Ultrathin-structure low-frequency absorber based on electromagnetic metamaterial

Abstract

The invention discloses an ultra-thin structure low-frequency absorber based on an electromagnetic metamaterial. The ultra-thin structure low-frequency absorber is composed of a plurality of unit structure periodic arrays. Each unit structure comprises a metal resonance layer, a first dielectric layer, a metal patch layer, a second dielectric layer and a metal grounding layer from top to bottom; the metal resonance layer and the metal patch layer are etched on the two sides of the first dielectric layer, the metal grounding layer is attached to the lower side of the second dielectric layer, and the metal resonance layer and the metal patch layer are overlapped to form the antenna. The absorber achieves more than 90% of absorption at 0.3 GHz, the thickness of the absorber is 1 / 1072 of the incident wavelength, and the absorber has polarization insensitivity and wide-angle incidence stability. The low-frequency wave-absorbing characteristic comes from a strong capacitance effect between the metal resonance layer and the metal patch layer, and absorption can be realized in more frequency bands by changing the amplitude of the narrow slit and the size of the patch. According to the absorber, low-frequency absorption is achieved through an ultra-thin structure, design is simple, machining is convenient, and the absorber has high practical value in the fields of military stealth, long-distance communication, radar shielding and the like.

Description

Technical Field

[0001] The invention relates to a microwave absorber, and in particular to an ultra-thin structure low-frequency absorber based on electromagnetic metamaterials, which can be used in the fields of military stealth, long-distance communication, radar shielding, etc. Background Art

[0002] Electromagnetic absorption technology can not only improve the stealth performance and electromagnetic compatibility of special targets, but also be used to suppress electromagnetic radiation pollution. It has a wide range of applications in military and civilian technology. Metamaterial microwave absorbers can achieve efficient absorption of electromagnetic waves and are one of the frontiers and hot spots in the current absorber design field.

[0003] There are four main indicators for judging the quality of microwave absorbers - "thin, light, wide, and strong". "Thin" means that the relative thickness of the absorber should be small, where is the thickness of the absorber and is the wavelength of the electromagnetic wave; "light" means that the mass of the absorber should be light; "strong" means that the microwave absorber should have strong reflection loss to the incident electromagnetic wave. We usually believe that if it can absorb 90% of the incident wave energy, that is, the reflection loss reaches, its absorption strength is relatively excellent; "wide" means that the frequency range of the material reflection loss is wide. The thinning of the absorber can significantly reduce the weight of the overall system, which is especially important for applications such as aerospace, satellites, drones, and military equipment that have strict weight requirements. Especially in high-tech fields such as aerospace, military, and electronic communications, thin and light microwave absorbers will become an important factor in improving equipment performance and reliability.

[0004] Low-frequency microwave absorbers have always been the focus of researchers. Low-frequency microwave absorbers usually work in a lower microwave frequency range, generally between a few hundred megahertz (MHz) and several gigahertz (GHz). These absorbers are mainly used to absorb lower frequency microwave signals. Due to the longer wavelength of low-frequency microwaves, absorbers usually need to be larger in size and thicker in thickness to achieve effective absorption of incident electromagnetic waves. Low-frequency electromagnetic waves have strong penetrating power. Reducing or shielding unwanted low-frequency waves is the core of concern in the microwave industry. Therefore, low-frequency microwave absorbers play a vital role in radar systems, communication systems, electromagnetic interference protection and other fields.

