A ferromagnetic medium type metamaterial invisible cloak and its preparation method

Abstract

The present invention relates to the field of electromagnetic stealth metamaterial devices, and in particular to a ferromagnetic metamaterial stealth cloak and a preparation method thereof. The stealth cloak comprises an angular metal reflector and a ferromagnetic metamaterial layer, wherein the ferromagnetic metamaterial layer comprises ferromagnetic metamaterial strip units arranged on the surface of the angular metal reflector in a phase gradient periodic sequence. Any phase gradient period includes 2 to 12 ferromagnetic metamaterial strip units, and the number of these units is the same. The stealth cloak achieves broadband electromagnetic wave absorption within 8.1 to 15.5 GHz and can camouflage scattered field characteristics in background echo scenarios at 12 GHz. Furthermore, the cloak has the advantages of being polarization-insensitive, angle-insensitive, simple to prepare, and low-cost.

Description

Technical Field

[0001] The present invention belongs to the field of electromagnetic stealth metamaterial devices, and in particular relates to a ferromagnetic medium type metamaterial stealth cloak and a preparation method thereof. Background Art

[0002] Electromagnetic metamaterials have attracted considerable research attention due to their comprehensive ability to manipulate electromagnetic waves in multiple dimensions. Compared to traditional natural materials, their physical properties primarily depend on artificially designed metaatoms and their arrangement. By designing the metallic resonant structure of metaatoms and implementing specific arrangements, metamaterials can precisely manipulate the properties of electromagnetic waves in multiple dimensions, including amplitude, phase, polarization, and transmission direction. Phase-gradient metamaterials based on the generalized Snell's law can deflect reflected waves to achieve anomalous reflection, further promoting the development of stealth cloaks constructed from them. By altering the electromagnetic scattering field characteristics of a target, stealth cloaks can achieve effective camouflage in background echo scenarios, reducing the target's potential for detection. These capabilities demonstrate significant strategic application potential in military concealment and communications.

[0003] At present, invisibility cloaks are generally made of traditional metal-based metamaterials, which continue the metal-based resonant structure's strong dependence on electromagnetic wave frequency, polarization angle and incident angle, making it difficult to adapt to the increasingly complex electromagnetic environment and meet the needs of modern applications of radar detection technology gradually moving towards broadband. Getting rid of dependence on metal resonant structures and relying solely on dielectric material units to achieve amplitude and phase response to electromagnetic waves is an effective way to solve this dilemma.

[0004] In summary, there is an urgent need for an invisible cloak that can get rid of the dependence on metal resonant structures and is insensitive to polarization and angle. Summary of the Invention

[0005] The present invention aims to solve the problem of eliminating the dependence of the invisible cloak on the metal resonant structure and reducing the sensitivity to polarization and angle.

[0006] To achieve the above objectives, the present invention provides a ferromagnetic metamaterial stealth cloak in a first aspect, wherein the stealth cloak is composed of an angular metal reflector and a ferromagnetic metamaterial layer, wherein the ferromagnetic metamaterial layer is composed of ferromagnetic metamaterial strip units arranged on the surface of the angular metal reflector in a phase gradient periodic sequence;

[0007] Wherein, any phase gradient period includes 2-12 ferromagnetic medium metamaterial strip units and the number is the same.

[0008] A second aspect of the present invention provides a method for preparing the above-mentioned invisible cloak, wherein the method comprises:

[0009] S1: Spherical carbonyl iron powder and polyurethane are mixed in a mass ratio of (1-4):1, stirred for 8-15 minutes, and then placed in an ultrasonic oscillator and ultrasonically oscillated at a temperature below 30°C for 8-15 minutes. The stirring and oscillation process is repeated twice to obtain a homogeneous ferromagnetic mixed glue;

[0010] S2: spraying a polyurethane release agent evenly on the surface of the concave strip mold. After the aqueous medium in the release agent evaporates, a dense inert film at the molecular scale is formed on the mold surface.

[0011] S3: Drop a curing agent into the ferromagnetic mixed glue and stir evenly, inject the ferromagnetic mixed glue into the rectangular strip groove inside the concave strip mold, and cure for 10-12 hours to obtain a ferromagnetic medium metamaterial strip unit;

[0012] S4: Use a bending machine to mechanically bend the metal plate along the long side with a bending angle of 60-150 degrees, and place the corner tip upward to obtain an angled metal reflector;

[0013] S5: Polyurethane is evenly applied on the surface of the angular metal reflector, and the ferromagnetic medium metamaterial strip units are bonded on the surface of the angular metal reflector in a phase gradient periodic sequence. After the polyurethane is cured, a ferromagnetic medium metamaterial stealth cloak is obtained.

