Out-of-band wave-absorbing electromagnetic window based on transverse quasi-cavity resonance

Abstract

The invention discloses an out-of-band wave-absorbing electromagnetic window based on transverse quasi-cavity resonance, and relates to the technical field of artificial electromagnetic materials. An impedance layer is arranged and forms a series resonance circuit, so that incident electromagnetic waves excite transverse quasi-cavity resonance on metal wires of inductance structure units, absorption of low-frequency-band electromagnetic waves (C wave band) is achieved, and the electromagnetic window has the advantages of being simple in structure, low in cost and high in efficiency. Then, incident and reflected electromagnetic waves excite a surface plasmon polariton (SSPP) mode on the metal grid bars, so that energy is located in gaps of the metal grid bars and the second dielectric substrate, and the second dielectric substrate realizes absorption of high-frequency electromagnetic waves (Ku wave band), namely, compatible synergistic absorption of low-frequency resonance absorption of the impedance layer and high-frequency SSPP mode absorption of the high-frequency wave-absorbing structure is realized; meanwhile, efficient transmission of a middle wave band (X wave band) is achieved through the frequency selection surface on the lowermost layer, and finally absorption and transmission integration of vertical resonance regulation and transverse electromagnetic coupling is achieved under a wide frequency band.

Description

Technical Field

[0001] This invention relates to the field of artificial electromagnetic materials technology, and in particular to an out-of-band absorbing electromagnetic window based on transverse quasi-cavity resonance. Background Technology

[0002] With the rapid development of radar detection technology and the widespread coverage of WIFI networks, traditional radar absorbers can no longer meet the application needs of current military and civilian fields. At present, while ensuring normal communication within the operating frequency band, it is particularly important to reduce the out-of-band radar cross section (RCS), that is, to achieve an integrated absorption-transmission-absorption design.

[0003] There are generally two technical means to achieve integrated absorption-transmission-absorption design. One is to open a window in a given absorption broadband and realize the transmission passband through metamaterial design. The other is to design their respective functional broadbands separately and minimize the coupling between the functional broadbands to achieve the sum of their functions.

[0004] The two types of electromagnetic absorbing windows mentioned above are mainly designed based on the resonant mode analysis under vertical incidence. The designed electromagnetic absorbing windows mainly rely on impedance matching and resonance in the vertical direction to absorb waves, that is, they focus on the propagation, reflection and transmission of electromagnetic waves in the vertical direction. However, when the electromagnetic absorbing window operates in a wide frequency band, electromagnetic waves incident from different directions will act in both the vertical and horizontal directions, and the resonant modes at different frequencies in the vertical and horizontal directions will interact with each other. It can be seen that the current electromagnetic absorbing window ignores the horizontal electromagnetic coupling that occurs between periodic units and between different layers of units in a two-dimensional plane through induced current, near field and surface waves, etc. Ultimately, it is difficult to achieve compatible and coordinated absorption of vertical resonance control and horizontal electromagnetic coupling in a wide frequency band. Summary of the Invention

[0005] This invention provides an out-of-band absorbing electromagnetic window based on transverse quasi-cavity resonance, which can solve the problems existing in the prior art.

[0006] This invention provides an out-of-band absorbing electromagnetic window based on transverse quasi-cavity resonance, comprising periodically arrayed absorbing units, each of which includes an impedance layer, a high-frequency absorbing structure, and a high-transmission frequency-selective backplate arranged sequentially from top to bottom. The impedance layer includes a first dielectric substrate and inductor structure units arranged on the first dielectric substrate. The inductor structure units are metal wires with a meandering shape, and fixed resistors are connected between the metal wires, so that the metal wires, the dielectric substrate and the fixed resistors form a series LC resonant circuit. When the frequency of the incident electromagnetic wave is the same as the frequency of the series LC resonant circuit, a first-order transverse quasi-cavity resonance is excited in the metal wires. The induced current is concentrated on the fixed resistor and converted into heat energy, thereby realizing the absorption of low-frequency electromagnetic waves to form a low-frequency absorbing band. The high-frequency absorbing structure includes a vertically extending cross-shaped second dielectric substrate and metal grids arranged on the second dielectric substrate. The metal grids are arranged at equal intervals from top to bottom on the second dielectric substrate and their length gradually increases. The incident electromagnetic wave is absorbed at low frequency by the impedance layer and reflected by the high-transmission frequency-selective backplate, which excites the surface plasmon polariton (SSPP) mode on the metal grids. This localizes the electromagnetic field energy in the gaps between the metal grids and the second dielectric substrate. The absorption of high-frequency electromagnetic waves is achieved through the strong dielectric loss of the second dielectric substrate, thus forming a high-frequency absorbing broadband.

