P-band broadband and low-RCS NiZnCu ferrite composite metasurface based on 1-bit coding

Abstract

The invention discloses a NiZnCu ferrite composite metasurface with a P wave band broadband and a low RCS (Radar Cross Section) based on 1-bit coding. Firstly, the impedance matching condition of the ferrite is improved through Mn < 2 + > ion doping, so that when the thickness of the NiZnCu ferrite is 2 mm, effective wave absorption with the reflection loss smaller than-10 dB is achieved within the range of 0.25 GHz to 1.0 GHz. Furthermore, NiZnCu ferrite is combined with a sandwich structure (square metal sheet / FR4 / metal back plate, 6 mm) to construct a 1-bit coding metasurface structure unit, optimal array arrangement is obtained by adopting a genetic algorithm, and directional reflection is reduced to the greatest extent. And finally, full-wave simulation software is used for verification, and the result shows that the NiZnCu ferrite composite coding metasurface can further reduce the RCS by using the diffuse reflection effect on the basis of keeping the ferrite wave absorbing effect, the range of the RCS is 0.50 GHz-0. 75 GHz, and the maximum RCS reduction value can reach 29.4 dB.

Description

Technical Field

[0001] The invention belongs to the field of electromagnetic wave absorption materials and artificial electromagnetic supersurfaces, and specifically relates to a P-band broadband, low RCS NiZnCu ferrite composite supersurface based on 1-bit coding. Background Art

[0002] The frequency range of P-band electromagnetic waves is between 0.23GHz and 1GHz, and its corresponding wavelength spans from meter level to decimeter level. With its long-distance propagation capability and excellent anti-interference characteristics, the P-band has become the main working frequency band for current long-range early warning radar detection. In order to improve the battlefield survivability of aircraft and other equipment, the use of absorbing materials to reduce the intensity of radar echoes, reduce the radar cross section (RCS), and enhance the concealment of equipment has become an important strategy. However, for P-band electromagnetic waves with relatively long wavelengths, the absorption effect of traditional absorbing materials such as hydroxy iron and graphite is not ideal.

[0003] NiZn ferrite is considered as the preferred P-band absorber due to its unique electric / magnetic dual loss mechanism and excellent impedance matching characteristics. It can effectively guide electromagnetic waves into the material and rapidly attenuate, so it is considered as the preferred P-band absorber. However, existing technical solutions, such as ion doping, composite with conductive materials, interface design, etc., are difficult to achieve the application requirements of large bandwidth and strong absorption under light weight and thin thickness conditions. Based on artificially designed metamaterials (such as metal pattern / dielectric / metal backplane-sandwich structure), although the equivalent electromagnetic parameters can be adjusted by changing the structure of the metamaterial to match it with the free space to achieve high-intensity absorption, it often faces the problem of narrow absorption band. In order to further improve the performance of P-band absorbers, some people have proposed a solution to construct absorber metamaterials with NiZn ferrite as the dielectric layer. By using the electromagnetic resonance effect and Fabry-Perot interference effect, the electromagnetic loss of ferrite is amplified to further enhance the absorption. Under the condition of thickness less than 10mm, the excellent performance of reflection loss (RL) less than -10dB in the entire P-band is achieved. However, due to the high density of NiZn ferrite, metamaterials constructed with single ferrite still face challenges in lightweighting.

[0004] In addition to the above-mentioned absorption enhancement schemes, the coded metasurface constructed by carefully designing structural units and their spatial arrangement can flexibly control scattered waves, achieve diffuse reflection effects, effectively reduce RCS, and enhance target stealth performance. Summary of the invention

[0005] However, to date, there has been no report on how to organically combine the wave absorption effect of ferrite with the diffuse reflection effect of coded metasurface to achieve high-performance RCS reduction in the P-band.

[0006] The object of the present invention is to propose a new technical solution for reducing RCS to overcome the deficiencies in the existing technologies, and to provide a NiZnCu ferrite composite metasurface based on 1-bit coding, which can synergistically utilize the wave absorption effect of ferrite and the diffuse reflection effect of the coded metasurface to achieve P-band broadband RCS reduction under relatively light weight and thin conditions.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the NiZnCu ferrite composite metasurface based on 1-bit coding and having P-band broadband and low RCS provided by the present invention is composed of 2 types and 36×36 metasurface structural units; wherein, the metasurface unit from bottom to top includes: a metal backplane, an intermediate dielectric layer, a square metal patch layer and a top NiZnCu ferrite, and adjacent layers are closely attached and geometric centers coincide; wherein, the side length of the square metal patch layer is a, the period of the metasurface structural unit is p, the thickness of the intermediate dielectric layer is h1, and the thickness of the NiZnCu ferrite is h2.

