A geometric kink-based flexible frequency selective surface and applications

Abstract

The present application belongs to the technical field of electromagnetic compatibility, and particularly relates to a flexible frequency selective surface based on geometric kink and application. The flexible frequency selective surface designed by the present application has the advantages of simple structure, good angle stability and good bending angle, and can realize the passband effect in the range of 5.08-6.01 GHz, has good angle stability within the electromagnetic wave incidence angle of 0-60°, and maintains stable frequency selection performance within the bending angle of 0-180°, has good curved surface conforming ability, and has application prospect in the fields of radar antenna cover, electromagnetic protection and communication technology.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic compatibility technology, and specifically relates to a flexible frequency selective surface based on geometric kinks and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] A frequency selective surface (FSS) is an artificial periodic structure composed of specific resonant elements arranged in a two-dimensional periodic pattern. This structure allows for precise control over the frequency, incident angle, and polarization of electromagnetic waves, achieving a specific filtering effect, i.e., frequency selectivity. Due to its unique electromagnetic wave manipulation capabilities, FSSs have been widely used in various fields such as radar radomes, electromagnetic protection, and communication technology. With technological advancements and increasing demands, more complex curved surface structures are required for FSSs, such as in streamlined stealth design for aircraft and conformal antenna design. These complex curved surface structures are driving the development of flexible FSS technology.

[0004] Currently, research mainly focuses on enabling flexible spectral splitters (FSSs) to be effectively applied in complex curved surface conditions through material selection and structural design. For example, Chen et al. successfully fabricated a flexible FSS using ultrathin polyvinyl chloride (PVC) as the substrate, which maintained 70% passband transmittance even when the conformal bending angle reached 77.35°. Yang et al. used polydimethylsiloxane (PDMS) as the substrate material to fabricate a flexible FSS that achieved 60° angular stability and a conformal bending angle of 128° while maintaining good frequency selectivity. However, for some extreme applications, these conformal bending angles are still insufficient, and the fabrication of such flexible FSSs presents structural challenges.

[0005] Meanwhile, further exploration of conformal bending angles in this field is often accompanied by high requirements for angular stability. Geometric kinks are considered a good solution to the angular stability problem, but since the resonance peak of a single geometric kink is usually singular and narrow, a better solution needs to be found for FSS, which requires broadband characteristics. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a flexible frequency selective surface based on geometric kinks and its application. This flexible frequency selective surface has the advantages of simple structure, good angular stability, and good bending angle. It can achieve passband effect in the range of 5.08~6.01 GHz, while having good angular stability within the electromagnetic wave incident angle range of 0~60° and maintaining stable frequency selective performance within the bending angle range of 0~180°, exhibiting good conformal surface capability.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0008] In a first aspect, the present invention provides a flexible frequency selective surface based on geometric kinks, the flexible frequency selective surface comprising a dielectric substrate and geometric kink structure units attached to the dielectric substrate;

[0009] The geometric knot structure unit includes a first Möbius knot and a second Möbius knot of different sizes, with a spacing d between them of 14~16 mm;

[0010] The radius r of the first Möbius knot and the second Möbius knot are both 4~4.9 mm, the coil diameter a is both 1~2 mm, and the deviation coefficient b is both 1~2 mm.

[0011] The operating frequency of the flexible frequency selective surface is 5.08~6.01 GHz.

[0012] Preferably, the radius r of the first Möbius knot is 4~4.1 mm, the coil diameter a is 1~2 mm, and the deviation coefficient b is 1~2 mm.

[0013] Preferably, the radius r of the second Möbius knot is 4.7~4.9 mm, the coil diameter a is 1~2 mm, and the deviation coefficient b is 1~2 mm.

[0014] Preferably, the geometric knot structure unit is periodically extended in the xy plane.

[0015] Preferably, the dielectric substrate is made of PET film and foam, with a relative permittivity of 1 to 1.2, a length p of 30 to 35 mm, a width w of 15 to 19.8 mm, and a height h of 12 to 15 mm.

[0016] Preferably, the Möbius knot is obtained by topological transformation of the classic Möbius strip. The middle part of the Möbius strip is hollowed out, leaving only the edges to form two overlapping edge lines. The edge lines are then replaced with metal wires, which is the Möbius knot.

[0017] Preferably, the Möbius knot is made of metal; more preferably, the metal is selected from one or more of silver, gold, aluminum, iron, tin, copper, and stainless steel.