[0007] Preferably, the inductor structure unit of the impedance layer is composed of metal wires with a U-shaped meandering shape, and the meandering metal wires are centrally symmetrical to form a dual-inductor series structure. A fixed resistor R1 is connected between series inductors L1 and L2. The inductor structure unit and the first dielectric substrate together form an equivalent capacitance C1. The entire impedance layer constitutes a series LC resonant circuit.

[0008] Preferably, the inductance values ​​of series inductors L1 and L2 are adjusted by adjusting the depth and spacing of the U-shaped bends in the metal wires, so as to make the resonant frequency of the series LC resonant circuit consistent with the frequency of the low-frequency incident electromagnetic wave.

[0009] Preferably, the metal grids on the high-frequency absorbing structure are in the form of a periodic rectangular grid array, and the unit period is set to half of the unit period of the impedance layer inductor structure; The period of the metal grid in the high-frequency absorbing structure is matched with the period of the inductor structure unit in the impedance layer, so that the metal grid is compatible with the impedance layer and the high-transmission frequency-selective backplane in terms of electromagnetic characteristics.

[0010] Preferably, the high-transmittance frequency-selective backplane includes a third dielectric substrate and a metal patch disposed on the surface of the third dielectric substrate, and multiple square ring gaps are formed on the metal patch so that multiple square metal patches are formed inside the metal patch. The third dielectric substrate and the multiple square metal patches inside the metal patch form a parallel LC resonant circuit. By adjusting the side length of the square metal patch and the width of the square ring gap, the values ​​of inductance and capacitance in the parallel LC resonant circuit are adjusted so that the resonant frequency of the parallel LC resonant circuit is set at the preset transmission center frequency.

[0011] Preferably, in the first absorbing frequency band of 4.0 GHz to 8.0 GHz and the second absorbing frequency band of 12.0 GHz to 18.0 GHz, the out-of-band absorbing electromagnetic window has an energy absorption rate of more than 90% for incident electromagnetic waves; At a center frequency of 10.0 GHz, an out-of-band absorbing electromagnetic window produces a transmission window with a bandwidth of 0.5 GHz and an insertion loss of 1 dB.

[0012] Preferably, the out-of-band absorbing electromagnetic window absorbs waves within a first absorbing frequency band of 4.0 GHz to 8.0 GHz and a second absorbing frequency band of 12.0 GHz to 18.0 GHz. At a center frequency of 10.0 GHz, an out-of-band absorbing electromagnetic window allows for wave transmission.

[0013] Preferably, both the first dielectric substrate and the third dielectric substrate are polytetrafluoroethylene (PTFE) dielectric plates (F4B). The polytetrafluoroethylene dielectric plate F4B has a relative permittivity of 2.65 and a loss tangent of 0.001.