[0005] Lawrence from the University of Exeter was one of the first researchers to focus on the concept of ultra-thin structure absorbers. In 2009, he reported a polarization-independent thin structure microwave absorber with a thickness of only 1 / 130 of the working wavelength and a minimum absorption frequency of 20 GHz. Although the absorber achieved multi-band, the absorption effect was not good. In 2019, Professor Huang Weiqing of Hunan University reported a multi-band ultra-thin ideal metamaterial absorber based on a split-ring resonator. Three discrete absorption peaks were obtained at 1.8 GHz, 3 GHz, and 4.1 GHz. The ratios of the thickness of the dielectric sheet to the wavelengths of the three absorption peaks were 1 / 100, 1 / 59, and 1 / 43, respectively, which were all smaller than the three-band absorption devices at the time. In 2020, Jin Yi's team at Zhejiang University achieved a new breakthrough in ultra-thin structure absorbers, reporting a metamaterial absorber with a thickness of only 1 / 474 of the working wavelength and an absorption frequency of 1.5 GHz, but the only drawback was that the absorber did not achieve polarization-independent properties. Kim achieved a new breakthrough in absorber thickness in 2022. He reported an article that achieved absorption at 1.5 GHz, and the relative thickness was only 1 / 1250 of the working wavelength. Although the above reports have made breakthroughs in thickness, low-frequency absorption below 1 GHz has always been a problem. Bui Xuan Khuyen of Hanyang University paid attention to the difficulties of low-frequency absorption and reported an ultra-low frequency multi-band absorber in 2017. The absorber achieved absorption at 0.3 GHz and 0.36 GHz, but the thickness was relatively large, only 1 / 378 and 1 / 320 of the working wavelength, and the ultra-thin design was not achieved.

[0006] In summary, ultra-thin structure absorbers and ultra-low frequency absorbers have attracted the attention of researchers in recent years, but there are few reports on high-performance absorbers that take into account both low frequency and ultra-thinness, especially ultra-thin structure absorbers below 1 GHz. Since the wavelength of low-frequency electromagnetic waves is long, the absorber needs to be thick enough to effectively absorb these long-wavelength electromagnetic waves. Low-frequency waves are more easily reflected, and a sufficiently thick absorption layer can eliminate reflection, increase energy absorption, and reduce the influence of the transmission layer. An absorber that can achieve both low-frequency absorption and ultra-thin structure is a hot spot and difficulty in current absorber research. Summary of the invention

[0007] Purpose of the invention: In order to break through the traditional thickness of metamaterial absorbers and overcome the difficulty of microwave absorbers in absorbing microwaves at low frequencies, the present invention provides a design of an ultra-thin low-frequency absorber based on electromagnetic metamaterials. This absorber has the advantages of ultra-thin structure, low-frequency absorption, polarization insensitivity, and large-angle incident stability. It is also simple in design, small in size, and easy to process. It has high practical value in the fields of military stealth, long-distance communication, and radar shielding.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] An ultra-thin structure low-frequency absorber based on electromagnetic metamaterials, characterized in that: it comprises more than one absorber unit structure arranged in a spatial periodic square, the absorber module is composed of a metal resonance layer (1), a first dielectric layer (2), a metal patch layer (3), a second dielectric layer (4), and a metal grounding layer (5) from top to bottom, and the geometric centers of the layers overlap vertically; the metal resonance layer is a metal surface formed by engraving two orthogonal curved narrow slits, the curved narrow slits extend from the center of the unit structure to the midpoints of the four sides of the unit structure, the curved narrow slits between adjacent unit structures are mutually connected, and the narrow slits have rotational symmetry; the metal patch layer is a perfect circular metal surface, and the center of the circle overlaps vertically with the intersection of the two orthogonal curved narrow slits; the metal resonance layer and the metal patch layer are respectively etched on both sides of the first dielectric layer; the metal grounding layer is attached to one side of the second dielectric layer, and the first dielectric layer with structures etched on both sides and the second dielectric layer with one side attached to the metal surface together constitute an ultra-thin structure low-frequency absorber based on electromagnetic metamaterials.

[0010] Preferably, the metal resonance layer, metal patch layer and metal grounding layer are made of copper, and the electrical conductivity is 5.8×10 7 S / m, thickness h=0.01mm.

[0011] Preferably, the unit structure period p=8.5 mm.

[0012] Preferably: the narrow slit is a sine function Description, where A is the amplitude, is the initial phase, ω=2π / p, and the two narrow slits are orthogonal to each other.

[0013] Preferably, the narrow gaps between the adjacent unit structures are interconnected.

[0014] Preferably, the first dielectric layer is made of polyimide film, with a relative dielectric constant ε=4, a loss tangent tan(δ)=0.005, and a thickness d 1 =0.002mm.

[0015] Preferably, the metal patch layer is a perfect circular metal surface, and the circular radius r=4.1 mm.

