Polarization-independent switchable frequency selective absorption transmitter

Abstract

The invention provides a polarization-independent switchable frequency selective absorption transmitter. The polarization-independent switchable frequency selective absorption transmitter comprises a loss layer and a switching layer, the loss layer and the switching layer are distributed up and down, and an air spacing layer is arranged between the loss layer and the switching layer; the loss layer comprises a first dielectric substrate, an upper loss layer and a lower loss layer, the upper loss layer and the lower loss layer are attached to the upper surface and the lower surface of the dielectric substrate respectively, and the upper loss layer and the lower loss layer are distributed orthogonally; the switching layer comprises a second dielectric substrate, a metal layer and four PIN diodes; the metal layer is attached to the upper surface of the second dielectric substrate, the metal layer is provided with a square annular gap, and the four PIN diodes are all arranged in the square annular gap. The loss layer and the lower loss layer are in a Z-shaped structure in central symmetry and comprise two interdigital structures. According to the invention, stable switching of two modes of absorption-transmission-absorption and absorption-reflection-absorption can be realized, characteristics of broadband absorption, low insertion loss and polarization independence are realized, and the adaptability to a complex electromagnetic environment is improved.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave absorption technology, specifically to a polarization-independent switchable frequency-selective absorption transducer. Background Technology

[0002] In today's era of rapid technological advancement, the electromagnetic environment is becoming increasingly complex. With the widespread application of wireless communication technology, electronic devices, and various electromagnetic systems, electromagnetic interference problems are becoming more and more serious. As a key device capable of effectively suppressing electromagnetic reflection and reducing electromagnetic interference, the performance of microwave absorbers is crucial for ensuring the normal operation of various electronic systems and optimizing the electromagnetic environment. Traditional microwave absorbers are typically based on fixed structural and material designs, possessing relatively fixed absorption frequencies and bandwidths. In relatively simple and stable electromagnetic environments, these traditional absorbers can play a certain role, converting the energy of incident electromagnetic waves into other forms of energy such as heat through the electromagnetic loss characteristics of the materials, thereby reducing the intensity of reflected electromagnetic waves. On the one hand, due to their fixed frequency response characteristics, they are difficult to adapt to the absorption requirements of electromagnetic waves of different frequencies. When the frequency in the electromagnetic environment changes, traditional absorbers may fail to achieve effective absorption at the new frequency point, resulting in poor absorption of specific frequency electromagnetic waves, or even complete failure.

[0003] Electromagnetic functional devices play a crucial role in radar, communication, and electromagnetic compatibility (EMC) fields. Among them, frequency selective surfaces (FSS) have become a research hotspot due to their ability to transmit or reflect electromagnetic waves in specific frequency bands. FSSs exhibit excellent electromagnetic transmission performance within the antenna's operating frequency band, while reflecting electromagnetic waves outside the transmission band. However, their single-function nature makes them unsuitable for complex electromagnetic environments. Based on this, frequency selective absorbers-transmitters (FSRs) were proposed. Their core characteristic is the absorption of electromagnetic waves on both sides of the transmission (or reflection) band, forming an "absorption-transmission-absorption" (ATA) or "absorption-reflection-absorption" (ARA) frequency band distribution. This effectively suppresses out-of-band scattering and enhances the anti-interference capability of electromagnetic systems.

[0004] A typical design approach for traditional FSRs combines a lossy resistive element with a lossless bandpass FSS: the lossy resistive element absorbs electromagnetic waves at a specific frequency and presents infinite impedance at its resonant frequency (simulating a parallel LC circuit); the bandpass FSS at the bottom is also equivalent to a parallel LC circuit, forming a transmission window when both resonate at the same frequency, achieving selective transmission and out-of-band absorption of electromagnetic waves. However, traditional FSRs have significant limitations: they only support a single mode (such as a fixed ATA mode), cannot switch between transmission and reflection functions according to dynamic electromagnetic environments, and are difficult to adapt to dynamically changing application scenarios; while some reconfigurable FSRs can achieve mode adjustment, they suffer from low reliability, narrow absorption bandwidth, and polarization sensitivity, making them difficult to meet practical application requirements.

