Surface electromagnetic wave wave vector and impedance matched wave absorbing structure

Abstract

The application discloses a surface electromagnetic wave wave-absorbing structure matched with wave vectors and impedance, and is applied to the surface of an aircraft. The structure is a three-layer stacked three-dimensional structure. The bottom layer is a full-coverage reflecting layer. The middle layer is a flexible material medium substrate. The top layer is a plurality of resistance film resonant metal units. The structure solves the problem of surface wave suppression by only relying on a physical mechanism, and can realize surface wave regulation and attenuation, and has the characteristics of a wide frequency band, ultra-thinness, light weight and conformality.

Description

Technical Field

[0001] This invention relates to the field of metamaterials, and in particular to a surface electromagnetic wave absorbing structure with wave vector and impedance matching. Background Technology

[0002] In modern aerospace engineering, improving the low observability of aircraft has become a key design objective. It not only represents advanced aerodynamic and materials technology but also directly relates to flight safety and operational efficiency. This performance is typically quantified by radar cross-section. With technological advancements, the suppression of specular reflections by aircraft has become relatively mature through aerodynamic shape optimization and the application of composite radar-absorbing structures. The main challenge now lies in non-spectral scattering, which includes various physical mechanisms such as edge scattering, tip scattering, and surface wave traveling wave scattering. Among these, surface wave traveling wave scattering is the most prominent. When electromagnetic waves act on the surface of an aircraft at a specific angle, they excite surface waves to propagate along the surface. When these traveling waves encounter structural discontinuities, they transform into strong backward-radiated waves, forming significant echo signals. Therefore, suppressing surface waves is an effective means to further reduce the radar cross-section and improve the low observability of aircraft.

[0003] Surface wave suppression stems from three physical effects: intrinsic material loss, mode coupling and conversion, and radiation loss. Intrinsic material loss is caused by the inherent properties of the medium or conductor, such as polarization relaxation loss in dielectric materials, ohmic loss in conductive materials, or hysteresis loss in magnetic materials. Mode coupling and conversion couples the propagating surface wave energy to other propagation modes or local modes, converting them into modes with higher losses, making them easier to absorb, or converting the propagating surface wave into a cutoff wave, causing the energy to dissipate rapidly. Radiation loss couples the propagating surface wave energy into free space for radiation, thereby reducing the energy propagating along the surface. Designing the structure with periodic or gradual characteristics disrupts the surface wave propagation conditions, ensuring that the phase matching conditions meet the requirements for radiation into space.

[0004] While existing surface wave suppression technologies have made some progress, they still have many shortcomings. Absorbers relying on intrinsic material losses can dissipate energy, but achieving bandwidth absorption requires multi-layered structures, leading to significant increases in thickness and weight, which cannot meet the lightweight and conformal requirements of modern aircraft. Metamaterial designs based on mode coupling and conversion suffer from narrow bandwidth and angle sensitivity; their complex microstructures require extremely high processing precision, and their structural stability is insufficient, making them unsuitable for the broadband, all-angle absorption needs of practical applications. Radiation loss-based methods, such as high-impedance surfaces, can only change the energy propagation path and cannot generate secondary scattering based on the lost electromagnetic energy. Improved schemes integrating active devices introduce complex bias networks, resulting in thicker structures, reduced reliability, and limited engineering applicability.

[0005] Existing technologies focus on a single physical mechanism to suppress surface waves (this mechanism utilizes the intrinsic loss of materials to attenuate surface waves, resulting in attenuation structures that are thick, bulky, narrow-bandwidth, and difficult to bend). This fails to achieve a synergistic optimization of precise surface wave control and efficient dissipation, making it difficult to balance performance, size, bandwidth, and integration. Therefore, there is an urgent need for a surface electromagnetic wave absorbing structure that can achieve surface wave control and attenuation while also being wide-bandwidth, ultra-thin, lightweight, and conformal. Summary of the Invention

[0006] This invention provides a surface electromagnetic wave absorbing structure with wave vector and impedance matching, which solves the problem of suppressing surface waves by relying solely on physical mechanisms.