[0014] This invention provides an out-of-band absorbing electromagnetic window based on transverse quasi-cavity resonance, which has the following advantages compared with the prior art: This invention, by setting an impedance layer and forming a series resonant circuit, excites a first-order transverse quasi-cavity resonance in the metal lines of the inductor structure unit when incident electromagnetic waves are emitted. The resistance in this resonance absorbs the induced current and converts it into heat energy to absorb low-frequency (C-band) electromagnetic waves. The incident electromagnetic waves, after being absorbed at low frequencies by the impedance layer, are reflected by a high-transmission frequency-selective backplane (high reflection in C-band and Ku-band, high transmission in X-band), exciting surface plasmon polariton (SSPP) modes on the metal grid strips. This localizes the electromagnetic field energy within the gaps between the metal grid strips and the second dielectric substrate, and utilizes… The absorption of high-frequency (Ku band) electromagnetic waves is achieved by utilizing the strong dielectric loss of the second dielectric substrate itself. The entire process utilizes the lateral quasi-cavity resonance in the metal wire structure. At the same time, by designing a meandering inductor and metal grid structure, the lateral distribution and resonance order of the induced current are actively controlled. This achieves compatible and synergistic absorption of low-frequency resonance absorption of the impedance layer and high-frequency SSPP mode absorption of the high-frequency absorbing structure. The absorption of electromagnetic waves is directly converted from vertical resonance to lateral coupling absorption. Finally, compatible and synergistic absorption of vertical resonance modulation and lateral electromagnetic coupling is achieved in a wide bandwidth.

[0015] Furthermore, this invention utilizes the lowest frequency-selective surface to achieve efficient transmission in the middle band (X-band), ultimately realizing the integration of vertical resonant modulation and transverse electromagnetic coupling in a wide frequency band. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the transverse quasi-cavity resonance modulation principle provided in an embodiment of the present invention; Figure 2 The diagram shows the resonant current distribution and S-parameters under polarized incident radiation of the metal wire quasi-cavity resonant structure provided in the embodiment of the present invention; wherein, (a) is the first-order quasi-cavity resonant current distribution and S-parameters under y-polarized incident radiation of the metal wire structure, (b) is the second-order quasi-cavity resonant current distribution and S-parameters under x-polarized incident radiation of the U-shaped metal wire, and (c) is the second-order quasi-cavity resonant current distribution and S-parameters under y-polarized incident radiation of the U-shaped metal wire. Figure 3 A schematic diagram of the components and filtering characteristics of the transverse quasi-cavity resonant structure provided in an embodiment of the present invention is shown; wherein, (a) is the inductive element unit 1 and its filtering characteristics, and (b) is the capacitive element unit 2 and its filtering characteristics; Figure 4 A schematic diagram of the integrated absorption-transmission structure of an external absorbing electromagnetic window based on transverse quasi-cavity resonance provided in an embodiment of the present invention; Figure 5 A schematic diagram of an integrated absorption-transmission structure circuit based on a transverse quasi-cavity resonance external absorbing electromagnetic window provided for an embodiment of the present invention; Figure 6 A schematic diagram of an upper low-frequency absorbing unit based on a transverse quasi-cavity resonance external absorbing electromagnetic window provided in an embodiment of the present invention; Figure 7 A schematic diagram of the overall structural unit and the middle high-frequency absorbing structure of an external electromagnetic window based on transverse quasi-cavity resonance provided for embodiments of the present invention; Figure 8 A schematic diagram of the simulation results of a unit structure based on transverse quasi-cavity resonance with an external electromagnetic window under y-polarized electromagnetic wave incidence, provided for an embodiment of the present invention. Figure 9 A schematic diagram of the simulation results of a unit structure based on transverse quasi-cavity resonance with an external electromagnetic window under y-polarized electromagnetic wave incidence, provided for an embodiment of the present invention. Figure 10 This invention provides a schematic diagram of the surface current distribution and longitudinal cross-sectional energy flow of a unit structure with an externally absorbing electromagnetic window based on transverse quasi-cavity resonance at three characteristic frequency points of 3.8 GHz, 9.8 GHz, and 15.0 GHz under γ-polarized electromagnetic wave incident conditions. Figure 11 This is a schematic diagram of an experimental sample based on a transverse quasi-cavity resonance external electromagnetic window provided in an embodiment of the present invention. Detailed Implementation

[0017] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0018] Currently, with the rapid development of radar detection technology and the widespread coverage of WIFI networks, traditional radar absorbers can no longer meet the application needs of current military and civilian fields. At present, while ensuring normal communication within the operating frequency band, reducing the out-of-band radar cross section (RCS) has become particularly important, that is, realizing an integrated absorption-transmission-absorption design. There are two main technical routes to achieve this goal: one is to open a window in a given absorption bandwidth and realize the transmission passband through metamaterial design; the other is to design separate functional bandwidths and minimize the coupling between the functional bandwidths to achieve the sum of their functions. However, the transmission efficiency of electromagnetic windows is not high, generally only 80%; and the out-of-band absorption bandwidth is not wide enough to cover the common main absorption bands; moreover, the absorption-transmission compatibility is poor, and it is difficult to achieve a compatible balance between high-performance transmission and high-performance absorption.