[0005] Furthermore, reconfigurable FSRs based on liquid metal (EGaIn) suffer from insufficient reliability: While these structures achieve mode switching by controlling the injection / removal of liquid metal in microchannels, emphasizing the self-healing properties of the liquid metal, its fluidity can lead to changes in interface wettability or seal failure during long-term use, severely impacting the reliability of the reconfiguration function. Tuned FSRs based on varactor diodes have functional limitations: These structures, by changing the capacitance of the varactor diodes to synchronously tune the resonant frequencies of the top and bottom FSSs, can only achieve tuning in the pass-through frequency band and cannot switch to the "ARA" mode, resulting in a single operating mode and a high insertion loss, reaching up to 3dB. Dual-mode FSRs based on PIN diodes have narrow absorption bandwidth and are polarization-sensitive: These structures achieve mode switching through the switching states of two layers of PIN diodes, but the absorption bandwidth is narrow (relative bandwidth less than 60%), failing to meet broadband absorption requirements. Simultaneously, the structure is sensitive to electromagnetic wave polarization direction, exhibiting significant performance differences under different polarizations (TE / TM), limiting applications in various polarization scenarios.

[0006] Therefore, developing an FSR that combines mode switchability, broadband absorption, low insertion loss, polarization independence, and high reliability has become an urgent technical problem to be solved. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a polarization-independent switchable frequency-selective absorber-transmitter. Through a layered structure design of "double-layer orthogonal loss layer + bottom diode switchable layer", combined with interdigital resonators and equivalent circuit modulation, it can achieve stable switching between "ATA" (absorption-transmission-absorption) and "ARA" (absorption-reflection-absorption) modes. At the same time, it has broadband absorption, low insertion loss and polarization-independent characteristics, improving its adaptability to complex electromagnetic environments.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention provides a polarization-independent switchable frequency-selective absorber-transmitter, comprising a loss layer and a switching layer; the loss layer and the switching layer are distributed vertically, with an air gap between them; the loss layer comprises a first dielectric substrate, an upper loss layer, and a lower loss layer, the upper and lower loss layers being attached to the upper and lower surfaces of the dielectric substrate respectively, and the upper and lower loss layers having the same structure and being orthogonally distributed; the switching layer comprises a second dielectric substrate, a metal layer, and four PIN diodes; the metal layer is attached to the upper surface of the second dielectric substrate, and the metal layer has a square annular slit, within which the four PIN diodes are disposed.

[0010] Furthermore, both the upper and lower loss layers are centrally symmetrical Z-shaped structures, including two interdigitated structures. Each interdigitated structure includes a main arm, a lumped resistor, a central cross resonator, and interdigitated arms. The inner sides of both ends of the main arm are connected to a first S-shaped structure via a first connecting arm. The central cross resonator includes a second S-shaped structure and a second connecting arm. The outer end of the lumped resistor is connected to a first S-shaped structure, and the inner end of the lumped resistor is connected to a second S-shaped structure. The second S-shaped structure is connected to the interdigitated arms via a second connecting arm, and the interdigitated arms are provided with several interdigitated fingers. The interdigitated fingers of the two interdigitated structures are parallel and spaced apart. The interdigitated arms of the two interdigitated structures are connected via a third connecting arm.

[0011] Furthermore, the two first S-shaped structures are symmetrically distributed about the centerline of the main arm.

[0012] Furthermore, the connection point between the third connecting arm and the interdigital arm is the midpoint of the interdigital arm.

[0013] Furthermore, the main arm is parallel to the interdigital arm, and the interdigital fingers are perpendicular to the interdigital arm.

[0014] Furthermore, both the first dielectric substrate and the second dielectric substrate are F4BM265 dielectric substrates.

[0015] Furthermore, the resistance value of the lumped resistor is 100Ω.

[0016] Furthermore, the metal layer is made of copper, as are the upper and lower loss layers.

[0017] Furthermore, the four PIN diodes are respectively distributed at the center of the four sides of the square annular gap.

[0018] This invention uses solid-state PIN diodes (on / off state) to achieve mode switching, avoiding the fluidity defects of liquid metal. By directly changing the reflection / transmission characteristics of the bottom layer through the diode's "on / off" state, ATA and ARA mode switching is achieved. The orthogonal Z-shaped interdigitated structure (vertically distributed in the upper and middle layers) achieves polarization independence.

[0019] The beneficial effects of this invention are:

[0020] (1) The mode switching reliability of this invention is higher and there is no risk of physical failure:

[0021] This invention uses a solid-state PIN diode as the core switching component, and achieves mode control through the switching of the electrical state of "ON" / "OFF": the diode exhibits a stable low resistance (R) in the on state. ON=1.5Ω), exhibiting a stable capacitance in the cutoff state (COFF=0.05pF). Compared to existing reconfigurable FSRs based on liquid metal (EGaIn), this invention eliminates the physical flow loss of liquid metal, significantly improving structural stability and mode switching reliability during long-term use, and avoiding the risks of seal failure or changes in interface characteristics due to fluidity.

