously fixing the thickness of each air dielectric layer, forming the final sample. The absorbing structure of the present invention exhibits a reflection coefficient ≤-15dB within a 27.2GHz ultra-wide bandwidth, demonstrating ultra-wideband high-performance absorption performance. Furthermore, the structure is thinner and lighter (total thickness ≤4.5mm), eliminating the need for high-loss materials (film and dielectric plate) that affect absorption performance, and simplifying the molding method.

[0025] According to some preferred embodiments, the thickness of the metal base plate is 0.1~1mm; the present invention does not specifically limit the material of the metal base plate, and those skilled in the art can conventionally select metal materials suitable for the wave-absorbing structure; in the present invention, the metal plate can be, for example, an aluminum plate or a copper plate.

[0026] According to some preferred embodiments, the upper metasurface layer, the middle metasurface layer, the lower metasurface layer, and the metal base plate are uniformly provided with the fixing holes around their perimeter.

[0027] According to some preferred embodiments, the upper substrate layer, the middle substrate layer, and the lower substrate layer are FR4 substrates; in this invention, the FR4 substrate is a glass fiber reinforced epoxy resin laminate; the upper resonant layer, the middle resonant layer, and the lower resonant layer each include a plurality of periodically arranged basic units, wherein the basic unit is a square annular carbon black film region (square annular structure), and the plurality of the basic units are arranged in an array with the same arrangement period in the x and y directions, for example, as... Figure 2As shown; in this invention, the arrangement period P is, for example, 8.5~9.5 mm, preferably 9 mm; in this invention, the arrangement period refers to the distance between the geometric centers of two adjacent basic units in the metasurface layer; that is, in this invention, all three resonant layers are based on an FR4 substrate, for example, a carbon black film with a certain surface sheet resistance and a certain periodic pattern is screen-printed on the substrate, and then the pattern is processed by laser trimming technology, that is, the edge of the pattern is processed by laser trimming technology. In other words, the edge burrs and excess carbon black material generated during the screen printing process are removed by ablation along the contour of the square annular pattern with a laser beam, so that the edge of the square annular pattern is smooth and the size is accurate.

[0028] In this invention, the thickness of the upper resonant layer, the middle resonant layer and the lower resonant layer is equal to the thickness of the carbon black film they each include, and their thickness is typically in the micrometer range (e.g., 5~20μm). Compared to the millimeter-scale substrate layer, air dielectric layer and metal base plate, this thickness has a negligible impact on the total thickness of the absorbing structure.

[0029] According to some preferred embodiments, such as Figures 3 to 5 As shown, the outer side length of the square annular carbon black film region in the upper resonant layer is 4.5~5.1mm, the width of the square ring is 0.2~0.5mm, and the surface sheet resistance of the carbon black film is 110~140Ω / sq; the outer side length of the square annular carbon black film region in the middle resonant layer is 6.5~7.3mm, the width of the square ring is 0.8~1.3mm, and the surface sheet resistance of the carbon black film is 70~100Ω / sq; the outer side length of the square annular carbon black film region in the lower resonant layer is 8.5~8.9mm, the width of the square ring is 2.0~2.5mm, and the surface sheet resistance of the carbon black film is 140~170Ω / sq.

[0030] According to some preferred embodiments, the thickness t2 of the upper air medium layer is 0.7~1.1mm, the thickness t1 of the middle air medium layer is 0.7~1.1mm, and the thickness t0 of the lower air medium layer is 1.5~2.0mm.

[0031] According to some preferred embodiments, the thickness t3 of the upper substrate layer, the middle substrate layer and the lower substrate layer is 0.17~0.27mm.