[0009] According to an embodiment of the present invention, the composition of the NiZnCu ferrite is Ni 0.4 Zn 0.5 Cu 0.06 Mn 0.04 Fe2O4, and it is prepared by the solid-phase sintering method. It is experimentally confirmed in the present invention that by doping with Cu 2+ , Mn 2+ ions, the impedance matching condition of the NiZn ferrite and the attenuation ability of electromagnetic waves are improved. When the atomic stoichiometric numbers of Cu and Mn are 0.06 and 0.04 respectively, the overall wave absorption effect is the best. The wave absorption ability of the NiZnCu ferrite is investigated by using CST MicrowaveStudio software. When the thickness h2 is 2 mm, the NiZnCu ferrite can achieve a wave absorption effect with a reflection loss less than -10 dB in the range of 0.25 GHz - 1.0 GHz.

[0010] According to an embodiment of the present invention, both the square metal patch layer and the metal backplane are made of copper material with a thickness of 0.03 mm.

[0011] According to an embodiment of the present invention, the intermediate dielectric layer uses a common FR4 epoxy resin composite material with a dielectric constant of 4.4 and a loss tangent of 0.02. The thickness h1 of the FR4 is optimized by using CST Microwave Studio software. When the thickness h1 is 6 mm, the resonance peak of the metasurface is within the P-band range.

[0012] According to an embodiment of the present invention, the metasurface structural unit is square, and its period p is 100 mm.

[0013] According to an embodiment of the present invention, the 1-bit encoded metasurface is composed of two unit structures with a reflection phase difference of 180°, which are represented by the binary digital states "0" and "1" respectively. The CST Microwave Studio software is used to construct the NiZnCu composite encoded metasurface structural unit and optimize the value of a to achieve a response with a reflection phase difference close to 180°. Among them, the side length a of the square metal patch is 91 mm corresponding to the unit code "0", and the side length a of 84 mm corresponds to the unit code "1".

[0014] According to an embodiment of the present invention, in order to achieve the diffuse reflection effect to reduce the target RCS, after designing and optimizing the encoded metasurface structural unit, these units are used to construct a metasurface array to omnidirectionally disperse the incident electromagnetic wave. The metasurface array is regarded as an M×N matrix, where M is the number of units along the x-axis and N is the number of units along the y-axis. In the array designed in the present invention, there are 36 units along both the x-axis and the y-axis. In order to reduce the influence of the change of the boundary condition on the reflection characteristics of the structural unit, a supercell composed of 3×3 identical units is used to fill the 12×12 encoded matrix to obtain a metasurface array with 36×36 structural units. The genetic algorithm is used for optimization to obtain the 12×12 optimal coding sequence matrix. The basic parameters of the genetic algorithm are that the number of individuals in the initial population is 300, the maximum number of evolution generations is set to 1000, the crossover rate is 10%, and the mutation rate is 5%.

[0015] Based on the above technical solutions, the beneficial effects of the present invention include:

[0016] The present invention provides a Mn 2+ ion-doped NiZnCu ferrite. The Mn 2+ ion doping can improve the impedance matching condition of the ferrite. When the thickness is 2 mm, the Ni 0.4 Zn 0.5 Cu 0.06 Mn 0.04 Fe2O4 component ferrite can achieve effective wave absorption with a reflection loss less than -10 dB in the range of 0.25 GHz to 1.0 GHz.

[0017] The present invention provides an innovative ferrite composite coding metasurface, which combines the wave absorption characteristics of ferrite and the diffuse reflection mechanism of coding metasurface to effectively reduce the RCS. In the P band (0.25 GHz - 1.0 GHz), due to the wave absorption effect of ferrite, the composite coding metasurface can achieve an RCS reduction of more than 10 dB. In particular, in the frequency band of 0.50 GHz to 0.75 GHz, due to the diffuse reflection effect of the composite coding metasurface, a further significant reduction in RCS is achieved, with a maximum of 29.4 dB. The present invention provides an innovative and practical solution for the field of radar stealth technology, which can improve the problem of large density of traditional single ferrite under the condition of thinning (~8 mm). It not only broadens the thinking of researchers, but also improves the flexibility of technology application, and has important value and broad application prospects in many fields. Description of the Drawings

[0018] Figure 1 It is the surface morphology diagram of NiZnCu ferrite in the embodiment of the present invention.