[0022] (2) The present invention offers more flexible mode switching, covering both ATA and ARA modes:

[0023] To address the limitation of existing technologies where varactor diode-based FSRs can only tune the transmission frequency band and cannot switch to ARA mode, this invention achieves dynamic switching between two core modes through a bottom switchable layer diode switch design. The two modes can be directly switched through diode bias voltage, covering "transmission-absorption" and "reflection-absorption" scenarios, and the flexibility is far superior to existing solutions that can only be tuned.

[0024] (3) Wider absorption bandwidth to meet the needs of broadband applications:

[0025] To address the problem of narrow absorption bandwidth (less than 60%) of FSR based on PIN diodes in existing technologies, this invention optimizes the structure of the top and middle positive cross-finger loss layers to achieve a wider absorption band and meet the requirements of broadband electromagnetic absorption.

[0026] (4) Polarization-independent properties, adaptable to all polarization scenarios

[0027] To address the problem of polarization sensitivity (significant differences in polarization performance between TE and TM) in existing PIN diode-based FSR technologies, this invention employs an orthogonal symmetrical design (vertically distributed) of the upper and middle interdigital structures to ensure consistent electromagnetic performance under TE and TM polarization, thus resolving the polarization sensitivity issue. This enables polarization-independent characteristics and adaptability to electromagnetic wave scenarios with arbitrary polarization directions.

[0028] (5) Low insertion loss

[0029] This invention achieves broadband absorption and mode switching while maintaining excellent transmission efficiency: the insertion loss in the transmission / reflection bands is extremely low, far lower than the signal attenuation level of traditional structures. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a switchable frequency selective absorption transducer according to an embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram of the loss layer in an embodiment of the present invention;

[0032] Figure 3 This is a schematic diagram of the switching layer in an embodiment of the present invention;

[0033] Figure 4 The reflection coefficients (S) of TE and TM polarization when the diode is off and on in the embodiments of the present invention are... 11 ) and transmission coefficient (S 21 (a) Curve graph, where a represents the off state and b represents the on state;

[0034] Figure 5 The reflection coefficient (S) of the electromagnetic wave obliquely incident on TE and TM polarization when the diode is turned off in the embodiment of the present invention. 11 ) and transmission coefficient (S 21 () Curve diagram, where a is TM polarized oblique incidence and b is TE polarized oblique incidence;

[0035] Figure 6 This is a graph showing the absorption rate under TM and TE polarization when the diode is disconnected according to an embodiment of the present invention, where a is TM polarization and b is TE polarization;

[0036] Figure 7 These are S-parameter curves and absorption rate diagrams under TM and TE polarizations when the diode is conducting and obliquely incident according to an embodiment of the present invention. Here, a is the TM polarization S-parameter curve, b is the TE polarization S-parameter curve, c is the absorption rate curve under TM polarization, and d is the absorption rate curve under TE polarization.

[0037] Label name in the image:

[0038] 1. Main arm; 2. Lumped resistor; 3. Center cross resonator; 4. Interdigitated arm; 5. Interdigitated finger; 6. Third connecting arm. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] like Figure 1 As shown, this embodiment of the invention provides a polarization-independent switchable frequency selective absorber and transmitter, which adopts a three-layer stacked design of "loss layer + air gap layer + switching layer". The loss layer and the switching layer are distributed vertically, and the air gap layer is between the loss layer and the switching layer. Broadband matching is achieved through the air gap layer, and the height of the air gap layer is h = 5.1 mm.

[0041] like Figure 1 and 2As shown, the loss layer includes a first dielectric substrate, an upper loss layer, and a lower loss layer. Both the upper and lower loss layers are made of copper. The second dielectric substrate is an F4BM265 dielectric substrate (dielectric constant 2.65, loss tangent 0.001, thickness t1 = 1 mm). The upper and lower loss layers are attached to the upper and lower surfaces of the dielectric substrate, respectively, and have identical structures, orthogonally distributed. Both the upper and lower loss layers are centrally symmetrical Z-shaped structures, including two interdigitated structures. Each interdigitated structure includes a main arm 1, a lumped resistor 2, a central cross resonator 3, and an interdigitated arm 4.

