A transreflective switchable frequency selective surface structure and a unit structure thereof

Abstract

The present application relates to a kind of transmissive reflection switchable frequency selective surface structure and its unit structure, frequency selective surface unit structure, comprising: first metal layer, dielectric substrate and second metal layer are sequentially arranged from top to bottom;First metal layer includes: cross fractal structure, cross connection square ring and four photoelectric diodes, wherein, cross fractal structure is arranged on the upper surface of dielectric substrate;Cross connection square ring is located in the outside of cross fractal structure;Four photoelectric diodes are connected between the four end portions of cross fractal structure and cross connection square ring respectively.By the conduction and shutdown of photoelectric diode, the switching of transmission mode and reflection mode is realized, not easy to be destroyed by heat, can be compatible with various electromagnetic scenes, stability is high, can be flexibly switched between transmission mode and reflection mode under 11.1GHz frequency, realizes the dynamic regulation of electromagnetic wave.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic protection technology, specifically relating to a frequency-selective surface structure and its unit structure that allows for switching between transmission and reflection. Background Technology

[0002] A frequency selective surface (FSS) is a two-dimensional periodic array structure composed of resonant elements that exhibits the characteristics of an electromagnetic wave space filter. It can be designed to transmit and reflect electromagnetic waves within a specific frequency band. FSSs have wide applications in radomes, absorbers, space filters, shielding devices, and wireless communication systems.

[0003] With the development of electromagnetic wave technology, the electromagnetic environment is becoming increasingly complex. In modern communication, how to effectively control or suppress the characteristic signals of targets, significantly reduce the radar cross section (RCS) of antenna systems, and achieve radar stealth has always been a pressing problem to be solved. However, this often conflicts with the electrical performance of antenna systems. Many radar stealth technologies cause a decrease in the radiation performance of antennas, resulting in a decrease in the overall efficiency of the system. Therefore, how to balance radar stealth capability and signal transmission capability has become a hot research topic in the industry, and more and more researchers are beginning to explore switchable and reconfigurable reflectors. These reflectors can flexibly switch between transmission and reflection bands, thus simultaneously achieving electromagnetic wave shielding within the operating frequency band and long-range communication capabilities. They can better adapt to complex and changing electromagnetic environments, enriching the application scenarios of various antennas.

[0004] With the rapid development of high-energy technologies such as lasers, microwaves, and particle beams, higher demands are being placed on the high-energy protection technology of frequency-selective surfaces that can switch between transmission and reflection. Existing frequency-selective surfaces that can switch between transmission and reflection cannot maintain stable performance when high-energy technologies generate instantaneous high temperatures, and therefore cannot meet the application requirements of current high-energy scenarios. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a frequency-selective surface structure with switchable transmission and reflection, and its unit structure. The technical problem to be solved by this invention is achieved through the following technical solution:

[0006] A first aspect of the present invention provides a frequency-selective surface unit structure with switchable transmission and reflection, comprising:

[0007] The first metal layer, the dielectric substrate, and the second metal layer are arranged sequentially from top to bottom;

[0008] The first metal layer includes: a cross-shaped fractal structure, cross-connected square rings, and four photodiodes, wherein,

[0009] The cross-shaped fractal structure is disposed on the upper surface of the dielectric substrate;

[0010] The cross-connecting square ring is located on the outside of the cross-shaped fractal structure;

[0011] The four photodiodes are respectively connected between the four ends of the cross-shaped fractal structure and the cross-connecting square ring;

[0012] The centers of the cross-shaped fractal structure and the intersecting square ring coincide, and both are centrally symmetrical structures.

[0013] In one feasible embodiment, the cross-shaped fractal structure includes: a central rectangular portion and four zigzag fractal portions, wherein the central rectangular portion is disposed at the center of the upper surface of the dielectric substrate;

[0014] The four fractal parts are respectively connected to the four sides of the central rectangle.

[0015] In one feasible implementation, the fractal portion comprises: a first rectangular portion, a second rectangular portion, and a slit, wherein,

[0016] The first rectangular portion connects to the edge of the central rectangular portion;

[0017] The second rectangular portion is disposed perpendicular to the first rectangular portion and connected to one side of the first rectangular portion;

[0018] The slit is perpendicular to the first rectangular portion and extends from the other side of the first rectangular portion into the interior of the second rectangular portion.

