Three-dimensional water-based frequency selective absorber with convertible electromagnetic performance

Abstract

The invention discloses a three-dimensional water-based frequency selective absorber with convertible electromagnetic performance. The three-dimensional water-based frequency selective absorber comprises a plurality of symmetrical three-dimensional gradient structure dielectric square waveguide frequency selective surface unit structures and periodic water-based metamaterial absorber units, the three-dimensional gradient structure dielectric square waveguide frequency selective surface unit structure has broadband transmission performance with high frequency selectivity. The periodic water-based metamaterial absorber unit is packaged around the frequency selective surface unit structure and has ultra-wideband absorption performance; three transmission poles and two transmission zero points are generated by cascading three metal square rings up and down in the three-dimensional gradient structure dielectric square waveguide frequency selective surface unit structure, so that a high-frequency-selectivity broadband band-pass three-dimensional frequency selective surface is realized; by controlling the on-off of water in the periodic water-based metamaterial absorber unit, the conversion of transmission band external absorption and reflection electromagnetic characteristics is realized. According to the invention, the transmission bandwidth is expanded, the absorption frequency band is wide, the absorption rate is high, and dual polarization can be realized.

Description

Technical Field

[0001] The invention belongs to the technical field of broadband wave-absorbing frequency selection, and in particular relates to a three-dimensional water-based frequency selective absorber with convertible electromagnetic properties. Background Art

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

[0003] At present, the electromagnetic stealth of shipborne platforms is generally achieved by reducing the Radar Cross Section (RCS), mainly by the following two methods: 1) Shape stealth, that is, by designing a unique structural shape, the electromagnetic waves reflected by the target do not return along the incident wave path, thereby reducing the single-station RCS of the target. 2) Material stealth, that is, by coating the surface of the weapon platform with high-loss absorbing materials, the incident electromagnetic waves are converted into heat, thereby reducing the RCS. For example, the stealth hull structure adopts a high-performance small waterplane catamaran design, and the upper body surface is closed by multiple trapezoidal or rectangular planes. At the same time, the ship is also covered with an absorbing coating. The bridge adopts stealth measures such as a pointed bow, a flat superstructure, and a reduced freeboard height. As an important device in the shipborne platform, the antenna's RCS is an important part of the electromagnetic scattering of the ship. Under the premise of not affecting the normal operation of the antenna, it is particularly critical to effectively reduce the antenna's RCS.

[0004] Frequency Selective Surface (FSS) is a spatial filtering periodic structure that has the characteristics of out-of-band reflected electromagnetic waves and in-band low-loss transmitted electromagnetic waves, so that the out-of-band opponent's incoming waves can be reflected to other paths while ensuring the normal communication of our antenna. In view of the above characteristics, FSS has become the mainstream technology in the field of electromagnetic stealth radome design today. However, the FSS stealth radome reduces the radar RCS at the expense of increasing the RCS in other directions. It can achieve electromagnetic stealth under single-base station radar detection, but with the development of multi-base station radar technology, its single-station stealth will lose its meaning. In view of the above background, it is urgent to adopt new technical solutions to achieve "omnidirectional" electromagnetic stealth.

[0005] Frequency Selective Rasorber (FSR) is a composite structure combining FSS and absorber. It can transmit electromagnetic waves with low loss within the transmission band, and absorb electromagnetic waves outside the band instead of reflecting them. The stealth radome formed by it can not only ensure the normal transmission of signals within the working frequency band, but also reduce the electromagnetic scattering of the antenna in an "omnidirectional" manner. In short, FSR has the electromagnetic characteristics of absorbing waves outside the band / transmitting waves within the band. FSR is a new direction and new mechanism in the field of antenna stealth technology research. It is an important research content of the new generation of omnidirectional stealth radomes and is of great significance for further improving stealth performance. In recent years, liquid dielectric materials represented by water have gradually attracted attention, and their applications in antennas, electromagnetic metamaterial absorbers, electromagnetic metasurfaces, etc. have also been reported one after another. Water-based metamaterial frequency selective absorber is a technical solution that introduces the concept of water into FSR design. Compared with traditional solid-state FSR, water-based FSR has certain special advantages. 1) Water naturally has 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 within a wide frequency band, thereby meeting the requirements of the FSR out-of-band absorption bandwidth without the need to load lumped resistance. 2) Water has strong plasticity. By introducing new metamaterial resonant structures into the water-based metamaterial unit structure, the transmission band can be widened. 3) Water is one of the most common liquids in nature. It is transparent and environmentally friendly. The currently mature 3D printing technology makes it relatively easy to encapsulate water, which can reduce the difficulty of device processing. 4) Water is inexpensive, which can greatly reduce the processing cost of devices. 5) Water has fluidity. The electromagnetic properties of FSR can be reconstructed by regulating the volume and shape of water and other physical parameters.

