A cement-based honeycomb electromagnetic absorbing composite structure with adjustable working frequency band

Abstract

This invention provides a cement-based honeycomb electromagnetic absorbing superstructure with adjustable operating frequency. The composite structure comprises, from bottom to top, a cement-based lossy base plate and a retractable cement-metal honeycomb composite plate. This cement-based electromagnetic absorbing superstructure achieves excellent absorption performance. The operating frequency can be adjusted by stretching and shrinking the cement-metal honeycomb composite plate. Within this operating frequency band, the peak reflectivity is less than -20 dB, and the operating bandwidth (less than -10 dB) exceeds 4 GHz.

Description

Technical Field

[0001] The present invention relates to the field of cement-based materials and structures, and in particular to a design method for a cement-based honeycomb electromagnetic wave absorbing structure with adjustable absorption frequency band. Background Art

[0002] As the world's most widely used and widely used building material, cement-based materials play a vital role in the construction of modern infrastructure. With the increasing application of electronic information technology, improving the radar absorption and stealth capabilities of building structures has become an urgent need. Furthermore, with the widespread adoption of 5G and 6G communication technologies, contemporary society faces a series of challenges, including information confidentiality, electromagnetic interference resistance, and human electromagnetic radiation protection. This further highlights the importance of developing electromagnetic absorption technology in civil construction. The incident frequency band of electromagnetic waves in real-world environments is uncertain. Adjustable operating frequency electromagnetic absorbers can ensure effective absorption of electromagnetic waves in the target frequency band, providing stable radar absorption and stealth effects in variable electromagnetic environments. However, currently, cement-based absorbers primarily take the form of conventional flat-plate absorbers, whose absorption properties are primarily determined by the material's natural properties and the size and thickness of the absorber sample. Once designed and fabricated, the operating frequency band cannot be actively adjusted. Improving the adaptability of cement-based absorbers to real-world electromagnetic environments and enabling them to adjust their operating frequency band are crucial for the practical application of cement-based absorber structures. Summary of the Invention

[0003] The purpose of this invention is to provide a cement-based electromagnetic wave absorbing structure that can actively adjust its operating frequency band, thereby improving its adaptability to working environments and engineering practicality. To this end, the present invention adopts the following technical solutions:

[0004] A cement-based honeycomb electromagnetic wave absorbing composite structure with adjustable working frequency band, whose absorption center frequency is f0; characterized in that the composite structure comprises, from bottom to top, a cement-based lossy bottom plate and a scalable and adjustable cement-metal honeycomb composite plate.

[0005] On the basis of adopting the above technical solutions, the present invention may also adopt the following further technical solutions or use these further technical solutions in combination:

[0006] The cement-based lossy bottom plate is preferably made of a cement-based material having good electromagnetic loss characteristics, such as a cement-based material containing mineral admixtures, a cement-based material added with an absorbent, and the like.

[0007] The thickness t of the cement-based loss base plate cement Determined by the following formula:

[0008]

[0009] Where c is the speed of light, ε r and μ r are the relative permittivity and relative magnetic permeability of cement-based materials, respectively.

[0010] The structure of the retractable cement-metal honeycomb composite panel consists of a retractable metal honeycomb core and a cement-based thin shell medium cast on its surface. The center frequency f0 of the wave absorption can be controlled by adjusting different degrees of retraction.

[0011] The honeycomb uses a hexagon as a basic unit, and the opposite sides of the hexagon are parallel.

[0012] The retractable metal honeycomb core uses a deformable metal sheet as a raw material, and is manufactured into a honeycomb panel that can be stretched and contracted by bonding / welding at intervals according to the designed size.

[0013] The retractable metal honeycomb core is made of a deformable metal sheet. The honeycomb is based on a hexagon as a basic unit. The opposite sides of the hexagon are parallel. To ensure the adjustable wave absorption frequency band of the structure, the internal angle θ of the hexagon can be changed within a range of 5°-120°. To ensure the wave absorption characteristics of the structure in the working frequency band, the honeycomb structure period T, i.e., the distance between the opposite sides of the hexagon, is determined by the following formula:

[0014] κc / f L ≤T≤κc / f H (2)

[0015] Among them, f L and f H are the lowest and highest values ​​of the designed working frequency band of the absorbing superstructure, and κ is taken as 1 / 2.

[0016] The cement-based thin-shell medium is preferably made of a tough cement-based material. This allows the flexible cement-metal honeycomb composite panel to be stretched and adjusted as needed after fabrication, and then assembled with the cement-based lossy base plate, facilitating precise adjustment of the absorbing frequency band. The tough cement-based material can be a similar material currently used in other applications.

[0017] The tough cement-based material is a tough cement-based material with added fibers.

[0018] Preferably, the material of the cement-based thin shell medium has good electromagnetic loss characteristics, such as cement-based materials containing mineral admixtures, cement-based materials added with absorbents, etc.

