CN114498056B - A Broadband Absorbing Honeycomb Composite Structure - Google Patents

Abstract

The invention belongs to the field of radar wave-absorbing materials, and relates to a broadband wave-absorbing honeycomb composite structure. The structure design of the present invention is simple and flexible. Based on the good wave-absorbing performance of the wave-absorbing honeycomb itself, by introducing the bottom metasurface below the wave-absorbing honeycomb to adjust the metamaterial unit structure to design anisotropic reflection frequency points, combining the excellent performance of the two structures, aiming at optimizing The half-wavelength reflection peak problem of the absorbing honeycomb itself changes the propagation path length and direction of the electromagnetic wave in the absorbing honeycomb, and the electromagnetic wave cannot form interference constructiveness on the surface of the composite structure and the path in the absorbing honeycomb becomes Long, so strong absorption is formed at the design frequency point, the absorption performance of the half-wavelength band is optimized, and the absorption bandwidth is broadened, and the underlying metasurface does not affect the performance of other frequency bands of the absorbing cell. The structure of the invention has broadband wave-absorbing performance, insensitive to polarization, simple structure and the like, and can be applied to the field of radar wave-absorbing.

Description

A Broadband Absorbing Honeycomb Composite Structure

technical field

The invention belongs to the field of radar wave-absorbing materials, and relates to a broadband wave-absorbing honeycomb composite structure.

Background technique

The birth of radar technology invented during World War II accelerated the pace of war, and stealth technology came into being to enhance the penetration performance of weapons and equipment. Stealth technology is divided into shape stealth and electromagnetic absorbing structure stealth, which play an extremely important role in the increasingly complex electromagnetic wave environment of the modern battlefield. In recent years, with the development of radar technology and communication technology, especially 5G, people's demand for broadband absorbing structures is becoming more and more urgent.

Traditional broadband absorbing structures such as absorbing foam and Jaumann absorbing body sacrifice thickness while obtaining broadband absorbing performance, most of which are above 400mm or even 600mm, and have poor mechanical properties. The wave-absorbing honeycomb structure is an excellent wave-absorbing structure that combines mechanical properties and broadband wave-absorbing properties. Therefore, it has been studied and applied abroad as early as the last century. The most famous application belongs to the US B-2 bomber.

The absorbing honeycomb is made of aramid paper honeycomb impregnated with absorbing slurry. It has broadband absorbing performance in the radar band 2-18GHz. However, due to the thickness of the absorbing honeycomb itself, there will be half the wavelength of the propagation distance. Interference is long, there is a strong reflection peak at half the wavelength, and the absorbing performance in this frequency band is poor. If the strong reflection peak can be solved and the reflectivity of the absorbing honeycomb half frequency band can be optimized, the absorption can be broadened. The bandwidth of the wave cell makes the overall performance more excellent.

There are two known solutions to the strong reflection peak at one-half wavelength. One is to load the metamaterial to the side wall of the honeycomb hole: insert the metamaterial unit with a resonant frequency at one-half wavelength into the honeycomb hole, close to the side wall of the absorbing honeycomb, and each honeycomb hole has six Three metamaterial units are loaded symmetrically on the sidewall, and the resonant absorption of the metamaterial at one-half wavelength is used to solve the problem of reflection peak. The other is to load the absorbing structure into the honeycomb hole: load the polarization-insensitive absorbing structure with a resonant frequency at one-half wavelength in the honeycomb hole, and use the absorbing structure to optimize the performance of the half-wavelength band . Although the above method can optimize the absorbing performance of the absorbing honeycomb at one-half wavelength, the addition of metamaterials in the first scheme will seriously affect the absorbing performance of other frequency bands, and because of the large number of honeycomb holes, the composite structure The preparation is complex and cumbersome and the cost is too high. Due to the limitation of the honeycomb pore size, the second solution cannot actually prepare the composite structure, and only stays in the simulation stage. Moreover, due to the addition of a wave-absorbing structure, the dielectric of the overall structure will change, which will also be inevitable. affect the performance of other frequency bands.