[0016] Preferably, the second dielectric layer is made of polytetrafluoroethylene plate, with a relative dielectric constant ε=2.2, a loss tangent tan(δ)=0.001, and a thickness d 2 =0.9mm.

[0017] Preferably, the metal resonant pattern is processed by a chemical etching process on the upper side of the first dielectric layer, and the metal patch pattern is processed by a chemical etching process on the lower side.

[0018] Preferably, a metal copper film is applied to the lower side of the second dielectric layer as a metal grounding layer.

[0019] The present invention provides an ultra-thin structure low-frequency absorber based on electromagnetic metamaterials, which has the following beneficial effects compared with the prior art:

[0020] 1. The ultra-thin structure low-frequency absorber based on electromagnetic metamaterials of the present invention achieves perfect low-frequency absorption at 0.3 GHz, with an absorption rate of more than 90%.

[0021] 2. The ultra-thin low-frequency absorber based on electromagnetic metamaterials of the present invention has ultra-thin characteristics and a total structural thickness of only 0.932 mm, which is only 1 / 1072 of the wavelength of the absorption frequency. The relative thickness of the absorber structure reaches the leading level of the currently reported work.

[0022] 3. The ultra-thin structure low-frequency absorber based on electromagnetic metamaterials of the present invention has excellent characteristics such as low-frequency absorption, polarization insensitivity, polarization stability, and large-angle incident stability. It plays an important role in the fields of military stealth, long-distance communication, and radar shielding.

[0023] 3. The ultra-thin low-frequency absorber based on electromagnetic metamaterial of the present invention adopts polytetrafluoroethylene plate and polyimide film as dielectric layer, and the metamaterial absorber can be bent and folded to a certain extent, so it has better adaptability to the covering environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the wave absorbing principle of an ultra-thin structure low-frequency absorber based on electromagnetic metamaterials according to the present invention;

[0025] Figure 2 This is a schematic diagram of the structural layering of an ultra-thin low-frequency absorber based on electromagnetic metamaterials according to the present invention;

[0026] Figure 3 This is a schematic diagram of the structure of a metal resonance layer of an ultra-thin structure low-frequency absorber based on electromagnetic metamaterials according to the present invention;

[0027] Figure 4 This is a schematic diagram of the metal patch layer structure of an ultra-thin structure low-frequency absorber based on electromagnetic metamaterials according to the present invention;

[0028] Figure 5 A side view of an ultra-thin structure low-frequency absorber based on electromagnetic metamaterials according to the present invention;

[0029] Figure 6 This is a 3D schematic diagram of an ultra-thin structure low-frequency absorber based on electromagnetic metamaterials according to the present invention;

[0030] Figure 7This is an absorption spectrum diagram of an ultra-thin structure low-frequency absorber based on electromagnetic metamaterials described in the present invention;

[0031] Figure 8 Absorption spectra of different polarization angles of an ultra-thin structure low-frequency absorber based on electromagnetic metamaterials described in the present invention;

[0032] Fig. 9 This is an absorption spectrum diagram of an ultra-thin structure low-frequency absorber based on electromagnetic metamaterials under different incident angles in TE mode according to the present invention;

[0033] Fig.10 This is an absorption spectrum diagram of an ultra-thin structure low-frequency absorber based on electromagnetic metamaterials at different incident angles in TM mode described in the present invention. DETAILED DESCRIPTION

[0034] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0035] like Figure 1 As shown, the present invention provides an ultra-thin structure low-frequency absorber based on electromagnetic metamaterials, comprising more than one absorber unit structure arranged in a square in a spatial period, the absorber module, such as Figure 2 As shown, from top to bottom, there are metal resonance layer (1), first dielectric layer (2), metal patch layer (3), second dielectric layer (4), and metal ground layer (5), and the geometric centers of each layer overlap vertically; Figure 3 As shown, the metal resonance layer is a metal surface formed by two orthogonal curved narrow slits, the curved narrow slits extend from the center of the unit structure to the midpoints of the four sides of the unit structure, the curved narrow slits between adjacent unit structures are interconnected, and the narrow slits have rotational symmetry; Figure 4 As shown, the metal patch layer is a perfect circular metal surface, and the center of the circle coincides with the intersection of two orthogonal curved narrow slits in the vertical direction; the metal resonance layer and the metal patch layer are respectively etched on both sides of the first dielectric layer; the metal grounding layer is attached to one side of the second dielectric layer, as shown in FIG. Figure 5 As shown, the first dielectric layer with etching structures on both sides and the second dielectric layer with metal surface attached on one side together constitute an ultra-thin structure low-frequency absorber based on electromagnetic metamaterials. Figure 6 This is a 3D schematic diagram of the absorber.