[0014] Beneficial effects:

[0015] (1) By designing and regulating the composition ratio and thickness of the ferromagnetic medium composite material strip unit, the amplitude and phase response of the electromagnetic wave is controlled, thus getting rid of the strong dependence of the electromagnetic response on the metal resonant junction and avoiding the resulting narrowband and angle sensitivity problems.

[0016] (2) Ferromagnetic medium composite materials are used to prepare phase gradient metamaterials to further prepare stealth cloaks. The in-band scattering characteristic camouflage effect and out-of-band wide-band electromagnetic wave absorption effect are integrated into the same design. Compared with existing stealth cloaks, the working frequency band is wider and the stealth mechanism is more diverse.

[0017] (3) The phase gradient unit is prepared using a mold casting process, which simplifies the preparation process and greatly reduces the preparation cost compared to the unit that relies on the metal resonant structure.

[0018] Figures in the specification

[0019] Figure 1 Schematic diagram of the reflection characteristics of a strip unit of a ferromagnetic medium composite material.

[0020] Figure 2 These are the electromagnetic parameters of the ferromagnetic metamaterial strip unit of the ferromagnetic metamaterial stealth cloak according to Example 1 of the present invention.

[0021] Figure 3 is the amplitude phase of the ferromagnetic medium metamaterial strip unit.

[0022] Figure 4 This is the 3D printing mold diagram.

[0023] Figure 5 This is a sample picture of the ferromagnetic medium metamaterial stealth cloak according to Example 1 of the present invention.

[0024] Figure 6 Simulation and measured results of reflection loss of ferromagnetic phase gradient metamaterial with 10 phase periods.

[0025] Figure 7 This is the near-field simulation result of the corner metal reflector of Example 1 of the present invention.

[0026] Figure 8 These are the near-field simulation results of the ferromagnetic medium metamaterial stealth cloak according to Example 1 of the present invention.

[0027] Figure 9 These are the far-field simulation and test results of the corner metal reflector of Example 1 of the present invention.

[0028] Figure 10 These are the far-field simulation and test results of the ferromagnetic medium metamaterial stealth cloak according to Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0030] A first aspect of the present invention provides a ferromagnetic metamaterial stealth cloak, wherein the stealth cloak is composed of an angular metal reflector and a ferromagnetic metamaterial layer, wherein the ferromagnetic metamaterial layer is a ferromagnetic metamaterial strip unit arranged on the surface of the angular metal reflector in a phase gradient periodic sequence;

[0031] Wherein, any phase gradient period includes 2-12 ferromagnetic medium metamaterial strip units and the number is the same.

[0032] In the present invention, the ferromagnetic medium-type metamaterial unit has two upper and lower interfaces in the vertical direction, namely the upper interface in contact with the air layer and the lower interface in contact with the metal reflector. Unlike the metal-based resonant structure that relies on electromagnetic resonance to generate reflection amplitude and phase characteristics, the dielectric unit relies on the interference of the front interface reflection wave and the rear interface reflection wave to synthesize the reflection wave, thereby realizing the amplitude and phase control of the reflection wave.

[0033] In the present invention, according to the specification Figure 1 It can be seen that the composition ratio of the ferromagnetic medium metamaterial strip unit determines its electromagnetic parameters, and further determines its impedance characteristics and attenuation characteristics. The former determines the characteristics of the front interface reflected wave at the interference surface, and the latter determines the characteristics of the rear interface reflected wave at the interference surface. Therefore, the reflection characteristics of the ferromagnetic medium metamaterial unit can be controlled by composition regulation.

[0034] According to the present invention, the absorption bandwidth of the invisible cloak is 8.1-15.5 GHz.

[0035] According to the present invention, the phase gradient of the ferromagnetic medium metamaterial strip unit is 15°-180°.

[0036] According to the present invention, the bending angle of the angular metal reflector is 60-150°. In an embodiment of the present invention, the bending angle of the angular metal reflector is 120°.

[0037] According to the present invention, the surface arrangement is as follows: the ferromagnetic medium metamaterial strip unit starts from the bend of the angular metal reflector and is arranged in a phase gradient periodic order to the left and right sides, and the angular metal reflector is symmetrical along the angle bisector of the bend.