[0006] In summary, water-based metamaterial frequency selective absorber, as a new concept of FSR, has great development potential and can provide new ideas for the development of a new generation of shipborne stealth radomes.

[0007] However, there are still some technical problems to be solved in the reported water-based FSR designs. Water is a high electromagnetic loss material, and FSR needs to pass through water to establish an independent transmission channel. In the reported designs, parallel plate waveguide structures with internally loaded inductors are mostly used to construct transmission channels. The problems brought about by this design are: 1) limited transmission bandwidth; 2) the connection between water units is cut off, resulting in limited absorption bandwidth and absorption intensity; 3) it is difficult to achieve dual polarization. The above problems limit the application of water-based FSR in the field of low RCS stealth radomes. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a three-dimensional water-based frequency selective absorber with convertible electromagnetic properties in view of the deficiencies of the above-mentioned prior art. By combining a three-dimensional periodic water-based metamaterial absorber with a three-dimensional gradient structure dielectric square waveguide frequency selective surface, a new type of frequency selective absorber with wide-band low insertion loss transmission in the mid-frequency band and wide-band absorption in the high-frequency and low-frequency bands is designed. The conversion of broadband absorption and reflection characteristics outside the mid-frequency transmission band can be achieved by controlling the on-off of water, thereby expanding the transmission bandwidth, having a wide absorption bandwidth and a high absorption rate, and realizing dual polarization.

[0009] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0010] A three-dimensional water-based frequency selective absorber with switchable electromagnetic properties, comprising a plurality of three-dimensional gradient structure dielectric square waveguide frequency selective surface unit structures and periodic water-based metamaterial absorber units of symmetrical design;

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

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

[0013] In the three-dimensional gradient structure dielectric square waveguide frequency selective surface unit structure, three metal square rings are cascaded up and down to generate three transmission poles and two transmission zeros, thereby realizing a high frequency selectivity broadband bandpass three-dimensional frequency selective surface;

[0014] By controlling the on-off of water in the periodic water-based metamaterial absorber unit, the conversion of absorption and reflection electromagnetic properties outside the transmission band is achieved.

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

[0016] The above-mentioned three-dimensional gradient structure dielectric square waveguide frequency selective surface unit structure is divided into three interconnected upper, middle and lower sections, the upper section is a square dielectric column made of 3D printed resin material; the middle section and the lower section are filled with 3D printed resin material and the side walls are plated with metal to form a dielectric waveguide structure; the middle section is a dielectric square waveguide structure, and its lateral size is the same as the square dielectric column in the upper section, and the upper and lower surfaces are respectively plated with metal square rings of the same size; the lower section is a linear gradient structure dielectric square waveguide, and its lateral size increases linearly in the longitudinal direction, and the whole is in the shape of a square horn; and a single-layer dielectric substrate is provided below the linear gradient structure dielectric square waveguide, and a metal square ring is plated on the back of the substrate.

[0017] The size of the above-mentioned single-layer dielectric substrate is slightly larger than the lower surface of the linear gradient structure dielectric square waveguide.

[0018] The above-mentioned periodic water-based metamaterial absorber unit is encapsulated around the three-dimensional gradient structure medium square waveguide frequency selective surface unit structure by 3D printing photosensitive resin material.

[0019] The above-mentioned periodic water-based metamaterial absorber unit includes a lower water-based structure and an upper water-based structure encapsulated by 3D printing resin material. The lower water-based structure fills the gap between adjacent frequency selective surface units, and its height is the same as the height of the linear gradient structure medium square waveguide in the lower section; the upper water-based structure is a periodically arranged square water column unit, the water column unit is located at the diagonal position of the frequency selective surface unit structure, and the water column unit is connected to the lower water-based structure.