[0032] This invention preferably achieves multi-level resonant coupling and impedance matching of electromagnetic waves over a wide frequency band by precisely matching the three-layer square ring structure of the resonant layers with the three-layer air dielectric layers, combined with the optimized combination of the area size and surface sheet resistance of each layer of square annular carbon black film. This allows the invention to obtain a wider absorption bandwidth and stronger absorption performance with a thinner thickness. Specifically, the size of the three-layer square rings increases in a gradient, and the sheet resistance values ​​are distributed differently. Combined with the optimized thickness of the air dielectric layers, the lower air dielectric layer is the thickest (1.5~2.0mm), providing sufficient phase accumulation space for the relatively low-frequency end of the absorption bandwidth (e.g., around 12.8GHz), while the upper and middle air dielectric layers are thinner (0.7~1.1mm) to match the high-frequency impedance. Together, they construct a superposition of multiple resonant modes over a wide frequency band, thereby achieving ultra-wideband high-performance absorption with a reflection coefficient ≤-15dB in the range of 12.8GHz to 40GHz with a total thickness of only 4.5mm. This invention reveals that, if not configured in this way—for example, if the size difference of the square ring basic unit is too small or the thickness distribution of the air dielectric layer is improper—the absorption peaks of each resonant layer will not be able to continuously cover the signal, resulting in narrowed bandwidth or in-band reflection spikes. If the sheet resistance deviates from the preferred range, impedance matching will be disrupted, reducing absorption efficiency. If the thickness of the lower air dielectric layer is insufficient, the absorption performance at relatively low frequencies will deteriorate. Therefore, the parameter range defined in this invention is key to realizing an ultra-wideband, high-performance, and lightweight absorbing structure.

[0033] According to some preferred embodiments, the fixing holes are twelve M5-sized holes; in the fabrication of the microwave absorbing structure, each metasurface layer and the metal base plate have twelve M5-sized holes in the same position, and the fixing holes are made using laser drilling technology, thereby ensuring the consistency of the hole positions in each layer of material and also facilitating the vertical alignment of the multi-layer materials; and / or the nylon fasteners include nylon bolts and nylon nuts; in this invention, the nylon bolts and nylon nuts are adapted to each other, and the fixing holes and the through holes are both adapted to the nylon bolts.

[0034] In a second aspect, the present invention provides a method for fabricating an ultra-wideband high-performance microwave absorbing structure based on air medium according to the first aspect of the present invention, the method comprising the following steps: (1) Prepare an upper metasurface layer, an intermediate metasurface layer, and a lower metasurface layer; specifically, step (1) is, for example, providing three FR4 substrates as an upper substrate layer, an intermediate substrate layer, and a lower substrate layer respectively, forming multiple periodically arranged square annular carbon black film regions on the upper substrate layer, the intermediate substrate layer, and the lower substrate layer by screen printing process, and then trimming the edges by laser etching to obtain an upper resonant layer, an intermediate resonant layer, and a lower resonant layer respectively; the upper resonant layer and the upper substrate layer constitute an upper metasurface layer, the intermediate resonant layer and the intermediate substrate layer constitute an intermediate metasurface layer, and the lower resonant layer and the lower substrate layer constitute a lower metasurface layer; in this invention, a carbon black film with a preset square annular pattern and a preset surface sheet resistance is formed on the FR4 base plate by screen printing process; this invention does not specifically limit the screen printing process, and those skilled in the art can choose conventionally; (2) Laser drilling is performed at the preset positions of the upper metasurface layer, the middle metasurface layer, the lower metasurface layer and the metal base plate to form multiple fixing holes with one-to-one correspondence. (3) Provide multiple nylon gaskets, each of which has through holes; (4) Stack the layers in the following order from top to bottom: upper metasurface layer, multiple nylon gaskets, middle metasurface layer, multiple nylon gaskets, lower metasurface layer, multiple nylon gaskets, and metal base plate, so that each through hole is aligned with each fixing hole, and that the through holes of each nylon gasket are aligned with the positions of the fixing holes in each metasurface layer and the metal base plate, to obtain the stacked body; (5) Pass the nylon fasteners through the corresponding fixing holes and through holes of each layer of the stack and lock them in sequence, so that each nylon gasket is pressed between two adjacent layers to form an upper air medium layer, a middle air medium layer and a lower air medium layer, thus obtaining an ultra-wideband high-performance absorbing structure based on air medium.

