Three-dimensional water-based frequency selective absorber with switchable electromagnetic properties

Abstract

The application discloses a three-dimensional water-based frequency selective absorber with switchable electromagnetic properties, comprising a plurality of symmetrically designed three-dimensional gradient structure medium square waveguide frequency selective surface unit structures and periodic water-based metamaterial absorber units; the three-dimensional gradient structure medium square waveguide frequency selective surface unit structure has wideband transmission performance with high frequency selectivity; the periodic water-based metamaterial absorber unit is encapsulated around the frequency selective surface unit structure and has super wideband absorption performance; three transmission poles and two transmission zeros are generated in the three-dimensional gradient structure medium square waveguide frequency selective surface unit structure through cascading three metal square rings in an up-down mode, so that a high-frequency-selectivity wideband three-dimensional frequency selective surface is realized; the transmission out-of-band absorption and the conversion of reflection electromagnetic characteristics are realized by controlling the on-off of water in the periodic water-based metamaterial absorber unit. The application expands the transmission bandwidth, has wide absorption frequency band and high absorption rate, and can realize dual polarization.

Description

Technical Field

[0001] This invention belongs to the field of broadband absorbing frequency selective technology, specifically relating to a three-dimensional water-based frequency selective absorber with convertible electromagnetic properties. Background Technology

[0002] Stealth technology, also known as low observable technology (LOT), is a technology that uses a combination of various technical means to change the detectability signal characteristics of a target object in multiple frequency bands such as electromagnetic, sound waves, and thermal energy, including radar, infrared, laser, visible light, and sound, thereby reducing the probability of the target object being detected, identified, tracked, and attacked.

[0003] Currently, electromagnetic stealth of shipborne platforms is generally achieved by reducing the radar cross section (RCS), mainly through two methods: 1) Shape stealth, which involves designing a unique structural shape so that the electromagnetic waves reflected by the target do not return along the incident wave path, thereby reducing the target's single-station RCS. 2) Material stealth, which involves coating the surface of the weapon platform with high-loss absorbing materials, so that the incident electromagnetic waves are converted into heat, thereby reducing the RCS. For example, stealth ship structures adopt high-performance small waterplane area catamaran designs, with the upper surface composed of multiple trapezoidal or rectangular planes, and the ship is also coated with a radar-absorbing coating. The bridge adopts stealth measures such as a pointed bow, a flat superstructure, and a reduced freeboard. As an important piece of equipment in shipborne platforms, the antenna's RCS is a significant part of the ship's electromagnetic scattering. Effectively reducing the antenna's RCS without affecting its normal operation is particularly crucial.

[0004] A frequency selective surface (FSS) is a spatially filtered periodic structure that possesses the characteristics of reflecting electromagnetic waves out of band and transmitting electromagnetic waves with low differential loss within band. This allows it to reflect incoming waves from outside the band to other paths while ensuring normal communication for friendly antennas. Given these characteristics, FSS has become the mainstream technology in the field of electromagnetic stealth radome design. However, the reduction of radar RCS by FSS stealth radomes comes at the cost of increasing RCS in other directions. While it can achieve electromagnetic stealth under single-base radar detection, its single-base stealth capability becomes meaningless with the development of multi-base radar technology. Therefore, there is an urgent need to adopt new technical solutions to achieve "omnidirectional" electromagnetic stealth.