[0018] Preferably, the processing technology of the Möbius knot is one or more of 3D printing, printed circuit board processing, and machining.

[0019] In a second aspect, the present invention provides an application of the above-mentioned flexible frequency selective surface based on geometric kinks in the fields of radar radomes, electromagnetic protection, and communication technologies.

[0020] In a second aspect, the present invention provides a radar radome for covering the radiation direction of an antenna system, the radar radome being composed of the flexible frequency selective surface based on geometric kinks as described in the first aspect.

[0021] The beneficial effects achieved by one or more technical solutions of the present invention are as follows:

[0022] (1) The flexible frequency selective surface based on geometric kink obtained by the present invention has a passband bandwidth of 0.93 GHz (5.08~6.01 GHz) with a bandwidth of 16.77% and an insertion loss of less than 1 dB in the frequency band of 5.11~5.80 GHz. It also has two -10 dB stopbands with bandwidths of 0.03 and 0.04 GHz at 5.02~5.05 GHz and 6.06~6.10 GHz, respectively.

[0023] (2) The flexible frequency selective surface based on geometric kink obtained by the present invention has good angular stability within the electromagnetic wave incident angle of 0~60°, including TE polarization mode and TM polarization mode.

[0024] (3) The flexible frequency selective surface based on geometric kink obtained by the present invention maintains stable frequency selective performance within the bending angle of 0~180° and has good surface conformal capability. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the flexible frequency-selective surface based on geometric kinks in Embodiment 1 of the present invention, wherein 1: first Möbius kink; 2: second Möbius kink; 3: foam substrate;

[0026] Figure 2 The diagram shows the structure of a Möbius knot obtained by topological transformation of the classic Möbius strip.

[0027] Figure 3The following are partial schematic diagrams of the flexible frequency selection surface based on geometric kinks in embodiments 1-3 of the present invention, wherein (a) is a geometric kink structure unit, (b) is a top view of the flexible frequency selection surface, and (c) is a side view of the flexible frequency selection surface.

[0028] Figure 4 The figure shown is a simulation result diagram of Embodiment 1 of the present invention, and the curves of transmission coefficient as a function of incident angle under TE and TM polarization.

[0029] Figure 5 The simulation results are shown in Embodiment 2 of the present invention, and the transmission coefficient under TE and TM polarization varies with the incident angle.

[0030] Figure 6 The simulation results are shown in Embodiment 3 of the present invention, and the transmission coefficient under TE and TM polarization varies with the incident angle.

[0031] Figure 7 The simulation results are shown in the comparative example of this invention, and the transmission coefficients under TE and TM polarizations vary with the incident angle.

[0032] Figure 8 The figure shown is a measured result diagram of the embodiment of the present invention, and a curve showing the change of transmission coefficient with bending angle. Detailed Implementation

[0033] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0034] Based on the Möbius knot structure obtained in the previous research of this research group (a Möbius knot with topological resonance characteristics, metamaterial design and electromagnetic topological properties based on metallic Möbius knot, Zhang Wenjin, Master's thesis of Shandong University, May 20, 2021, Chapter 3), the inventor designed a flexible frequency selective surface based on geometric knot, which solved the problems of limited bending angle and complex structure of flexible frequency selective surfaces.

[0035] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0036] Example 1: This example provides a flexible frequency-selective surface based on geometric kinks and analyzes its transmittance simulation curve.

[0037] like Figure 1 As shown, the flexible frequency selection surface based on geometric kinks includes a dielectric substrate 3 and geometric kink structure units attached to the dielectric substrate.

[0038] Among them, the geometric knot structure unit includes a first Möbius knot and a second Möbius knot. The Möbius knot was prepared using the content of Chapter 3 of "Metamaterial Design and Electromagnetic Topological Properties Based on Metallic Möbius Knots · Zhang Wenjin · Shandong University Master's Thesis · May 20, 2021".

[0039] like Figure 2 As shown, the Möbius knot is obtained by topological transformation of the classic Möbius strip. The middle part of the Möbius strip is hollowed out, leaving only the edges, forming two overlapping edge lines. The edge lines are then replaced with metal wires, which is the Möbius knot.

[0040] like Figure 3 As shown in (a), the specific parameters of the geometric knot structure unit are set as follows:

[0041] The first Möbius knot has a kink radius of r = 4 mm, a coil diameter of a = 1 mm, and a deviation coefficient of b = 1 mm.