[0019] Figure 2 It is the XRD test result diagram of NiZnCu ferrite in the embodiment of the present invention.

[0020] Figure 3 It is the test result diagram of the dielectric constant ε of NiZnCu ferrite in the range of 0.1 GHz - 1 GHz in the embodiment of the present invention.

[0021] Figure 4 It is the test result diagram of the magnetic permeability μ of NiZnCu ferrite in the range of 0.1 GHz - 1 GHz in the embodiment of the present invention.

[0022] Figure 5 It is the reflection loss diagram of 2 - mm - thick NiZnCu ferrite in the range of 0.1 GHz - 1 GHz in the embodiment of the present invention.

[0023] Figure 6 It is the unit structure diagram of the coded composite metasurface in the embodiment of the present invention.

[0024] Figure 7 It is the phase difference diagram of the coded composite metasurface in the embodiment of the present invention.

[0025] Figure 8 It is the reflection loss diagram of the coded composite metasurface in the embodiment of the present invention.

[0026] Figure 9 It is the schematic diagram of the array in the embodiment of the present invention.

[0027] Figure 10Shows the far-field patterns of the array of exemplary embodiments of the present invention and the uncoded array at 0.62 GHz. Among them, (a) is the far-field pattern of the copper sheet, (b) is the far-field pattern of the metasurface with 36×36 arrangement of structural unit "0" (a = 91 mm), (c) is the far-field pattern of the metasurface with 36×36 arrangement of structural unit "1" (a = 84 mm), and (d) is the far-field pattern of the array of exemplary embodiments.

[0028] Figure 11 Shows the RCS comparison of the array of embodiments of the present invention with the copper sheet and the uncoded array in the range of 0.1 GHz - 1 GHz.

[0029] Figure 12 Is the RCS reduction of the array of embodiments of the present invention with the copper sheet and the uncoded array in the range of 0.1 GHz - 1 GHz. Detailed implementation manners

[0030] To make the objectives, technical solutions and advantages of the present invention clearer, the following further describes the present invention in detail with reference to specific embodiments and the accompanying drawings. However, those skilled in the art know that the present invention is not limited to the drawings and the following embodiments.

[0031] The present invention proposes a 1-bit coded P-band broadband and low RCS NiZnCu ferrite composite metasurface, which is composed of 2 types and 36×36 metasurface structural units. The metasurface structural units from bottom to top include: a metal copper backplane, an intermediate dielectric layer, a square metal patch layer, and a top layer of NiZnCu ferrite. The adjacent layers are closely attached and their geometric centers coincide.

[0032] The composition of NiZnCu ferrite is Ni 0.4 Zn 0.5 Cu 0.06 Mn 0.04 Fe2O4, and it is prepared by the solid-phase sintering method.

[0033] After determining the chemical formula of NiZnCu ferrite, according to the total mass of the ferrite, the molar amount of each metal element is calculated, and then the mass of each required metal oxide is calculated.

[0034] Weigh a certain mass of metal oxides with an electronic balance, put the powder materials into a ball mill tank equipped with zirconia grinding balls. The mass ratio of the grinding balls to the powder materials is 10:1, and anhydrous ethanol is added as the grinding medium. Seal the ball mill tank and install it on a planetary ball mill. Set the parameters of the ball mill to 300 r / min. After continuous operation for 4 h, take it out and sieve it, and place the mixed slurry in a blast drying oven for drying.

[0035] Load the dried powder into a crucible and place it in a box-type muffle furnace. Set the heating rate to 5 °C / min and the cooling method to furnace cooling. Keep it at 950 °C for 4 h for the preliminary reaction of the ferrite raw materials to obtain the desired ferrite crystal phase.

[0036] Place the pre-sintered ferrite powder in a ball mill jar and continuously ball mill for 4 h. After drying, obtain ferrite fine powder. Weigh a certain mass of the ferrite fine powder and place it in a mortar. Add a PVA solution with a mass fraction of 5% and grind and mix evenly to obtain ferrite clay with good fluidity and dispersibility.

[0037] Take a certain mass of ferrite clay and place it in a metal mold. Under a pressure of 6 MPa, continuously press for 1 min with an electric tablet press. After demolding, obtain a ferrite ceramic blank with a good appearance. Place the ferrite ceramic blank in a box-type muffle furnace and keep it at 600 °C for 2 h to volatilize the PVA in the ceramic blank completely. Subsequently, keep it at the set sintering temperature of 1200 °C for 6 h to obtain a ceramic sample with good density.