[0005] A frequency selective absorber (FSR) is a composite structure combining an electromagnetic oscillator (FSS) and an absorber. It enables low-loss transmission of electromagnetic waves within the transmission band, while absorbing rather than reflecting electromagnetic waves outside the band. Stealth radomes constructed from FSRs not only ensure normal signal transmission within the operating frequency band but also reduce electromagnetic scattering "omnidirectionally." In short, FSRs possess electromagnetic characteristics of out-of-band absorption and in-band transmission. FSRs represent a new direction and mechanism in antenna stealth technology research and are an important research topic for next-generation omnidirectional stealth radomes, significantly contributing to further improvements in stealth performance. In recent years, liquid media materials, represented by water, have gradually attracted attention, and their applications in antennas, electromagnetic metamaterial absorbers, and electromagnetic metasurfaces have been reported. Water-based metamaterial frequency selective absorbers are a technical solution that introduces the concept of water into FSR design. Compared with traditional solid-state FSRs, water-based FSRs possess certain unique advantages. 1) Water naturally possesses strong dispersion and high loss electromagnetic properties. By rationally designing and optimizing the structural parameters of water-based metamaterials, impedance matching with free space can be achieved over a wide frequency band, thereby meeting the requirements of the out-of-band absorption bandwidth of FSR without the need for additional lumped resistance; 2) Water has strong plasticity. By introducing new metamaterial resonant structures into the water-based metamaterial unit structure, the transmission frequency band can be broadened; 3) As one of the most common liquids in nature, water is transparent and environmentally friendly. With the relatively mature 3D printing technology, water encapsulation is relatively easy, reducing the processing difficulty of devices; 4) Water is inexpensive, which can significantly reduce the processing cost of devices; 5) Water has fluidity. By controlling the physical parameters such as the volume and shape of water, the electromagnetic performance of FSR can be reconstructed.

[0006] In conclusion, water-based metamaterial frequency selective absorbers, as a novel concept of FSR, have great development potential and can provide new ideas for the development of next-generation shipborne stealth radomes.

[0007] However, several technical challenges remain to be addressed in the reported water-based FSR designs. Water is a high-loss electromagnetic material, and FSRs need to establish independent transmission channels through it. However, most reported designs employ parallel-plate waveguide structures with internally loaded inductors to construct these transmission channels. This design introduces several problems: 1) limited transmission bandwidth; 2) severing the connection between water elements, resulting in limited absorption bandwidth and intensity; and 3) difficulty in achieving dual polarization. These issues limit the application of water-based FSRs in the field of low RCS stealth radomes. Summary of the Invention

[0008] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a three-dimensional water-based frequency selective absorber with convertible electromagnetic properties. By combining a three-dimensional periodic water-based metamaterial absorber with a three-dimensional gradient structure dielectric square waveguide frequency selective surface, a novel frequency selective absorber with mid-frequency wideband low insertion loss transmission and high-frequency and low-frequency wideband absorption is designed. By controlling the on / off state of the water, the conversion between broadband absorption and reflection characteristics outside the mid-frequency transmission band can be achieved, thus expanding the transmission bandwidth. The absorption bandwidth is wide and the absorption rate is high, and dual polarization can be realized.

[0009] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0010] A three-dimensional water-based frequency selective absorber with convertible electromagnetic properties includes several three-dimensional gradient structure dielectric square waveguide frequency selective surface unit structures with symmetrical design and periodic water-based metamaterial absorber units.

[0011] The three-dimensional gradient structure dielectric square waveguide frequency selective surface unit structure has high frequency selectivity broadband transmission performance.

[0012] The periodic water-based metamaterial absorber unit is encapsulated around the frequency-selective surface unit structure and has ultra-wideband absorption performance.

[0013] The three-dimensional gradient structure dielectric square waveguide frequency selective surface unit structure generates three transmission poles and two transmission zeros by cascading three metal square rings, thereby realizing a high frequency selective broadband bandpass three-dimensional frequency selective surface.

[0014] By controlling the flow of water in a periodic water-based metamaterial absorber unit, the conversion between absorption and reflection electromagnetic properties outside the transmission band can be achieved.

[0015] To optimize the above technical solution, the specific measures also include:

[0016] The aforementioned three-dimensional gradient structure dielectric square waveguide frequency selective surface unit structure is divided into three interconnected segments: upper, middle, and lower. The upper segment is a square dielectric pillar made of 3D printed resin material. The middle and lower segments are filled with 3D printed resin material and have metal-plated sidewalls to form a dielectric waveguide structure. The middle segment is a dielectric square waveguide structure with the same lateral dimension as the square dielectric pillar in the upper segment, and metal square rings of the same size are plated on the upper and lower surfaces respectively. The lower segment is a linearly gradient structure dielectric square waveguide with its lateral dimension increasing linearly in the longitudinal direction, giving it an overall square horn shape. A single-layer dielectric substrate is located below the linearly gradient structure dielectric square waveguide, and a metal square ring is plated on the back of the substrate.

[0017] The dimensions of the aforementioned single-layer dielectric substrate are slightly larger than the lower surface of the linearly graded dielectric square waveguide.