[0042] The second Möbius knot has a kink radius of r = 4.8 mm, a coil diameter of a = 1 mm, and a deviation coefficient of b = 1 mm.

[0043] The distance between the first and second Möbius knots is d = 15 mm.

[0044] like Figure 3 As shown in (b) and (c), the relative permittivity of the foam substrate is 1, the length p is 30 mm, the width w is 15 mm, and the height h is 13 mm.

[0045] The simulation frequency range is 4~8 GHz, and the results are as follows: Figure 4 As shown, when the incident angle of the electromagnetic wave is 0°, the transmission coefficient S in TE polarization mode and TM polarization mode is... 21 The insertion loss is greater than -3 dB in the 5.08–6.01 GHz band, with a relative bandwidth of 16.77%. The insertion loss is less than 1 dB in the 5.11–5.80 GHz band. There are -10 dB stopbands with bandwidths of 0.03 GHz (5.02–5.05 GHz) and 0.04 GHz (6.06–6.10 GHz) on the left and right sides of the passband, respectively. The transition bands are 5.05–5.08 GHz and 6.01–6.06 GHz, with bandwidths of 0.03 GHz and 0.05 GHz, respectively.

[0046] At the same time, such as Figure 4As shown, the structure exhibits good angular stability within the electromagnetic wave incident angle range of 0 to 60°, and can still maintain more than 89.24% of the -3 dB passband, including TE polarization mode and TM polarization mode, when the incident angle is 60°.

[0047] Example 2: This example provides a flexible frequency-selective surface based on geometric kinks and analyzes its transmittance simulation curve.

[0048] The difference between the flexible frequency selective surface obtained in this embodiment and that in Embodiment 1 lies in the difference in the parameters of the geometric kink structure unit and the dielectric substrate.

[0049] The specific parameter settings for the geometric knot structure unit in this embodiment are as follows:

[0050] The first Möbius knot has a kink radius of r = 4.1 mm, a coil diameter of a = 1.5 mm, and a deviation coefficient of b = 1.5 mm.

[0051] The second Möbius knot has a kink radius of r = 4.7 mm, a coil diameter of a = 1.5 mm, and a deviation coefficient of b = 1.5 mm.

[0052] The distance between the first and second Möbius knots is d = 14 mm.

[0053] The foam substrate has a relative permittivity of 1.2, a length of p = 30.6 mm, a width of w = 17.2 mm, and a height of h = 15 mm.

[0054] The simulation frequency range is 4~8 GHz, and the results are as follows: Figure 5 As shown, when the incident angle of the electromagnetic wave is 0°, the transmission coefficient S in TE polarization mode and TM polarization mode is... 21 It is greater than -3 dB in the 5.24–5.84 GHz frequency band, with a relative bandwidth of 10.83%. Meanwhile, as... Figure 5 As shown, the structure exhibits good angular stability within the electromagnetic wave incident angle range of 0 to 60°, and can still maintain more than 73.33% of the -3 dB passband at an incident angle of 60°, including the TE polarization mode and the TM polarization mode.

[0055] Example 3: This example provides a flexible frequency-selective surface based on geometric kinks and analyzes its transmittance simulation curve.

[0056] The difference between the flexible frequency selective surface obtained in this embodiment and that in Embodiment 1 lies in the difference in the parameters of the geometric kink structure unit and the dielectric substrate.

[0057] The specific parameter settings for the geometric knot structure unit in this embodiment are as follows:

[0058] The first Möbius knot has a kink radius of r = 4.1 mm, a coil diameter of a = 2 mm, and a deviation coefficient of b = 2 mm.

[0059] The second Möbius knot has a kink radius of r = 4.9 mm, a coil diameter of a = 2 mm, and a deviation coefficient of b = 2 mm.

[0060] The distance between the first and second Möbius knots is d = 16 mm.

[0061] The foam substrate has a relative permittivity of 1.1, a length of p = 35 mm, a width of w = 19.8 mm, and a height of h = 12 mm.

[0062] The simulation frequency range is 4~8 GHz, and the results are as follows: Figure 6 As shown, when the incident angle of the electromagnetic wave is 0°, the transmission coefficient S in TE polarization mode and TM polarization mode is... 21 It is greater than -3 dB in the 5.14–5.93 GHz frequency band, with a relative bandwidth of 14.27%. Meanwhile, as... Figure 6 As shown, the structure exhibits good angular stability within the electromagnetic wave incident angle range of 0 to 60°, and can still maintain more than 62.03% of the -3 dB passband, including TE polarization mode and TM polarization mode, when the incident angle is 60°.

