A magnetic wave-absorbing metamaterial and its preparation method

Abstract

The present invention discloses a magnetic wave-absorbing metamaterial, which comprises a matrix material; and a metamaterial unit array disposed on the matrix material, the metamaterial unit array comprising a plurality of metamaterial units arranged in a lattice; both the metamaterial units and the matrix material comprise soft magnetic powder and a polymer substrate, the mass ratio of the soft magnetic powder in the metamaterial units is 50%-80%, the soft magnetic powder is stacked and formed along the magnetic force, and the mass ratio of the soft magnetic powder in the matrix material is 20%-60%. This material can better absorb electromagnetic waves in a relatively wide frequency band. The present invention also provides a preparation method of the magnetic wave-absorbing metamaterial, and this method is simple and efficient.

Description

Technical Field

[0001] The present invention belongs to the field of microwave absorbing materials, and particularly relates to a magnetic microwave absorbing metamaterial and a preparation method thereof. Background Art

[0002] With the development of communication technologies, problems such as multi-antenna interference, electromagnetic radiation, and pollution have become increasingly serious, and the demand for electromagnetic wave absorption (microwave absorption) has become more and more urgent. Modern electronic products are becoming more and more powerful, and electronic circuits are becoming more and more complex. The problem of electromagnetic interference (EMI) is becoming more and more prominent, and microwave absorbing materials for anti-electromagnetic interference gradually show their value.

[0003] Electromagnetic compatibility design is actually an optimization design for the electromagnetic interference generated in electronic products, so that they can become products that meet the electromagnetic compatibility standards of various countries or regions. However, the designs of many electronic products cannot completely eliminate electromagnetic interference at the source. At this time, the final solution to the EMI problem requires the use of microwave absorbing materials.

[0004] Microwave absorbing materials can convert the energy of electromagnetic waves into other forms of energy and dissipate it through attenuation. Microwave absorbing materials were first applied in the field of stealth technology to absorb and attenuate radar wave signals and improve the anti-radar detection ability of weapon and equipment systems. With the rapid development of electronic communication technologies and the continuous progress of modern military engineering application technologies, there is also an urgent need for a microwave absorbing material with multiple functions such as broadband and structured in electromagnetic compatibility and anti-electromagnetic radiation interference.

[0005] Most traditional microwave absorbing sheets are composed of single-layer microwave absorbing sheets, which are formed by microwave absorbing materials and composite matrices to give a specific thickness to achieve the electromagnetic wave absorption performance in a specific frequency band. With the diversification of microwave absorption scenarios, various specially designed microwave absorbing sheets such as multi-layer broadband microwave absorption and structured design metamaterial microwave absorption have evolved.

[0006] By designing the structure, arrangement method of the unit cell and setting the electromagnetic parameters, metamaterials can flexibly control the characteristics of scattered electromagnetic waves such as frequency, polarization, amplitude, and phase. Therefore, metamaterials have received extensive attention in the field of microwave absorption. Metamaterial absorbers mainly absorb electromagnetic waves through the resonant loss of their own structures.

[0007] According to different loss mechanisms, microwave absorbing materials can be divided into resistance loss type, dielectric loss type, and magnetic loss type. Magnetic loss type microwave absorbing materials usually use magnetic materials such as ferrites, carbonyl iron powders, and metal soft magnetic powders as absorbents. Comparatively, they have good microwave absorption performance at 8-18 GHz, but their microwave absorption performance at 4-8 GHz is not ideal, and they have a large specific gravity and low mechanical strength, which cannot meet the comprehensive performance requirements of engineering practice for microwave absorbing materials. Moreover, in the preparation process, complex molds and structural units greatly increase the cost, which has become a key factor restricting their development. Summary of the Invention

[0008] The present invention provides a magnetic wave-absorbing metamaterial, which can preferably absorb electromagnetic waves in a relatively wide frequency band.

[0009] A magnetic wave-absorbing metamaterial, comprising:

[0010] A matrix material;

[0011] And a metamaterial unit array, arranged on the matrix material, comprising a plurality of metamaterial units, and the plurality of metamaterial units are arranged in a lattice;

[0012] Both the metamaterial unit and the matrix material comprise soft magnetic powder and a polymer substrate. The mass ratio of the soft magnetic powder in the metamaterial unit is 50%-80%, and the soft magnetic powder is formed by stacking along the magnetic force. The mass ratio of the soft magnetic powder in the matrix material is 20%-60%.