[0019] Based on the shortcomings of current solutions, this invention explores the electromagnetic properties of biomimetic circuit element structures based on the principle of transverse quasi-cavity resonance modulation. Based on this, through circuit design, following the two aforementioned technical routes, an out-of-band high-absorption electromagnetic window is designed and implemented; specifically: I. Basic Principles.

[0020] 1. Principle of transverse quasi-cavity resonance modulation.

[0021] like Figure 1 As shown, the simplest model for transverse quasi-cavity resonance modulation is the metal short-wire model. In 1996, Pendry's team first proposed achieving a negative permittivity through metal short wires; research shows that periodic metal short wires can be analyzed using the Drude model, expressed as:

[0022] .

[0023] in: Let be the equivalent dielectric constant of the short metal wire. The vacuum permittivity, n For electron density, m and e These represent electron mass and electron charge, respectively. The damping coefficient is... The plasma frequency of the metal is given; however, this model relies on the premise of continuous electrical connection between the metal short wires of the unit cells, which has significant limitations. Subsequently, other researchers discovered that the metal short wires can exhibit the intrinsic properties of bulk metal, forming an electric resonator; the model at this point satisfies the Lorentz model, expressed as: .

[0024] in: The incident wave frequency, This is the resonant frequency of the electric resonator; when the incident wave frequency is less than the resonant frequency... When, dielectric constant When the frequency is close to zero, the electric resonator can generate a transmission passband; however, when the incident wave frequency is greater than the resonant frequency... When, dielectric constant If the value is less than zero, electromagnetic waves cannot pass through the electric resonator; thus, the short-wire structure of metal has filtering characteristics and is often used in the design of frequency selective surfaces.

[0025] like Figure 2 As shown, when an electromagnetic wave is incident on a short-wire metal structure, the free electrons in the metal are driven by the applied electric field to move in the opposite direction of the electric field. At this time, the stationary metal cations and electrons move relative to each other, forming two currents in the same direction. The two currents with a phase difference of π are coherently superimposed in the transverse dimension to form a first-order quasi-cavity resonance. At this time, the overall structure is equivalent to a homogeneous material. Since the relative permittivity of the "material" is greater than 1, the wave velocity and wavelength in the "material" are smaller than those in the vacuum. It can be regarded as the electric scale of the wave. By observing the distribution of induced current on the surface of the structure, we can help to study the transmission law and characteristics of waves in the structure.

[0026] By further extending the short-wire metal structure and observing its surface current distribution, it was found that the thickness of the dielectric must be optimized to ensure the efficient electromagnetic properties of the structure. This means that changes in the metal structure first alter the electrical thickness of the unit cells, which in turn changes the electrical size of the wave within the structure. For example, after changing the short wires in the metal structure, the order of the quasi-cavity resonant current on the surface of the structure will also change accordingly. Figure 2 As shown; therefore, by designing a specific metal wire structure, it is possible to control the resonance of quasi-cavity electromagnetic waves of different orders in the transverse dimension, thereby enabling functional design.

[0027] 2. An out-of-band absorbing electromagnetic window based on a loaded LC resonant structure.