[0036] The metal resonance layer, metal patch layer and metal grounding layer are made of copper, and the conductivity is 5.8×10 7 S / m, thickness h=0.01mm.

[0037] The unit structure period p=8.5 mm.

[0038] The narrow slit is a sine function Description, where A is the amplitude, is the initial phase, ω=2π / p, and the two narrow slits are orthogonal to each other.

[0039] The narrow gaps between the adjacent unit structures are interconnected.

[0040] The first dielectric layer is made of polyimide film, with a relative dielectric constant ε=4, a loss tangent tan(δ)=0.005, and a thickness d 1 =0.002mm.

[0041] The metal patch layer is a perfect circular metal surface, and the circular radius r=4.1 mm.

[0042] The second dielectric layer is made of polytetrafluoroethylene plate, with a relative dielectric constant ε=2.2, a loss tangent tan(δ)=0.001, and a thickness d 2 =0.9mm.

[0043] The metal resonant pattern is processed by chemical etching process on the upper side of the first dielectric layer, and the metal patch pattern is processed by chemical etching process on the lower side.

[0044] The lower side of the second dielectric layer is covered with a metal copper film as a metal grounding layer.

[0045] Since the metamaterial absorber uses a subwavelength structure, the larger the unit structure size of the absorber, the lower the absorption frequency. Therefore, in different absorption frequency ranges, the processing method of the metamaterial absorber is different. The size of the unit structure of the microwave metamaterial absorber is based on millimeters, so it is usually processed using printed circuit board technology. In the present invention, we use polytetrafluoroethylene plates and polyimide films as dielectric layers and copper as metal layers. We obtain a metal resonant structure and a metal patch structure by chemically etching both sides of a polyimide film covered with copper on both sides, and affix a metal film to one side of the polytetrafluoroethylene plate dielectric as a metal grounding layer.

[0046] The preparation process of the ultra-thin structure low-frequency absorber based on electromagnetic metamaterials described in this embodiment is as follows:

[0047] (1) Ingredients: Through the ingredients, polyimide film and polytetrafluoroethylene plate with electromagnetic parameters close to those of the materials used in the simulation are obtained.

[0048] (2) Impregnation: The prepared polyimide film and polytetrafluoroethylene plate are placed in an organic impregnation solution with a vacuum pressure of 0.05 MPa, taken out and kept in a preheated infrared drying oven for 40 min to 60 min.

[0049] (3) Assembly: Use a cardboard cutter and a copper foil cutter to cut the polyimide film, polytetrafluoroethylene plate and copper foil into sufficiently large squares.

[0050] (4) Hot pressing: Place the copper plate and glass fiber plate into a hot press for pressing, set the time to 35 min and the temperature to 240 °C.

[0051] (5) Polishing: To make the copper-clad dielectric board smoother, use fine water sandpaper to polish and clean it.

[0052] (6) Rubbing: Rubbing the printed circuit board sketch exported from CAD onto the cleaned metal surface.

[0053] (7) Patterning: Use tape to cover the metal surface and remove the tape outside the pattern on the copper foil surface.

[0054] (8) Corrosion: The corrosion liquid is a ferric chloride aqueous solution with a concentration range of 30% to 40%. Select an appropriate temperature (below 50°C) and gently brush with a brush or clamp the circuit board with a wooden stick and shake it slightly to speed up the corrosion. After the corrosion is completed, rinse with clean water.

[0055] (9) Peeling off the film: Peel off the tape attached to the metal surface.

[0056] (10) Cleaning: Use a dilute acetone solution as the cleaning liquid, dip a cotton ball into it and gently wipe off the protective paint on the surface to obtain the corresponding product.

