CN113216508A

CN113216508A - Cement composite board based on super surface technology

Info

Publication number: CN113216508A
Application number: CN202110469231.7A
Authority: CN
Inventors: 徐世烺; 王晓冉; 李庆华
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2021-04-28
Filing date: 2021-04-28
Publication date: 2021-08-06

Abstract

The invention discloses a cement composite board based on a super-surface technology, which comprises a conductive surface layer, a dielectric layer, a cement substrate, a functional composite layer and a shielding bottom board, wherein the conductive surface layer, the dielectric layer, the cement substrate, the functional composite layer and the shielding bottom board are sequentially arranged; the conductive surface layer is formed by conductive surfaces with periodically arranged stripes; the functional composite layer is formed by sandwiching a layer of carbon nano tube periodic conductive surface layer between two wave-transparent substrates. The cement-based composite board based on the super-surface technology integrates the building material into the medium layer of the super-surface structure, and utilizes the resonance characteristic of the multiple conductive layers, thereby realizing the super-surface perfect wave-absorbing structure capable of bearing. The absorption rate is high, the working frequency band is wide, the preparation process is simple and convenient, and the bearing and durability performance is good.

Description

Cement composite board based on super surface technology

Technical Field

The invention relates to the field of wave-absorbing structures for buildings. In particular to a cement-based composite board which is based on a super-surface technology, integrates building materials into a super-structure material and has the characteristic of perfect absorption of electromagnetic waves by a super surface.

Background

Due to the rapid increase in the use of radio communication and electronic equipment, electromagnetic wave radiation has become a new pollution. Electromagnetic interference not only affects the operation of various electronic devices, but also directly affects the human body and even promotes the growth of tumors. Therefore, in the field of building structures, the absorption of electromagnetic waves has attracted the attention of researchers. The wave absorbing performance of traditional building materials, such as cement-based materials, is mainly realized by adding wave absorbing agents into the building materials. The addition of the wave absorbing agent can change the microscopic pore structure and the structure of the conductive network of the material, thereby changing the impedance matching characteristic of the material and the attenuation characteristic of electromagnetic waves in the material, and further improving the electromagnetic wave absorption performance of the material. Therefore, the current research on building wave absorbing materials mainly focuses on mixing the wave absorbing agent into the cement-based material through a mixing process.

The wave-absorbing performance enhancing effect of the traditional method depends on the wave-absorbing performance of each component of the cement-based material, and the optimal selection and the optimal mixing amount of the wave-absorbing agent are determined through continuous proportioning tests. Therefore, the disadvantages are also significant. First, fundamentally, the wave-absorbing performance of a cement-based material depends on the arrangement characteristics of the material molecules, and the control of specific absorption characteristics cannot be realized through artificial design. Therefore, the process of designing the wave-absorbing material by researchers is passive, and the wave-absorbing performance of the prepared material cannot be actively controlled. Second, researchers must try to find materials whose natural impedance matches free space. However, the materials matched with natural impedance are required to be close to air impedance, and most of the materials are loose and porous materials, which does not meet the design idea of reinforcing and toughening the building materials. Thirdly, the preparation of the wave-absorbing material is greatly influenced by factors such as materials, environment, maintenance and the like of various places, and the industrialized and unified production is difficult to realize. Fourthly, compared with an advanced electromagnetic wave absorbing structure, the method has a very limited effect of improving the wave absorbing performance.

Metamaterials provide an ideal solution to the above-mentioned problems. Metamaterial, super surfaces are a subject of rapid development in recent years. The metamaterial not only has singular electromagnetic characteristics, but also has wide application prospect. The super-surface can be dimensioned artificially to work at all sub-optical frequencies, which has proven the feasibility of microwave, millimeter wave, terahertz, infrared and near-infrared ranges. Through artificial design, the electromagnetic wave absorption rate can reach nearly 100% in a specific frequency band, and the characteristic of perfect absorption is shown. In addition, after the metamaterial is designed, the metamaterial can be produced in a batch and unified mode, and stable performance is guaranteed.