[0007] This invention provides a surface electromagnetic wave absorbing structure with wave vector and impedance coordinated matching, applicable to the surface of an aircraft. The structure is a three-layer stacked three-dimensional structure, with a fully covered reflective layer at the bottom, a flexible material dielectric substrate in the middle, and multiple resistive film resonant metal units at the top. Each resistive film resonant metal unit includes a first radiator, a second radiator, and a third radiator. The first radiator has a first vertical segment, and the third radiator has a third vertical segment. The first and third vertical segments are arranged opposite each other in the horizontal direction. The first vertical segment has a first horizontal segment extending toward the third radiator at both ends, and the third vertical segment has a third horizontal segment extending toward the first radiator at both ends. A second radiator is disposed between the first and third radiators and includes a second vertical segment and a second horizontal segment. The second horizontal segment extends from the first vertical segment to the third vertical segment. The first and third horizontal segments are spaced apart, and the second vertical segment extends vertically from both sides of the second horizontal segment.

[0008] Furthermore, the reflective layer is made of metal or a conductive composite material.

[0009] Furthermore, the reflective layer is made of copper.

[0010] Furthermore, the flexible material substrate is made of polyethylene terephthalate.

[0011] Furthermore, the resistive film resonant metal unit is made of ITO resistive film.

[0012] Furthermore, the process for obtaining the structural dimensions of each layer is as follows:

[0013] S1: A surface wave is excited by a surface transmission waveguide that is incident on the surface of the aircraft at a large angle with a plane wave, and the magnetic field distribution of the surface wave is obtained.

[0014] S2: Record the spatial distribution of the real part of the magnetic field along the x-direction, perform spatial peak spacing analysis, extract the surface wave wavelength, calculate the surface wave vector, and establish the target dispersion curve related to the surface wave vector and frequency.

[0015] S3: Preset the initial size parameters of the initial surface electromagnetic wave absorbing structure and construct an equivalent geometric model;

[0016] S4: Use the target dispersion curve as the equivalent geometric model to fit the target curve to the surface wave.

[0017] S5: Initialize the boundary conditions of the equivalent geometric model, wherein the boundary conditions are the structural dimension parameters of each layer of the geometric model;

[0018] S6: Based on the geometric model under the boundary conditions, perform simulation to obtain the corresponding dispersion curve, and determine whether the fitting degree between the dispersion curve and the target curve reaches the target preset value: if yes, output the size parameters of each layer of the surface electromagnetic wave absorbing structure; if no, adjust the boundary conditions according to the surface wave fitting target curve until the fitting degree meets the target preset value.

[0019] Furthermore, by adjusting the boundary conditions, the wave impedance satisfies the transverse resonance equation when the surface wave propagates on the surface electromagnetic wave absorbing structure:

[0020]

[0021] in, The propagation constant is given by the subscript sw, which indicates a surface wave. The average surface impedance of the surface electromagnetic wave absorbing structure; This refers to the wave impedance of the upper half-space of the surface electromagnetic wave absorbing structure, i.e., the wave impedance of the air layer. This refers to the wave impedance of the lower half-space of the surface electromagnetic wave absorbing structure, i.e., the wave impedance of the dielectric substrate and the reflective layer.

[0022] This invention proposes a surface electromagnetic wave absorbing structure with coordinated wave vector and impedance matching, used to realize a low-observability metamaterial structure for aircraft. This structure integrates the two major functions of surface wave "wave vector matching" and "impedance attenuation" within the same superconducting material unit. Through a synergistic mechanism of matching followed by attenuation, it effectively suppresses backscattering of surface waves at electromagnetic discontinuities, thereby significantly reducing the RCS of the aircraft. When surface waves propagate to the metamaterial structure, the wave vector matching design allows the surface waves to enter the attenuation structure without reflection. The real part of the metamaterial's impedance is adjusted using a variable-resistance material ITO, increasing the attenuation constant and achieving surface wave energy dissipation. Simultaneously, the attenuation structure employs a flexible dielectric material, allowing the superconducting material structure to be flexibly fitted in front of electromagnetic defects that easily induce traveling wave scattering, further enhancing the metamaterial's surface wave attenuation effect and its adaptability in practical applications. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The following are the surface wave excitation simulation results provided in the embodiments of the present invention: Figure 1 (a) is a schematic diagram of the surface wave excitation model; Figure 1 (b) Schematic diagram of the simulation of the surface wave transmission coefficient; Figure 1 (c) is a schematic diagram of the magnetic field distribution excited by surface waves at 15 GHz;

[0025] Figure 2 This is a simulation diagram of the real part of the magnetic field strength of the surface wave along the x-direction provided in an embodiment of the present invention: Figure 2 (a) 12GHz; Figure 2 (b) 14GHz; Figure 2 (c) 16GHz; Figure 2 (d) 18GHz;

[0026] Figure 3 This is the surface wave target dispersion curve extracted according to the embodiments of the present invention;