[0018] The aforementioned periodic water-based metamaterial absorber unit is encapsulated around the frequency selective surface unit structure of the three-dimensional gradient structure dielectric square waveguide using 3D-printed photosensitive resin material.

[0019] The aforementioned periodic water-based metamaterial absorber unit includes a lower water-based structure and an upper water-based structure encapsulated with 3D-printed resin material. The lower water-based structure fills the gaps between adjacent frequency-selective surface units, and its height is the same as the height of the lower linearly gradient structure dielectric square waveguide. The upper water-based structure consists of periodically arranged square water column units, which are located diagonally opposite to the frequency-selective surface unit structure. The water column units are connected to the lower water-based structure.

[0020] The sidewalls of each of the aforementioned upper water column units are plated with metal.

[0021] The above-mentioned conversion of electromagnetic properties of absorption and reflection outside the transmission band is achieved by controlling the on / off state of water in the periodic water-based metamaterial absorber unit. Specifically, when water is filled, the three-dimensional water-based frequency selective absorber exhibits electromagnetic properties of broadband low-loss transmission in the mid-frequency band and broadband absorption in the high and low frequency bands; when the water is drained, the three-dimensional water-based frequency selective absorber exhibits electromagnetic properties of broadband low-loss transmission in the mid-frequency band and broadband reflection in the high and low frequency bands.

[0022] The present invention has the following beneficial effects:

[0023] This invention relates to a dual-polarized three-dimensional water-based metamaterial frequency selective absorber with convertible electromagnetic properties, comprising a three-dimensional gradient-structured dielectric square waveguide frequency selective surface and a periodic water-based metamaterial absorber. A broadband bandpass three-dimensional frequency selective surface is achieved by cascading metal square rings within the three-dimensional gradient-structured dielectric square waveguide. Water is filled into the gaps between adjacent three-dimensional frequency selective surface units, and square water columns are loaded at diagonal positions of the frequency selective surface units, encapsulated with 3D-printed material to form a periodic water-based metamaterial absorber. This invention introduces the concept of water into FSR design. By controlling the flow of water, this invention achieves the conversion between ultra-wideband absorption and reflection characteristics outside the transmission band. By loading metal around the square water columns, the absorption and transmission paths are further isolated, reducing the difference loss within the passband and achieving low-loss broadband transmission. Simultaneously, due to the symmetrical design of the unit structure, dual polarization can be achieved. This invention has broad application prospects in the field of shipborne low RCS stealth radomes.

[0024] This invention achieves a novel FSR structure design that combines mid-frequency broadband transmission and high- and low-frequency broadband absorption through the unit structure design of three-dimensional water-based metamaterials. This FSR exhibits dual-polarization low reflection (S... 11The -10dB band is 3.7GHz to 18GHz, with a relative bandwidth of 132%, achieving absorption performance with an absorption rate greater than 90% in the 3.7GHz to 8.7GHz (FBW: 64.5%) and 14.4GHz to 18GHz (FBW: 22.2%) bands. This invention possesses high-selectivity, wideband, and low-insertion-loss transmission performance, with a -3dB transmission window band of 9.2GHz to 14GHz and a relative bandwidth of 41.4%, which is superior to most reported FSR structures. Furthermore, this invention utilizes a three-dimensional gradient structure frequency-selective surface design to achieve interconnection between water-based unit structures, solving the technical challenge of achieving dual polarization in mid-frequency transmission and high / low-frequency absorption water-based metamaterial FSRs. This invention fully utilizes the fluidity of water, controlling the on / off state of the water to achieve electromagnetic switching between the absorption and reflection bands, exhibiting excellent reconfigurability. In summary, the electromagnetic performance of this invention surpasses currently reported related designs, providing a new approach to the design of frequency-selective absorbers and possessing high application value in the field of shipborne antenna stealth. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the 3×3 unit structure of the present invention;

[0026] Figure 2 This is a schematic diagram of the unit structure of the present invention;

[0027] Figure 3 This is a three-dimensional schematic diagram of the three-dimensional gradient structure dielectric waveguide FSS unit of the present invention;

[0028] Figure 4 This is a layered structure diagram of the three-dimensional gradient structure dielectric waveguide FSS unit of the present invention;

[0029] Figure 5 This is a unit structure diagram of the present invention after removing the upper 3D printing resin material;

[0030] Figure 6 This is the S-parameter curve of the three-dimensional gradient structure dielectric waveguide FSS of the present invention under the condition of normal incidence of TE(TM) wave;

[0031] Figure 7 This is the S-parameter curve of the 3D FSR under water injection conditions when the TE(TM) wave is normally incident.