[0028] Metamaterial structural units are typically two-dimensional, and therefore can be equivalent to a two-port circuit model. This equivalent method, compared to other metamaterial analysis methods, makes it easier to determine the properties of metamaterials and perform qualitative analysis. When electromagnetic waves are incident on the structure, certain metallic structures will exhibit capacitive or inductive resonance with the induced current generated by the incident electric field; for example... Figure 3 As shown, based on the characteristics of capacitors and inductors, two biomimetic component units were designed, denoted as Unit 1 and Unit 2, respectively. The black arrows in the figure represent the direction of the induced current. The through-strip structure of Unit 1 acts as an inductor by effectively increasing the movement distance of electrons in the short metal wire, allowing low-frequency electromagnetic waves to pass through while reflecting high-frequency electromagnetic waves. The blocking strip of Unit 2 increases the capacitance by blocking the connection of the structure and increasing the area of ​​the plates, thus producing a capacitor effect, allowing high-frequency electromagnetic waves to pass through while reflecting low-frequency electromagnetic waves. This is consistent with the conclusion in circuit theory that inductors have "low resistance to low current" and capacitors have "high resistance to high current". The relevant parameters of the two units are: w=0.4mm, g=0.2mm, t=0.2mm, c=0.3mm, b=2mm. l1=2.7mm, l2=3.55mm, the dielectric substrate material is F4B (relative permittivity εr=2.65+0.001j), and the thickness is 1.0mm; In addition, the energy loss of circuits in circuits mainly comes from the ohmic loss of resistors. Taking the design of metamaterials in the electromagnetic microwave band as an example, since its wavelength scale is on the millimeter scale, and the current circuit board manufacturing process can achieve the millimeter scale of resistor package size, in the unit design of the microwave band, resistors can be directly soldered onto the structure, and the resistance value and package size of the resistors can be customized, which makes the functional design of metamaterial units more convenient.

[0029] Through the above design verification, the simulation and mapping of the most basic components in the circuit structure have been realized. By adjusting the relevant parameters of the above unit 1 and unit 2 structures, the numerical control of inductance and capacitance can be achieved, while the resistor only needs to be manually set to the optimal solution.

[0030] 3. Circuit performance design and analysis with external electromagnetic window.

[0031] like Figure 4 As shown, an electromagnetic window with external absorption generally consists of three layers, from top to bottom: an impedance layer, a sandwich structure, and a frequency-selective reflective backplate. The impedance layer is the main energy-dissipating layer for electromagnetic waves. The backplate reflects electromagnetic waves in the absorption band while allowing electromagnetic waves in the communication band to pass through, forming the electromagnetic window. The sandwich structure mainly serves to support the impedance layer and the backplate, and its thickness should ensure that the overall structure meets the quarter-wavelength condition for quasi-cavity resonance.

[0032] according to Figure 4 The structure shown, combined with two-port network circuit design, can be used to design a...Figure 5 The equivalent circuit of the external absorbing electromagnetic window; shown in the figure. Z 0 represents the free space impedance, which has a value of 377.0 Ω; Z r and Z f These are the equivalent impedances of the impedance layer and the frequency-selective reflector backplane, respectively. Z d The impedance of the interlayer is negligible because the interlayer material is generally chosen to have a relatively low permittivity similar to air and low loss. Based on the circuit diagram, the transmission matrix of the current circuit can be calculated as follows:

[0033] .

[0034] in: θ =βt, β=2π / λ, and the transmission coefficient can be calculated from the circuit's transmission matrix as follows: .

[0035] Based on the obtained transmission coefficient, it can be seen that when Z r and Z f When both are infinite, the transmission coefficient is approximately 1, at which point electromagnetic waves can pass through the structure; Z r The value depends on its own circuit structure. Therefore, by combining the unit structures of different circuit elements and adjusting the relevant characteristics of the analog circuit, the desired effect can be achieved. Z r The control; adjusting the unit structure parameters to make L1 and C1 approach zero, and adjusting the resonant frequency of parallel L2 and C2 to the absorption frequency point, can be achieved by means of Z r The resistors in the branch circuit achieve efficient absorption of electromagnetic waves; outside the absorption band, by adjusting L3 and C3 in the circuit structure, the resonant frequency of the bandpass frequency-selective backplane is designed to achieve efficient wave transmission outside the absorption band.

[0036] 4. An out-of-band electromagnetic window based on loaded lumped elements.