[0038] According to the present invention, the arrangement of the ferromagnetic medium metamaterial strip units is symmetrical along the angle bisector of the bend.

[0039] According to the present invention, the number of ferromagnetic medium metamaterial strip units in the phase gradient period is 2, 4, 6, 9 or 12.

[0040] In the present invention, since there is a strong coupling relationship between the reflection amplitude and phase of the ferromagnetic medium metamaterial strip unit, that is, the absorption peak frequency point corresponds to the phase point of the reflection phase, this makes the reflection amplitude difference large in the unit combination with a small phase gradient, resulting in poor interference effect. Therefore, in order to remove the strong coupling relationship between the reflection amplitude and phase of the metamaterial unit, the present invention further introduces the dimension of unit thickness to achieve unit amplitude and phase decoupling. Figure 2It can be seen that for a combination of units with different thicknesses, the interference surface between the two is located on the upper surface of the thicker unit. Therefore, the reflected wave of the thinner unit will produce a phase change in the space from the upper surface to the interference surface, while the amplitude does not change. The changes in amplitude and phase are no longer synchronous, that is, the decoupling of amplitude and phase is achieved.

[0041] A second aspect of the present invention provides a method for preparing the above-mentioned invisible cloak, wherein the method comprises:

[0042] S1: Spherical carbonyl iron powder and polyurethane are mixed in a mass ratio of (1-4):1, stirred for 8-15 minutes, and then placed in an ultrasonic oscillator and ultrasonically oscillated at a temperature below 30°C for 8-15 minutes. The stirring and oscillation process is repeated twice to obtain a homogeneous ferromagnetic mixed glue;

[0043] S2: spraying a polyurethane release agent evenly on the surface of the concave strip mold. After the aqueous medium in the release agent evaporates, a dense inert film at the molecular scale is formed on the mold surface.

[0044] S3: Drop a curing agent into the ferromagnetic mixed glue and stir evenly, inject the ferromagnetic mixed glue into the rectangular strip groove inside the concave strip mold, and cure for 10-12 hours to obtain a ferromagnetic medium metamaterial strip unit;

[0045] S4: Use a bending machine to mechanically bend the metal plate along the long side with a bending angle of 60-150 degrees, and place the corner tip upward to obtain an angled metal reflector;

[0046] S5: Polyurethane is evenly applied on the surface of the angular metal reflector, and the ferromagnetic medium metamaterial strip units are bonded on the surface of the angular metal reflector in a phase gradient periodic sequence. After the polyurethane is cured, a ferromagnetic medium metamaterial stealth cloak is obtained.

[0047] In the present invention, the concave strip mold is made by 3D printing.

[0048] In the present invention, there is no particular limitation on the metal plate, as long as it is a metal plate made of a highly conductive metal. In a preferred embodiment of the present invention, the metal plate is an aluminum plate.

[0049] According to the present invention, the width of the rectangular groove in the concave strip mold is 2-10 mm, and the height is 0.7-4.2 mm.

[0050] In the present invention, there is no particular limitation on the length of the rectangular groove in the concave strip mold, as long as the prepared ferromagnetic medium metamaterial strip unit meets the length requirement of the angular metal reflector.

[0051] In the present invention, there is no special requirement for the length, width and thickness of the diagonal metal reflector.

[0052] According to the present invention, in S5, the polyurethane curing conditions include: polyurethane curing time of 10-12 hours, and polyurethane curing temperature of 20-50°C.

[0053] According to the present invention, any phase gradient period includes 2-12 ferromagnetic medium metamaterial strip units and the number is the same.

[0054] According to the present invention, the phase gradient of the ferromagnetic medium metamaterial strip unit is 15°-180°.

[0055] Test Method

[0056] The technical solutions of the present invention are described in further detail below with reference to the embodiments. Obviously, the embodiments described herein are only some embodiments of the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments implemented by those of ordinary skill in the art without making creative improvements are within the scope of protection of the present invention.

[0057] Example 1

[0058] Preparation of ferromagnetic metamaterial invisible cloak

[0059] The preparation method of the ferromagnetic medium type metamaterial stealth cloak is as follows:

[0060] S1. The mass ratio of spherical carbonyl iron powder to polyurethane is 2:1. Add 200g of spherical carbonyl iron powder and 100g of polyurethane to a disposable plastic cup, stir with a rotor mixer for 15 minutes, and then place in an ultrasonic oscillator and ultrasonically oscillate at a temperature below 30°C for 15 minutes. Set the temperature to 30°C and repeat the stirring and oscillation process twice to obtain a homogeneous ferromagnetic mixed glue solution.

