| n modern society,while various electronic devices and electronic products bring convenience to our lives,the electromagnetic interference and electromagnetic radiation generated have also caused many harmful effects on our bodies and the surrounding environment.How to reduce the harm caused to us by these electronic devices and products has become a hot issue in scientific research.At present,there are two main methods for dealing with electromagnetic interference and electromagnetic radiation: electromagnetic shielding and electromagnetic absorption.Although the former is simple to operate,it cannot eliminate the electromagnetic wave from the root cause,and after the electromagnetic wave is reflected on the surface of the shielding material,the reflected wave will also overlap with the incident wave,causing secondary pollution to the environment,which limits the application of this method..The latter is to prepare the absorbing material to convert electromagnetic waves into thermal energy or other forms of energy to absorb the loss of electromagnetic waves,which can solve the damage caused by electromagnetic interference and electromagnetic radiation from the root cause.Cement is the most common building material,and many scientists have tried to use cement as a base material to prepare absorbing materials.However,due to the dense structure of the cement material,electromagnetic waves will generate a lot of reflection on the surface,which reduces the wave-absorbing performance of the cement-based wave-absorbing material.This requires the introduction of a large number of bubbles into the cement-based material or the addition of porous materials to improve the wave-permeability of its surface,but this will cause the strength of the cement-based wave-absorbing material to be greatly reduced,which greatly limits the actual engineering.Applications.At the same time,cement will also produce a lot of waste gas and waste water that are harmful to the environment during the production process.Alkali excitation material is a new type of environmentally friendly building material,generally made of slag,fly ash,and alkali excitation agent.Compared with cement,alkali-excited materials have good mechanical properties and high strength,especially early strength.The use of alkali-excited materials instead of cement as the substrate can facilitate the formation and demolding of the wave-absorbing composite material after adding the wave-transmitting aggregate,and at the same time reduce the use of high-energy consumption cement.Expanded perlite is an inorganic material with a honeycomb structure inside,its dielectric constant is low,it is a wave-permeable aggregate,and it has good compatibility with cement and other cementing materials.In this paper,expanded perlite is selected To improve the wave-transmitting properties of alkali-activated gelling materials.Both metallic copper powder and nickel powder can cause dielectric loss to electromagnetic waves.The nickel-coated copper powder prepared by coating a layer of nickel on the copper surface is not only chemically stable,but also has good electromagnetic wave absorption performance.Copper powder is used as a wave absorbing agent to improve the wave absorbing performance of the gelled composite material.In summary,this article first chose to add nickel-coated copper powder to ordinary portland cement,and studied the strength,dielectric constant,and magnetic permeability of the amount of nickel-coated copper powder to ordinary portland cement-based absorbing materials,The effect of shielding effectiveness and wave absorption performance,the optimal mix ratio of nickel-coated copper powder in cementitious materials was analyzed.Secondly,the expanded perlite was added to the alkali-excited material to improve the impedance matching of the alkali-excited composite material.The dielectric constant,permeability,and The influence of the wave-transmitting property and the wave-absorbing property determinesthe optimal ratio of expanded perlite in the alkali-excited wave-absorbing material.Finally,on the basis of the above research,the expanded perlite and nickel-coated copper powder were added to the alkali-excited base material in composite;under the combined action of the two,the wave absorption properties of the alkali-excited base composite were studied,and finally the composite added nickel The optimal mixing ratio of the alkali-excited wave-absorbing material of copper-clad powder and expanded perlite.The main research conclusions of this article are as follows:(1)The nickel-coated copper powder will make the 28-day compressive strength of the composite material lower and the real and imaginary parts of the dielectric constant increase.In the frequency band of 0 ? 3GHz,the dielectric loss ability of the composite material to electromagnetic waves gradually becomes stronger with the increase of the content of nickel-coated copper powder.When the content of nickel-coated copper powder is the largest(20%),the dielectric of the composite material The maximum value of the imaginary part of the constant reaches 5.3.At the same time,nickel-coated copper powder can improve the wave absorption performance of cement-based materials.In the frequency bands of 2 ?4GHz and 26.5 ? 40.0GHz,as the amount of nickel-coated copper powder increases,the minimum reflectivity of the composite material will decrease,and the material's wave absorption performance will increase.Among them,when the content of nickel-coated copper powder is up to 20%,the cement-based composite material has the best wave absorption performance,and its minimum reflectance is-33.5d B at the frequency of 10 GHz.(2)The greater the amount of expanded perlite with the same particle size,the smaller the 28-day compressive strength and the real part of the dielectric constant of the alkali-excited composite material.When the particle size of the expanded perlite is small(less than 6mm),the imaginary part of the dielectric constant of the composite material will increase with the increase of the amount of expanded perlite,and when the particle size of the expanded perlite continues to increase(6 ? 8mm),the imaginary part of the dielectric constant of the composite material will decrease instead.At the same time,the larger the diameter of expanded perlite at the same dosage,the smaller the real part of the dielectric constant of thecomposite.Expanded perlite can reduce the effective dielectric constant of the alkali-excited material,improve the material's impedance matching characteristics,and improve its electromagnetic wave transmission performance.When the particle size of the expanded perlite is within a certain range,as the volume of the expanded perlite increases,the volume increase,The material's wave-transmitting performance is gradually enhanced.(3)On the premise of first using expanded perlite to improve the impedance matching characteristics of the alkali-excited material,when the nickel-coated copper powder continues to be added to the alkali-excited material,the absorbing performance of the composite material is significantly improved.When the test frequency is low(1 ? 4GHz),as the content of nickel-coated copper powder increases,the absorbing performance of the composite material gradually increases.When the content of nickel-coated copper powder is10%,15% and 20% respectively,the reflectivity of the composite material in the frequency band of 2 to 4 GHz is all less than-10 d B,and the effective absorption bandwidth is 6.25 times that of the blank sample.2GHz.When the test frequency is higher(18?40GHz),the effect of improving the absorbing performance of the composite material after the addition of nickel-coated copper powder is better than that in the low frequency band(0?4GHz),and the absorbing performance of the composite material also increases with the The content of nickel-coated copper powder increases and increases.Among them,in the frequency bands of18.0 ? 26.5GHz and 26.5 ? 40.0GHz,the reflectivity of all the samples with added nickel-coated copper powder are all less than-10 d B,which are all effective absorption.When the maximum amount of nickel-coated copper powder is 20%,the minimum reflectivity of the composite material reaches-22.99 d B at 26.45 GHz. |
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