[0019] In one feasible implementation, the cross-connecting square ring includes four triangular structures, four square ring connecting portions, and four connecting lines, wherein,

[0020] The four triangular structures are respectively disposed at the ends of the four fractal parts, and there is a gap between each triangular structure and each fractal part;

[0021] The four square rings are connected between each pair of adjacent triangular structures.

[0022] The four connecting lines are respectively connected to the midpoint of each of the square ring connecting parts.

[0023] In one feasible embodiment, the four photodiodes are respectively disposed at the intervals between the four triangular structures and the four fractal portions, with the positive terminal of the photodiode connected to the fractal portion and the negative terminal of the photodiode connected to the triangular structure.

[0024] In one feasible embodiment, the dielectric substrate and the central rectangular portion are concentric squares;

[0025] The width of the first rectangular portion is equal to the side length of the central rectangular portion;

[0026] The long axis of the first rectangular portion is located on the axis of the dielectric substrate.

[0027] In one feasible embodiment, the triangular structure is an isosceles triangle, with the apex of the triangular structure facing the edge of the dielectric substrate, and the median of the triangular structure located on the axis of the dielectric substrate.

[0028] The four connecting lines extend from the midpoint of each of the square ring connecting portions to the four corners of the dielectric substrate.

[0029] In one feasible implementation, the second metal layer comprises four rectangular structures;

[0030] The four rectangular structures are all located on the lower surface of the dielectric substrate, and the four rectangular structures extend from the midpoints of the four sides of the dielectric substrate toward the center of the dielectric substrate.

[0031] In one feasible embodiment, the materials of both the first metal layer and the second metal layer include one of copper Cu, aluminum Al, and gold Au.

[0032] The material of the dielectric substrate includes: flexible flame-retardant material.

[0033] A second aspect of the present invention provides a frequency-selective surface structure with switchable transmission and reflection, comprising M×N periodically arranged unit structures, wherein the unit structures are the frequency-selective surface unit structures with switchable transmission and reflection provided in the first aspect of the present invention.

[0034] Where M and N are positive integers.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] The present invention discloses a unit structure of a frequency-selective surface structure that can switch between transmission and reflection modes by turning on and off a photodiode. It is not easily damaged by heat, is compatible with various electromagnetic scenarios, has high stability, and can flexibly switch between transmission and reflection modes at a frequency of 11.1 GHz, thereby achieving dynamic control of electromagnetic waves. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of a unit structure of a transmissive and reflective switchable frequency selectable surface structure provided in an embodiment of the present invention;

[0038] Figure 2 It is a side view of a unit structure of a transmissive-reflective switchable frequency selective surface structure provided by an embodiment of the present invention;

[0039] Figure 3 It is a schematic structural diagram of a first metal layer provided by an embodiment of the present invention;

[0040] Figure 4 It is a schematic structural diagram of a character-shaped fractal part provided by an embodiment of the present invention;

[0041] Figure 5 It is a schematic structural diagram of a second metal layer provided by an embodiment of the present invention;

[0042] Figure 6 It is a schematic structural diagram of a transmissive-reflective switchable frequency selective surface structure provided by an embodiment of the present invention;

[0043] Figure 7 It is a simulation diagram of the filtering performance of a transmissive-reflective switchable frequency selective surface structure provided by an embodiment of the present invention when the photodiode is turned on in the TE polarization mode;

[0044] Figure 8 It is a simulation diagram of the filtering performance of a transmissive-reflective switchable frequency selective surface structure provided by an embodiment of the present invention when the photodiode is blocked in the TE polarization mode;

[0045] Figure 9 It is a simulation diagram of the filtering performance of a transmissive-reflective switchable frequency selective surface structure provided by an embodiment of the present invention when the photodiode is turned on in the TM polarization mode;

[0046] Figure 10 It is a simulation diagram of the filtering performance of a transmissive-reflective switchable frequency selective surface structure provided by an embodiment of the present invention when the photodiode is blocked in the TM polarization mode;