[0020] The side walls of each of the above-mentioned upper water column units are plated with metal.

[0021] The above-mentioned conversion of absorption and reflection electromagnetic characteristics outside the transmission band is achieved by controlling the on-off of water in the periodic water-based metamaterial absorber unit. Specifically, when filled with water, the three-dimensional water-based 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 three-dimensional water-based 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.

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

[0023] The invention discloses a dual-polarization three-dimensional water-based metamaterial frequency selective absorber with convertible electromagnetic properties, comprising a three-dimensional gradient structure medium square waveguide frequency selective surface and a periodic water-based metamaterial absorber; a broadband bandpass three-dimensional frequency selective surface is realized by cascading metal square rings in the three-dimensional gradient structure medium square waveguide; water is filled in 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, and packaged with 3D printing materials to form a periodic water-based metamaterial absorber. The invention introduces the concept of water into the FSR design, and realizes the conversion of ultra-wideband absorption and reflection characteristics outside the transmission band by controlling the on-off of water; metal is loaded around the square water column to further isolate the absorption and transmission paths, reduce the difference loss in the passband, and realize low-loss broadband transmission; at the same time, due to the symmetric design of the unit structure, dual polarization can be realized, and the invention has broad application prospects in the field of shipborne low RCS stealth radar covers.

[0024] The present invention realizes a novel FSR structure design with both mid-frequency broadband transmission and high- and low-frequency broadband absorption through the unit structure design of three-dimensional water-based metamaterials. 11<-10dB) frequency band is 3.7GHz~18GHz, the relative bandwidth is 132%, and the absorption rate is greater than 90% in the frequency bands of 3.7GHz~8.7GHz (FBW: 64.5%) and 14.4GHz~18GHz (FBW: 22.2%); the present invention has high selectivity, broadband and low insertion loss transmission performance, the -3dB transmission window frequency band is 9.2GHz~14GHz, the relative bandwidth is 41.4%, and the transmission bandwidth is better than most of the FSR structures reported; at the same time, the present invention realizes the connection between water-based unit structures by adopting a three-dimensional gradient structure frequency selective surface design, and solves the technical problem that medium-frequency transmission, high- and low-frequency absorption type water-based metamaterial FSR is difficult to achieve dual polarization; the present invention makes full use of the fluidity of water, and realizes the electromagnetic switching from the absorption band to the reflection band by controlling the on-off of water, and has good reconfigurable performance. In summary, the electromagnetic performance of the present invention is better than the related designs reported so far, and provides a new idea for the design of frequency selective absorbers, and has a high application value in the field of shipborne antenna stealth. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0028] Figure 4 It is a hierarchical structure diagram of a 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 layer of 3D printing resin material;

[0030] Figure 6 It 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 is the S parameter curve of 3D FSR when TE (TM) wave is normally incident under the water injection condition of the present invention;

[0032] Figure 8 It is the S parameter curve of 3D FSR when TE (TM) wave is normally incident under the water-depleted condition of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] Although the steps in the present invention are arranged with numbers, they are not used to limit the order of the steps. Unless the order of the steps is clearly stated or the execution of a certain step requires other steps as a basis, the relative order of the steps can be adjusted. It is understood that the term "and / or" used in this article involves and covers any and all possible combinations of one or more of the associated listed items.

[0035] The present invention is a dual-polarized three-dimensional water-based metamaterial frequency selective absorber with switchable electromagnetic properties. The three-dimensional gradient structure medium square waveguide frequency selective surface and the three-dimensional periodic water-based metamaterial absorber work together to form electromagnetic properties of low insertion loss broadband transmission in the mid-frequency band and broadband absorption in the high and low frequency bands. By controlling the on-off of water to put the water in two states of filling and emptying, the electromagnetic properties of broadband absorption and broadband reflection outside the transmission band of the frequency selective absorber can be switched. At the same time, the unit structure is symmetrically designed, and the frequency selective absorber can achieve 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 three-dimensional gradient structure dielectric square waveguide frequency selective surface has a broadband transmission performance with high frequency selectivity;

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

[0039] The frequency selective surface unit structure is divided into three interconnected sections, including a square dielectric column in the upper section, a dielectric square waveguide structure in the middle section, and a dielectric square waveguide with a square horn-shaped linear gradient structure in the lower section.