[0032] Figure 8 This is the S-parameter curve of the 3D FSR when the TE(TM) wave is normally incident under the water drainage condition of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] Although the steps in this invention are arranged by reference numerals, this is not intended to limit the order of the steps. Unless the order of the steps is explicitly stated or the execution of a step requires other steps as a basis, the relative order of the steps can be adjusted. It is understood that the term "and / or" as used herein refers to and covers any and all possible combinations of one or more of the associated listed items.

[0035] This invention relates to a dual-polarized three-dimensional water-based metamaterial frequency-selective absorber with convertible electromagnetic properties. The frequency-selective surface of the three-dimensional gradient-structured dielectric square waveguide and the three-dimensional periodic water-based metamaterial absorber work together to achieve low insertion loss broadband transmission in the mid-frequency band and broadband absorption in the high and low frequency bands. By controlling the flow of water, allowing it to be in a filled or drained state, the electromagnetic characteristics of the frequency-selective absorber can be switched between broadband absorption and broadband reflection outside the transmission band. Furthermore, by employing a symmetrical unit structure design, the frequency-selective absorber achieves electromagnetic properties that are insensitive to the polarization of the incident wave.

[0036] like Figure 1-5 As shown, the frequency selective absorber of the present invention specifically includes a three-dimensional gradient structure dielectric square waveguide frequency selective surface and a three-dimensional periodic water-based metamaterial absorber.

[0037] The frequency selective surface of the three-dimensional gradient structure dielectric square waveguide has high frequency selectivity and broadband transmission performance.

[0038] The periodic water-based metamaterial absorber unit is located around the frequency selective surface unit of the three-dimensional gradient structure dielectric square waveguide and is encapsulated with 3D printed photosensitive resin material, exhibiting ultra-wideband absorption performance. The frequency selective surface and the water-based metamaterial absorber work together to form electromagnetic properties of mid-frequency broadband low-loss transmission and high- and low-frequency broadband absorption.

[0039] The frequency selective surface unit structure is divided into three interconnected sections: an upper section consisting of a square dielectric pillar, a middle section consisting of a dielectric square waveguide structure, and a lower section consisting of a square horn-shaped linearly tapered dielectric square waveguide structure.

[0040] The upper section is a square dielectric pillar made of 3D printed resin material; the middle and lower sections have metal-plated sidewalls and are filled with the same 3D printed resin material to form a dielectric waveguide structure; the middle section is a dielectric square waveguide structure with the same lateral dimension as the upper dielectric pillar, and its upper and lower surfaces are plated with metal square ring structures of the same size; the lower section is a linearly gradient dielectric square waveguide with the lateral dimension increasing linearly in the longitudinal direction, and the whole is square horn-shaped; below the gradient dielectric waveguide is a single-layer dielectric substrate, and the back of the substrate is also plated with an array of metal square ring structures. The substrate unit size is slightly larger than the lower surface of the upper gradient waveguide.

[0041] The three-dimensional periodic water-based metamaterial absorber unit is located around the frequency selective surface unit. It adopts a two-layer structure. The lower water-based structure fills the gaps between adjacent units of the frequency selective surface of the three-dimensional gradient structured dielectric square waveguide, and its height is the same as that of the lower linear gradient structured dielectric square waveguide. The upper water-based structure consists of periodically arranged square water columns, with the water column units located at the diagonal positions of the frequency selective surface unit. The water columns are connected to the lower water structure below, and the sidewalls of each water column unit are plated with metal, thereby achieving further isolation between the absorption path and the transmission path and reducing the difference loss in the transmission band. The two water-based structures are also encapsulated with the same 3D printed resin material as the frequency selective surface unit.