[0042] The inner sides of both ends of the main arm 1 are connected to first connecting arms, which are perpendicular to the main arm 1. The inner ends of the two first connecting arms are connected to a first S-shaped structure, which is symmetrically distributed about the centerline of the main arm 1. The first S-shaped structure consists of a series of vertical segments connected sequentially from the outside to the inside, each vertical segment being parallel to the main arm 1. The inner end of each first connecting arm is connected to the end of the first vertical segment. The length of the main arm 1 is w1 = 2.2 mm, the length of each vertical segment of the first S-shaped structure is w2 = 0.6 mm, and the sum of the width of the main arm 1, the length of the first connecting arms, and the height of the first S-shaped structure is w4, which is w4 = 0.7 mm.

[0043] The central cross resonator 3 includes a second S-shaped structure and a second connecting arm. The second S-shaped structure is composed of "vertical segment-horizontal segment-vertical segment-horizontal segment-vertical segment" connected sequentially from the outside to the inside. The inner end of the vertical segment of the second S-shaped structure is connected to the second connecting arm, which is connected to the interdigitated arm 4. The sum of the height of the second S-shaped structure and the length of the second connecting arm is w3, where w3 = 0.95 mm. The distance between the two vertical segments in the second S-shaped structure is g = 0.1 mm.

[0044] The lumped resistor 2 is distributed between the first S-shaped structure and the second S-shaped structure. The outer end of the lumped resistor 2 is connected to the inner vertical segment of the first S-shaped structure, and the inner end of the lumped resistor 2 is connected to the outer vertical segment of the second S-shaped structure. The resistance value of the lumped resistor 2 is 100Ω, and electromagnetic wave absorption in a specific frequency band is achieved through circuit simulation principles.

[0045] The second S-shaped structure is connected to the interdigitated arm 4 via a second connecting arm. Several interdigitated fingers 5 are arranged on the interdigitated arm 4. The interdigitated fingers 5 of two interdigitated structures are parallel and spaced apart, with a spacing s = 0.1 mm. The distance g = 0.1 mm between one interdigitated finger 5 and the interdigitated arm 4 of another interdigitated structure. The two interdigitated arms 4 are connected by a third connecting arm 6, and the connection point between the third connecting arm and the interdigitated arm 4 is the midpoint of the interdigitated arm 4. The distance a = 1.85 mm between the two interdigitated arms 4. The main arm 1 is parallel to the interdigitated arm 4, and the interdigitated fingers 5 are perpendicular to the interdigitated arm 4.

[0046] like Figure 3 As shown, the switching layer includes a second dielectric substrate, a metal layer, and four PIN diodes. The metal layer is a square copper sheet (grounded) with a side length P = 7 mm. The second dielectric substrate is an F4BM265 dielectric substrate (dielectric constant 2.65, loss tangent 0.001, thickness t2 = 1 mm). The metal layer is attached to the upper surface of the second dielectric substrate and has a square annular slit. The square annular slit divides the metal layer into a square annular metal sheet (ring width w6 = 0.5 mm) and a square metal sheet (side length w5 = 5.74 mm). The four PIN diodes are loaded within the square annular slit and are distributed at the center of the four sides of the square annular slit. The electromagnetic response of the bottom layer can be changed by the "on / off" state of the diodes.

[0047] Effect test:

[0048] Figure 4 a is the reflection coefficient of TE and TM polarization when the diode is turned off in Example 1 (S 11 ) and transmission coefficient (S 21 (Line graph.) Figure 4 As shown in Figure a, when the diode is turned off, the reflection coefficient (S) in the 5.93–16.89 GHz frequency band varies under different polarization states. 11 The transmittance (S) remained below -10 dB throughout the 9.77–11.56 GHz frequency band. 21 The insertion loss is always above -3dB, with 0.38dB under TM polarization and 0.46dB under TE polarization. Figure 4 b is the reflection coefficient of TE and TM polarization when the diode in Example 1 is turned on (S 11 ) and transmission coefficient (S 21 (Line graph.) Figure 4 As shown in b, when the diode is turned on, under TE polarization, the S frequency bands in the 5.99–8.56 GHz and 13.63–16.51 GHz bands... 11 Always below -10dB; under TM polarization, S in the 6.15–8.51GHz and 13.01–16.42GHz bands 11 It remains below -10dB. The operating mode at this time is ARA mode (diode path): the reflection band is 9.8-12.1GHz (relative bandwidth 13%, -3dB standard), the insertion loss is as low as 0.33dB (at 10.44GHz), and the absorption bands on both sides are 5.6-9.13GHz (relative bandwidth 47%) and 12.35-17GHz (relative bandwidth 31%).