[0027] Figure 4 This is a schematic diagram illustrating the influence of wave vector matching on surface wave propagation characteristics provided in an embodiment of the present invention: Figure 4 (a) Wave vector mismatch magnetic field distribution; Figure 4 (b) Wave vector matching magnetic field distribution;

[0028] Figure 5 The metamaterial electromagnetic analysis model provided in this embodiment of the invention is as follows: Figure 5 (a) is a metasurface structure used to support TM-type surface waves propagating along the x-axis; Figure 5 (b) is the equivalent transmission line model of the model;

[0029] Figure 6 This is a schematic diagram showing the unit, structure, and dimensions of the surface electromagnetic wave absorbing structure provided in the embodiments of the present invention;

[0030] Figure 7 A schematic diagram showing the fitting of the surface electromagnetic wave absorbing structure and the dispersion curve of the excited surface wave target provided in an embodiment of the present invention;

[0031] Figure 8A simulation diagram of a surface electromagnetic wave absorbing structure provided for an embodiment of the present invention: Figure 8 (a) Simulation of the overall structure of the surface electromagnetic wave absorbing structure; Figure 8 (b) is the attenuation structure part;

[0032] Figure 9 The surface wave attenuation effect of different ITO sheet resistances provided in the embodiments of the present invention;

[0033] Figure 10 A schematic diagram comparing S21 before and after the presence or absence of a surface electromagnetic wave absorbing structure, provided in an embodiment of the present invention;

[0034] Figure 11 This is a schematic diagram illustrating the field strength variation of surface waves on a surface electromagnetic wave absorbing structure, provided in an embodiment of the present invention.

[0035] Figure 12 Comparison diagram of electromagnetic fields with and without surface electromagnetic wave absorbing structures provided in embodiments of the present invention: Figure 12 (a) shows the magnetic field distribution at 15 GHz without the surface electromagnetic wave absorbing structure; Figure 12 (b) shows the magnetic field distribution at 15 GHz for the surface electromagnetic wave absorbing structure;

[0036] Figure 13 Simulation results of the conformal surface electromagnetic wave absorbing structure provided in the embodiments of the present invention: Figure 13 (a) is a simulation model of a 90° bend; Figure 13 (b) represents the transmission coefficient for different bending angles;

[0037] Figure 14 Comparison diagrams showing the presence and absence of a surface electromagnetic wave absorbing structure under bending conditions, provided in embodiments of the present invention: Figure 14 (a) shows the magnetic field distribution at 15 GHz without the surface electromagnetic wave absorbing structure; Figure 14 (b) shows the magnetic field distribution at 15 GHz for the surface electromagnetic wave absorbing structure;

[0038] Figure 15 Schematic diagram of traveling wave scattering at three types of electromagnetic defect sites provided in embodiments of the present invention: Figure 15 (a) indicates the protruding position; Figure 15 (b) indicates the location of the gap; Figure 15 (c) indicates the location of the step;

[0039] Figure 16 A schematic diagram of the field strength at the electromagnetic defect location of the surface electromagnetic wave absorbing structure provided in an embodiment of the present invention;

[0040] Figure 17 The surface electromagnetic wave absorbing structure provided in the embodiments of the present invention: Figure 17 (a) is a photograph of an ITO resistive film; Figure 17 (b) is the test environment;

[0041] Figure 18 The following is a diagram showing the measured results provided for an embodiment of the present invention: Figure 18 (a) has no surface electromagnetic wave absorbing structure; (b) has a surface electromagnetic wave absorbing structure.

[0042] Figure 19 This is a comparison chart of experimental and simulation results with and without surface electromagnetic wave absorbing structure provided in an embodiment of the present invention;

[0043] In the figure, 1-reflective layer; 2-flexible material dielectric substrate; 3-resistive film resonant metal unit. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0045] Example 1

[0046] This invention provides a surface electromagnetic wave absorbing structure with wave vector and impedance coordinated matching, applicable to the surface of an aircraft. The structure is a three-layer stacked three-dimensional structure, with a fully covered reflective layer 1 at the bottom, a flexible material dielectric substrate 2 in the middle, and multiple resistive film resonant metal units 3 at the top. Each resistive film resonant metal unit includes a first radiator, a second radiator, and a third radiator. The first radiator has a first vertical segment, and the third radiator has a third vertical segment. The first and third vertical segments are arranged opposite each other in the horizontal direction. The first vertical segment has a first horizontal segment extending toward the third radiator at both ends, and the third vertical segment has a third horizontal segment extending toward the first radiator at both ends. The second radiator is located between the first and third radiators and includes a second vertical segment and a second horizontal segment. The second horizontal segment extends from the first vertical segment to the third vertical segment. The first and third horizontal segments are spaced apart, and the second vertical segment extends vertically from both sides of the second horizontal segment.