Contents of the invention

In view of the above existing problems or deficiencies, in order to solve the problem of the strong reflection peak of the existing wave-absorbing honeycomb at half the wavelength, the present invention provides a broadband wave-absorbing honeycomb composite structure, which can effectively solve the strong reflection peak at half the wavelength. Reflection problem. The composite structure includes a bottom metasurface and a wave-absorbing honeycomb arranged above the bottom metasurface. The structure achieves effective absorption of more than 90% of the electromagnetic wave in the broadband range of 2-18 GHz and is insensitive to polarization. The preparation is simple and easy to implement. For the composite structure, since the metasurface is placed on the bottom surface, it will not affect the dielectric of the absorbing honeycomb itself, so it will not affect the absorption performance of the overall structure in other frequency bands, and its main structure aramid paper honeycomb meets the requirements of "Aircraft Structure With the specification of aramid paper-based honeycomb core material (GJB 1874-94), it has the specified mechanical properties.

A broadband wave-absorbing honeycomb composite structure includes a bottom metasurface and a wave-absorbing honeycomb arranged above the bottom metasurface.

The wave-absorbing honeycomb is a honeycomb structure composed of honeycomb cells with a wave-absorbing coating, and is prepared by impregnating the wave-absorbing slurry with the aramid paper honeycomb.

The underlying metasurface is a metal-medium-metal three-layer laminated structure, the lower layer is a metal backplane, the middle layer is a dielectric layer, and the top layer is a metasurface unit periodic structure of metal graphics. When the bottom metasurface is incident on the electromagnetic wave in the half-wavelength band, anisotropic reflection is formed at the designed frequency point, which changes the electromagnetic wave path and eliminates the interference construct, thereby reducing the reflectivity and optimizing the wave-absorbing performance of the composite structure in the half-wavelength band .

Further, the wave-absorbing honeycomb achieves an effective absorption of more than 90% of the electromagnetic wave on average in the entire frequency band in the 2-18GHz broadband range and is not sensitive to polarization. Except for the half-wavelength reflection peak frequency band, the average reflectance of other frequency bands Below -15dB.

The design principle of the broadband absorbing honeycomb composite structure is that when the electromagnetic wave is incident on the composite structure, the absorbing honeycomb itself has broadband absorbing performance at 2-18GHz, and for the strong reflection peak of the absorbing honeycomb in the half wavelength band, The optimization of the metasurface reduces the reflection and broadens the bandwidth of the entire absorbing honeycomb composite structure. The strong reflection peak in the half-wavelength band is due to the fact that the propagation path of the electromagnetic wave in the absorbing honeycomb structure is two half-wavelengths, resulting in interference and constructive formation. The entire broadband absorbing honeycomb composite structure is formed by introducing the underlying metasurface. When the electromagnetic wave is vertically incident on the broadband absorbing honeycomb composite structure, it is vertically incident on the underlying metasurface after passing through the absorbing honeycomb. The parameters of the underlying metasurface units are different, and the reflection phase Therefore, the gradient unit arrangement forms a gradient phase structure layout, which makes the electromagnetic wave deflect the reflection angle. The propagation path length and propagation direction of the electromagnetic wave in the absorbing honeycomb change, the electromagnetic wave cannot form interference constructivity on the surface of the composite structure and the path becomes longer in the absorbing honeycomb, so strong absorption is formed at the design frequency point, and the dichotomy is optimized. The absorbing performance of one wavelength band.

To sum up, the wave-absorbing honeycomb composite structure provided by the present invention is simple and flexible in design. Based on the good wave-absorbing performance of the wave-absorbing honeycomb itself, the anisotropic reflection frequency point is designed by adjusting the structure of the metamaterial unit in conjunction with the bottom layer metasurface, and the bottom layer supersurface The surface is set under the absorbing honeycomb, combining the excellent performance of the two structures, aiming at optimizing the half-wavelength reflection peak problem of the absorbing honeycomb itself, widening the absorbing bandwidth, and the underlying metasurface does not affect other frequency bands of the absorbing honeycomb performance. The structure of the invention has broadband wave-absorbing performance, insensitive to polarization, simple structure and the like, and can be applied to the field of radar wave-absorbing.