[0049] Figure 5 'a' is the S-parameter curve of the electromagnetic wave obliquely incident on TM polarization when the diode is cut off, as shown in the figure. Figure 5As shown in Figure a, when the diode is open and the angle of incidence of electromagnetic waves reaches 30 degrees, the absorption and transmission performance of electromagnetic waves under TE polarization remains almost unchanged. Under TM polarization, there is a resonant point in the mid-frequency band, which basically coincides with the low-frequency absorption band and the mid-frequency transmission band. Due to the increased angle of incidence, impedance mismatch occurs, and there is also a jumping resonant point in the high-frequency band. This can be seen as the high-frequency absorption band narrowing as the incident angle increases, but it does not affect the absorption-transmission-absorption working mode. The transmission frequency band is 9.73-11.56GHz (relative bandwidth 17%), with an insertion loss as low as 0.46dB (at 10.41GHz). The absorption frequency bands on both sides are 5.58-9.19GHz (relative bandwidth 49%) and 12.17-17.42GHz (relative bandwidth 35%). Figure 5 b is the S-parameter curve of the electromagnetic wave obliquely incident on TE polarization when the diode is cut off, as shown in the figure. Figure 5 As shown in b, under TE polarization, as the incident angle of electromagnetic waves increases, the overall performance is only slightly different from that of electromagnetic waves with perpendicular incident angle, and the performance is stable. In ATA mode, the relative bandwidth of low-frequency absorption reaches 49% (5.58-9.19GHz), and the relative bandwidth of high-frequency absorption reaches 35% (12.17-17.42GHz).

[0050] Figure 6 a is the S-parameter curve of TM polarization when the diode is in the circuit, such as Figure 6 As shown in Figure a, according to the formula, the absorption rate A = 1 - S11 2 -S21 2 Under TM polarization, there is a resonant point in the middle of the left transition band. Figure 5 The fact that one of the resonant points in point a coincides with another indicates that resonance at that frequency does not affect the absorption-transmission-absorption operating mode. As the incident angle increases, the resonant point shifts slightly, but the overall absorption performance remains stable, verifying the design's adaptability to different polarization states. Figure 6 b is the S-parameter curve of TE polarization when the diode is in the circuit, such as Figure 6 As shown in b, under TE polarization, the overall absorption performance remains stable as the incident angle increases. In ARA mode, the relative bandwidth of low-frequency absorption reaches 47% (5.6-9.13GHz), and the relative bandwidth of high-frequency absorption reaches 31% (12.35-17GHz).

[0051] Figure 7 a is the S-parameter curve of electromagnetic wave obliquely incident on TE polarization when the diode is in the circuit. Figure 7 b is the S-parameter curve of electromagnetic wave oblique incidence under TM polarization when the diode is in the circuit. Figure 7 c is the absorption rate curve of electromagnetic waves obliquely incident on TE polarization when the diode is in the circuit. Figure 7 d is the absorption rate curve of electromagnetic waves obliquely incident on TM polarization when the diode is in the circuit. From Figure 7As shown, when the diode is conducting and the oblique incidence angle reaches 30 degrees, the absorber's operating mode remains unchanged: absorption-reflection-absorption. The jump resonant point under TE polarization can be considered as the high-frequency absorption band narrowing with increasing angle, due to impedance mismatch. Overall, the reflection coefficient (S) under TE and TM polarization... 11 ) and transmission coefficient (S 21 The curves almost completely overlap, and the absorption and transmission performance are consistent. Although there are slight differences in bandwidth in the high-frequency band, the overall response trend is consistent and has no substantial impact on the ARA mode. It can adapt to electromagnetic wave scenarios with arbitrary polarization direction.

[0052] This invention solves the problem that traditional FSRs only support a single ATA mode and cannot adapt to complex electromagnetic environments. It aims to achieve stable switching between ATA and ARA modes. By controlling the "on / off" state of the diode, the structure can dynamically switch between absorption-transmission-absorption and absorption-reflection-absorption characteristics as needed, thereby improving its adaptability to complex electromagnetic environments.