[0035] The method of this invention can achieve high-precision mass production of the resonant layer through a combination of screen printing and laser trimming. It replaces the traditional adhesive film lamination with nylon mechanical fixing, eliminating the need for high-loss materials that affect absorption performance, such as adhesive film and dielectric plate. The molding method is simpler, requiring no complicated curing process, and the assembly is simple and quick, making it suitable for large-scale production.

[0036] According to some preferred embodiments, the positions of the nylon gaskets correspond one-to-one with the fixing holes; the thickness of each nylon gasket located between the upper metasurface layer and the intermediate metasurface layer corresponds to the thickness of the upper air medium layer, that is, the thickness of each nylon gasket located between the upper metasurface layer and the intermediate metasurface layer is equal and corresponds to the thickness of the upper air medium layer; the thickness of each nylon gasket located between the intermediate metasurface layer and the lower metasurface layer corresponds to the thickness of the intermediate air medium layer, that is, the thickness of each nylon gasket located between the intermediate metasurface layer and the lower metasurface layer is equal and corresponds to the thickness of the intermediate air medium layer; the thickness of each nylon gasket located between the lower metasurface layer and the metal base plate corresponds to the thickness of the lower air medium layer, that is, the thickness of each nylon gasket located between the lower metasurface layer and the metal base plate is equal and corresponds to the thickness of the lower air medium layer.

[0037] The present invention will be further described below by way of examples, but the scope of protection of the present invention is not limited to these embodiments. The present invention may have many other embodiments, and those skilled in the art can make various corresponding changes and modifications based on the present invention without departing from its spirit and essence. However, all such corresponding changes and modifications should fall within the scope of protection of the appended claims. Unless otherwise specified, the experimental methods used in the following embodiments and comparative examples are conventional methods. Unless otherwise specified, the materials used in the following embodiments and comparative examples are commercially available.

[0038] Example 1 This embodiment provides an ultra-wideband high-performance microwave absorbing structure based on air medium and its fabrication method, such as... Figure 1As shown, from top to bottom, it includes: an upper metasurface layer: including an upper resonant layer and an upper substrate layer, the upper substrate layer using an FR4 substrate with a thickness of 0.2 mm; an upper air dielectric layer with a thickness of 0.9 mm; an intermediate metasurface layer: including an intermediate resonant layer and an intermediate substrate layer, the intermediate substrate layer using an FR4 substrate with a thickness of 0.2 mm; an intermediate air dielectric layer with a thickness of 1.1 mm; a lower metasurface layer: including a lower resonant layer and a lower substrate layer, the lower substrate layer using an FR4 substrate with a thickness of 0.2 mm; a lower air dielectric layer with a thickness of 1.7 mm; and a metal base plate, made of aluminum with a thickness of 0.2 mm. The upper, middle, and lower metasurface layers, as well as the metal base plate, are each provided with a plurality of corresponding fixing holes. Specifically, each of the upper, middle, and lower metasurface layers, as well as the metal base plate, has twelve M5-sized fixing holes, which are evenly distributed around the perimeter of the upper, middle, and lower metasurface layers and the metal base plate. The upper, middle, and lower air medium layers are each supported by a plurality of nylon gaskets, each corresponding to a fixing hole. Each nylon gasket has a through hole for nylon fasteners to pass through. The upper, middle, and lower metasurface layers, the metal base plate, and the nylon gaskets are connected by nylon fasteners passing through the fixing holes and the through holes. The upper, middle, and lower resonant layers each comprise multiple periodically arranged basic units. Each basic unit is a square annular carbon black film region (10 μm thick). These basic units are arranged in an array with the same period P in both the x and y directions, with a period P of 9 mm. Specifically, the outer side length of the square annular carbon black film region in the upper resonant layer is 4.8 mm, the ring width is 0.3 mm, and the sheet resistance of the carbon black film is 120 Ω / sq. The outer side length of the square annular carbon black film region in the middle resonant layer is 6.5 mm, the ring width is 1.1 mm, and the sheet resistance of the carbon black film is 80 Ω / sq. The outer side length of the square annular carbon black film region in the lower resonant layer is 8.8 mm, the ring width is 2.2 mm, and the sheet resistance of the carbon black film is 150 Ω / sq.