[0047] Specifically, the reflective layer is made of metal or a conductive composite material. Surface waves are electromagnetic waves that propagate along the interface between different media. Their energy is mainly concentrated near the interface and decays exponentially in the direction perpendicular to the interface. A reflective layer made of metal or a conductive composite material has good conductivity, and combined with a flexible dielectric substrate, it can guide the electromagnetic waves to propagate along the surface.

[0048] Preferably, the reflective layer is made of copper. This complements the advantages of using copper. Copper has an electrical conductivity of 5.96 × 10⁻⁶. 7 With a S / m ratio, copper's high conductivity enables it to achieve nearly 99% reflection in the design frequency band, effectively forming an electrical boundary. Simultaneously, copper is easy to precision etch or machine, allowing for the creation of complex microstructures required for metamaterials; its surface can form a stable oxide layer, resisting environmental corrosion and facilitating long-term device operation.

[0049] Specifically, the flexible dielectric substrate is made of polyethylene terephthalate (PET). A surface wave propagation waveguide is formed by covering an ideal metal surface (i.e., the reflective layer) with a dielectric layer and then coating it with a protective and absorbing coating (i.e., the flexible dielectric substrate). Surface waves are excited by incident a plane wave at a large angle onto this waveguide. The flexible dielectric substrate, as the waveguide medium, guides electromagnetic waves to propagate along the surface, while the metal layer, with its good conductivity, forms a reflective interface, effectively enhancing the excitation efficiency of surface waves. PET, as the dielectric substrate, possesses excellent flexibility and mechanical strength, allowing it to be bent and conform to curved surfaces, making it suitable for wearable devices and conformal metamaterials; its dielectric properties are stable in the microwave band. ≈3.3, =0.02), which is beneficial for achieving low-loss, controllable surface wave propagation; at the same time, PET is lightweight, low-cost, and chemically resistant, making it suitable for large-scale manufacturing. Alternative materials such as polyimide (PI) and polydimethylsiloxane (PDMS) can also be used. The reflective layer and the dielectric layer are combined to excite surface waves.

[0050] Specifically, the resistive film resonant metal unit is made of ITO resistive film. The resistive film resonant metal unit is made of indium tin oxide (ITO). Its sheet resistance... The resistance of ITO can be continuously controlled over a wide range through deposition processes (such as sputtering oxygen partial pressure). Secondly, ITO combines conductivity and dielectric loss, enabling efficient conversion of surface wave electric field energy into Joule heat. By adjusting the resistance of the ITO layer, the dissipation rate of surface waves along the propagation path is controlled, ultimately converting electromagnetic energy into heat energy. Variable resistance elements such as lumped resistors can be used as alternatives, but this will affect its conformal performance.

[0051] Preferably, the process for obtaining the structural dimensions of each layer is as follows:

[0052] S1: Based on the target frequency band, a surface waveguide is used to excite surface waves by incident plane waves at a large angle onto the surface of the aircraft, thus obtaining the magnetic field distribution of the surface waves. In specific implementation, the target frequency band is selected based on the radar's detection frequency. The dimensions of the reflective layer 1 and the flexible material dielectric substrate 2 are obtained through simulation based on the target frequency band and are not limited thereto. In this embodiment, the target frequency band is 12-18GHz, therefore the reflective layer uses copper with a thickness of 0.035mm, and the flexible material dielectric substrate uses polyethylene terephthalate with a thickness of 1.2mm. Figure 1 As shown in (a), the left side uses a horizontally polarized wave for excitation, and the right side uses a port for reception. The propagation curve of the surface wave generated by this excitation structure is shown in Figure 1. Figure 1 As shown in (b), the transmission coefficients are all greater than -10dB, and the transmission characteristics are good in the frequency band of 12-18GHz. Figure 1 (c) shows the magnetic field distribution of the excited surface wave.