[0053] To address the reliability issues of reconfigurable FSRs based on liquid metal (EGaIn), such as interface wettability changes and seal failures caused by the fluidity of the liquid metal, this invention employs solid-state PIN diodes as switching elements. Mode control is achieved through diode electrical state switching, avoiding the physical defects of liquid metal and improving the long-term reliability and stability of the structure. To address the limitation of tuned FSRs based on varactor diodes, which can only tune the pass-through frequency band and cannot switch to ARA mode, this invention uses a bottom switchable layer diode switch design. This not only achieves stable transmission in the pass-through frequency band (ATA mode) but also creates a reflective surface at the bottom through diode conduction, achieving reflection frequency band characteristics (ARA mode), breaking through the limitation of single tuning function and expanding the flexibility of mode switching. To address the narrow absorption bandwidth (less than 60%) and polarization sensitivity of dual-mode FSRs based on PIN diodes, this invention optimizes the positive cross-finger loss layer structure of the top and middle layers, achieving a wider absorption bandwidth (up to 49% relative bandwidth). Both figures are significantly higher than the lower than 60% of existing technologies, meeting the requirements for broadband electromagnetic absorption. Simultaneously, structural symmetry ensures consistent electromagnetic performance under TE and TM polarization, resolving polarization sensitivity issues. Furthermore, this invention maintains excellent transmission efficiency while achieving broadband absorption and mode switching, with extremely low insertion loss in the transmission / reflection bands (0.46dB in ATA mode and 0.33dB in ARA mode), far below the signal attenuation levels of traditional structures.

[0054] In summary, through structural innovation and parameter optimization, this invention comprehensively surpasses existing technologies in terms of reliability, mode flexibility, bandwidth, polarization adaptability, and transmission efficiency, and is better able to meet the application requirements in complex electromagnetic environments.

[0055] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A polarization-independent switchable frequency-selective absorber-transmitter, characterized in that, Includes a loss layer and a switching layer; The loss layer and the switching layer are distributed vertically, with an air gap layer between them. The loss layer includes a first dielectric substrate, an upper loss layer, and a lower loss layer. The upper loss layer and the lower loss layer are respectively attached to the upper and lower surfaces of the dielectric substrate, and the upper loss layer and the lower loss layer have the same structure and are orthogonally distributed. The switching layer includes a second dielectric substrate, a metal layer, and four PIN diodes; The metal layer is attached to the upper surface of the second dielectric substrate, and the metal layer is provided with a square annular slit, in which the four PIN diodes are all disposed.

2. The polarization-independent switchable frequency-selective absorber-transmitter according to claim 1, characterized in that, Both the upper and lower loss layers are centrally symmetrical Z-shaped structures, including two interdigitated structures; The interdigitated structure includes a main arm (1), a lumped resistor (2), a central cross resonator (3), and interdigitated arms (4); The inner sides of both ends of the main arm (1) are respectively connected to a first S-shaped structure through a first connecting arm. The central cross resonator (3) includes a second S-shaped structure and a second connecting arm. The outer end of the lumped resistor (2) is connected to a first S-shaped structure, and the inner end of the lumped resistor (2) is connected to a second S-shaped structure. The second S-shaped structure is connected to the interdigitated arm (4) through a second connecting arm. Several interdigitated fingers (5) are provided on the interdigitated arm (4). The interdigitated fingers (5) of the two interdigitated structures are parallel and intersected at intervals. The interdigitated arms (4) of the two interdigitated structures are connected through a third connecting arm (6).

3. A polarization-independent switchable frequency-selective absorber-transmitter according to claim 2, characterized in that, The two first S-shaped structures are symmetrically distributed about the centerline of the main arm (1).

4. A polarization-independent switchable frequency-selective absorber-transmitter according to claim 2, characterized in that, The connection point between the third connecting arm and the interdigital arm (4) is the midpoint of the interdigital arm (4).

5. A polarization-independent switchable frequency-selective absorber-transmitter according to claim 2, characterized in that, The main arm (1) is parallel to the interdigital arm (4), and the interdigital fingers (5) are perpendicular to the interdigital arm (4).

6. A polarization-independent switchable frequency-selective absorber-transmitter according to claim 1, characterized in that, Both the first dielectric substrate and the second dielectric substrate are F4BM265 dielectric substrates.

7. A polarization-independent switchable frequency-selective absorber-transmitter according to claim 2, characterized in that, The resistance value of the lumped resistor (2) is 100Ω.

8. A polarization-independent switchable frequency-selective absorber-transmitter according to claim 1, characterized in that, The metal layer is made of copper, as are the upper and lower loss layers.

9. A polarization-independent switchable frequency-selective absorber-transmitter according to claim 1, characterized in that, The four PIN diodes are respectively located at the center of the four sides of the square annular gap.

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