[0037] This invention further optimizes the traditional absorber with lumped resistance and achieves passband windowing within the absorber's absorption bandwidth by designing the relationship between transverse quasi-cavity resonance and frequency. This allows adjustment of the transmission window frequency without affecting the absorption bandwidth. To verify the feasibility of the design, full-wave simulation was performed on the structure, and samples were fabricated for actual testing. Simulation and test data show that the designed structure has a transmission window at 9.9 GHz with a bandwidth of 0.5 GHz and an insertion loss of less than 0.2 dB under x-polarized and y-polarized incident conditions. The electromagnetic wave absorption rate exceeds 90% in both the 5.8 GHz-7.8 GHz and 11.8 GHz-18.0 GHz frequency bands. Furthermore, the designed out-of-band electromagnetic window still exhibits stable electromagnetic wave absorption and filtering characteristics within the -45° to 45° incident angle range.

[0038] II. Unit structure design.

[0039] Based on the fundamental principles and design concepts of layered, circuit-based, and frequency-band-based unit structures analyzed above, since the circuit involves three frequency bands (low, medium, and high) with three parallel branches, it is necessary to design the units in layers and then combine them to obtain an ultra-wideband out-of-band electromagnetic window with high transmittance. By increasing the curling degree of the inductor unit and realizing the series connection of two inductors, the inductance value can be increased, which can further reduce the resonant frequency of the series L1C1 circuit. At the same time, a fixed resistor (resistance value of 500 ohms) is connected between the series inductors as a loss source R1. The metal structure on the back of the dielectric substrate is the same as the front structure. By rotating it by 90°, the sensitivity of the unit to incident wave polarization is reduced. The relevant structural parameters are: p=20.0mm, g=0.5mm, l1=6.5mm, l2=3.5mm, l3=2.5mm, d=1.5mm, t=0.4mm, D=12.0mm.

[0040] Considering the relatively fixed structure of the absorber, namely a three-layer structure of impedance layer-dielectric-backplane, a high-transmittance frequency-selective backplane was designed at the bottom of the structural unit before the high-frequency absorbing unit. This type of backplane functions similarly to the frequency-selective backplane of a conventional absorber, acting as a reflective backplane for the absorbing impedance layer to reflect as many incident waves as possible, thereby improving the absorption efficiency of the impedance layer. The difference lies in that its passband opening and closing must not affect other frequency bands. The high-frequency absorbing structure uses a metal grid structure to replace the dielectric layer in the traditional absorber architecture. While achieving high-frequency absorption, it provides structural support for the impedance layer and backplane, giving the overall structure good mechanical properties. The high-frequency absorbing structure is as follows: Figure 7 As shown; the structural unit period is p / 2, which can achieve period matching with the impedance layer and the high-transmission frequency-selective backplane; the relevant structural parameters are: h=D=12.0mm, t4=0.4mm, ld=3.7mm, lc=7.2mm, j=k=0.2mm.

[0041] III. Simulation Verification.

[0042] After combining the various design layers, a full-wave simulation was performed on the unit to observe its overall electromagnetic characteristics; the results are as follows. Figure 8 and Figure 9 As shown, the unit as a whole achieves integrated absorption and transmission within the 4.0GHz-18.0GHz frequency range, maintaining an efficient absorption rate of over 90% in both the 4.0GHz-8.0GHz and 12.0GHz-18.0GHz bands; and generates a transmission window with a bandwidth of 0.5GHz and an insertion loss of 1dB at the 10.0GHz frequency point. (Due to the overall symmetry of the unit, the electromagnetic functions of x-polarization and y-polarization are considered equivalent, and the simulation uses y-polarized electromagnetic waves as representative).

[0043] like Figure 10 As shown, at 3.8 GHz, the upper inductor structure unit undergoes series LC resonance, which increases the surface current intensity on the metal line, raises the voltage at the resistor end, and enhances the loss, thus forming a low-frequency absorption band. At this time, due to the long wavelength of the low-frequency electromagnetic wave, the length of the middle metal grid is limited, and it is impossible to excite plasmons. The bottom frequency selection is equivalent to a metal backplate, so the absorption performance of the structure in the low-frequency band is relatively stable. At 10.0 GHz, the electromagnetic wave has a longer wavelength and slower wave speed after passing through the upper and middle layers. The electromagnetic wave resonates at the second-order frequency selection backplate and is then transmitted, forming an electromagnetic window. At 15.0 GHz, the electromagnetic wave is reflected by the square patch frequency selection structure and excites the SSPP mode on the metal grid, which enhances the local electric field. Under the strong dielectric loss of the FR4 dielectric substrate, a high-frequency absorption broadband is formed.

