Electromagnetic wave-absorbing material for improving large-angle oblique incidence based on FSS

Abstract

The invention belongs to the field of electromagnetic wave-absorbing materials, and particularly relates to an electromagnetic wave-absorbing material for improving large-angle oblique incidence based on FSS. Based on the characteristics that a magnetic material has magnetic loss and electrical loss at the same time, the single-layer magnetic material with the thickness smaller than or equal to 3 mm is adopted and combined with the FSS to excite induced current and generate harmonic peaks under TM polarization, so that broadband absorption is achieved within the frequency band of 2-18 GHz during large-angle (60-80 degrees) oblique incidence, the thin type large-angle broadband wave-absorbing effect under TM polarization is achieved, and the wide-angle broadband wave-absorbing effect under TM polarization is achieved. The wave absorbing performance under TE polarization is kept unchanged; on the premise that the thickness is not increased, the stealth requirement of a radar for large-angle detection of a protected target in practical application is met, the problems that the wave absorbing performance of an existing wave absorbing material is seriously deteriorated under large-angle oblique incidence of electromagnetic waves and the thickness is large are solved, and therefore the survivability of the target is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the field of electromagnetic wave absorbing materials, in particular to an electromagnetic wave absorbing material for improving large-angle oblique incidence based on FSS. Background Art

[0002] Radar stealth technology mainly includes shape design, application of radar absorbing materials, etc. When the shape is determined, the application of radar absorbing materials becomes the most important means. In the case of large thickness, electric loss absorbing materials can achieve broadband absorption, but their disadvantage is that they require a large enough space; magnetic materials have large magnetic losses and can achieve good absorbing effects under thin coatings. Therefore, in the case of thin thickness, how to use magnetic materials to broaden the absorbing frequency band has become an urgent problem to be solved. On the other hand, when the aircraft has a good shape stealth design, there is no vertical incidence of electromagnetic waves, but the absorbing performance of absorbing materials under large-angle (60-80°) oblique incidence of electromagnetic waves is significantly attenuated compared to vertical incidence. In current military applications, ultra-thin absorbing materials with large-angle broadband absorption characteristics have attracted much attention.

[0003] At present, absorbing materials have the problem of serious deterioration of absorbing performance and large thickness when electromagnetic waves are incident at large angles. Patent CN116780206 adopts the method of adding an air layer between two layers of magnetic materials. When the incident angle reaches 70°, good absorption can still be achieved in the 2-7GHz frequency band. However, due to the addition of the air layer, the thickness increases and the total thickness is 12.4mm. Patent CN110137691 uses two layers of different magnetic materials and periodically punches holes on the magnetic materials. Under TM polarization, when the incident angle reaches 60°, good absorption is achieved in the 2-18GHz frequency band, but the total thickness is 8.84mm. Both of the above solutions can achieve large-angle absorption, but at the expense of the thickness of the absorbing material.

[0004] Patent CN106299721 uses a method of loading a metal frequency selective surface (FSS) between magnetic material layers. The thickness of the absorbing material is 2.2 mm, and good absorption is achieved in the 4-18 GHz frequency band. The absorption performance can only be maintained within 30°. Patent CN103579776 uses a periodically arranged absorbing material with circular through holes, and a metal film is set in the through holes. The total thickness is 3 mm, and good absorption is achieved in the 6-18 GHz frequency band. The absorption performance can only be maintained within 45°. However, the obvious shortcoming of these solutions is that the absorbing performance is seriously deteriorated under large-angle oblique incidence. Summary of the invention

[0005] In view of the above-mentioned problems and deficiencies, and in order to solve the problems of serious deterioration of the absorbing performance of existing absorbing materials under large-angle oblique incidence of electromagnetic waves and large thickness, the present invention provides an electromagnetic absorbing material based on FSS to improve large-angle oblique incidence. Without increasing the thickness of the absorbing material, a method of combining a layer of magnetic material with FSS is adopted, and by adjusting the structural parameters of FSS, when the electromagnetic wave is incident at a large angle, the absorbing performance under TM polarization is improved while maintaining the absorbing performance under TE polarization unchanged.

[0006] The specific technical scheme of the present invention is:

[0007] An electromagnetic absorbing material based on FSS to improve large-angle oblique incidence, composed of absorbing material units arranged in a periodic (matrix) manner. The absorbing material unit is a square laminated structure with a period of p, which includes a metal base plate, a magnetic material layer and FSS from bottom to top, and the thickness of the magnetic material layer does not exceed 3mm.