[0042] The three-dimensional gradient-structured dielectric square waveguide frequency-selective surface and the three-dimensional periodic water-based metamaterial absorber work together to achieve electromagnetic properties with low insertion loss broadband transmission in the mid-frequency band and broadband absorption in the high and low frequency bands. Furthermore, by controlling the flow of water, allowing it to be in both filled and drained states, the frequency-selective absorber can switch between broadband absorption and broadband reflection outside the transmission band. Simultaneously, by employing a symmetrical unit structure design, the frequency-selective absorber achieves electromagnetic properties that are insensitive to incident wave polarization.

[0043] When water fills the area around the frequency-selective surface unit and forms periodic water columns, the frequency-selective absorber exhibits electromagnetic characteristics of broadband low-loss transmission in the mid-frequency band and broadband absorption in the high and low frequency bands. When the water is drained, the frequency-selective absorber exhibits electromagnetic characteristics of broadband low-loss transmission in the mid-frequency band and broadband reflection in the high and low frequency bands. That is, by controlling the flow of water, the conversion between out-of-band absorption and reflection electromagnetic characteristics can be achieved.

[0044] When electromagnetic waves are incident on the selective absorber, they interact with the three-dimensional periodic water-based metamaterial absorber layer and the three-dimensional frequency selective surface layer, respectively. Since the insertion loss of the three-dimensional periodic water-based metamaterial absorber layer and the three-dimensional frequency selective surface layer in the transmission band is very small, electromagnetic waves in the mid-frequency transmission band can be transmitted with minimal insertion loss. Electromagnetic waves in the high-frequency and low-frequency absorption bands will be absorbed by the water material of the three-dimensional periodic water-based metamaterial absorber layer, achieving broadband absorption.

[0045] The mid-frequency broadband transmission window is formed by the combined action of a three-dimensional periodic water-based metamaterial absorber layer and a three-dimensional frequency-selective surface layer, creating a low-insertion-loss, highly selective broadband transmission window. When electromagnetic waves are incident on the frequency-selective absorber, they interact with both the three-dimensional periodic water-based metamaterial absorber layer and the three-dimensional frequency-selective surface layer. In the unit structure of the three-dimensional periodic water-based metamaterial absorber layer, a water column design is used at the diagonally orthogonal position of the transmission square waveguide, which greatly reduces the insertion loss caused by water loss. By loading square PECs around the water column unit, the absorption path and transmission path are further isolated, allowing electromagnetic waves to pass through the absorbing layer with low insertion loss.

[0046] The low-frequency and high-frequency absorption bands are formed by the combined action of a three-dimensional periodic water-based metamaterial absorber layer and a three-dimensional frequency-selective surface layer. Within the unit structure, water is filled into the gaps between units created by gradient square waveguides, and square water columns are loaded at the four corners of the waveguides. The water is then covered with the same 3D-printed resin material, achieving a fusion of the absorption and transmission paths. This design scheme ensures connectivity between the water units, preventing them from being separated by PEC (polyethylene terephthalate), thus guaranteeing the structure's absorption bandwidth and intensity.

[0047] In the embodiments, Figure 1 and Figure 2 The diagram shows a 3×3 unit structure and a single unit three-dimensional structure of the present invention. The overall structure consists of two parts: a three-dimensional gradient structure dielectric square waveguide frequency selective surface and a periodic water-based metamaterial absorber. The upper layer of both parts is made of 3D printed resin material (ε). r =2.55, tanδ=0.001) covering, presenting a checkerboard-like periodic distribution when viewed from the outside. The height h of the unit in this invention is 19.5mm, and the period p is 15.5mm.

[0048] Figure 2 and Figure 3 The diagram shows the overall three-dimensional schematic diagram and layered structure diagram of the three-dimensional gradient structure dielectric waveguide FSS unit of the present invention. The upper section of the FSS unit structure is a square dielectric column made of the above-mentioned 3D printed resin material, with a height of h4 = 7mm and a side length of l2 = 8.5mm. The middle and lower sections are filled with the same 3D printed resin material, and the side walls are plated with metal. The metal patches are made of copper to form a dielectric waveguide structure.