[0047] Figure 11 It is a simulation diagram of the angular stability performance of a transmissive-reflective switchable frequency selective surface structure provided by an embodiment of the present invention when the photodiode is turned on in the TE polarization mode;

[0048] Figure 12 It is a simulation diagram of the angular stability performance of a transmissive-reflective switchable frequency selective surface structure provided by an embodiment of the present invention when the photodiode is blocked in the TE polarization mode;

[0049] Figure 13 It is a simulation diagram of the angular stability performance of a transmissive-reflective switchable frequency selective surface structure provided by an embodiment of the present invention when the photodiode is turned on in the TM polarization mode;

[0050] Figure 14 This is a simulation diagram of the angular stability performance of a frequency-selective surface structure with switchable transmission and reflection provided by an embodiment of the present invention when the photodiode is blocked in TM polarization mode.

[0051] Figure label:

[0052] 1: First metal layer; 11: Cross-shaped fractal structure; 111: Central rectangular portion; 112: Z-shaped fractal portion; 1121: First rectangular portion; 1122: Second rectangular portion; 1123: Gap; 12: Cross-connecting square ring; 121: Triangular structure; 122: Square ring connecting portion; 123: Connecting line; 13: Photodiode; 2: Dielectric substrate; 3: Second metal layer; 31: Rectangular structure. Detailed Implementation

[0053] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0054] Example 1

[0055] Please see Figure 1 and Figure 2 , Figure 1 This is a schematic diagram of a unit structure of a transmissive and reflective switchable frequency selective surface structure provided in an embodiment of the present invention. Figure 2 This is a side view of a unit structure of a transmissive and reflective switchable frequency selectable surface structure provided in an embodiment of the present invention.

[0056] This embodiment provides a frequency-selective surface unit structure with switchable transmission and reflection, comprising: a first metal layer 1, a dielectric substrate 2, and a second metal layer 3 arranged sequentially from top to bottom. The first metal layer 1 includes: a cross-shaped fractal structure 11, a cross-connecting square ring 12, and four photodiodes 13, wherein the cross-shaped fractal structure 11 is disposed on the upper surface of the dielectric substrate 2. The cross-connecting square ring 12 is located outside the cross-shaped fractal structure 11, and the four photodiodes 13 are respectively connected between the four ends of the cross-shaped fractal structure 11 and the cross-connecting square ring 12. The centers of the cross-shaped fractal structure 11 and the cross-connecting square ring 12 coincide, and both are centrally symmetrical structures.

[0057] Specifically, the cross fractal structure 11 is disposed at the center of the upper surface of the dielectric substrate 2. When the photodiode 13 is off, the cross fractal structure 11 and the cross-connected square loop 12 are in a separated state. When the photodiode 13 is on, the cross fractal structure 11 and the cross-connected square loop 12 are in a connected state. In the transmission mode, the external optical signal turns off the photodiode 13, and the photocurrent changes the current path on the surface of the first metal layer 1. At this time, the surface current is mainly concentrated on the cross-connected square loop 12, reducing the reflection and enabling the electromagnetic wave to pass through effectively. Conversely, in the reflection mode, by adjusting the optical signal to turn on the photodiode 13, the surface current is mainly concentrated on the cross fractal structure 11. At this time, the on state of the photodiode 13 increases the equivalent impedance of the first metal layer 1, preventing the transmission of the electromagnetic wave and causing the electromagnetic wave to be reflected, achieving the stealth effect. In this embodiment, by precisely controlling the on and off states of the photodiode 13, the switching between the transmission mode and the reflection mode is achieved, and it can flexibly switch between the transmission and reflection modes at a frequency of 11.1 GHz, realizing the dynamic regulation of electromagnetic waves. Moreover, since both the cross fractal structure 11 and the cross-connected square loop 12 are centrosymmetric structures, that is, the first metal layer 1 is a centrosymmetric structure, the frequency selective surface unit structure provided in this embodiment has good angular stability and polarization stability.