[0008] The thickness h of the magnetic material layer is 0.1-3 mm, and plays the role of electromagnetic loss and mechanical support of FSS.

[0009] In order to solve the problem that the absorbing performance of the absorbing material is seriously deteriorated when the electromagnetic wave is incident at a large angle, the FSS excites an induced current under TM polarization to generate a resonance peak, so that the FSS is combined with the magnetic material layer under large-angle oblique incidence, thereby improving the absorbing performance in the 2-18 GHz frequency band, realizing large-angle broadband absorption under TM polarization, and keeping the absorbing performance under TE polarization unchanged.

[0010] Furthermore, the magnetic material layer only uses a single layer of magnetic material.

[0011] Furthermore, the FSS is a rectangular long strip metal unit, and under TM polarization, an electric field component exists in the long side direction of the metal unit and is arranged on the magnetic material layer, and the length of the metal unit is l and the width is w.

[0012] Furthermore, the period p is 2-10 mm, and the metal unit size is 0.1≤w≤l≤p≤10 mm.

[0013] The thin, wide-angle, broadband absorbing material under TM polarization provided by the present invention realizes electromagnetic absorption at a relatively thin absorbing material thickness (≤3 mm) based on the characteristics of magnetic materials having both magnetic loss and electrical loss. In order to improve the problem of serious deterioration of absorbing performance when electromagnetic waves are incident at large angles, FSS is used to excite an induced current under TM polarization to generate a resonance peak, so that FSS is combined with the magnetic material layer under large angles of oblique incidence, improving the absorbing performance in the 2-18 GHz frequency band, and keeping the absorbing performance of the absorbing material under TE polarization unchanged.

[0014] In summary, the present invention constructs an absorbing material combining a magnetic material layer and FSS to improve the absorbing performance under TM polarization when the electromagnetic wave is obliquely incident at a large angle (60-80°), realizes broadband absorption in the 2-18 GHz frequency band, and keeps the absorbing performance under TE polarization unchanged, thereby realizing a large-angle broadband absorbing effect under TM polarization. Without increasing the thickness, the stealth requirements of radar for large-angle detection of protected targets in practical applications are met, thereby significantly improving the survivability of the target. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Electromagnetic parameters of the magnetic materials used in the examples.

[0016] Figure 2 It is a three-dimensional exploded schematic diagram of two different models of the embodiment and the comparative example.

[0017] Figure 3 Schematic diagram comparing the simulation results of TM and TE of two models under 60° oblique incidence in Example 1.

[0018] Figure 4 Schematic diagram comparing the simulation results of TM and TE of the two models under 70° oblique incidence in Example 2.

[0019] Figure 5 Schematic diagram showing the comparison of simulation results of TM and TE of two models under 80° oblique incidence in Example 3 DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described in detail below in conjunction with the embodiments and drawings.

[0021] An electromagnetic absorbing material based on FSS to improve large-angle oblique incidence, such as Figure 2 As shown in (b), it includes, from bottom to top: a metal base plate, a magnetic material layer and FSS. Figure 2 (a) is a comparative example, from bottom to top: a metal base plate and a magnetic material layer, and Figure 2 The structure of (b) is compared to explore the influence of introducing FSS on the absorption effect when electromagnetic waves are incident at large angles.

[0022] In this embodiment and the comparative example, the real part of the dielectric constant of the magnetic material is 17 to 14 (dispersion), and the imaginary part of the dielectric constant is 1 to 3 (dispersion). Figure 1As shown, between 2 and 18 GHz, the real part of the magnetic permeability of the magnetic material gradually decreases from 4.5 to 1.5, and the imaginary part of the magnetic permeability stabilizes at around 1.5. The specific size parameters of the absorbing material unit are: magnetic material layer thickness h = 1.5 mm, metal FSS unit length l = 6 mm, width w = 1 mm, unit period p = 8 mm. The thin, large-angle, broadband absorbing material under TM polarization designed according to the contents of this embodiment is implemented and verified. When the incident angles of the electromagnetic wave are 60°, 70°, and 80°, respectively, the specific implementation verification results are as follows;

[0023] Example 1

[0024] like Figure 3 As shown in the figure, when the electromagnetic wave is incident at 60°, Figure 2 The two models in the simulation are simulated, and the simulation results are as follows: Under TM polarization, only 1.5mm of magnetic material can achieve -10dB absorption in the 4.5-18GHz band. By combining FSS with magnetic materials, the absorbing performance in the 2-18GHz band is improved without increasing the thickness of the absorbing material, and a deeper absorption peak of -27dB is generated near 3.8GHz. And under TE polarization, the absorbing performance can remain unchanged.