[0038] The surface morphology of NiZnCu ferrite in this example is as Figure 1 shown. It can be seen from Figure 1 that the grains on the sample surface are closely connected, the grain sizes are relatively uniform, and there are a small number of pores inside the grains and at the grain boundaries, indicating that the ferrite ceramic sample has achieved densification at this time. Figure 2 This is the XRD test result diagram of NiZnCu ferrite. The diffraction peak positions correspond to the characteristic peak positions of ZnFe2O4, and no other impurity peaks appear in the XRD curve, indicating that NiZnCu ferrite has formed a single spinel ferrite phase.

[0039] In this example, the complex permittivity and complex permeability of NiZnCu ferrite in the P band are measured by an Agilent E4991A impedance analyzer. The specific parameters are as Figure 3 and 4 shown. Import the measured complex permittivity and complex permeability parameters into the full-wave simulation software CST Microwave Studio, construct a 2-mm-thick NiZnCu ferrite model, use periodic boundary conditions and a frequency-domain solver, and calculate the reflection amplitude, as Figure 5 shown. It can be seen that the 2-mm-thick NiZnCu ferrite achieves an electromagnetic wave absorption effect with a reflection loss less than -10 dB in the range of 0.25 GHz - 1.0 GHz.

[0040] To further reduce the reflection amplitude, in this example, the NiZnCu ferrite material is combined with a coded metasurface. By using the wave absorption effect of the ferrite and the diffuse reflection effect of the metasurface, the RCS is effectively reduced.

[0041] Figure 6 Figure 1 shows a schematic diagram of a metasurface unit of an exemplary embodiment, which from bottom to top are a copper metal backplane, an FR4 dielectric layer, a square metal patch layer, and a NiZnCu ferrite layer. In terms of structural parameters, the period of the metasurface unit is p, the thickness of the FR4 is h1, the thickness of the ferrite is h2, the side length of the rectangular metal sheet is a, and the metal thickness is 0.03 mm. In terms of material parameters, the conductivity of copper metal is 6.7×10 7 S / m, the relative permittivity and loss tangent of FR4 are 4.4 and 0.02 respectively, and the complex relative permittivity and complex permeability of the ferrite are obtained from experimental data ( Figure 3 and 4 ).

[0042] The wavefront modulation function of the coded metasurface depends on the characteristics and spatial arrangement of the structural units. To achieve a diffuse reflection effect to reduce the target RCS, this embodiment uses a 1-bit coded metasurface, which includes two structural units with similar reflection amplitudes and a reflection phase difference of nearly 180°, represented by the binary digital states "0" and "1" respectively. For this purpose, the CST Microwave Studio software is used to construct the unit structure of the NiZnCu composite coded metasurface ( Figure 6 ), and using the periodic boundary condition, parametric sweep, and frequency domain solver, the reflection amplitude and phase in the P band under normal incidence are calculated, as shown in Figure 7 and 8 . Keeping p = 100 mm, h1 = 6 mm, and h2 = 2 mm unchanged, when the side length a of the square metal patch is 91 mm and 84 mm respectively (corresponding to the binary digital states "0" and "1"), the two structural units have similar reflection amplitudes and the reflection phase difference satisfies 180°±37° in the frequency range of 0.59 GHz - 0.66 GHz, meeting the target design requirements.

[0043] Furthermore, to maximize the RCS reduction, it is necessary to optimize the spatial layout of the two structural units of the 1-bit coded metasurface. For this purpose, a genetic algorithm is used to obtain an optimal coded metasurface array that can omnidirectionally disperse (diffusely reflect) the incident electromagnetic wave.

[0044] For an M×N metasurface array, its far-field radiation function is expressed as:

[0045]

[0046] where is the radiation characteristic of the metasurface structural unit, which is related to the characteristics of the unit itself, p is the period of the structural unit, θ and are the elevation angle and azimuth angle in the spherical coordinate system respectively, and k is the wave number of light in the medium.

[0047] The optimal coding sequence matrix is obtained by optimization using the genetic algorithm, and the fitness function of this optimization problem is given by the following formula:

[0048]

[0049] In MATLAB, the optimal solution of a 12×12 array matrix is obtained by applying this algorithm, as Figure 9 shown, where "0" and "1" correspond to two structural units with a = 91 mm and 84 mm respectively.

[0050] To reduce the influence of boundary condition changes on the reflection characteristics of structural units, a supercell composed of 3×3 identical structural units is used to fill the 12×12 coding matrix, obtaining a metasurface array with 36×36 structural units, and the size of the array is 360×360 mm 2 .