[0058] In this embodiment, please refer to Figure 3 , the cross fractal structure 11 includes: a central rectangular portion 111 and four L-shaped fractal portions 112. Among them, the central rectangular portion 111 is disposed at the center of the upper surface of the dielectric substrate 2. The four L-shaped fractal portions 112 are respectively connected to the four sides of the central rectangular portion 111.

[0059] Furthermore, please refer to Figure 4 , the L-shaped fractal portion 112 includes: a first rectangular portion 1121, a second rectangular portion 1122, and a slit 1123. Among them, the first rectangular portion 1121 is connected to the side of the central rectangular portion 111. The second rectangular portion 1122 is disposed perpendicular to the first rectangular portion 1121 and is connected to one side of the first rectangular portion 1121. The slit 1123 is disposed perpendicular to the first rectangular portion 1121 and extends from the other side of the first rectangular portion 1121 into the interior of the second rectangular portion 1122. Specifically, the first rectangular portion 1121, the second rectangular portion 1122, and the slit 1123 form the L-shaped fractal portion 112.

[0060] In this embodiment, please refer to Figure 3The cross-connecting square ring 12 includes four triangular structures 121, four square ring connecting portions 122, and four connecting lines 123. The four triangular structures 121 are respectively located at the ends of the four fractal portions 112, and there is a gap between each triangular structure 121 and each fractal portion 112. The four square ring connecting portions 122 are respectively connected between every two adjacent triangular structures 121. The four connecting lines 123 are respectively connected at the midpoint of each square ring connecting portion 122.

[0061] In this embodiment, four photodiodes 13 are respectively disposed at the intervals between the four triangular structures 121 and the four fractal portions 112, and the positive terminal of the photodiode 13 is connected to the fractal portion 112, and the negative terminal of the photodiode 13 is connected to the triangular structure 121.

[0062] In this embodiment, the dielectric substrate 2 and the central rectangular portion 111 are concentric squares. The width of the first rectangular portion 1121 is equal to the side length of the central rectangular portion 111. The long axis of the first rectangular portion 1121 lies on the axis of the dielectric substrate 2. The triangular structure 121 is an isosceles triangle, with its apex facing the edge of the dielectric substrate 2, and its median lying on the axis of the dielectric substrate 2. Four connecting lines 123 extend from the midpoint of each square ring connecting portion 122 to the four corners of the dielectric substrate 2. It should be understood that the long axis of the first rectangular portion 1121 is the axis of the first rectangular portion 1121 along its length.

[0063] Please see Figure 5 In this embodiment, the second metal layer 3 includes four rectangular structures 31. The four rectangular structures 31 are all located on the lower surface of the dielectric substrate 2, and the four rectangular structures 31 extend from the midpoint of the four sides of the dielectric substrate 2 toward the center of the dielectric substrate 2.

[0064] Specifically, the long axis of the first rectangular portion 1121 is aligned with the midline of the triangular structure 121. A photodiode 13 is disposed between the end of the first rectangular portion 1121 and the base of the triangular structure 121. The positive terminal of the photodiode 13 is connected to the first rectangular portion 1121, and the negative terminal of the photodiode 13 is connected to the triangular structure 121. Square ring connecting portions 122 are connected between the base corners of every two adjacent triangular structures 121, and the four square ring connecting portions 122 and the outer edges of the four triangular structures 121 form a square. The axis of the rectangular structure 31 coincides with the axis of the dielectric substrate 2, and there is a gap between the ends of the four rectangular structures 31. It should be understood that the dielectric substrate 2 has two mutually perpendicular axes; the axes of two rectangular structures 31 coincide with one axis of the dielectric substrate 2, and the axes of the other two rectangular structures 31 coincide with the other axis of the dielectric substrate 2. In this embodiment, both the first metal layer 1 and the second metal layer 3 are centrosymmetric structures and axially symmetric structures.

[0065] In this embodiment, the materials of the first metal layer 1 and the second metal layer 3 both include one of copper (Cu), aluminum (Al), and gold (Au). The material of the dielectric substrate 2 includes a flexible flame-retardant material. Furthermore, the dielectric substrate 2 has a relative permittivity of 2.65, an electrical cutting loss of 0.0001, a thickness of 0.3 mm, and the thicknesses of the first metal layer 1 and the second metal layer 3 are 0.017 mm to 0.035 mm. The side length of the dielectric substrate 2 is 9 mm. Exemplarily, the material of the dielectric substrate 2 is F4B substrate.