Description of drawings

Fig. 1 is a structural representation of the present invention;

Fig. 2 is the top plan view of embodiment bottom metasurface;

Fig. 3 is the structural representation of embodiment top layer metasurface unit;

Fig. 4 is a schematic diagram of a wave-absorbing honeycomb structural unit of the present invention;

Fig. 5 is the comparison chart of reflectivity test with traditional wave-absorbing honeycomb structure when the uniform plane wave of the embodiment is vertically incident;

Fig. 6 shows the sensitivity of Example 1 to the polarization mode when a uniform plane wave is incident vertically.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

Example:

The broadband wave-absorbing honeycomb composite structure of this embodiment is sequentially from bottom to top the Cu metal bottom plate layer, the middle FR4 medium layer above the Cu metal layer, the top layer metasurface composed of a periodic array of metasurface units, and the wave absorbing material impregnated Honeycomb, as shown in Figure 1. r ₀ is the outer length of the blank honeycomb, t ₀ is the thickness of the aramid fiber paper, t ₁ is the thickness of the absorbing slurry coating, and the height of the entire absorbing honeycomb structure is h.

The real part of the dielectric constant of the underlying metasurface is electric 4.2≦ε _r '≦4.7, the loss tangent angle is 0.021≦tanδ _ε ≦0.023, the real part of the equivalent relative permeability is 0.995≦μ _r '≦1.005, and the loss tangent angle is 0.01 ≦ _tanδμ ≦0.05. The thickness of the Cu metal base layer is 0.05mm, and the thickness of the FR4 dielectric layer is 1mm; the metasurface unit array is Cu metal patch with a thickness of 0.05mm, as shown in Figure 2.

The metasurface unit is a square with side length a ₀ = 13mm, and the metal pattern is a square copper patch. According to the supersurface design, the side length of the square copper patch is 8.5mm≦w≦12.5mm, and there are 8 different sizes. The metasurface units are arranged on the entire xoy plane, and the x direction is arranged periodically according to the gradient of the side length of the unit patch, and two identical units in the y direction are a group, and the gradient is arranged periodically. The unit sizes of the eight metal patches are 8.5mm, 10.3mm, 10.67mm, 10.85mm, 11.00mm, 11.20mm, 11.50mm and 12.50mm. The phase gradient is designed by adjusting the side length of the copper patch unit, so as to design the anisotropic scattering metasurface. The structure of the metasurface unit is shown in Figure 3. The overall size of the underlying metasurface is 300*300mm, consisting of 23*23 metasurface units. .

The wave-absorbing honeycomb is made of aramid paper honeycomb impregnated with wave-absorbing slurry. The cross-section of the honeycomb cell unit of the wave-absorbing honeycomb is a regular hexagon, and the real part of the equivalent relative permittivity is 1.45 ≦ε _r '≦2.00, the loss tangent angle is 0.6≦tanδ _ε ≦1.8, the real part of the equivalent relative permeability is 0.945≦μ _r '≦1.005, the loss tangent angle is 0.01≦tanδ _μ ≦0.05. As shown in Figure 4, the specific parameters of the absorbing honeycomb are: r ₀ =2.75mm, t ₀ =0.05mm, t ₁ =0.06mm, h=20mm. The absorbing honeycomb itself has excellent absorbing performance in the broadband 2-18GHz, the average reflectance in the 2-4GHz frequency band is below -20dB, and the average reflectance in the 8-18GHz frequency band is below -15dB.

The performance of the broadband absorbing honeycomb composite structure designed in this embodiment is compared with that of the traditional absorbing honeycomb structure under the condition of vertical incidence of uniform plane waves, as shown in FIG. 5 . For a traditional absorbing honeycomb with a thickness of 20mm and the real part of the dielectric constant is 1.45≦ε _r '≦2.00, and the loss tangent angle is 0.6≦tanδ _ε ≦1.8, half the wavelength corresponds to the 4-8GHz frequency band, so at 4 There is a strong reflection peak at the -8GHz frequency band. The composite absorbing honeycomb structure of the present invention is added to the metasurface, which optimizes the absorbing performance of this frequency band, making the overall structure absorbing bandwidth increase, and has at least - in the full frequency band of 2-18GHz The reflectivity below 10dB, of which the reflectivity of 2-7GHz is lower than -10dB, and there is a -25dB absorption peak at 3GHz; the reflectivity of the 7-10GHz frequency band is lower than -15dB, and there is a -35dB absorption peak at 9GHz frequency; 10-12GHz The reflectivity is lower than -10dB; the overall reflectivity of the 12-18GHz frequency band is lower than -15dB. The structure is not sensitive to the polarization mode, as shown in Figure 6, the reflectivity curves of the two polarization modes are basically the same.