[0049] The middle section is a dielectric square waveguide structure with the same lateral dimensions as the upper dielectric pillar, a height of h2 = 5.25 mm, and side lengths of the upper and lower surfaces l2 = 8.5 mm. The upper and lower surfaces are each plated with a metal square ring structure of the same size, with an outer side length l... p1 = 3.9mm, inner side length l p2=2.1mm;

[0050] The lower section is a linearly graded dielectric square waveguide, with its lateral dimensions increasing linearly in the longitudinal direction. It has an overall square horn shape with a height of h3 = 6.75 mm and a side length of l3 = 14.5 mm on the lower surface. Below the graded dielectric waveguide is a layer of 3D-printed resin material with a side length l1 = 15.5 mm and a thickness t = 0.25 mm, and a single-layer dielectric substrate with a side length l1 = 15.5 mm and a thickness t = 0.25 mm. The substrate is made of PTFE material (ε... r =2.1, tanδ=0.0002) is composed of a metal square ring structure array on the back side of the substrate, and the substrate unit size is slightly larger than the lower surface of the upper gradient waveguide.

[0051] Figure 5 The diagram shows the unit structure of the present invention after removing the upper 3D printing material. The periodic water-based metamaterial absorber unit is located around the frequency selective surface unit. The structure consists of two layers: the upper water-based structure comprises periodically arranged square water columns, each located diagonally opposite the frequency selective surface unit. Each water column has a side length g1 = 2.6 mm and a height h1 = 9.5 mm. The water columns are connected to the lower water structure, and each water column unit has a metal-plated sidewall. Each metal patch has a length g2 = 6.1 mm and a width g3 = 2.9 mm. The lower water-based structure fills the gaps between adjacent units on the frequency selective surface of the three-dimensional gradient structure dielectric square waveguide. Its side length is the same as the dielectric substrate, l1 = 15.5 mm, and its height is h3 = 6.75 mm, the same as the height of the lower linear gradient structure dielectric square waveguide. Both water-based structures are encapsulated with the same 3D printing resin material as the frequency selective surface unit.

[0052] Figure 6 The figure shows the S-parameter curves of the three-dimensional graded dielectric waveguide FSS in an embodiment of the present invention under the condition of normal incidence of TE(TM) waves. Figure 6 It can be seen that the three-dimensional FSS structure has a wide transmission window in the mid-frequency band and a steep out-of-band group edge, exhibiting high frequency selectivity. The -3dB band range is 9.0GHz to 14GHz, with a relative bandwidth of 43.4%. Due to the mutual coupling of the three cascaded metal square rings in the FSS unit structure, there are three transmission poles within the transmission band, located at 9.65GHz, 11.1GHz, and 13.0GHz, respectively. Simultaneously, the FSS exhibits strong reflection characteristics outside the transmission band, with two transmission zeros at 7.4GHz and 17.6GHz, enhancing the frequency selectivity of the FSS and laying the foundation for the subsequent integration of water-based metamaterial unit structures. Furthermore, its unit is symmetrically designed, achieving the aforementioned electromagnetic properties for both TE and TM incident polarized waves.

[0053] Figure 7 The figure shows the S-parameter curves of the three-dimensional FSR under the condition of normal incidence of TE wave in the water injection situation in an embodiment of the present invention. Figure 7 As can be seen, this invention possesses electromagnetic characteristics of broadband transmission in the mid-frequency band and broadband absorption in the high and low frequency bands. It exhibits low reflection characteristics (reflection coefficient S) in the 3.7GHz–18GHz frequency range. 11 <-10dB), with a relative bandwidth of 132%. It achieves absorption efficiency greater than 90% in the 3.7GHz–8.7GHz (FBW: 64.5%) and 14.4GHz–18GHz (FBW: 22.2%) frequency bands. The -3dB transmission frequency band is 9.2GHz–14GHz, with a relative bandwidth of 41.4%, which is comparable to the transmission bandwidth of the FSS without water-based metamaterials (e.g., <-10dB). Figure 6 The results are largely consistent with those shown. The device exhibits a minimum insertion loss of 0.95 dB at 12 GHz. Simultaneously, the symmetrical unit cell design ensures the device's polarization insensitivity.