[0066] The frequency-selective surface unit structure with transmittance and reflection switchability provided in this embodiment achieves the transmittance and reflection switching function through photodiodes. It is not easily damaged by heat, is compatible with various electromagnetic environments, and exhibits high stability. It flexibly switches between transmittance and reflection modes near 11.1 GHz, simultaneously ensuring signal transmission in the X-band and the stealth capability of the antenna system. Furthermore, this embodiment uses a flexible material as the dielectric substrate, possessing better conformal capabilities and greater practical application value. The surface unit structure provided in this embodiment has a surface size of only 9mm*9mm, meeting the trend of miniaturization and the requirements of processing technology. Moreover, since the first metal layer 1 and the second metal layer 3 are centrosymmetric structures, this frequency-selective surface unit structure has good angular stability and polarization stability, with minimal changes in resonant frequency and bandwidth when irradiated by incident waves at different angles.

[0067] Example 2

[0068] Please see Figure 6 , Figure 6 This is a schematic diagram of a frequency-selective surface structure that can switch between transmission and reflection, provided in an embodiment of the present invention.

[0069] This embodiment provides a frequency-selective surface structure with switchable transmission and reflection, comprising M×N periodically arranged unit structures. This unit structure is the frequency-selective surface unit structure with switchable transmission and reflection provided in Embodiment 1 of this invention, where M and N are positive integers. For example, M and N are both 10, 20, or 40.

[0070] Example 3

[0071] Based on Embodiment 1 and Embodiment 2, this embodiment further defines the geometric parameters of the frequency-selective surface unit structure with switchable transmission and reflection, and simulates the surface structure composed of the surface unit structure to analyze the performance of the surface structure composed of the surface unit structure.

[0072] Please combine Figure 3 , Figure 4 and Figure 5In this embodiment, the width W1 of the first rectangular portion 1121 in the transmittance-reflection switchable frequency selective surface unit structure is 1.3 mm, the length L1 of the first rectangular portion 1121 is 1.25 mm, the width W2 of the second rectangular portion 1122 is 0.5 mm, the length L3 of the second rectangular portion 1122 is 0.6 mm, the width W3 of the gap 1123 is 0.1 mm, the distance L2 between the second rectangular portion 1122 and the first rectangular portion 1121 is 1.05 mm, the width W4 of the square ring connecting portion 122 is 0.1 mm, the height L4 of the triangular structure 121 is 1.4 mm, the distance d between the vertices of every two adjacent triangular structures 121 is 6.2 mm, the width W5 of the connecting line 123 is 0.3 mm, the width W6 of the rectangular structure 31 is 0.4 mm, the length L5 of the rectangular structure 31 is 2.5 mm, the side length p of the dielectric substrate 2 is 9.0 mm, and the thickness t of the dielectric substrate 2 is 0.3 mm.

[0073] In this embodiment, the frequency-selective surface structure with switchable transmission and reflection includes 5×5 periodically arranged unit structures.

[0074] Furthermore, in order to verify the performance of the frequency-selective surface structure (FSS) with switchable transmission and reflection provided in this embodiment, multiple performance simulation analyses of the FSS structure were performed using the commercial simulation software CST.