[0053] S2: The spatial distribution of the real part of the magnetic field is recorded along the x-direction. Spatial peak spacing analysis is performed to extract the surface wave wavelength, calculate the surface wave vector, and establish a target dispersion curve relating the surface wave vector to the frequency. In practice, the magnetic field distribution of the surface wave on the surface wave excitation structure exhibits obvious evanescent wave characteristics. Using a field monitor, the spatial distribution of the real part of the magnetic field along the x-direction can be recorded, such as... Figure 2 As shown, where, Figure 2 (a) Real part of the magnetic field strength of the surface wave along the x-direction at 12 GHz; Figure 2 (b) Real part of the magnetic field strength of the 14 GHz surface wave along the x-direction; Figure 2 (c) The real part of the magnetic field strength of the 16GHz surface wave along the x-direction; Figure 2 (d) Real part of the magnetic field strength of the 18 GHz surface wave along the x-direction. Spatial peak spacing analysis is performed on this distribution to extract the surface wave wavelength λ, calculate the surface wave vector, and establish a frequency-dependent dispersion curve, such as... Figure 3 As shown.

[0054] Traditional space absorbers are matched to free-space waves, thus absorbing incident space waves without reflection. However, due to the different dispersion characteristics of surface waves compared to space waves, traditional absorbers experience a mismatch effect, leading to a decrease in absorption performance. To ensure stable propagation of excited surface waves and prevent decoupling and scattering, wave vector matching is necessary. Wave vector matching refers to the equal horizontal components of the wave vectors at the interface between two media, allowing wave energy to be transmitted to the second medium without reflection; otherwise, scattering will occur at the interface. The effect of wave vector matching on surface wave transmission characteristics is as follows: Figure 4 As shown, Figure 4(a) is a metamaterial structure with wave vector mismatch. When excited surface waves propagate onto the metamaterial structure, significant scattering occurs. Figure 4 (b) The metasurface structure with wave vector matching can achieve good transmission of surface waves and avoid scattering.

[0055] S3: Preset the initial size parameters of the initial surface electromagnetic wave absorbing structure and construct an equivalent geometric model.

[0056] Specifically, the size and structure of metamaterials affect their equivalent impedance, and changes in impedance can adjust the wave vector matching of the dispersion curve. Presetting initial size parameters provides a basis for subsequent adjustments to the size parameters of the surface electromagnetic wave absorbing structure and for achieving impedance adjustment.

[0057] S4: Use the target dispersion curve as the equivalent geometric model to fit the target curve to the surface wave.

[0058] In practical implementation, to achieve wave vector matching between surface waves and metamaterials, the dispersion curve is key to controlling the propagation and attenuation behavior of surface waves. As the core characterizing the propagation properties of surface waves, the dispersion curve is determined by the relationship between the wave vector *f* and frequency. The mapping relationship represents the different propagation characteristics of surface waves, regulating their transmission and attenuation behavior. Therefore, the target dispersion curve is used as an equivalent geometric model to fit the target curve to the surface wave.

[0059] S5: Initialize the boundary conditions of the equivalent geometric model, wherein the boundary conditions are the structural dimension parameters and corresponding impedances of each layer of the geometric model;

[0060] The size parameters of the surface electromagnetic wave absorbing structure are preset. By adjusting the size parameters of the resistive film resonant metal unit, the overall impedance of the metamaterial can be changed. The change in impedance affects the dispersion characteristics of the metamaterial, thereby achieving a fit with the dispersion curve of the excited surface wave.

[0061] In this embodiment, the resistive film resonant metal unit is made of metal, making the surface electromagnetic wave absorbing structure a metal patch-type metamaterial. The impedance of the metal patch-type metamaterial is capacitive, and it is characterized by a constant impedance. It is indicated that it supports transverse magnetic surface waves, characterized by a longitudinal propagation constant. ,in It is the free space wavenumber. The form of the surface current is... Propagation constant diagonal frequency The dependence is given by the transverse resonance equation of the structure, which is:

[0062]

[0063]

[0064]

[0065]

[0066] in, The average surface impedance of the surface electromagnetic wave absorbing structure; This refers to the wave impedance of the upper half-space of the surface electromagnetic wave absorbing structure, i.e., the wave impedance of the air layer. The wave impedance is the wave impedance of the lower half-space of the surface electromagnetic wave absorbing structure, i.e., the wave impedance of the dielectric substrate and the reflective layer. The absolute dielectric constant of metamaterials With vacuum permittivity The ratio, i.e. = / (Dimensionless number, vacuum) = 1); It is the free space wavenumber; The thickness of the dielectric layer in the metamaterial; It is the free-space wave impedance; The propagation constant is represented by the subscript. Represents surface waves; To control the modulation depth, the impedance fluctuation amplitude is controlled; Indicates the position along the x-axis in the coordinate system; For the local modulation period, control phase accumulation, where, middle , For deviation. Function This reflects the phase shift introduced by the reflection from the metal base plate.