[0061] S2: Design the 3D-printed mold's rectangular inner grooves to have dimensions of 4.2 mm × 250 mm × 2.08 mm in height, length, and width. Periodically arrange 24 rectangular inner grooves in the mold. Use a polyurethane release agent to evenly spray the concave mold surface. After the aqueous medium in the release agent evaporates, a dense, molecular-scale inert film forms on the mold surface.

[0062] S3: Add polyurethane curing agent to the ferromagnetic mixed glue, stir evenly, and then inject it into the inner groove of the rectangular parallelepiped of the concave mold to solidify the ferromagnetic mixed glue inside the mold. After 24 hours, the ferromagnetic mixed glue is completely solidified to form a ferromagnetic medium composite material. After demolding, unit 1 in the phase gradient unit combination is obtained.

[0063] The preparation parameters of other units of the phase gradient unit combination are shown in Table 1 below. The length and width of the rectangular groove of the concave strip mold remain unchanged, and the height is adjusted accordingly according to the thickness of the unit.

[0064] S4: Use a bending machine to mechanically rigidly bend an aluminum plate with a size of 500 mm × 250 mm × 2 mm along the center line of the 500 mm long side at a bending angle of 120° and place it with the corner tip facing upward to obtain a corner metal reflector;

[0065] S5: Apply polyurethane evenly on the surface of the angular metal reflector, combine 12 ferromagnetic medium composite material strip units in the order of phase gradient period on the upper surface of the angular metal reflector and bond them. Each end of the angular metal reflector contains 10 phase periods, and the two ends are symmetrical along the angular bisector of the angular metal reflector. Let it stand for 24 hours. After the polyurethane adhesive is cured, a ferromagnetic medium metamaterial stealth cloak is obtained. The storage area is under the angular metal reflector.

[0066] Table 1 Information of each unit in the phase gradient unit combination of Example 1

[0067]

[0068]

[0069] As can be seen from Table 1, the present invention performs two-dimensional regulation of the reflection characteristics through the composition and thickness of the ferromagnetic medium metamaterial strip unit, preferably obtaining a phase gradient unit combination consisting of a group of 12 units with a phase gradient of 30°, and the ratio is the mass ratio of spherical carbonyl iron powder and polyurethane.

[0070] Attached to the instruction manual Figure 3 It can be seen that the phase period combination of Example 1 includes 12 units whose reflection phases present a gradient change and whose reflection amplitudes are close to 0.5.

[0071] Instructions attached Figure 4 The concave strip mold and rectangular strip groove of Example 1, and the ferromagnetic medium type metamaterial strip unit made therefrom.

[0072] Instructions attached Figure 5 This is the ferromagnetic medium metamaterial stealth cloak prepared in Example 1, and the storage area is under the angular metal reflector.

[0073] Instructions attached Figure 6 The minimum absorption peak of the ferromagnetic medium metamaterial slab composed of 10 phase-periodic ferromagnetic medium metamaterial strip units prepared in Example 1 is -52 dB, and the effective absorption bandwidth (RL≤-10 dB) is 8.1-15.5 GHz.

[0074] In Example 1, the s-scattering field characteristic camouflage function of the ferromagnetic medium metamaterial stealth cloak in the background echo scene is described as follows:

[0075] Instructions attached Figure 7 This is the near-field simulation result of the scattering field of the corner metal reflector under vertical incidence of electromagnetic waves. Dividing the corner metal reflected wave along the angle bisector is equivalent to placing a metal plate in an oblique incidence scenario of electromagnetic waves. The reverse direction of the reflected wave and the direction of the incident wave are symmetrical along the normal of the metal plate. Therefore, the scattering field of the corner metal reflector tends to be oblique, and there are two strong scattering beams, which are symmetrical along the angle bisector. This is the scattering field characteristic of the corner metal reflector.