[0039] The fabrication method of the ultra-wideband high-performance absorbing structure based on air medium described in this embodiment includes the following steps: (1) Three FR4 substrates are provided as the upper substrate layer, the middle substrate layer and the lower substrate layer respectively. Multiple periodically arranged square annular carbon black film regions are formed on the upper substrate layer, the middle substrate layer and the lower substrate layer by screen printing process. After laser trimming, the upper resonant layer, the middle resonant layer and the lower resonant layer are obtained respectively. The upper resonant layer and the upper substrate layer constitute the upper metasurface layer, the middle resonant layer and the middle substrate layer constitute the middle metasurface layer, and the lower resonant layer and the lower substrate layer constitute the lower metasurface layer. (2) Laser drilling is performed at the preset positions of the upper metasurface layer, the middle metasurface layer, the lower metasurface layer and the metal base plate to form M5-sized fixing holes with one-to-one correspondence. The fixing holes are evenly distributed around the surface of the upper metasurface layer, the middle metasurface layer, the lower metasurface layer and the metal base plate. (3) Provide multiple (12) nylon gaskets with a thickness of 0.9mm, multiple (12) nylon gaskets with a thickness of 1.1mm and multiple (12) nylon gaskets with a thickness of 1.7mm, respectively corresponding to the preset thickness of the upper air medium layer, the middle air medium layer and the lower air medium layer, and each nylon gasket is provided with a through hole; (4) Stack the layers in the following order from top to bottom: upper metasurface layer, multiple nylon pads with a thickness of 0.9 mm, middle metasurface layer, multiple nylon pads with a thickness of 1.1 mm, lower metasurface layer, multiple nylon pads with a thickness of 1.7 mm, and metal base plate, aligning each through hole with each fixing hole to obtain a stacked body. (5) Pass the nylon fasteners through the corresponding fixing holes and through holes of each layer of the stack and lock them in sequence, so that each nylon gasket is pressed between two adjacent layers to form an upper air medium layer, a middle air medium layer and a lower air medium layer, thus obtaining an ultra-wideband high-performance absorbing structure based on air medium.

[0040] The electrical performance of the absorbing structure in this embodiment is calculated; when an electromagnetic wave signal is incident perpendicularly from the upper resonant layer onto the metal base plate, the electromagnetic reflection characteristics of the absorbing structure are calculated, such as... Figure 6 and Figure 7 The reflection coefficient curves of the absorbing structure in this embodiment are given for both horizontal and vertical polarization states. Figure 6 and Figure 7 As can be seen, the structure exhibits excellent ultra-wideband absorption performance under both polarization conditions, indicating that the structure is insensitive to electromagnetic wave polarization angles. This suggests that the symmetrical design of the resonant layer pattern in this embodiment enables the absorption structure to possess electromagnetic wave polarization angle insensitivity. Figure 6 and Figure 7As can be seen from the dashed line, the reflection coefficient of the structure proposed in this invention is ≤-15dB in the range of 12.8GHz to 40GHz, and the absorption bandwidth is as high as 27.2GHz. This shows that the absorbing structure of this invention achieves high bandwidth and high performance absorption under the conditions of small thickness and simple molding scheme.

[0041] Comparative Example 1 Comparative Example 1 is essentially the same as Example 1, except that the dimensions of the square annular basic unit, the sheet resistance, and the thickness of the air dielectric layer in each resonant layer are different from those in Example 1. In this comparative example, the outer side length of the square annular carbon black film region in the upper resonant layer is 5.5 mm, the width of the square ring is 0.6 mm, and the surface sheet resistance of the carbon black film is 150 Ω / sq; the outer side length of the square annular carbon black film region in the middle resonant layer is 6.0 mm, the width of the square ring is 1.5 mm, and the surface sheet resistance of the carbon black film is 120 Ω / sq; the outer side length of the square annular carbon black film region in the lower resonant layer is 7.5 mm, the width of the square ring is 2.8 mm, and the surface sheet resistance of the carbon black film is 180 Ω / sq. The thickness of the upper air dielectric layer is 0.9 mm, the thickness of the middle air dielectric layer is 1.1 mm, and the thickness of the lower air dielectric layer is 1.3 mm.