[0067] The transverse resonance equation describes the transverse resonance condition that must be satisfied for surface waves to propagate on a metamaterial. The entire metasurface structure can be considered as a transverse resonant system. Specifically: the metamaterial impedance is determined by the average surface impedance. This indicates that the wave impedance of the upper half-space (air) is... The wave impedance of the lower half-space (dielectric substrate + metal base plate) is The three impedances are connected in parallel in the transverse equivalent circuit. When the sum of their admittances is zero, the system resonates, and surface waves can propagate stably. The ability of metamaterials to control surface waves depends on their equivalent impedance characteristics. By adjusting the metamaterial unit structure or geometry to change the equivalent impedance, the dispersion characteristics can be effectively designed.

[0068] The dispersive properties of surface waves in metamaterials are determined by their boundary conditions, which are defined by the metamaterial's equivalent impedance. The surface wave dispersive properties can be designed by adjusting the metamaterial's unit cell structure or geometry to change its equivalent impedance. Electromagnetic analysis of metamaterial structures can be modeled using penetrable impedance boundary conditions (PIBC), such as... Figure 5 As shown, the metasurface structure that supports TM-type surface waves propagating along the x-axis is as follows: Figure 5 As shown in (a), the equivalent transmission line model of the model is as follows: Figure 5 As shown in (b).

[0069] S6: Based on the geometric model under the boundary conditions, perform simulation to obtain the corresponding dispersion curve, and determine whether the fitting degree between the dispersion curve and the target curve reaches the target preset value: if yes, output the size parameters of each layer of the surface electromagnetic wave absorbing structure; if no, adjust the boundary conditions according to the surface wave fitting target curve until the fitting degree meets the target preset value.

[0070] Preferably, the bottom total reflective metal layer is a fully covered copper layer, the middle dielectric substrate is made of flexible polyethylene terephthalate with a dielectric constant of ν = 3.5, and the top layer is a resonant structure composed of an ITO resistive film. The final output structural dimensions are shown in Table 1, with the following specific dimensions: w = l = 4.2 mm, a = 4.2 mm, b = 2.8 mm, t = 1.2 mm, d = 0.56 mm, g = 0.56 mm, g1 = 0.8 mm, h = 0.035 mm, and the ITO thickness is 10 mm. The PET thickness is 1.2mm. The three-dimensional structure and dimensions of the metamaterial unit are as follows: Figure 6 As shown.

[0071] To further illustrate the attenuation performance of the surface electromagnetic wave absorbing structure (i.e., surface wave attenuation structure or metamaterial structure) provided by this invention, simulations were performed to verify it from different aspects:

[0072] (1) Surface wave attenuation effect of metamaterials

[0073] To verify the surface wave attenuation performance of the designed surface electromagnetic wave absorbing structure, the surface wave attenuation structure was placed after the surface wave excitation structure to form an integrated surface wave excitation-attenuation system. Figure 10 The transmission curves before and after the attenuation structure are compared, clearly showing the attenuation performance of the structure. The transmission coefficient S without the attenuation structure is shown. 21Maintaining a value above -10 dB within the target frequency band of 12-18 GHz indicates good propagation of electromagnetic waves in this band. On the transmission curve after applying the attenuation structure, the transmission coefficient within the same frequency band shows a significant decrease, dropping below -20 dB. Electric field probes were placed at equal intervals along the x-direction at a position 5 mm above the attenuation structure to monitor the surface wave field strength on the attenuation structure; the field strength changes are as follows... Figure 11 As shown, the energy of the surface wave decreases with increasing propagation distance on the attenuation structure, and the field strength decreases significantly. At the center frequency of 15 GHz, the field strength values ​​are 50.84 dB, 36.94 dB, 21.77 dB, 10.13 dB, and 1.83 dB, respectively. After loading the attenuation structure, the surface wave field strength decreases by 49.01 dB. Simulation results show that the attenuation structure effectively suppresses the propagation of surface waves in the 12-18 GHz range, and the energy is rapidly dissipated.

[0074] Figure 12 (a) and Figure 12 (b) shows the magnetic field distribution of the un-attenuated structure and the attenuated structure, respectively. By comparison, it can be clearly found that after the attenuated structure is applied, the propagation of the surface wave shows a significant attenuation trend. At this time, the energy is almost completely absorbed by the top ITO layer and converted into heat energy for dissipation.