[0040] The upper section is a square dielectric column made of 3D printed resin material; the side walls of the middle and lower sections are plated with metal, and the same 3D printed resin material is filled inside to form a dielectric waveguide structure; the middle section is a dielectric square waveguide structure with the same lateral dimensions as the upper section dielectric column, and its upper and lower surfaces are respectively plated with metal square ring structures of the same size; the lower section is a linear gradient structure dielectric square waveguide, the lateral dimensions of which increase linearly in the longitudinal direction and are shaped like a square horn as a whole; below the gradient structure dielectric waveguide is a single-layer dielectric substrate, and the back of the substrate is also plated with a metal square ring structure array, and 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, and adopts an upper and lower two-layer structure. The lower water-based structure fills the gaps between adjacent units of the three-dimensional gradient structure medium square waveguide frequency selective surface, and its height is the same as the height of the linear gradient structure medium square waveguide in the lower section; the upper water-based structure is a periodically arranged square water column, the water column unit is located at the diagonal position of the frequency selective surface unit, the bottom of the water column is connected to the lower water structure, and the side wall of each water column unit is plated with metal, thereby achieving further isolation of the absorption path and the transmission path, and reducing the difference loss in the transmission band; the two-layer water-based structure is also encapsulated with the same 3D printing resin material as that in the frequency selective surface unit.

[0042] The three-dimensional gradient structure dielectric square waveguide frequency selective surface and the three-dimensional periodic water-based metamaterial absorber work together to form electromagnetic properties of low insertion loss broadband transmission in the mid-frequency band and broadband absorption in the high and low frequency bands. By controlling the on-off of water to put the water in two states of filling and emptying, the frequency selective absorber can achieve electromagnetic property switching between broadband absorption outside the transmission band and broadband reflection. At the same time, the unit structure is symmetrically designed, and the frequency selective absorber can achieve electromagnetic properties that are insensitive to the polarization of the incident wave.

[0043] When water is filled around the frequency selective surface unit and the periodic water column, the frequency selective absorber presents electromagnetic characteristics of low-loss transmission in the mid-band broadband and wide-band absorption in the high and low frequency bands; when the water is drained, the frequency selective absorber presents electromagnetic characteristics of low-loss transmission in the mid-band broadband and wide-band reflection in the high and low frequency bands. That is, by controlling the on and off of water, the conversion of the absorption and reflection electromagnetic characteristics outside the transmission band 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 losses of the three-dimensional periodic water-based metamaterial absorber layer and the three-dimensional frequency selective surface layer in the transmission band are very small, electromagnetic waves in the intermediate frequency transmission band can be transmitted with extremely small insertion losses, and electromagnetic waves in the high-frequency and low-frequency absorbing bands will be absorbed by the water material of the three-dimensional periodic water-based metamaterial absorber layer, thereby achieving broadband absorption.

[0045] The broadband transmission window in the mid-frequency band is formed by the three-dimensional periodic water-based metamaterial absorber layer and the three-dimensional frequency selective surface layer to form a low insertion loss, high selectivity, broadband transmission window; when the electromagnetic wave is incident on the frequency selective absorber, it interacts with the three-dimensional periodic water-based metamaterial absorber layer and the three-dimensional frequency selective surface layer respectively, and in the unit structure of the three-dimensional periodic water-based metamaterial absorber layer, a unit water column design is placed at a diagonal orthogonal position of the transmission square waveguide, so that the insertion loss caused by water loss is greatly reduced; by loading square PEC around the water column unit, further isolation of the absorption path and the transmission path is achieved, so that the electromagnetic wave can pass through the absorbing layer with low insertion loss.

[0046] The absorption bands of low and high frequency bands are formed by the three-dimensional periodic water-based metamaterial absorber layer and the three-dimensional frequency selective surface layer. In the unit structure, the unit gaps generated by the gradient square waveguide are filled with water, and square water columns are loaded at the four corners of the square waveguide. The same 3D printing resin material is covered on top of the water to achieve the fusion of the absorption path and the transmission path. Through this design, the water units are connected without being separated by PEC, thus ensuring the absorption bandwidth and absorption intensity of the structure.