[0044] This invention, based on the principle of transverse quasi-cavity resonance modulation, achieves a low-insertion-loss out-of-band absorbing electromagnetic window through layered, frequency-band-specific, and circuit-specific design. The experimental sample is shown below. Figure 11 As shown, the designed structure maintains high-efficiency absorption in the 4.0GHz-8.0GHz and 12.0GHz-18.0GHz ranges, and achieves high-efficiency transmission at the 10.0GHz frequency point. Specifically, this invention achieves high-efficiency electromagnetic absorption in the low-frequency C-band (4-8GHz) and high-frequency Ku-band (12GHz-18GHz), with an average absorption efficiency of over 80%, reaching 90% near the center frequency band; it also achieves high-efficiency electromagnetic transmission in the X-band (8-12GHz), with a transmission efficiency of over 85% in the center 0.5GHz bandwidth and an insertion loss of over -1dB.

[0045] The high-performance out-of-band electromagnetic window of this invention achieves the characteristics of "out-of-band suppression and in-band transmission" through technologies such as frequency selective surface (FSS). Its core function is to allow electromagnetic waves of specific frequency bands used by our radar and communications to pass freely while effectively absorbing or suppressing electromagnetic waves operating "out of band" from the enemy or other interference sources. At the same time, it directly improves the battlefield survivability of weapons and equipment, significantly reduces the signal characteristics (radar cross section) of aircraft and other equipment under radar detection, and is one of the key technologies for achieving stealth. Its intelligent control capability (such as dynamically switching states according to threat frequency bands) can effectively cope with complex electromagnetic countermeasures environments. In addition to high-end military equipment, this technology is rapidly expanding into the civilian field. For example, when used in aircraft windows and automotive sunroofs, it can effectively manage electromagnetic radiation and thermal effects while ensuring the transmission of communication signals and visible light. Its derived metamaterial absorbers have broad application prospects in medical precision equipment, electromagnetic protection of low-altitude economic drones, and energy-saving glass for buildings, promoting the development of new materials and high-end manufacturing industries.

[0046] This invention achieves excellent performance with an average absorption rate of over 90% in two wide frequency bands, 4 GHz and 6 GHz, through the synergy of low-frequency resonant absorption of the impedance layer and high-frequency SSPP mode absorption of the structural sandwich. It fundamentally resolves the contradiction of performance trade-off caused by the coupling of absorption and transmission functions. Through the layered control mechanism of transverse quasi-cavity resonance, the absorption and transmission functions are decoupled and independently optimized in physical space (different layers) and frequency domain space (different frequency bands).

[0047] This invention precisely maps complex metal microstructures (winding lines, grids, patches) into equivalent lumped circuit models of inductance (L), capacitance (C), and resistance (R). In specific design, circuit synthesis and optimization can be performed first based on the target frequency band and performance indicators to quickly determine the ideal values ​​of L, C, and R. Then, through the established mapping relationship between geometric parameters (such as line length, line width, and spacing) and circuit parameters, the specific structural dimensions can be deduced, making the performance of the final product highly predictable before processing.

[0048] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An out-of-band absorbing electromagnetic window based on transverse quasi-cavity resonance, characterized in that, Includes: periodically arrayed absorbing units, each of which includes an impedance layer, a high-frequency absorbing structure, and a high-transmission frequency-selective backplate arranged from top to bottom; The impedance layer includes a first dielectric substrate and inductor structure units arranged on the first dielectric substrate. The inductor structure units are metal wires with a meandering shape, and fixed resistors are connected between the metal wires, so that the metal wires, the dielectric substrate and the fixed resistors form a series LC resonant circuit. When the frequency of the incident electromagnetic wave is the same as the frequency of the series LC resonant circuit, a first-order transverse quasi-cavity resonance is excited in the metal wires. The induced current is concentrated on the fixed resistor and converted into heat energy, thereby realizing the absorption of low-frequency electromagnetic waves to form a low-frequency absorbing band. The high-frequency absorbing structure includes a vertically extending cross-shaped second dielectric substrate and metal grids arranged on the second dielectric substrate. The metal grids are arranged at equal intervals from top to bottom on the second dielectric substrate and their length gradually increases. The incident electromagnetic wave is absorbed at low frequency by the impedance layer and reflected by the high-transmission frequency-selective backplate, which excites the surface plasmon polariton (SSPP) mode on the metal grids. This localizes the electromagnetic field energy in the gaps between the metal grids and the second dielectric substrate. The absorption of high-frequency electromagnetic waves is achieved through the strong dielectric loss of the second dielectric substrate, thus forming a high-frequency absorbing broadband.