[0042] The electrical performance of the absorbing structure in this comparative example was calculated under the same conditions as in Example 1. The results show that the absorbing structure in this comparative example exhibits a reflection peak with a reflection coefficient higher than -15dB, achieving dual-band broadband absorption with absorption bandwidths of 9.4GHz and 8.4GHz, respectively, breaking the record for ultra-wideband absorption performance.

[0043] Comparative Example 2 Comparative Example 2 is basically the same as Example 1, except that the size and sheet resistance of the square annular substrate unit of each resonant layer are different from those of Example 1. That is, in this comparative example, the outer side length of the square annular carbon black film region of the upper resonant layer, the middle resonant layer and the lower resonant layer is 7.0 mm, the width of the square ring is 1.1 mm, and the sheet resistance is 80 Ω / sq.

[0044] The electrical performance of the absorbing structure in this comparative example was calculated under the same conditions as in Example 1. The results show that the effective absorption bandwidth of the absorbing structure in this comparative example, with a reflection coefficient ≤ -15dB in the frequency range of 12.8GHz to 40GHz, is only 10.5GHz, and the absorption curve exhibits multiple sharp reflection peaks, failing to form continuous broadband coverage. Compared with Example 1, the absorption bandwidth of Comparative Examples 1 and 2 is significantly narrowed. This indicates that optimizing the combination of the area size of each layer of square annular carbon black film, the surface sheet resistance, and the thickness of the air dielectric layer are key to achieving multi-level resonant coupling and impedance matching of electromagnetic waves in a wide frequency band, enabling this invention to achieve a wider absorption bandwidth and stronger absorption performance with a thinner thickness.

[0045] Comparative Example 3 This comparative example provides a microwave absorbing structure using adhesive film bonding, which is basically the same as that in Example 1, except that: the layers are fixed together by adhesive film bonding, and a solid dielectric layer is provided instead of an air dielectric layer; in this comparative example, the upper metasurface layer is bonded to the middle metasurface layer, the middle metasurface layer is bonded to the lower metasurface layer, and the lower metasurface layer is bonded to the metal base plate by adhesive film layers with a thickness of 0.1 mm, and polymethyl methacrylate (PMI) foam board is used as the dielectric layer instead of the original air dielectric layer, with the thicknesses of the three dielectric layers being 0.9 mm, 1.1 mm, and 1.7 mm, respectively. The square ring size, sheet resistance, and basic unit arrangement period of each resonant layer are the same as in Example 1. This microwave absorbing structure is prepared using a conventional lamination process, and the layers are bonded together by adhesive film bonding and then hot-pressed and cured.

[0046] The electrical performance of the absorbing structure in this comparative example was calculated under the same conditions as in Example 1. The results show that the effective absorption bandwidth of the absorbing structure in this comparative example with a reflection coefficient ≤ -15dB in the frequency range of 12.8GHz to 40GHz is only 14.5GHz, and the lowest reflection coefficient is only -23.4dB.

[0047] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-performance, ultra-wideband microwave absorbing structure based on air medium, characterized in that, From top to bottom, they include: The upper metasurface layer includes an upper resonant layer and an upper substrate layer; Upper air medium layer; The intermediate metasurface layer includes an intermediate resonant layer and an intermediate substrate layer; Intermediate air medium layer; The lower metasurface layer includes the lower resonant layer and the lower substrate layer; Lower air medium layer; Metal base plate; The upper metasurface layer, the middle metasurface layer, the lower metasurface layer, and the metal base plate are provided with multiple fixing holes with corresponding positions. The upper air medium layer, the middle air medium layer and the lower air medium layer are each supported by a plurality of nylon gaskets. Each nylon gasket corresponds to a fixing hole, and each nylon gasket is provided with a through hole for nylon fasteners to pass through. The upper metasurface layer, the middle metasurface layer, the lower metasurface layer, the metal base plate, and each nylon gasket are connected by nylon fasteners passing through the fixing holes and the through holes.