[0047] In the embodiment, Figure 1 and Figure 2 The schematic diagram of the 3×3 unit structure and the schematic diagram of the three-dimensional structure of a single unit of the present invention are shown; the overall structure is composed of two parts: a three-dimensional gradient structure medium square waveguide frequency selective surface and a periodic water-based metamaterial absorber, and the upper layers of the two parts are both made of 3D printed resin material (ε r =2.55, tanδ=0.001) and is covered with a chessboard-like periodic distribution from the outside. The height h of the unit of the present invention is 19.5 mm, and the period p is 15.5 mm.

[0048] Figure 2 and Figure 3 The figure 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 printing resin material, with a height of h4=7mm and a side length of l2=8.5mm; the middle section and the lower section structure are filled with the same 3D printing resin material, the side walls are plated with metal, and the metal patch is 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 section dielectric column, height h2 = 5.25 mm, and upper and lower surface side length l2 = 8.5 mm; the upper and lower surfaces are plated with metal square ring structures of the same size, and the outer side length of the metal square ring patch is l p1 =3.9mm, inner side length l p2=2.1mm;

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

[0051] Figure 5 The unit structure after removing the upper layer of 3D printing material of the present invention is shown; wherein the periodic water-based metamaterial absorber unit is located around the frequency selective surface unit, and the structure is divided into two layers, the upper water-based structure is a periodically arranged square water column, the water column unit is located at the diagonal position of the frequency selective surface unit, the side length g1=2.6mm, the height h1=9.5mm, the bottom of the water column is connected to the lower water structure, and the side wall of each water column unit is plated with metal, and the length g2=6.1mm and the width g3=2.9mm of each metal patch; the lower water-based structure is filled in the gap between adjacent units of the three-dimensional gradient structure medium square waveguide frequency selective surface, the side length is the same as the medium substrate, which is l1=15.5mm, and the height is h3=6.75mm, which is the same as the height of the linear gradient structure medium square waveguide in the lower section; the two-layer water-based structure is also encapsulated with the same 3D printing resin material as in the frequency selective surface unit.

[0052] Figure 6 The figure shows the S parameter curve of the three-dimensional gradient structure dielectric waveguide FSS in the embodiment of the present invention under the condition of normal incidence of TE (TM) wave. Figure 6 It can be seen that the three-dimensional FSS structure has a broadband transmission window in the mid-frequency band and a steep out-of-band group edge, with high frequency selectivity. The -3dB band ranges from 9.0GHz to 14GHz, and the relative bandwidth reaches 43.4%. Due to the mutual coupling of the three cascaded metal square rings in the FSS unit structure, there are three transmission poles in the transmission band, located at 9.65GHz, 11.1GHz and 13.0GHz respectively. At the same time, the FSS exhibits strong reflection characteristics outside the transmission band, with two transmission zeros at 7.4GHz and 17.6GHz, respectively, which enhances the frequency selection performance of the FSS and lays the foundation for the subsequent combination of water-based metamaterial structure unit structures. In addition, its unit is symmetrically designed, and the above electromagnetic performance can be achieved for both TE and TM incident polarized waves.

[0053] Figure 7 The S parameter curve of the three-dimensional FSR under the condition of normal incidence of TE wave under the condition of water injection in the embodiment of the present invention is shown. Figure 7 It can be seen that the present invention has an electromagnetic characteristic 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 11 <-10dB), with a relative bandwidth of 132%. The absorption function with an absorption rate greater than 90% is achieved in the frequency bands of 3.7GHz to 8.7GHz (FBW: 64.5%) and 14.4GHz to 18GHz (FBW: 22.2%). The -3dB transmission band range is 9.2GHz to 14GHz, with a relative bandwidth of 41.4%, which is comparable to the transmission bandwidth of FSS without water-based metamaterial structure (such as Figure 6 The device has a minimum insertion loss of 0.95dB at 12GHz. At the same time, the symmetrical unit structure design ensures the polarization insensitivity of the device.