2. The out-of-band absorbing electromagnetic window based on transverse quasi-cavity resonance according to claim 1, characterized in that, The inductor structure unit of the impedance layer is composed of metal wires with a U-shaped meandering shape, and the meandering metal wires are centrally symmetrical to form a dual-inductor series structure. A fixed resistor R1 is connected between series inductors L1 and L2. The inductor structure unit and the first dielectric substrate together form an equivalent capacitance C1. The entire impedance layer constitutes a series LC resonant circuit.

3. The out-of-band absorbing electromagnetic window based on transverse quasi-cavity resonance according to claim 2, characterized in that, By adjusting the depth and spacing of the U-shaped bends in the metal wires, the inductance values ​​of the series inductors L1 and L2 can be adjusted to match the resonant frequency of the series LC resonant circuit with the frequency of the low-frequency incident electromagnetic wave.

4. The out-of-band absorbing electromagnetic window based on transverse quasi-cavity resonance according to claim 1, characterized in that, The metal grids on the high-frequency absorbing structure are arranged in a periodic rectangular grid array, and the unit period is set to half of the unit period of the impedance layer inductor structure. The period of the metal grid in the high-frequency absorbing structure is matched with the period of the inductor structure unit in the impedance layer, so that the metal grid is compatible with the impedance layer and the high-transmission frequency-selective backplane in terms of electromagnetic characteristics.

5. The out-of-band absorbing electromagnetic window based on transverse quasi-cavity resonance according to claim 1, characterized in that, The high-transmittance frequency-selective backplane includes a third dielectric substrate and a metal patch disposed on the surface of the third dielectric substrate, and multiple square ring gaps are formed on the metal patch so that multiple square metal patches are formed inside the metal patch. The third dielectric substrate and the multiple square metal patches inside the metal patch form a parallel LC resonant circuit. By adjusting the side length of the square metal patch and the width of the square ring gap, the values ​​of inductance and capacitance in the parallel LC resonant circuit are adjusted so that the resonant frequency of the parallel LC resonant circuit is set at the preset transmission center frequency.

6. The out-of-band absorbing electromagnetic window based on transverse quasi-cavity resonance according to claim 1, characterized in that, Within the first absorbing frequency band of 4.0 GHz to 8.0 GHz and the second absorbing frequency band of 12.0 GHz to 18.0 GHz, the out-of-band absorbing electromagnetic window has an energy absorption rate of over 90% for incident electromagnetic waves. At a center frequency of 10.0 GHz, an out-of-band absorbing electromagnetic window produces a transmission window with a bandwidth of 0.5 GHz and an insertion loss of 1 dB.

7. The out-of-band absorbing electromagnetic window based on transverse quasi-cavity resonance according to claim 1, characterized in that, In the first absorbing frequency band from 4.0 GHz to 8.0 GHz and the second absorbing frequency band from 12.0 GHz to 18.0 GHz, out-of-band absorbing electromagnetic windows absorb waves. At a center frequency of 10.0 GHz, an out-of-band absorbing electromagnetic window allows for wave transmission.

8. The out-of-band absorbing electromagnetic window based on transverse quasi-cavity resonance according to claim 5, characterized in that, Both the first dielectric substrate and the third dielectric substrate are polytetrafluoroethylene dielectric plates F4B; The polytetrafluoroethylene dielectric plate F4B has a relative permittivity of 2.65 and a loss tangent of 0.001.

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