2. The ultra-wideband high-performance absorbing structure according to claim 1, characterized in that: The upper metasurface layer, the middle metasurface layer, the lower metasurface layer, and the metal base plate are all uniformly provided with the fixing holes around their perimeter.

3. The ultra-wideband high-performance absorbing structure according to claim 1, characterized in that: The upper substrate, middle substrate, and lower substrate are FR4 substrates.

4. The ultra-wideband high-performance absorbing structure according to claim 1, characterized in that: The upper resonant layer, the middle resonant layer, and the lower resonant layer each include a plurality of periodically arranged basic units. The basic unit is a square annular carbon black film region, and the plurality of basic units are arranged in an array with the same arrangement period in the x and y directions.

5. The ultra-wideband high-performance absorbing structure according to claim 3, characterized in that: The outer side length of the square annular carbon black film region in the upper resonant layer is 4.5~5.1mm, the width of the square ring is 0.2~0.5mm, and the surface sheet resistance of the carbon black film is 110~140Ω / sq. The outer side length of the square annular carbon black film region in the intermediate resonant layer is 6.5~7.3mm, the width of the square ring is 0.8~1.3mm, and the surface sheet resistance of the carbon black film is 70~100Ω / sq; The outer side length of the square annular carbon black film region of the lower resonant layer is 8.5~8.9mm, the width of the square ring is 2.0~2.5mm, and the surface sheet resistance of the carbon black film is 140~170Ω / sq.

6. The ultra-wideband high-performance absorbing structure according to claim 1, characterized in that: The thickness of the upper air medium layer is 0.7~1.2mm, the thickness of the middle air medium layer is 0.7~1.2mm, and the thickness of the lower air medium layer is 1.5~2.0mm.

7. The ultra-wideband high-performance absorbing structure according to claim 1, characterized in that: The fixing holes are twelve M5 specification holes; and / or The nylon fasteners include nylon bolts and nylon nuts.

8. The method for fabricating an ultra-wideband high-performance absorbing structure based on air medium according to any one of claims 1 to 7, characterized in that, The method includes the following steps: (1) Prepare the upper metasurface layer, the middle metasurface layer and the lower metasurface layer; (2) Laser drilling is performed at the preset positions of the upper metasurface layer, the middle metasurface layer, the lower metasurface layer and the metal base plate to form multiple fixing holes with one-to-one correspondence. (3) Provide multiple nylon gaskets, each of which has through holes; (4) Stack the layers in the following order from top to bottom: upper metasurface layer, multiple nylon gaskets, middle metasurface layer, multiple nylon gaskets, lower metasurface layer, multiple nylon gaskets, and metal base plate, aligning each through hole with each fixing hole to obtain a stacked body; (5) Pass the nylon fasteners through the corresponding fixing holes and through holes of each layer of the stack and lock them in sequence, so that each nylon gasket is pressed between two adjacent layers to form an upper air medium layer, a middle air medium layer and a lower air medium layer, thus obtaining an ultra-wideband high-performance absorbing structure based on air medium.

9. The preparation method according to claim 8, characterized in that, Step (1) is as follows: Three FR4 substrates are provided as the upper substrate, middle substrate and lower substrate respectively. Multiple periodically arranged square annular carbon black film regions are formed on the upper substrate, middle substrate and lower substrate by screen printing process. After laser trimming, the upper resonant layer, middle resonant layer and lower resonant layer are obtained respectively. The upper resonant layer and the upper substrate layer constitute an upper metasurface layer, the middle resonant layer and the middle substrate layer constitute an middle metasurface layer, and the lower resonant layer and the lower substrate layer constitute a lower metasurface layer.

10. The preparation method according to claim 8, characterized in that: The position of the nylon gasket corresponds one-to-one with the fixing hole; and / or The thickness of each nylon gasket located between the upper metasurface layer and the intermediate metasurface layer corresponds to the thickness of the upper air medium layer; the thickness of each nylon gasket located between the intermediate metasurface layer and the lower metasurface layer corresponds to the thickness of the intermediate air medium layer; and the thickness of each nylon gasket located between the lower metasurface layer and the metal base plate corresponds to the thickness of the lower air medium layer.

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