[0025] Example 2

[0026] like Figure 4 As shown in Figure 2, when the electromagnetic wave is incident at 70°, Figure 2 The two models in the simulation are simulated, and the simulation results are as follows: under TM polarization, the absorbing performance in the 0.5-18 GHz band gradually deteriorates when only 1.5 mm of magnetic material is used. By combining FSS with magnetic materials, the absorbing performance in the 2-18 GHz band is improved without increasing the thickness of the absorbing material, and the reflectivity reaches -10 dB in the 3-18 GHz band. And under TE polarization, the absorbing performance can be kept unchanged.

[0027] Example 3

[0028] like Figure 5 As shown in the figure, when the electromagnetic wave is incident at 80°, Figure 2 The simulation results show that under TM polarization, the absorbing performance in the 0.5-18 GHz band deteriorates seriously when only 1.5 mm of magnetic material is used. By combining FSS with magnetic material, the absorbing performance in the 2-18 GHz band is improved without increasing the thickness of the absorbing material, and the reflectivity reaches -8 dB in the 4-18 GHz band. And under TE polarization, the absorbing performance can be kept unchanged.

[0029] It can be seen from the above embodiments that the present invention is based on the characteristics of magnetic materials having both magnetic loss and electric loss. A single-layer magnetic material is used in combination with FSS under TM polarization to excite an induced current and generate a resonance peak, thereby achieving broadband absorption in the 2-18 GHz frequency band at a large-angle (60-80°) oblique incidence, achieving a thin large-angle broadband absorbing effect under TM polarization, and keeping the absorbing performance under TE polarization unchanged; the present invention meets the stealth requirements of radar for large-angle detection of protected targets in practical applications without increasing the thickness, solves the problems of serious deterioration of absorbing performance and large thickness of existing absorbing materials under large-angle oblique incidence of electromagnetic waves, thereby significantly improving the survivability of the target.

Claims

1. An electromagnetic absorbing material for improving large-angle oblique incidence based on FSS, characterized in that: The absorbing material units are arranged in a periodic manner. The absorbing material units are a square laminated structure with a period of p, and include a metal base plate, a magnetic material layer and FSS from bottom to top. The thickness of the magnetic material layer does not exceed 3 mm. The thickness h of the magnetic material layer is 0.1 to 3 mm, which plays the role of electromagnetic loss and mechanical support of FSS; The FSS excites an induced current under TM polarization to generate a resonance peak, so that the FSS combines with the magnetic material layer at large-angle oblique incidence, improves the wave absorption performance in the 2-18 GHz frequency band, realizes large-angle broadband wave absorption under TM polarization, and maintains the wave absorption performance under TE polarization unchanged.

2. The electromagnetic absorbing material for improving large-angle oblique incidence based on FSS as claimed in claim 1, characterized in that: The magnetic material layer is a single-layer magnetic material.

3. The electromagnetic absorbing material for improving large-angle oblique incidence based on FSS as claimed in claim 1, characterized in that: The FSS is a rectangular long strip metal unit. Under TM polarization, an electric field component exists in the long side direction of the metal unit and is arranged on the magnetic material layer. The length of the metal unit is l and the width is w.

4. The electromagnetic absorbing material for improving large-angle oblique incidence based on FSS as claimed in claim 3, characterized in that: The period p is 2-10 mm, and the metal unit size is 0.1≤w≤l≤p≤10 mm.

5. The electromagnetic wave absorbing material for improving large-angle oblique incidence based on FSS as claimed in claim 1, characterized in that: The arrangement period of the wave absorbing material units is arranged in a matrix manner.

6. The electromagnetic absorbing material for improving large-angle oblique incidence based on FSS as claimed in claim 1, characterized in that: The real part of the dielectric constant of the magnetic material is 17-14 dispersion, the imaginary part of the dielectric constant is 1-3 dispersion, the thickness of the magnetic material layer is h=1.5mm; the metal FSS unit has a length of l=6mm, a width of w=1mm, and a unit period of p=8mm.

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