However, the existing electromagnetic super-surface is fine in production and relatively complex in processing, does not have the functions of bearing, fire prevention, durability and the like, and cannot be directly used for building structures. In addition, the material for building also has the electromagnetic properties required by various surface layers and dielectric layers of the metamaterial, and cannot be integrated into the structure of the metamaterial and the super surface. The two barriers are difficult to combine the metamaterial and the wave-absorbing structure of the building. There is currently no relevant solution.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a cement-based composite board based on a super-surface technology, wherein a building material is integrated into a medium layer of a super-surface structure, and the resonance characteristics of multiple conducting layers are utilized, so that a super-surface perfect wave-absorbing structure capable of bearing load is realized. The absorption rate is high, the working frequency band is wide, the preparation process is simple and convenient, and the bearing and durability performance is good.

Therefore, the invention adopts the following technical scheme:

a cement-based composite board based on a super-surface technology can perfectly absorb electromagnetic waves and mainly comprises a conductive surface layer, a dielectric layer, a cement substrate, a functional composite layer and a shielding bottom plate from top to bottom. The bandwidth for perfectly absorbing the electromagnetic wave (reflectivity less than-15 dB, i.e. absorptivity greater than 97%) is not less than 50% of the total bandwidth.

Further, the conductive surface layer is a conductive surface periodically arranged by unit patterns; the unit pattern is in the form of a stripe pattern. The periodic conductive surface is ultrathin and is 0.01 mm-0.2 mm, the thickness is preferably not more than 0.1mm, and the most preferably 0.1 mm; so that incident waves can be transmitted inside the composite plate and further generate resonance; the period length is 5-100mm, namely the period length of the stripes in the conductive surface layer (1) is 5-100mm, the period length is further preferably 10-40 mm, and most preferably, the period length is 24mm, which is far larger than the conventional super-surface period size (generally several micrometers), so that the production in the cement industry is facilitated, and the perfect absorption characteristic of a cement plate can be met.

Furthermore, the dielectric layer is a wave-transparent substrate, the dielectric constant is less than 10, the wave-transparent rate is greater than 95%, and the thickness is 0.01mm-30 mm. Preferably, the dielectric layer is a silicon-aluminum ceramic fiber board with the thickness of 2-8 mm, and most preferably, the dielectric layer is a silicon-aluminum ceramic fiber board with the thickness of 5 mm.

Further, the preparation method comprises the following steps: the method is characterized in that slurry containing carbon nano tubes is coated on a wave-transparent substrate by using a mould-slurry spraying method, and specifically comprises the following steps: firstly, preparing a hollowed-out mould which is in accordance with the shape of the conductive surface layer, then uniformly spraying slurry containing carbon nano tubes to the hollowed-out part of the mould by using a spray head, then uniformly and flatly brushing the slurry by using a brush, fully distributing the hollowed-out part of the mould, and removing the mould. The preparation method breaks through the conventional technical prejudice, and the existing super-surface preparation needs to use solid metal, such as gold, copper and other materials, and is prepared by methods such as etching, optical printing and the like.

Furthermore, the cement base plate should have enough bearing capacity, the compressive strength is greater than 30MPa, preferably 30 MPa-1000 MPa, and the thickness is 1-50 mm. It should be noted that in the technical field of wave-absorbing materials, the metamaterial and the dielectric layer selected for the super surface should be wave-transmitting materials, but the invention just breaks through the technical bias in the field of metamaterial, integrates the cement substrate which is an incompletely wave-transmitting plate into the metamaterial, and enables the whole composite plate to have the characteristic of perfect wave absorption through the technical innovation design.

Furthermore, the functional composite layer is a key functional layer for endowing the cement composite plate coated with the super surface with excellent wave absorption performance, is a sandwich layer and is formed by sandwiching a carbon nano tube periodic conductive surface layer between two wave-transmitting substrates, and the preparation method of the conductive surface is the same as that of the conductive surface layer. The periodic conductive surface layer is formed by conductive surfaces with periodically arranged stripes; the carbon nano tube periodic conductive surface layer is in a stripe pattern, and the period length of the carbon nano tube periodic conductive surface layer is 5-100 mm. The wave-transparent substrate in the functional composite layer is a ceramic fiber board, the thickness is preferably 0.01mm-30mm, the thickness is further preferably 1-5 mm,

further, the shielding backplane should completely reflect electromagnetic waves, including but not limited to a well-conducting metal plate, a metal foil, a planar substrate made of a conductive material, and the like. The thickness is preferably as thin as possible, but is preferably 0.1 to 10mm, for the purpose of preventing the transmission of electromagnetic waves. Preferably, the shielding bottom plate is a metal copper plate, the thickness of the copper plate is 0.2-1 mm, and the thickness of the copper plate is 0.5mm most preferably.