[0057] The following briefly introduces the electromagnetic simulation calculation results of the present invention:

[0058] The present invention uses electromagnetic simulation software for calculation, adopts finite integration technology to divide the structure into grids, and applies Maxwell equations and boundary conditions to each grid for electromagnetic simulation calculation. Plane electromagnetic wave is used as the incident wave source of this simulation, and the incident wave vector is k, which is incident along the positive direction of the z-axis; E is the electric field vector and is parallel to the x-direction, and H is the magnetic field vector and is parallel to the y-direction. In the x and y directions, the boundary is set to the unit period Unit cell, and in the z direction, the boundary is set to the open boundary Open (add space). In this way, the entire boundary presents a Floquet periodic boundary, and this boundary setting can simulate the absorption effect of the absorbing unit after being expanded according to the periodic array.

[0059] The absorption performance of the ultra-thin structure low-frequency absorber based on electromagnetic metamaterials described in the present invention can be represented by an absorptivity A(ω), which can be derived from the reflectivity R(ω) and the transmittance T(ω). The derivation process is as follows: the sum of the absorptivity, reflectivity and transmittance is 1, that is, A(ω)+R(ω)+T(ω)=1, from which A(ω)=1-R(ω)-T(ω) can be obtained, and R(ω) and T(ω) can be represented by scattering parameters (S parameters), R(ω)=|S 11 | 2 , T(ω)=|S 21 | 2 Since the thickness of the bottom metal layer is greater than the skin depth of the metal copper film for the incident electromagnetic wave, the electromagnetic wave cannot be transmitted outward through the metal bottom plate, so T(ω) can be considered to be 0. Therefore, the absorption rate A(ω) can be simplified as follows: A(ω)=1-R(ω)=1-|S 11 | 2 , which is the expression for the absorptivity.

[0060] The absorption spectrum of the ultra-thin structure low-frequency absorber based on electromagnetic metamaterials described in the present invention is as follows: Figure 7 As shown, the absorber can have an absorption peak with high efficiency absorption in the 0.3 GHz band, with an absorption rate of more than 90%. The total thickness of the absorber is 0.932 mm, and the working wavelength at the absorption frequency is 1000 mm. It can be concluded that the overall thickness of the absorber is 1 / 1072 of the incident wavelength.

[0061] In practical applications, electromagnetic waves are often incident on the surface of electromagnetic metamaterial absorbers at a certain angle. Therefore, it is necessary to study the absorption of electromagnetic waves at different incident angles by the absorber. is the angle between the x-axis and the xoy plane, and the incident angle θ is defined as the angle between the position vector of the incident point source and the z-axis.

[0062] First, we explored the polarization angle The electromagnetic absorber of the present invention has C 4 The angle is symmetrical, so we only need to explore the angle change within the range of 1 / 4 period. While keeping the above settings unchanged, set θ to 0° and The variation range is set to 0°~90°. The absorption spectrum is as follows Figure 8 As shown, when a plane wave is incident vertically on the absorber, the polarization angle varies in the range of 0° to 90°, and the absorption spectrum shows good polarization angle stability at the absorption frequency, from which it can be concluded that the absorber of the present invention has the property of polarization insensitivity.

[0063] Secondly, we explored the corresponding absorption spectra when the electromagnetic wave is obliquely incident on the absorber surface in the TE mode and TM mode. The so-called TE mode here means that the electric field E of the incident wave is always parallel to the absorber surface; while the TM mode means that the magnetic field H of the incident wave is always parallel to the absorber surface. In the electromagnetic simulation software, the mode excitation is set to TE mode and TM mode respectively, and two numerical simulations are performed respectively. During the simulation, the polarization angle is set to 1. Set it to 0°, and let the incident angle θ vary between 0° and 80°. The corresponding absorption rates are as follows: Fig. 9 , Fig.10 As shown: In TE mode, the absorber can maintain high-efficiency absorption at an incident angle of 0° to 45°, and the absorption rate decreases gently as the incident angle increases further; in TM mode, the absorber always maintains high-efficiency absorption at an incident angle of 0° to 80°, but the absorption peak shifts to a certain extent as the angle increases. This is because the spacing between adjacent absorption units is too close, the coupling between units is extremely strong, and they are sensitive to changes in the angle of oblique incidence, which leads to poor stability in the absorption of electromagnetic waves and thus a shift.