[0075] Please see Figure 7 to Figure 10 , Figure 7 This is a simulation diagram of the filtering performance of a frequency-selective surface structure with switchable transmission and reflection provided in an embodiment of the present invention when the photodiode is turned on in TE polarization mode. Figure 8 This is a simulation diagram of the filtering performance of a frequency-selective surface structure with switchable transmission and reflection provided in an embodiment of the present invention when the photodiode is blocked in TE polarization mode. Figure 9 This is a simulation diagram of the filtering performance of a frequency-selective surface structure with switchable transmission and reflection provided by an embodiment of the present invention when the photodiode is turned on in TM polarization mode. Figure 10 This is a simulation diagram of the filtering performance of a frequency-selective surface structure with switchable transmission and reflection provided in an embodiment of the present invention when the photodiode is blocked in TM polarization mode. Figure 7 and Figure 8As can be seen from the return loss S11 and insertion loss S21, when the photodiode is on, the resonant frequency of the FSS structure in this embodiment is 11.1 GHz, the insertion loss S21 is -68.9 dB, and the bandwidth at -10 dB is 5.1 GHz. At this time, the FSS structure is in a reflection state. When the photodiode is off, the resonant frequency of the FSS structure in this embodiment is 11.1 GHz, the return loss S11 is -20.2 dB, and the bandwidth at -10 dB is 0.3 GHz. At this time, the FSS structure is in a transmission state. That is to say, in TE polarization mode, this FSS structure has the effect of flexibly switching between transmission mode and reflection mode for signals with frequencies around 11.1 GHz (10.9~11.2 GHz).

[0076] Furthermore, from Figure 9 and Figure 10 As can be seen from the return loss S11 and insertion loss S21, when the photodiode is on, the resonant frequency of the FSS structure in this embodiment is 11.1 GHz, the insertion loss S21 is -69.7 dB, and the bandwidth at -10 dB is 5.1 GHz. At this time, the FSS structure is in a reflection state. When the photodiode is off, the resonant frequency of the FSS structure in this embodiment is 11.1 GHz, the return loss S11 is -20.1 dB, and the bandwidth at -10 dB is 0.3 GHz. At this time, the FSS structure is in a transmission state. That is to say, in TM polarization mode, this FSS structure has the effect of flexibly switching between transmission mode and reflection mode for signals with frequencies around 11.1 GHz.

[0077] Furthermore, comprehensive Figure 7 to Figure 10 As can be seen, the FSS structure provided in this embodiment has good transmission and reflection switching performance in TE mode and TM mode, and the resonant frequency is always within the X-band, that is, it has excellent polarization stability.

[0078] Furthermore, to study the angular stability of the FSS structure in this embodiment, its frequency characteristics were obtained by irradiating it with incident waves at incident angles of 0°, 15°, 30°, and 45° in TE and TM modes. Please refer to [link to relevant documentation]. Figure 11 to Figure 14 , Figure 11 This is a simulation diagram of the angular stability performance of a frequency-selective surface structure with switchable transmission and reflection provided by an embodiment of the present invention when the photodiode is turned on in TE polarization mode. Figure 12 This is a simulation diagram of the angular stability performance of a frequency-selective surface structure with switchable transmission and reflection provided by an embodiment of the present invention when the photodiode is blocked in TE polarization mode. Figure 13 This is a simulation diagram of the angular stability performance of a frequency-selective surface structure with switchable transmission and reflection provided by an embodiment of the present invention when the photodiode is turned on in TM polarization mode. Figure 14This is a simulation diagram of the angular stability performance of a frequency selective surface structure (FSS) with transmittance and reflection switchable under TM polarization mode with photodiode isolation, provided in an embodiment of the present invention. This FSS structure exhibits good angular stability and excellent switching characteristics near 11.1 GHz. Under electromagnetic incident wave illumination at different angles, the frequency deviation is within an acceptable range, demonstrating excellent signal transmission capability and anti-interference ability. Figure 8 and Figure 9 The performance simulation diagrams show that, in TE and TM modes, when irradiated by incident waves with incident angles of 0°, 15°, 30°, and 45°, this FSS structure has the effect of switching between transmission and reflection modes in the X-band, demonstrating excellent filtering and shielding performance, thus confirming that this structure has excellent angular stability.

[0079] The photodiode-based transmittance and reflectance switchable frequency selective surface structure of this embodiment flexibly switches between transmission and reflection modes around 11.1 GHz, enabling simultaneous X-band signal transmission capability and electromagnetic protection capability of corresponding radio frequency systems under various electromagnetic scenarios. The surface structure provided in this embodiment has good angular and polarization stability, with minimal changes in resonant frequency and bandwidth when irradiated by incident waves at different angles. Furthermore, the resonant frequency shows no deviation when the incident wave is perpendicularly irradiated (incident angle of 0°) in TE and TM polarization modes, without affecting the structural performance.