Furthermore, the cement-based composite board based on the super-surface technology has the characteristics of wide frequency and high-efficiency radar wave absorption, and the following requirements are met: in the radiated electromagnetic wave frequency band (should be divided by L wave band, S wave band, C wave band, X wave band, Ku wave band, etc.), the ratio of the electromagnetic wave bandwidth with the absorptivity of more than 97% to the total bandwidth is not less than 50%.

Compared with the prior art, the invention has the following advantages:

the cement-based composite board based on the super-surface technology integrates the building material into the medium layer of the super-surface structure, and utilizes the resonance characteristic of the multiple conductive layers, thereby realizing the super-surface perfect wave-absorbing structure capable of bearing.

The invention combines the super surface technology, provides a scheme for integrating building materials into a super surface structure, and realizes a super surface wave-absorbing structure capable of bearing load. The cement-based composite board based on the super-surface technology has the advantages of high absorption rate, wide working frequency band, simple and convenient preparation process, and good bearing and durability properties. Compared with other wave-absorbing materials which achieve similar performance in the market, the wave-absorbing material has the advantages of low manufacturing cost, bearing and fire prevention and the like.

Drawings

FIG. 1 is a schematic structural composition of the present invention;

FIG. 2 is a detailed view of the composition of the fourth layer (functional composite sheet) of the present invention;

FIG. 3 is a graph of the reflectance of the present invention versus the reflectance of the control in example 1.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. The conditions not specified for the implementation are generally those in routine experiments.

Example 1

As shown in fig. 1, this example was prepared as follows: the upper conductive layer 1 (i.e. the conductive surface layer) is uniformly sprayed on the dielectric layer 2 by using 5% carbon nanotube aqueous slurry according to the die-slurry spraying method of the invention, the spraying thickness is 0.1mm, the pattern is a stripe pattern, the period length T is 24mm, and the coating proportion is 50%; the dielectric layer 2 is a silicon-aluminum ceramic fiber board with the thickness of 5mm, and the wave transmission rate is higher than 98%; the thickness of the cement substrate 3 is 15mm, and the standard compressive strength is 40 MPa; the total thickness of the composite functional layer 4 is 5mm, the composite functional layer 4 is of a sandwich layer structure, wave-transmitting materials on the upper layer and the lower layer of the sandwich layer are ceramic fiber boards with the thickness of 2.5mm, the upper layer is a ceramic fiber board 41, the lower layer is a ceramic fiber board 43, the middle layer is a periodic conductive layer 42, and the structure of the middle periodic conductive layer is the same as that of the upper conductive layer 1. The shield base plate 5 is a metal copper plate that totally (100%) reflects electromagnetic waves, and the thickness of the copper plate is 0.5 mm. The layers are bonded together with epoxy resin.

The validity of this example was verified in the X band (8-12 GHz). The wave absorbing performance is represented by reflectivity, and the reflectivity of the test piece in the range of 8-12GHz is tested by using an arch method. In order to prove the key influence of the composite functional layer 4 of the invention on the absorption performance, a control test is carried out. The experimental group is example 1, and the control group is the experimental group except for the composite functional layer 4. Two sets of wave absorbing property pairs are shown in figure 3.

(1) The effectiveness of the invention was tested against the test.

The reflection peak value of the control group is about-15.4 dB, the frequency band with the reflectivity lower than-15 dB (namely the absorptivity is more than 97 percent) is 10.04-10.64GHz, and accounts for 15 percent of the total bandwidth; and the experimental group, i.e. the peak reflectivity of the embodiment reaches-20 dB. In the range of 8-11GHz, the reflectivity is all lower than-15 dB, namely the bandwidth of perfectly absorbing electromagnetic waves in the X wave band (8-12GHz) accounts for more than 75% of the total bandwidth of the wave band.