[0064] The ultra-thin structure low-frequency absorber based on electromagnetic metamaterials described in the present invention breaks through the traditional thickness limitation of microwave absorbers, and the relative thickness reaches the leading level, overcoming the difficulty of microwave absorbers in absorbing waves at low frequencies, and is a high-efficiency absorber that takes into account ultra-thin structure and low-frequency absorption. At the same time, the present invention also has the advantages of polarization insensitivity, wide-angle incident stability, etc., simple design, small size, easy processing, and has high practical value in the fields of military stealth, long-distance communication and radar shielding.

[0065] The above specifically describes the preferred embodiments of the present invention. Of course, the present invention can also take forms different from the above-mentioned embodiments. Equivalent changes or corresponding modifications made by technicians familiar with the field without violating the spirit of the present invention should fall within the scope of protection of the present invention.

Claims

1. An ultra-thin structure low-frequency absorber based on electromagnetic metamaterials, characterized in that: The absorber module comprises more than one absorber unit structure arranged in a spatial periodic square, wherein the absorber module comprises, from top to bottom, a metal resonance layer (1), a first dielectric layer (2), a metal patch layer (3), a second dielectric layer (4), and a metal grounding layer (5), and the geometric centers of the layers overlap vertically; the metal resonance layer is a metal surface formed by engraving two orthogonal curved narrow slits, the curved narrow slits extending from the center of the unit structure to the midpoints of the four sides of the unit structure, the curved narrow slits between adjacent unit structures are mutually connected, and the slits have rotational symmetry; the metal patch layer is a true circular metal surface, and the center of the circle overlaps vertically with the intersection of the two orthogonal curved narrow slits; the metal resonance layer and the metal patch layer are respectively etched on both sides of the first dielectric layer; the metal grounding layer is attached to one side of the second dielectric layer, and the first dielectric layer with etched structures on both sides and the second dielectric layer with one side attached to the metal surface together constitute an ultra-thin structure low-frequency absorber based on electromagnetic metamaterials.

2. The ultra-thin structure low-frequency absorber based on electromagnetic metamaterial according to claim 1, characterized in that: The metal resonance layer, metal patch layer and metal grounding layer are made of copper, and the conductivity is 5.8×10 7 S / m, thickness h=0.01mm.

3. The ultra-thin structure low-frequency absorber based on electromagnetic metamaterial according to claim 1, characterized in that: The unit structure period p=8.5 mm.

4. The ultra-thin structure low-frequency absorber based on electromagnetic metamaterial according to claim 1, characterized in that: The narrow slit is described by a sine function y=Asin(ωx+φ), where A is the amplitude, φ is the initial phase, ω=2π / p, and the two narrow slits are orthogonal to each other.

5. The ultra-thin structure low-frequency absorber based on electromagnetic metamaterial according to claim 1, characterized in that: The narrow gaps between the adjacent unit structures are interconnected.

6. The ultra-thin structure low-frequency absorber based on electromagnetic metamaterial according to claim 1, characterized in that: The first dielectric layer is made of polyimide film, with a relative dielectric constant ε=4, a loss tangent tan(δ)=0.005, and a thickness d1=0.002 mm.

7. The ultra-thin structure low-frequency absorber based on electromagnetic metamaterial according to claim 1, characterized in that: The metal patch layer is a perfect circular metal surface, and the circular radius r=4.1 mm.

8. The ultra-thin structure low-frequency absorber based on electromagnetic metamaterial according to claim 1, characterized in that: The second dielectric layer is made of polytetrafluoroethylene plate, with a relative dielectric constant ε=2.2, a loss tangent tan(δ)=0.001, and a thickness d2=0.9 mm.

9. The ultra-thin structure low-frequency absorber based on electromagnetic metamaterial according to claim 1, characterized in that: The metal resonant pattern is processed by chemical etching process on the upper side of the first dielectric layer, and the metal patch pattern is processed by chemical etching process on the lower side.

10. The ultra-thin structure low-frequency absorber based on electromagnetic metamaterial according to claim 1, characterized in that: The lower side of the second dielectric layer is covered with a metal copper film as a metal grounding layer.

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