[0075] (2) Analysis of surface wave attenuation performance of metamaterials under bending conditions

[0076] The attenuation structure was bent to simulate its performance in specific application scenarios, and the impact of different bending conditions on the system's attenuation efficiency was analyzed. For example... Figure 13 As shown in (a), the attenuation structure is bent along the cylindrical surface. The transmission coefficient curves of the system before and after the bending are as follows: Figure 13 As shown in (b), within the 12-18 GHz frequency band, the transmission coefficient curve of the metamaterial structure remained stable after being bent at different angles, indicating that the structure could still achieve surface wave attenuation under bending conditions. However, the transmission coefficient decreased slightly with increasing bending angle. Due to the bending of the structure, there is a mismatch between the structure and the surface wave vector, resulting in a weakened ability to confine surface waves and causing small-amplitude scattering phenomena, such as... Figure 14 (b) The magnetic field distribution is shown.

[0077] (3) The effect of surface wave attenuation metamaterials on suppressing traveling wave scattering

[0078] When an electromagnetic wave is incident at a large angle on the interface between air and a medium, the incident electric field has an electric field component along the propagation direction of the interface, thereby exciting a surface traveling wave current. This current forms a surface traveling wave at the interface along the propagation direction. During propagation, the surface traveling wave encounters a discontinuous surface and generates an echo, resulting in backscattering. Figure 15To simulate three types of surface wave scattering, namely at the gap location, protrusion location, and step location, the main reason for backscattering in the non-specular reflection direction is that the continuity of the propagating surface traveling wave current is disrupted when it encounters abrupt structural changes or material boundaries. This current change causes the surface wave to radiate electromagnetic energy into space, forming observable backscattered waves.

[0079] A designed surface wave attenuation metamaterial structure was placed in front of three types of electromagnetic defects to attenuate traveling surface waves and suppress traveling wave scattering. To evaluate the effect, electric field probes were placed 30 mm above the traveling wave scattering points of the electromagnetic defects with and without the surface wave attenuation structure to monitor the field strength at those points. Simulation results are as follows. Figure 16 As shown, without the attenuation structure, the electric field strength is high, indicating that electromagnetic defects cause significant traveling wave scattering. After adding the attenuation structure, the field strength monitored by the probe at the same point decreases significantly. At the center frequency of 15 GHz, the field strengths at the three types of electromagnetic defect locations without the attenuation structure are 44.1 dB, 44.2 dB, and 47.4 dB, respectively. After adding the attenuation structure, the field strength decreases to 23.6 dB, 27.3 dB, and 27.9 dB, a decrease of approximately 20 dB. The attenuation structure absorbs surface wave energy, blocking the scattering path of the traveling wave from the electromagnetic defect, and the traveling wave scattering is effectively suppressed.

[0080] (4) Surface wave attenuation metamaterial test and analysis

[0081] To verify the attenuation performance of the designed surface wave attenuation metamaterial structure, a metamaterial sample measuring 201.6 mm × 147 mm was fabricated, consisting of an arrangement of 48 × 35 attenuation units. The fabrication process involved magnetron sputtering to coat ITO onto a PET surface, followed by photolithography to etch the designed ITO structure. The physical structure is shown below. Figure 17 As shown in (a), a copper-clad dielectric substrate and an ITO resistive film were bonded together using transparent adhesive. The copper-clad dielectric substrate measures 600 mm × 147 mm, forming an integral surface wave excitation-attenuation structure. This serves as a comparison with a surface wave excitation structure without a copper-clad dielectric substrate, showing the presence or absence of an attenuation structure.

[0082] The surface wave attenuation performance of the structure was measured using the free-space method in a microwave anechoic chamber, under environmental conditions such as... Figure 17 As shown in (b), two horn antennas are placed at the beginning and end of the surface wave attenuation structure, serving as the energy transmission and reception ports, respectively. The antennas are connected to a vector network analyzer via coaxial lines, and the attenuation effect of the surface wave is reflected by the transmission coefficient between the two ports in the 12-18 GHz range.

[0083] The actual test results are as follows Figure 19As shown, the measured results match the attenuation trend obtained from the simulation. However, numerical differences appear in some frequency bands, primarily due to two factors. Firstly, insufficient precision in the physical fabrication process. In micro-nano fabrication, ITO requires photolithography to form specific patterns, a process that significantly alters its electrical properties, leading to changes in resistance. Secondly, diffraction is unavoidable between the transmitting and receiving antennas. These two factors affect the measured results, resulting in some error compared to the simulation data. The consistency between the experimental and simulation results indicates that the designed metamaterial structure can achieve surface wave attenuation.