[0051] To comparatively analyze the RCS reduction performance of the NiZnCu ferrite composite coding metasurface, the embodiments of the present invention respectively construct, using the full-wave simulation software CST Microwave Studio, a coding metasurface composed of structural units "0" and "1", a metasurface composed of structural unit "0", a metasurface composed of structural unit "1", and a metal copper backplane, and their sizes are all 360×360 mm 2 . By using open boundary conditions, plane wave excitation, and a time-domain solver, the far-field distribution diagrams and monostatic RCS data at different frequencies are obtained.

[0052] Figure 10 Shown is the far-field distribution diagram of the 4 structures at a frequency of 0.62 GHz. It can be seen that compared with the other 3 regularly arranged structures, the ferrite-based composite coding metasurface not only achieves a diffuse reflection effect, but also has the lowest maximum scattering amplitude, realizing an effective reduction of RCS.

[0053] More intuitively, by extracting the far-field results, the monostatic RCS data at different frequencies are obtained, as Figure 11 and 12 shown. It can be seen that the ferrite-based composite coding metasurface achieves an RCS reduction effect of more than 10 dB within the P band (0.25 GHz - 1.0 GHz), and compared with the metasurfaces composed of structural units "0" and "1", not only is the RCS reduction bandwidth effectively broadened, covering 0.50 GHz - 0.75 GHz, but also its maximum RCS reduction value can reach 29.4 dB.

[0054] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A NiZnCu ferrite composite metasurface with broadband and low RCS in the P-band based on 1-bit coding, characterized in that, The metasurface is composed of 2 types and 36×36 metasurface structural units. The metasurface structural units include, from bottom to top: a metal backplane, an intermediate dielectric layer, a square metal patch layer, and a top layer of NiZnCu ferrite. Adjacent layers are closely attached and their geometric centers coincide.

2. The NiZnCu ferrite composite metasurface based on 1-bit coding for P-band broadband and low RCS according to claim 1, wherein The period p of the metasurface structural unit is 100 mm, the thickness h1 of the intermediate dielectric layer is 6 mm, the thickness h2 of the NiZnCu ferrite is 2 mm, and the thicknesses of the metal backplane and the square metal patch layer are 0.03 mm.

3. The NiZnCu ferrite composite metasurface based on 1-bit coding for P-band broadband and low RCS according to claim 1, characterized in that, The reflection phase difference between the 2 types of metasurface structural units is 180°, and is represented by binary digital states "0" and "1"; among them, the side length a value of the square metal patch corresponding to the unit code "0" is 91 mm, and the side length a value corresponding to the unit code "1" is 84 mm.

4. The NiZnCu ferrite composite metasurface based on 1-bit coding for P-band broadband and low RCS according to claim 1, wherein The composition of the top-layer NiZnCu ferrite is Ni 0.4 Zn 0.5 Cu 0.06 Mn 0.04 Fe2O4, and it is prepared by the solid-phase sintering method.

5. The NiZnCu ferrite composite metasurface based on 1-bit coding for P-band broadband and low RCS according to claim 1, characterized in that, Both the metal backplane and the square metal patch layer are made of copper material.

6. The NiZnCu ferrite composite metasurface based on 1-bit coding for P-band broadband and low RCS according to claim 1, wherein The intermediate dielectric layer uses FR4 epoxy resin composite material, with a dielectric constant of 4.4 and a loss tangent of 0.

02.

7. The NiZnCu ferrite composite metasurface based on 1-bit coding for P-band broadband and low RCS according to claim 3, characterized in that A supercell of 3×3 identical units is used to fill a 12×12 coding matrix, obtaining a metasurface array with 36×36 structural units.

8. The NiZnCu ferrite composite metasurface with P-band broadband and low RCS based on 1-bit coding according to claim 7, wherein, The metasurface is optimized using a genetic algorithm to obtain an optimal coding sequence matrix, including: for a metasurface array of M×N, the radiation function of its far field is expressed as: Among them, is the radiation characteristic of the metasurface structural unit, which is related to the characteristics of the unit itself. p is the period of the structural unit, and θ and are the elevation angle and azimuth angle in the spherical coordinate system respectively, and k is the wave number of light in the medium.

9. The NiZnCu ferrite composite metasurface based on 1-bit coding for P-band broadband and low RCS according to claim 8, wherein, The genetic algorithm is used to optimize and obtain an optimal coding sequence matrix. The basic parameters of the genetic algorithm are: the number of individuals in the initial population is 300, the maximum number of evolution generations is 1000, the crossover rate is 10%, and the mutation rate is 5%. The fitness function of this optimization problem is given by the following formula:

Images