[0054] Figure 8 The figure shows the S parameter curve of the three-dimensional FSR under the condition of normal incidence of TE wave under the condition of water emptying in the embodiment of the present invention. Figure 8 It can be seen that without water injection, the original absorption band of the frequency selective absorber switches to a reflection band, but the transmission window in the mid-frequency range is still maintained. 11 >-1dB) covers the low frequency band of 2GHz~8.63GHz (FBW:124.7%) and the high frequency band of 14.27GHz~18GHz (FBW:23.1%). The -3dB transmission band ranges from 9GHz to 13.95GHz, and the relative bandwidth reaches 43.13%. The transmission bandwidth is basically consistent with that in the water injection case, maintaining the stability of the transmission window performance under the two water injection states. At the same time, the above electromagnetic properties can be achieved for both TE and TM incident polarized waves. In summary, the present invention can realize electromagnetic switching from absorption band to reflection band, and has good reconfigurable performance.

[0055] It will be apparent to those skilled in the art that the 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 the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0056] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A three-dimensional water-based frequency selective absorber with switchable electromagnetic properties, characterized in that: Including several symmetrically designed three-dimensional gradient structure dielectric square waveguide frequency selective surface unit structures and periodic water-based metamaterial absorber units; The three-dimensional gradient structure dielectric square waveguide frequency selective surface unit structure has a broadband transmission performance with high frequency selectivity; The periodic water-based metamaterial absorber unit is encapsulated around the frequency selective surface unit structure and has ultra-wideband absorption performance; In the three-dimensional gradient structure dielectric square waveguide frequency selective surface unit structure, three metal square rings are cascaded up and down to generate three transmission poles and two transmission zeros, thereby realizing a high frequency selectivity broadband bandpass three-dimensional frequency selective surface; By controlling the on-off of water in the periodic water-based metamaterial absorber unit, the conversion of absorption and reflection electromagnetic properties outside the transmission band is achieved.

2. A three-dimensional water-based frequency selective absorber with switchable electromagnetic properties according to claim 1, characterized in that: The three-dimensional gradient structure dielectric square waveguide frequency selective surface unit structure is divided into three interconnected sections, the upper section is a square dielectric column made of 3D printed resin material; the middle section and the lower section are filled with 3D printed resin material and the side walls are plated with metal to form a dielectric waveguide structure; the middle section is a dielectric square waveguide structure, and its lateral size is the same as that of the square dielectric column in the upper section, and the upper and lower surfaces are respectively plated with metal square rings of the same size; the lower section is a linear gradient structure dielectric square waveguide, and its lateral size increases linearly in the longitudinal direction, and the whole is in the shape of a square horn; and a single-layer dielectric substrate is provided below the linear gradient structure dielectric square waveguide, and a metal square ring is plated on the back of the substrate.

3. A three-dimensional water-based frequency selective absorber with switchable electromagnetic properties according to claim 2, characterized in that: The size of the single-layer dielectric substrate is slightly larger than the lower surface of the linear gradient structure dielectric square waveguide.

4. The three-dimensional water-based frequency selective absorber with switchable electromagnetic properties according to claim 1, characterized in that: The periodic water-based metamaterial absorber unit is encapsulated around the three-dimensional gradient structure medium square waveguide frequency selective surface unit structure by 3D printing photosensitive resin material.

5. A three-dimensional water-based frequency selective absorber with switchable electromagnetic properties according to claim 1 or 4, characterized in that: The periodic water-based metamaterial absorber unit includes a lower water-based structure and an upper water-based structure encapsulated by 3D printing resin material. The lower water-based structure fills the gap between adjacent frequency selective surface units, and its height is the same as the height of the linear gradient structure medium square waveguide in the lower section; the upper water-based structure is a periodically arranged square water column unit, the water column unit is located at the diagonal position of the frequency selective surface unit structure, and the water column unit is connected to the lower water-based structure.

6. The three-dimensional water-based frequency selective absorber with switchable electromagnetic properties according to claim 5, characterized in that: The side walls of each upper water column unit are plated with metal.

7. The three-dimensional water-based frequency selective absorber with switchable electromagnetic properties according to claim 1, characterized in that: By controlling the on-off of water in the periodic water-based metamaterial absorber unit, the conversion of absorption and reflection electromagnetic characteristics outside the transmission band is achieved. Specifically, when filled with water, the three-dimensional water-based 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 three-dimensional water-based 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.

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