[0076] Instructions attached Figure 8 The figure shows the near-field simulation results of the scattering field of the ferromagnetic metamaterial stealth cloak prepared in Example 1 under normal electromagnetic wave incidence. Under a normal 12GHz electromagnetic wave incident background, the cloak surface is equivalent to an oblique incidence at a positive 30° angle. Due to the phase gradient distribution at the metamaterial interface, the reflected wave is abnormally deflected in the same direction as the incident wave, that is, it propagates along the positive 30° direction. Since the phase arrangement of the phase gradient metamaterials at both ends of the stealth cloak is symmetrical along the angle bisector, the reflected wave is also symmetrical along the angle bisector. That is, the reflected waves from the phase gradient metamaterials at both ends of the stealth cloak are reflected and propagated along the positive 30° direction. Observed at the scale of the stealth cloak, the reflected waves propagate vertically upward. This scattering field characteristic is similar to that of a metal plate horizontally attached to the ground. Therefore, the ferromagnetic metamaterial stealth cloak of the present invention achieves camouflage function due to its scattering field characteristics.

[0077] Instructions attached Figure 9 and instructions attached Figure 10 The far-field simulation and test results of the angular metal reflector and the ferromagnetic medium metamaterial stealth cloak under the background of vertical incidence of electromagnetic waves also show that the ferromagnetic medium metamaterial stealth cloak of the present invention can disguise its own angular scattering characteristics as the scattering characteristics of a flat plate, proving that it has the camouflage function of scattering field characteristics.

[0078] The above description is only a preferred specific implementation method of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, can make equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A ferromagnetic medium metamaterial stealth cloak, characterized in that: The invisibility cloak is composed of an angular metal reflector and a ferromagnetic medium metamaterial layer, wherein the ferromagnetic medium metamaterial layer is composed of ferromagnetic medium metamaterial strip units arranged on the surface of the angular metal reflector in a phase gradient periodic sequence; Wherein, any phase gradient period includes 2-12 ferromagnetic medium metamaterial strip units and the number is the same.

2. The invisibility cloak according to claim 1, characterized in that: The absorption bandwidth of the invisibility cloak is 8.1-15.5 GHz.

3. The invisibility cloak according to claim 1, characterized in that: The phase gradient of the ferromagnetic medium metamaterial strip unit is 15°-180°.

4. The invisibility cloak according to claim 1, characterized in that: The bending angle of the angled metal reflector is 60-150°; The surface arrangement is as follows: the ferromagnetic medium metamaterial strip units are arranged in a phase gradient periodic order to the left and right sides, starting from the bend of the angular metal reflector, and the angular metal reflector is symmetrical along the angle bisector of the bend; The arrangement of the ferromagnetic medium type metamaterial strip units is symmetrical along the angle bisector of the bend.

5. The invisibility cloak according to claim 1, characterized in that: The number of ferromagnetic medium metamaterial strip units in the phase gradient period is 2, 4, 6, 9 or 12.

6. The method for preparing the invisible cloak according to any one of claims 1 to 5, characterized in that: The method comprises: S1: Spherical carbonyl iron powder and polyurethane are mixed in a mass ratio of (1-4):1, stirred for 8-15 minutes, and then placed in an ultrasonic oscillator and ultrasonically oscillated at a temperature below 30°C for 8-15 minutes. The stirring and oscillation process is repeated twice to obtain a homogeneous ferromagnetic mixed glue; S2: spraying a polyurethane release agent evenly on the surface of the concave strip mold. After the aqueous medium in the release agent evaporates, a dense inert film at the molecular scale is formed on the mold surface. S3: Drop a curing agent into the ferromagnetic mixed glue and stir evenly, inject the ferromagnetic mixed glue into the rectangular strip groove inside the concave strip mold, and cure for 10-12 hours to obtain a ferromagnetic medium metamaterial strip unit; S4: Use a bending machine to mechanically bend the metal plate along the long side with a bending angle of 60-150 degrees, and place the corner tip upward to obtain an angled metal reflector; S5: Polyurethane is evenly applied on the surface of the angular metal reflector, and the ferromagnetic medium metamaterial strip units are bonded on the surface of the angular metal reflector in a phase gradient periodic sequence. After the polyurethane is cured, a ferromagnetic medium metamaterial stealth cloak is obtained.

7. The preparation method according to claim 6, characterized in that The width of the rectangular groove in the concave strip mold is 2-10 mm, and the height is 0.7-4.2 mm.

8. The preparation method according to claim 6, characterized in that In S5, the polyurethane curing conditions include: polyurethane curing time of 10-12 hours, and polyurethane curing temperature of 20-50°C.

9. The preparation method according to claim 6, characterized in that Any phase gradient period includes 2-12 ferromagnetic medium metamaterial strip units and the number is the same; The phase gradient of the ferromagnetic medium metamaterial strip unit is 15°-180°.

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