[0013] The center distance between the metamaterial units in the metamaterial unit array is 5-15 mm.

[0014] The metamaterial unit is a hemispherical body with a height of 1-5 mm and a diameter of 2-10 mm.

[0015] Due to the difference in the concentration of the soft magnetic powder between the metamaterial unit and the matrix, the magnetic permeability and dielectric constant of the wave-absorbing material show a regular distribution. Coupled with the size change of the structural unit and the difference in the array spacing, the electromagnetic wave incident on the wave-absorbing material undergoes coupled resonance with the array, effectively improving the impedance matching degree of the wave-absorbing sheet (that is, the ratio of the impedance of the wave-absorbing material to the impedance of free space is close to 1), thereby improving the wave-absorbing performance and the effective absorption bandwidth.

[0016] The soft magnetic powder is one or two of Ce2Fe 17 N3 powder, carbonyl iron powder.

[0017] The soft magnetic powder is a flaky soft magnetic powder.

[0018] The particle size of the soft magnetic powder is less than 10 μm, and the aspect ratio of diameter to thickness is 20-100:1.

[0019] When the particle size of the soft magnetic powder is less than 10 μm, a higher cut-off frequency can be obtained, and it can be applied to the GHz frequency band. The flaky magnetic powder has better shape anisotropy, and both the natural resonance frequency and the magnetic permeability are improved, and it is easy to be oriented and distributed under the action of a magnetic field, which is beneficial to increasing the wave-absorbing performance. And a suitable aspect ratio can ensure that the dielectric constant of the magnetic powder will not be too high due to flakiness, preventing impedance matching mismatch caused by too high dielectric constant.

[0020] The polymer substrate is a low-density polymer material, including one or more of polyolefin, silica gel, epoxy resin, and polyurethane.

[0021] The polyolefin is PE, PP or PB.

[0022] The thickness of the magnetic wave-absorbing metamaterial is 2 - 10 mm.

[0023] The application frequency band of the magnetic wave-absorbing metamaterial is 1 - 40 GHz.

[0024] The present invention also discloses a preparation method of a magnetic wave-absorbing metamaterial, including:

[0025] Mixing the sheet-shaped soft magnetic powder with a polymer substrate evenly to obtain a mixture, wherein the mass fraction of the soft magnetic powder is 30% - 70%;

[0026] Casting the mixture on a PET film to obtain a composite sheet, and placing the composite sheet on an acrylic plate for 2 - 10 minutes to obtain a metamaterial unit array, wherein the acrylic plate has a plurality of permanent magnet cylinders with a dot matrix distribution and N poles upward, and the sheet-shaped soft magnetic powder in the metamaterial unit is arranged along the magnetic field lines;

[0027] Heating and curing the metamaterial unit array to obtain the magnetic wave-absorbing metamaterial.

[0028] In the present invention, through the permanent magnet cylinders on the acrylic plate, the soft magnetic powder in the composite sheet with a certain viscosity is aggregated to form a metamaterial unit with a higher mass fraction of soft magnetic powder. And based on the dot matrix arrangement of the permanent magnet cylinders, a plurality of metamaterial unit dot matrices are formed in the matrix material with a lower mass fraction of soft magnetic powder. This is because the soft magnetic powder has a higher magnetic induction intensity, and under the action of the magnetic field of the permanent magnet cylinders, it will move closer to the approaching direction, and then form a metamaterial unit with a higher mass fraction of soft magnetic powder. And based on the magnetic direction with the N poles of the permanent magnet cylinders upward, the soft magnetic powder in the metamaterial unit can be arranged without being interfered by adjacent magnets, and a hemispherical metamaterial unit with a stable shape can be obtained.

[0029] The remanent magnetization intensity of the permanent magnet cylinder is 0.5 - 1.35 T.

[0030] The height of the permanent magnet cylinder is 1 - 5 mm, the diameter is 2 - 10 mm, and the distance between the permanent magnet cylinders is 5 - 15 mm.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] (1) By distributing metamaterial units with a higher mass fraction of soft magnetic powder on a matrix material with a lower mass fraction of soft magnetic powder, the present invention enables the emergence of regularly arranged structural units in the wave-absorbing material, effectively improving the matching degree between the impedance of the material and the free-space impedance. Moreover, due to the magnetic field lines distributed in the same direction through the soft magnetic powder in each metamaterial unit, the structure of the metamaterial unit is stably presented as a hemispherical shape, so as to obtain regularly arranged and uniformly shaped metamaterial units, enhance impedance matching, increase the effective absorption bandwidth, and achieve the purpose of broadband absorption of electromagnetic waves.