[0084] In summary, this invention employs a metamaterial structure integrating wave vector matching and impedance attenuation. This design exhibits highly efficient surface wave attenuation and traveling wave suppression capabilities across a wide bandwidth of 12-18 GHz. The integrated hierarchical design achieves precise control over the surface wave propagation characteristics through wave vector matching, enhancing its coupling efficiency with the attenuation structure. The impedance attenuation unit efficiently absorbs electromagnetic energy through dielectric loss and resistance dissipation mechanisms. By optimizing the parameter distribution of each unit, excellent matching and energy attenuation can be achieved across a wide bandwidth, significantly broadening the overall structure's operating bandwidth. This design achieves efficient electromagnetic wave attenuation while also meeting the requirements of conformal fit and thinness. This invention provides a high-performance, easily integrated, and innovative solution for low observability design and electromagnetic protection of aircraft.

[0085] It is understood that the same or similar parts in the above embodiments can be referred to each other, and the contents not described in detail in some embodiments can be referred to the same or similar contents in other embodiments.

[0086] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A surface electromagnetic wave absorbing structure with wave vector and impedance matching, applied to the surface of an aircraft, characterized in that, The structure is a three-layer stacked three-dimensional structure. The bottom layer is a fully covered reflective layer, the middle layer is a flexible material dielectric substrate, and the top layer is a plurality of resistive film resonant metal units. Each resistive film resonant metal unit includes a first radiator, a second radiator, and a third radiator. The first radiator has a first vertical segment, and the third radiator has a third vertical segment. The first and third vertical segments are arranged opposite each other in the horizontal direction. The first vertical segment has a first horizontal segment extending toward the third radiator at both ends, and the third vertical segment has a third horizontal segment extending toward the first radiator at both ends. The second radiator is located between the first and third radiators. The second radiator includes a second vertical segment and a second horizontal segment. The second horizontal segment extends from the first vertical segment to the third vertical segment. The second vertical segment is located within the second horizontal segment. The first and third horizontal segments are spaced apart, and the second vertical segment extends vertically from both sides of the second horizontal segment.

2. The structure according to claim 1, characterized in that, The reflective layer is made of metal or conductive composite material.

3. The structure according to claim 2, characterized in that, The reflective layer is made of copper.

4. The structure according to claim 1, characterized in that, The flexible material substrate is made of polyethylene terephthalate.

5. The structure according to claim 1, characterized in that, The resistive film resonant metal unit is made of ITO resistive film.

6. The structure according to any one of claims 1-5, characterized in that, The process for obtaining the structural dimensions of each layer is as follows: S1: A surface wave is excited by a surface transmission waveguide that is incident on the surface of the aircraft at a large angle with a plane wave, and the magnetic field distribution of the surface wave is obtained. S2: Record the spatial distribution of the real part of the magnetic field along the x-direction, perform spatial peak spacing analysis, extract the surface wave wavelength, calculate the surface wave vector, and establish the target dispersion curve related to the surface wave vector and frequency. S3: Preset the initial size parameters of the initial surface electromagnetic wave absorbing structure and construct an equivalent geometric model; S4: Use the target surface wave dispersion curve as the equivalent geometric model to fit the target curve to the surface wave; S5: Initialize the boundary conditions of the equivalent geometric model, wherein the boundary conditions are the dimension parameters of each layer of the geometric model and the corresponding impedance; S6: Based on the geometric model under the boundary conditions, perform simulation to obtain the corresponding dispersion curve, and determine whether the fitting degree between the dispersion curve and the target curve reaches the target preset value: if yes, output the size parameters of each layer of the surface electromagnetic wave absorbing structure; if no, adjust the boundary conditions according to the surface wave fitting target curve until the fitting degree meets the target preset value.

7. The structure according to any one of claims 1-6, characterized in that, After adjusting the boundary conditions, the wave impedance satisfies the transverse resonance equation when the surface wave propagates on the surface electromagnetic wave absorbing structure: ； in, The propagation constant is given by the subscript sw, which indicates a surface wave. The average surface impedance of the surface electromagnetic wave absorbing structure; This refers to the wave impedance of the upper half-space of the surface electromagnetic wave absorbing structure, i.e., the wave impedance of the air layer. This refers to the wave impedance of the lower half-space of the surface electromagnetic wave absorbing structure, i.e., the wave impedance of the dielectric substrate and the reflective layer.

Images