[0080] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A frequency-selective surface unit structure with switchable transmission and reflection, characterized in that, include: The first metal layer (1), the dielectric substrate (2), and the second metal layer (3) are arranged sequentially from top to bottom; The first metal layer (1) includes: a cross-shaped fractal structure (11), a cross-connected square ring (12), and four photodiodes (13), wherein, The cross-shaped fractal structure (11) is disposed on the upper surface of the dielectric substrate (2); The cross-connecting square ring (12) is located on the outside of the cross-shaped fractal structure (11); The four photodiodes (13) are respectively connected between the four ends of the cross-shaped fractal structure (11) and the cross-connecting square ring (12); The centers of the cross-shaped fractal structure (11) and the cross-connected square ring (12) coincide, and both are centrally symmetrical structures; The cross-shaped fractal structure (11) includes: a central rectangular portion (111) and four fractal portions (112), wherein the central rectangular portion (111) is disposed at the center of the upper surface of the dielectric substrate (2); The four fractal parts (112) are respectively connected to the four sides of the central rectangular part (111); The cross-connecting square ring (12) includes four triangular structures (121), four square ring connecting parts (122), and four connecting lines (123), wherein, The four triangular structures (121) are respectively disposed at the ends of the four fractal parts (112), and there is a gap between each triangular structure (121) and each fractal part (112); The four square ring connecting parts (122) are respectively connected between every two adjacent triangular structures (121); The four connecting lines (123) are respectively connected to the midpoint of each of the square ring connecting parts (122); The four photodiodes (13) are respectively disposed at the intervals between the four triangular structures (121) and the four fractal parts (112), and the positive terminal of the photodiode (13) is connected to the fractal part (112), and the negative terminal of the photodiode (13) is connected to the triangular structure (121).

2. The frequency-selective surface unit structure with switchable transmission and reflection according to claim 1, characterized in that, The fractal portion (112) includes: a first rectangular portion (1121), a second rectangular portion (1122), and a gap (1123), wherein, The first rectangular portion (1121) is connected to the edge of the central rectangular portion (111); The second rectangular portion (1122) is disposed perpendicular to the first rectangular portion (1121) and connected to one side of the first rectangular portion (1121); The slit (1123) is provided perpendicular to the first rectangular portion (1121) and extends from the other side of the first rectangular portion (1121) into the interior of the second rectangular portion (1122).

3. The frequency-selective surface unit structure with switchable transmission and reflection according to claim 2, characterized in that, The dielectric substrate (2) and the central rectangular portion (111) are concentric squares; The width of the first rectangular portion (1121) is equal to the side length of the central rectangular portion (111); The long axis of the first rectangular portion (1121) is located on the axis of the dielectric substrate (2).

4. The frequency-selective surface unit structure with switchable transmission and reflection according to claim 3, characterized in that, The triangular structure (121) is an isosceles triangle, and the apex of the triangular structure (121) is set towards the side of the dielectric substrate (2), and the midline of the triangular structure (121) is located on the axis of the dielectric substrate (2). The four connecting lines (123) extend from the midpoint of each of the square ring connecting portions (122) to the four corners of the dielectric substrate (2).

5. The frequency-selective surface unit structure with switchable transmission and reflection according to claim 1, characterized in that, The second metal layer (3) includes four rectangular structures (31); The four rectangular structures (31) are all located on the lower surface of the dielectric substrate (2), and the four rectangular structures (31) extend from the midpoint of the four sides of the dielectric substrate (2) toward the center of the dielectric substrate (2).

6. The frequency-selective surface unit structure with switchable transmission and reflection according to claim 1, characterized in that, The materials of the first metal layer (1) and the second metal layer (3) both include one of copper, aluminum, and gold; The material of the dielectric substrate (2) includes: flexible flame-retardant material.

7. A frequency-selective surface structure with switchable transmission and reflection, characterized in that, include A periodically arranged unit structure, wherein the unit structure is the frequency-selective surface unit structure with transmittance and reflection switchable as described in any one of claims 1 to 6; Where M and N are positive integers.

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