(2) Example economic, comparative functional analysis

The cost of this embodiment: the mechanical cost and labor cost of the 1-5 layer material adopted in the embodiment are 280 yuan/m². Compared with the performances and the manufacturing cost of a plurality of main wave-absorbing materials on the market:

the existing wave-absorbing materials on the market mainly rely on a foam porous structure to absorb a large amount of waves, and a wave-absorbing agent is coated on a substrate to prepare a wave-absorbing surface, and the wave-absorbing material is subjected to super-surface regulation and control and the like. The foam cellular structure is inexpensive, but occupies a large space and is not capable of sustaining force. The wave-absorbing adhesive tape is light, thin and soft, can be attached to the surface of a structure, but is not high in temperature resistance. The silica gel plate wave-absorbing material can work at 200 ℃, but is high in manufacturing cost, mainly used in key and small parts, and has the size of about 30 cm x 20 cm per part and the unit price of about 3000 yuan per part.

The wave-absorbing materials are mainly applied to the field of communication, can realize perfect absorption of certain frequency bands, but cannot be used as a force-holding component, and have high manufacturing cost; however, the existing cement-based wave-absorbing material in the field of buildings has very limited wave-absorbing performance, is difficult to achieve a perfect absorption level, and has relatively narrow applicable bandwidth. The invention introduces the concept of the super-structure material into the concrete structure for the first time, greatly improves the wave-absorbing performance of the concrete material, and utilizes the common building fireproof material and a very small amount of conductive slurry to coat and prepare the super-surface, thereby greatly reducing the manufacturing cost and leading the concrete wave-absorbing structure to be possible to be applied in a large amount in the engineering.

The present invention is described in detail, and the embodiments are only preferred embodiments of the present invention to help understanding the method and the core idea of the present invention, so as to enable those skilled in the art to understand the contents of the present invention and to implement the same, and not to limit the protection scope of the present invention. Any modification, equivalent change or improvement made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. The cement composite board based on the super-surface technology is characterized by comprising a conductive surface layer (1), a dielectric layer (2), a cement substrate (3), a functional composite layer (4) and a shielding bottom board (5) which are sequentially arranged;

the conductive surface layer (1) is formed by conductive surfaces with periodically arranged stripes;

the functional composite layer (4) is formed by sandwiching a layer of carbon nano tube periodic conductive surface layer between two wave-transparent substrates.

2. The cementitious composite slab based on super surface technology as claimed in claim 1, wherein: the thickness of the conductive surface layer (1) is 0.01 mm-0.2 mm.

3. The cementitious composite slab based on super surface technology as claimed in claim 1, wherein: the period length of the stripes in the conductive surface layer (1) is 5-100 mm.

4. The cementitious composite slab based on super surface technology as claimed in claim 1, wherein: the dielectric layer (2) is a wave-transparent substrate, and the thickness of the dielectric layer is 0.01mm-30 mm.

5. The cementitious composite slab based on super surface technology as claimed in claim 1, wherein: the dielectric layer (2) is a silicon-aluminum ceramic fiber board, and the thickness of the dielectric layer is 2-8 mm.

6. The cementitious composite slab based on super surface technology as claimed in claim 1, wherein: the preparation method of the conductive surface layer (1) is as follows:

and coating the slurry containing the carbon nano tube on the wave-transparent substrate by using a mould-slurry spraying method.

7. Cement composite panels based on super surface technology according to claim 6, characterized in that: the method is characterized in that slurry containing carbon nano tubes is coated on a wave-transparent substrate by using a mould-slurry spraying method, and specifically comprises the following steps:

firstly, preparing a hollowed-out mould which is in accordance with the shape of the conductive surface layer, then uniformly spraying slurry containing carbon nano tubes to the hollowed-out part of the mould by using a spray head, then uniformly and flatly brushing the slurry by using a brush, fully distributing the hollowed-out part of the mould, and removing the mould.

8. The cementitious composite slab based on super surface technology as claimed in claim 1, wherein: the compression strength of the cement substrate (3) is 30 MPa-1000 MPa, and the thickness is 1-50 mm.

9. The cementitious composite slab based on super surface technology as claimed in claim 1, wherein: the periodic conductive surface layer of the carbon nano tube in the functional composite layer (4) is a stripe pattern, and the periodic length of the stripe pattern of the periodic conductive surface layer of the carbon nano tube is 5-100 mm.

10. The cementitious composite slab based on super surface technology as claimed in claim 1, wherein: the thickness of the shielding bottom plate (5) is 0.1-10 mm.