[0033] (2) The present invention utilizes permanent magnet cylinders with a dot matrix distribution on an acrylic plate to cause soft magnetic powder with a certain fluidity to aggregate to form metamaterial units with a high mass fraction and a matrix material with a low mass fraction of soft magnetic powder. And with the N poles of each permanent magnet cylinder facing upward, the soft magnetic powder in each metamaterial unit is arranged along the same magnetic field line direction, presenting a stable hemispherical structural unit. The mold used in the preparation is relatively simple and the preparation method is efficient. Description of the Drawings

[0034] Figure 1 Schematic diagram of the magnetic wave-absorbing metamaterial structure provided for the specific implementation mode. Specific Implementation Mode

[0035] The present invention provides a preparation method for a magnetic wave-absorbing metamaterial, and the specific steps are as follows:

[0036] First, the high-performance powdered soft magnetic powder is made into flakes through ball milling or sand milling processes, and then the flaky magnetic powder is fully mixed and homogenized with a polymer substrate to form a paste-like composite. The paste-like composite is placed in a casting device for casting and forming to form a composite sheet on a PET film. Then, the composite sheet is placed on an acrylic plate with a plurality of permanent magnet cylinders (height 5 mm, diameter 2 - 10 mm, column spacing 5 - 15 mm) with a dot distribution and N poles all facing upward, heated and cured to form a magnetic wave-absorbing sheet with a dot-like high-concentration distribution of magnetic powder, as Figure 1 shown.

[0037] Comparative Example 1

[0038] The powdered rare-earth soft magnetic material cerium iron nitride is made into flakes through sand milling, and then the flaky cerium iron nitride magnetic powder is fully mixed and stirred evenly with liquid polyurethane with a mass fraction of 50% to form a paste-like composite. The paste-like composite is placed in a casting device for casting and forming to form a composite sheet on a PET film, heated and cured to form a composite wave-absorbing sheet with uniformly distributed magnetic powder, with a thickness of 5 mm. The magnetic wave-absorbing sheet is cut into a size of 300X300 mm and then the wave-absorbing performance is tested. Test results: wave-absorbing peak -12 dB, center frequency 16 GHz, effective absorption bandwidth (RL < -10 dB) 2 GHz

[0039] Example 1

[0040] The powdered rare-earth soft magnetic material cerium iron nitride is made into flaky powder by sanding, and then the flaky cerium iron nitride magnetic powder is fully mixed and stirred evenly with liquid polyurethane with a mass fraction of 50% to form a paste-like composite. The paste-like composite is cast and formed by a casting device to form a composite sheet on a PET film, and then the composite sheet is placed on an acrylic plate with a plurality of permanent magnet cylinders (height 5 mm, diameter 5 mm, column spacing 10 mm) with a dot distribution and all N poles facing upward. The remanent magnetization intensity of the permanent magnet cylinder is 0.5 T, and it is heated and cured to obtain a magnetic wave-absorbing metamaterial with dot-like high-concentration soft magnetic powder metamaterial units (soft magnetic powder mass fraction 60%) distributed in a low-concentration soft magnetic powder distribution matrix (soft magnetic powder mass fraction 40%), with a thickness of 5 mm. The metamaterial units in dot matrix stacking present a hemispherical shape, with a hemispherical diameter of 5 mm and a hemispherical center point spacing of 10 mm. The magnetic wave-absorbing sheet is cut into a size of 300X300 mm and then the wave-absorbing performance is tested. Test results: Absorption peak -20 dB, center frequency 17 GHz, effective absorption bandwidth (RL < -10 dB) 5 GHz.

[0041] Example 2

[0042] The powdered rare-earth soft magnetic material cerium iron nitride is made into flaky powder by sanding, and then the flaky cerium iron nitride magnetic powder is fully mixed and stirred evenly with liquid polyurethane with a mass fraction of 50% to form a paste-like composite. The paste-like composite is cast and formed by a casting device to form a composite sheet on a PET film, and then the composite sheet is placed on an acrylic plate with a plurality of permanent magnet cylinders (height 5 mm, diameter 5 mm, column spacing 10 mm) with a dot distribution and all N poles facing upward. The remanent magnetization intensity of the permanent magnet cylinder is 1 T, and it is heated and cured to obtain a magnetic wave-absorbing metamaterial with dot-like high-concentration soft magnetic powder metamaterial units (soft magnetic powder mass fraction 70%) distributed in a low-concentration soft magnetic powder distribution matrix (soft magnetic powder mass fraction 20%), where the thickness is 5 mm and the metamaterial units in dot matrix stacking present a hemispherical shape, with a hemispherical diameter of 5 mm and a hemispherical center point spacing of 10 mm. The magnetic wave-absorbing metamaterial is cut into a size of 300X300 mm and then the wave-absorbing performance is tested. Test results: Absorption peak -25 dB, center frequency 18 GHz, effective absorption bandwidth (RL < -10 dB) 8 GHz.