[0063] Comparative Example 1:

[0064] The difference between this comparative example and Example 1 is that only a single-size geometric kink structure unit is constructed. Specifically, an array is formed by periodically extending a unit with a kink radius of 4 mm (r), a coil diameter of 1 mm (a), and a deviation coefficient of 1 mm in the xy plane. A foam substrate (the same material and size as in Example 1) is attached below the structure unit, with a relative permittivity of 1, a length of 30 mm (p), a width of 15 mm (w), and a height of 13 mm.

[0065] The simulation frequency range is 4~8 GHz, and the results are as follows: Figure 7 The figure shows that the transmission coefficient S of a single-size geometric knot structure unit is... 21 There is only a single resonant peak at 6.08 GHz, which means that electromagnetic waves cannot pass through the structure at the resonant frequency. This single frequency blockade is the left or right arm of a passband FSS, but a passband FSS cannot be formed by a single geometric kink structure unit.

[0066] Test Example: This test example measures the bending properties of the flexible frequency-selective surface obtained in Example 1.

[0067] This experimental example verifies the bending performance of the designed flexible frequency-selective surface. The transmittance of the sample from Example 1 under bending conditions was measured using the free-space method. The test frequency range was 4–8 GHz, and the bending performance was primarily defined by the bending angle α. Figure 8 The test results show that the structure maintains stable frequency selectivity within the bending angle α=0~180° and has good conformal surface capability.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A flexible frequency-selective surface based on geometric kinks, characterized in that, The flexible frequency selective surface includes a dielectric substrate and a geometric kink structure unit attached to the dielectric substrate. The geometric knot structure unit includes a first Möbius knot and a second Möbius knot of different sizes, with a spacing d between them of 14~16 mm; The radius r of the first Möbius knot is 4~4.1 mm, the coil diameter a is 1~2 mm, and the deviation coefficient b is 1~2 mm; the radius r of the second Möbius knot is 4.7~4.9 mm, the coil diameter a is 1~2 mm, and the deviation coefficient b is 1~2 mm. The flexible frequency selective surface operates at a frequency of 5.08~6.01 GHz; The dielectric substrate is made of PET film and foam, with a relative permittivity of 1~1.2, a length p of 30~35 mm, a width w of 15~19.8 mm, and a height h of 12~15 mm. The flexible frequency selective surface, when the electromagnetic wave incident angle is 0°, exhibits a transmission coefficient S21 greater than -3 dB in both TE and TM polarization modes within the 5.08–6.01 GHz frequency band, with a relative bandwidth of 16.77%. The insertion loss is less than 1 dB in the 5.11–5.80 GHz frequency band. It has -10 dB stopbands with bandwidths of 0.03 GHz and 0.04 GHz on the left and right sides of the passband, respectively, with stopband frequency ranges of 5.02–5.05 GHz and 6.06–6.10 GHz. Transition bands exist at 5.05–5.08 GHz and 6.01–6.06 GHz, with bandwidths of 0.03 and 0.05 GHz, respectively. The Möbius knot is obtained by topological transformation of the classic Möbius strip. The middle part of the Möbius strip is hollowed out, leaving only the edges to form two overlapping edge lines. The edge lines are then replaced with metal wires, which is the Möbius knot.

2. The flexible frequency-selective surface based on geometric kinks as described in claim 1, characterized in that, The geometric knot structure unit is formed by periodic extension in the xy plane.

3. The flexible frequency-selective surface based on geometric kinks as described in claim 1, characterized in that, The Möbius knot is made of metal.

4. The flexible frequency-selective surface based on geometric kinks as described in claim 3, characterized in that, The metal is selected from one or more of silver, gold, aluminum, iron, tin, copper, and stainless steel.

5. The flexible frequency-selective surface based on geometric kinks as described in claim 1, characterized in that, The processing technology of the Möbius knot is one or more of 3D printing, printed circuit board technology, and machining.

6. The application of the flexible frequency selective surface based on geometric kinks as described in any one of claims 1 to 5 in the fields of radar radomes, electromagnetic protection, and communication technologies.

7. A radar radome, used to cover the radiation direction of an antenna system, characterized in that, The radar radome is composed of a flexible frequency-selective surface based on geometric kinks as described in any one of claims 1 to 5.

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