[0019] The cement-based electromagnetic absorbing superstructure of the present invention can achieve excellent absorbing performance technical indicators. The operating frequency band can be adjusted by stretching and shrinking the cement-metal honeycomb composite panel. The peak reflectivity within the operating frequency band is lower than -20dB, and the operating bandwidth (bandwidth below -10dB) exceeds 4GHz. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic diagram of the deformable honeycomb structure of the present invention;

[0021] Figure 2 This is a schematic diagram of the cement-based honeycomb electromagnetic wave absorbing composite structure of the present invention;

[0022] Figure 3 Graph showing the reflectivity of the cement-based honeycomb electromagnetic absorbing composite junction in the embodiment. DETAILED DESCRIPTION

[0023] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. It should be understood that the embodiments described are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Unspecified implementation conditions are generally the conditions in routine experiments.

[0024] like Figure 2 As shown, the cement-based honeycomb composite structure of this embodiment is composed of a cement-based lossy bottom plate 1 and a retractable cement-metal honeycomb composite plate 2 from bottom to top. The cement-based lossy bottom plate 1 is a flat plate, which is an ultra-high toughness cement-based material (UHTCC) with added PVA fiber, and has a thickness of 20 mm. The cement-metal honeycomb composite plate uses a retractable honeycomb metal plate as the core material, and the honeycomb structure period T = 14 mm. A thin layer of UHTCC with added PVA fiber is cast on the surface, and the material of the retractable honeycomb metal plate can be an aluminum alloy. The microwave reflectivity bow method test system is used to characterize the wave absorbing performance of the structure. The reflectivity of a single cement-metal honeycomb plate, a cement flat plate (cement-based lossy bottom plate 1), and a cement-based honeycomb electromagnetic wave absorbing composite structure were tested respectively, as shown in FIG. Figure 3 As shown. The cement-based honeycomb composite structure is u The wave absorption performance in the band (12-18GHz) is significantly enhanced. In this band, the average reflectivity of the cement-metal honeycomb composite panel, cement flat panel, and cement-based honeycomb electromagnetic wave absorbing composite structure are -6.3dB, -8.4dB, and -14.1dB, respectively. The cement-based honeycomb electromagnetic wave absorbing composite structure has a peak reflectivity of -26.4dB at 14.9GHz. The -10dB bandwidth of this frequency band reaches 4.6GHz (13.4-18GHz), while the -10dB bandwidth of the cement flat panel and cement-metal honeycomb composite panel alone is 0GHz. uIn this band, the significantly enhanced wave absorption characteristics of the cement-based honeycomb electromagnetic wave absorbing composite structure come from the impedance matching characteristics of the honeycomb structure on the wavefront, which allows electromagnetic waves to enter the structure without reflection. On the other hand, it comes from the electromagnetic wave loss mechanism of the fiber and cement-based materials, which fully attenuates the electromagnetic waves incident to the interior of the structure.

[0025] The present invention has been described in detail above. The above embodiments are merely preferred embodiments of the present invention and are intended to facilitate understanding of the method and core concepts of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any modifications, equivalent variations, or improvements made in accordance with the spirit and substance of the present invention shall be encompassed within the scope of protection of the present invention.

Claims

1. A cement-based honeycomb electromagnetic wave absorbing composite structure with adjustable working frequency, wherein the center frequency of the wave absorbing structure is f0; characterized in that: The composite structure comprises, from bottom to top, a cement-based lossy bottom plate and a scalable and adjustable cement-metal honeycomb composite plate; The structure of the retractable cement-metal honeycomb composite panel consists of a retractable metal honeycomb core and a cement-based thin shell medium cast on its surface. The center frequency f0 of the wave absorption can be adjusted by adjusting different degrees of retraction. The retractable metal honeycomb core is made of a deformable metal sheet. The honeycomb is based on a hexagon as a basic unit. The opposite sides of the hexagon are parallel. To ensure the adjustable wave absorption frequency band of the structure, the internal angle θ of the hexagon is variable within a range of 5°-120°. To ensure the wave absorption characteristics of the structure in the working frequency band, the honeycomb structure period T, i.e., the distance between the opposite sides of the hexagon, is determined by the following formula: κc / f L ≤T≤κc / f H (2) Among them, f L and f H are the lowest and highest values ​​of the designed working frequency band of the absorbing superstructure, and κc is taken as 1 / 2.

2. The cement-based honeycomb electromagnetic wave absorbing composite structure according to claim 1, characterized in that: The thickness of the cement-based loss base plate t cement Determined by the following formula: Where c is the speed of light, ε r and μ r are the relative permittivity and relative magnetic permeability of cement-based materials, respectively.

3. The cement-based honeycomb electromagnetic wave absorbing composite structure according to claim 1, characterized in that: The retractable metal honeycomb core uses a deformable metal sheet as a raw material, and is manufactured into a honeycomb panel that can be stretched and contracted by bonding / welding the sheet at intervals according to the designed size.

4. The cement-based honeycomb electromagnetic wave absorbing composite structure according to claim 1, characterized in that: The material of the cement-based thin shell medium is a tough cement-based material.

5. The cement-based honeycomb electromagnetic wave absorbing composite structure according to claim 4, characterized in that: The tough cement-based material is a tough cement-based material with added fibers.

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