[0043] Example 3

[0044] Pulverized rare-earth soft magnetic material cerium iron nitride is made into flaky powder through sanding, and then the flaky cerium iron nitride magnetic powder is fully mixed and stirred evenly with liquid polyurethane, with a mass fraction of 50%, to form a paste-like composite. The paste-like composite is placed in a casting device for casting and forming to form a composite sheet on a PET film. Then the composite sheet is placed on an acrylic plate with a plurality of permanent magnet cylinders (height 5 mm, diameter 5 mm, column spacing 15 mm) distributed in a dot pattern and with the N poles all facing upward. The remanent magnetization intensity of the permanent magnet cylinders is 1 T. It is heated and cured to form a magnetic wave-absorbing metamaterial with dot-like high-concentration soft magnetic powder metamaterial units (soft magnetic powder mass fraction 70%) distributed in a low-concentration soft magnetic powder distribution matrix (soft magnetic powder mass fraction 20%). The thickness is 5 mm, and the dot-like matrix-packed metamaterial units are hemispherical, with a hemispherical diameter of 5 mm and a distance of 15 mm between the centers of the hemispheres. The magnetic wave-absorbing sheet is cut into a size of 300X300 mm and then the wave-absorbing performance is tested. Test results: wave-absorbing peak -28 dB, center frequency 21 GHz, effective absorption bandwidth (RL < -10 dB) 12 GHz.

Claims

1. A magnetic wave-absorbing metamaterial, characterized in that Comprising: A substrate material; And a metamaterial unit array, disposed on the substrate material, including a plurality of metamaterial units, the plurality of metamaterial units being arranged in a lattice; Both the metamaterial unit and the substrate material include soft magnetic powder and a polymer substrate. The mass ratio of the soft magnetic powder in the metamaterial unit is 50%-80%, and the soft magnetic powder is formed by magnetic force stacking. The mass ratio of the soft magnetic powder in the substrate material is 20%-60%; The center spacing of the metamaterial units in the metamaterial unit array is 5-15 mm; The metamaterial unit is a hemisphere with a height of 1-5 mm and a diameter of 2-10 mm; The particle size of the soft magnetic powder is less than 10 μm, and the aspect ratio is 20-100:

1.

2. The magnetic absorbing metamaterial according to claim 1, characterized in that, The soft magnetic powder is one or both of Ce2Fe 17 N3 powder and carbonyl iron powder.

3. The magnetic wave-absorbing metamaterial according to claim 1, characterized in that The polymer substrate is a low-density polymer material, including one or more of polyolefin, silica gel, epoxy resin, and polyurethane.

4. The magnetic wave-absorbing metamaterial according to claim 1, wherein The thickness of the magnetic wave-absorbing metamaterial is 2-10 mm.

5. The preparation method of the magnetic wave-absorbing metamaterial according to any one of claims 1-4, characterized in that, Comprising: Mixing sheet-shaped soft magnetic powder and a polymer substrate evenly to obtain a mixture, wherein the mass fraction of the soft magnetic powder is 30%-70%; Casting the mixture on a PET film to obtain a composite sheet, and placing the composite sheet on an acrylic plate for 2-10 minutes to obtain a metamaterial unit array. Among them, the acrylic plate has a plurality of permanent magnet cylinders with a lattice distribution and N poles facing upward, and the sheet-shaped soft magnetic powder in the metamaterial unit is arranged along the magnetic field lines; Heating and curing the metamaterial unit array to form a magnetic wave-absorbing metamaterial.

6. The preparation method of the magnetic wave-absorbing metamaterial according to claim 5, characterized in that, The remanent magnetization intensity of the permanent magnet cylinder is 0.5-1.35 T.

7. The preparation method of the magnetic wave-absorbing metamaterial according to claim 5, wherein The height of the permanent magnet cylinder is 1-5 mm, the diameter is 2-10 mm, and the spacing between the permanent magnet cylinders is 5-15 mm.

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