It can be seen from the above embodiments that the structural design of the present invention is simple and flexible. Based on the good absorbing performance of the absorbing honeycomb itself, the anisotropic reflection frequency point is adjusted by introducing the bottom metasurface below the absorbing honeycomb to adjust the structure of the metamaterial unit, and combine the two structures The excellent performance, aiming at optimizing the half-wavelength reflection peak problem of the absorbing honeycomb itself, changes the propagation path length and propagation direction of the electromagnetic wave in the absorbing honeycomb, and the electromagnetic wave cannot form an interference construct on the surface of the composite structure and is in the The path in the absorbing cell becomes longer, so strong absorption is formed at the design frequency point, which optimizes the absorbing performance in the half-wavelength band and broadens the absorbing bandwidth, and the underlying metasurface does not affect the performance of other frequency bands of the absorbing cell. The structure of the present invention has the characteristics of broadband wave-absorbing performance, insensitive to polarization, and simple structure. It has a reflectivity below -10dB for incident electromagnetic waves in the full frequency band of 2-18GHz, and has excellent radar wave absorption performance and can be applied to radar wave absorption. field.

Claims (3)

1. A broadband wave-absorbing honeycomb composite structure, characterized in that: comprise the bottom metasurface and the wave-absorbing honeycomb arranged on the bottom bottom metasurface; The wave-absorbing honeycomb is a honeycomb structure composed of honeycomb cells with a wave-absorbing coating, which is prepared by impregnating aramid paper honeycomb with wave-absorbing slurry; The underlying metasurface is a metal-medium-metal three-layer laminated structure, the lower layer is a metal backplane, the middle layer is a dielectric layer, and the top layer is a metasurface unit periodic structure of metal graphics; the underlying metasurface is in the half-wavelength frequency band When the electromagnetic wave is incident, anisotropic reflection is formed at the designed frequency point, which changes the electromagnetic wave path and eliminates the interference phase, thereby reducing the reflectivity and optimizing the wave-absorbing performance of the composite structure in the half-wavelength band; Specifically, the underlying metasurface adopts: a Cu metal base layer with a thickness of 0.05mm, an intermediate FR4 dielectric layer with a thickness of 1mm, and the metasurface unit array is Cu metal patches with a thickness of 0.05mm; the real part of the dielectric constant of the underlying metasurface is Electricity 4.2≦ε _r '≦4.7, loss tangent angle 0.021≦tanδ _ε ≦0.023, real part of equivalent relative permeability 0.995≦μ _r '≦1.005, loss tangent angle 0.01≦tanδ _μ ≦0.05; The metasurface unit is a square with side length a ₀ =13mm, and the metal pattern is a square copper patch. The unit sizes of the square copper patch are 8.5mm, 10.3mm, 10.67mm, 10.85mm, 11.00mm, 11.20mm, 11.50mm and 12.50mm, a total of 8 different sizes; the metasurface units are on the entire xoy plane, the x direction is arranged periodically according to the gradient of the unit patch side length, and two identical units in the y direction are a group, and the gradient is periodically arranged. By adjusting the square The phase gradient is designed by using the side length of the copper patch unit, so as to design the anisotropic scattering metasurface. 2. The broadband wave-absorbing honeycomb composite structure as claimed in claim 1, characterized in that: the wave-absorbing honeycomb realizes an effective absorption of more than 90% of the electromagnetic wave in the 2-18GHz broadband range on average and is insensitive to polarization, Except for the half-wavelength reflection peak frequency band, the average reflectance of other frequency bands is below -15dB. 3. broadband wave-absorbing honeycomb composite structure as claimed in claim 1, is characterized in that: the cross-section of the honeycomb hole unit of described wave-absorbing honeycomb is a regular hexagon, and its equivalent relative permittivity is real after impregnating wave-absorbing slurry. The part is electrical 1.45≦ε _r '≦2.00, the loss tangent angle is 0.6≦tanδ _ε ≦1.8, the real part of the equivalent relative permeability is 0.945≦μ _r '≦1.005, and the loss tangent angle is 0.01≦tanδ _μ ≦0.05.

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