| Smoke screen technology is first used in the field of military stealth,and then developed into radar stealth technology,including coated and structural radar stealth technology.All of the above stealth technologies involve absorbing materials,so it is of great practical value to study how to apply absorbing materials in stealth technology.New absorbing materials are not only widely used in military stealth,aerospace and other military fields,personal protection,communication and civil fields,but also can be used as new smoke interference materials in smoke stealth.Through the synergistic action of composite materials,different absorption frequency bands,different absorption loss mechanisms and different physical characteristics are coordinated to achieve the "light,thin,wide and strong" absorption requirements.Therefore,simple and inexpensive electric loss multi-wall carbon nanotubes(MWCNTs)and magnetic loss nanometer iron tetroxide(Fe3O4)particles are selected to prepare composite materials,and their absorbing properties in the single-layer and multi-layer structures and large-scale spatial distribution are studied,which can be used for reference in the application and development of absorbing and stealth-like materials in the field of wave absorbing and stealth-like materials.At present,the research of absorbing stealth technology by experts and scholars is limited to millimeter thickness coating absorbing and structure absorbing,but there is no research on nano absorbing materials in large-scale space of meter scale.As one of the initial achievements of dynamic absorption in the air,this paper aims to study the absorption characteristics of MWCNTs/Fe3O4 composite particles from four aspects,that is,from the microscopic point of view to the single-layer thin plate,then to the multi-layer thin plate,and then to the large-scale space.Firstly,MWCNTs/Fe3O4 nanocomposites are prepared by blending MWCNTs and Fe3O4 with ball mill.The characteristics of MWCNTs/Fe3O4 nanocomposites after ball milling are characterized by XRD,TEM,FT-IR and network vector analyzer,and the microwave attenuation model of MWCNTs/Fe3O4 nanocomposites is established.The calculated reflectivity is compared with that calculated by free space transport model,which further reveals the absorption mechanism of MWCNTs/Fe3O4 nanocomposite particles.The reflectivity calculated by the model of microwave attenuation mechanism of MWCNTs/Fe3O4 nanocomposites decreases with the increase of frequency.And The results of the model are almost the same as those of the free space transport model.This study provides a good method for us to predict the microwave absorption capacity of MWCNTs/Fe3O4 nanocomposites and reduce the experimental blindness.Then,NBR powder and MW CNT s/Fe3 O4 nanocomposites are mixed,and MWCNTs/Fe3O4/NBR composite sheet is prepared by flat vulcanization machine.The MWCNTs/Fe3O4 nano composite powder and MWCNTs/Fe3O4/NBR composite sheet are characterized and tested by XRD,SEM,TEM,vibrating sample magnetometer and network vector analyzer,and the absorption properties of single-layer MWCNTs/Fe3O4/NBR composite sheet are studied.Through calculation and experiment,the reflection coefficient is between-23.28dB and-6.17dB,and the frequency band lower than-10dB is 2?6GHz.In the 2?8GHz band,the attenuation value calculated by the model is almost the same as that measured by the Free-Space method.And in the 8?18GHz band,the attenuation value calculated by the absorption model is larger than that measured by Free-Space method.Then,on the basis of the study of single-layer MWCNTs/Fe3O4/NBR composite thin plate,the absorbing characteristics of multi-layer MWCNTs/Fe3O4/NBR composite absorbing material in the presence of air layer are studied.COMSOL simulation is used to calculate the absorbing characteristics of the composite thin plate in space,and the four-port network matrix is used to calculate the absorbing characteristics of the composite thin plate in space.And then the Free-Space method is used to measure its reflection attenuation loss,and the results calculated by the three methods are compared and analyzed.The results of numerical simulation,four-port network matrix equivalent and Free-Space method are almost the same,and the three results show that in the frequency band of 6?14GHz,the reflection loss value is less than-10dB,that is to say,90%of the absorption electromagnetic wave.Compared with the results of single-layer thin plate absorption,the design of multi-layer absorption structure promotes the electromagnetic wave to enter the absorption layer as much as possible and absorb loss,and improves the absorption effect and broadens the frequency band.Finally,considering that MWCNTs/Fe3O4 nanocomposite particles have a good absorbing effect in the centimeter-wave frequency band,it is used as a new smokescreen to disperse in the large scale space at the scale of meters,and a kind of absorbing model of the spatial distribution of nanoparticles at the large scale(the thickness of the scale of meters)is established.MWCNTs/Fe3O4 nanoparticles are distributed in space with 7Kg,13Kg and 100Kg cloud detonation devices,and the wave absorbability of electromagnetic waves through these three large-scale spaces are studied.COMSOL is used for numerical simulation to calculate its reflectance R,and compared with the reflectance R' calculated by the transmission model.The wave absorption mechanism of MWCNTs/Fe3O4 particles in large scale space is revealed by comparing with the reflection coefficient values of the monolayer MWCNTs/Fe3O4/NBR thin plates with thickness of 2.71mm and the multilayer thin plates with thickness of 28.13mm. |
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