[0054] Figure 8 The figure shows the S-parameter curves of the three-dimensional FSR under the condition of normal incidence of TE wave in the water drainage case of this embodiment of the invention. Figure 8 As can be seen, without water injection, the original absorption band of the absorber at this frequency selects to switch to a reflection band, but still maintains the transmission window in the mid-frequency range. Its reflection band (reflection coefficient S) 11 The -1dB transmission band covers the low-frequency range of 2GHz to 8.63GHz (FBW: 124.7%) and the high-frequency range of 14.27GHz to 18GHz (FBW: 23.1%). The -3dB transmission band ranges from 9GHz to 13.95GHz, with a relative bandwidth of 43.13%. The transmission bandwidth remains essentially consistent with that under water-filled conditions, maintaining the stability of the transmission window performance under both water-filled and non-water-filled conditions. The aforementioned electromagnetic performance can be achieved for both TE and TM incident polarized waves. In summary, this invention can achieve electromagnetic switching between the absorption and reflection bands, exhibiting excellent reconfigurability.

[0055] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0056] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A three-dimensional water-based frequency-selective absorber with convertible electromagnetic properties, characterized in that, It includes several three-dimensional gradient structure dielectric square waveguide frequency selective surface unit structures with symmetrical design and several periodic water-based metamaterial absorber units; The three-dimensional gradient structure dielectric square waveguide frequency selective surface unit structure has high frequency selectivity broadband transmission performance. The periodic water-based metamaterial absorber unit is encapsulated around the frequency-selective surface unit structure and has ultra-wideband absorption performance. The three-dimensional gradient structure dielectric square waveguide frequency selective surface unit structure generates three transmission poles and two transmission zeros by cascading three metal square rings, thereby realizing a high frequency selective broadband bandpass three-dimensional frequency selective surface. By controlling the flow of water in a periodic water-based metamaterial absorber unit, the conversion between absorption and reflection electromagnetic properties outside the transmission band can be achieved. The three-dimensional gradient structure dielectric square waveguide frequency selective surface unit structure is divided into three interconnected segments: upper, middle, and lower. The upper segment is a square dielectric pillar made of 3D printed resin material. The middle and lower segments are filled with 3D printed resin material and have metal-plated sidewalls to form a dielectric waveguide structure. The middle segment is a dielectric square waveguide structure with the same lateral dimension as the square dielectric pillar in the upper segment, and metal square rings of the same size are plated on the upper and lower surfaces respectively. The lower segment is a linearly gradient structure dielectric square waveguide with its lateral dimension increasing linearly in the longitudinal direction, forming a square horn shape. A single-layer dielectric substrate is provided below the linearly gradient structure dielectric square waveguide, and a metal square ring is plated on the back of the substrate. The periodic water-based metamaterial absorber unit includes a lower water-based structure and an upper water-based structure encapsulated with 3D-printed resin material. The lower water-based structure fills the gaps between adjacent frequency-selective surface units, and its height is the same as the height of the lower section of the linearly gradient structured dielectric square waveguide. The upper water-based structure consists of periodically arranged square water column units, which are located diagonally opposite to the frequency-selective surface unit structure. The water column units are connected to the lower water-based structure.

2. The electromagnetically convertible three-dimensional water-based frequency-selective absorber according to claim 1, characterized in that, The dimensions of the single-layer dielectric substrate are slightly larger than the lower surface of the linearly graded dielectric square waveguide.

3. The electromagnetically convertible three-dimensional water-based frequency-selective absorber according to claim 1, characterized in that, The periodic water-based metamaterial absorber unit is encapsulated around the frequency selective surface unit structure of the three-dimensional gradient structure dielectric square waveguide by 3D printing photosensitive resin material.

4. A three-dimensional water-based frequency-selective absorber with convertible electromagnetic properties according to claim 1, characterized in that, The sidewalls of each upper water column unit are plated with metal.

5. A three-dimensional water-based frequency-selective absorber with convertible electromagnetic properties according to claim 1, characterized in that, By controlling the flow of water in the periodic water-based metamaterial absorber unit, the conversion between absorption and reflection electromagnetic properties outside the transmission band is achieved. Specifically, when water is filled, the three-dimensional water-based frequency selective absorber exhibits electromagnetic properties of broadband low-loss transmission in the mid-frequency band and broadband absorption in the high and low frequency bands; when the water is drained, the three-dimensional water-based frequency selective absorber exhibits electromagnetic properties of broadband low-loss transmission in the mid-frequency band and broadband reflection in the high and low frequency bands.

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