Design Of Carbonyl Iron Powder Based Broadband Absorbing Structure And Study On Additive Manufacturing Technology

In recent years,with the wide application of wireless communication technology,electromagnetic radiation in life is becoming more and more serious.The research and development of efficient microwave absorbing materials that can solve the problems of electromagnetic interference and electromagnetic pollution has a very broad market prospect.According to the different loss mechanism,the conventional materials used for microwave absorption can be divided into electrical loss type and magnetic loss type.In this paper,the most widely used magnetic loss carbonyl iron powder(spherical and flake powder)is selected as the microwave absorbing material.Carbonyl iron powder has unique onion carbon structure and excellent microwave absorption performance,but it also has some disadvantages,such as high density,poor corrosion resistance,narrow effective absorption frequency band and so on.Based on the electromagnetic parameters of single component microwave absorbing materials,this paper uses electromagnetic simulation software CST to design multi-layer and gradient microwave absorbing structures,and uses additive manufacturing to print multi-layer gradient microwave absorbing materials.The main absorbing frequency bands of carbonyl iron powder with different particle size,concentration and morphology are integrated to improve the disadvantage of narrow effective absorption frequency band of single carbonyl iron powder,and the spherical carbonyl iron powder is lightened to reduce its density.The main contents of this paper are as follows:(1)Carbonyl iron powder / polylactic acid(CIP / PLA)composite wire was prepared by screw extrusion,and CIP / PLA microwave absorbing material(function structure integrated bearing part)was formed by melt deposition technology(FDM).The 50 wt% CIP / PLA composite wires was successfully prepared through experiments,and the FDM printing process was explored.CIP/ PLA sample were prepared to test electromagnetic parameters and calculate electromagnetic reflection loss of the composite materials.The results show that the attenuation ability of the 50 wt% CIP / PLA Composite to the electromagnetic wave is weak,and the reflection loss value is﹣9 d B,this is because when the magnetic particle content is low,its saturation magnetization is small,resulting in low complex permeability and poor microwave absorption performance of CIP / PLA composites.(2)Polydimethylsiloxane(PDMS)with excellent performance and good environmental adaptability was selected as the printing precursor,CIP / PDMS printing ink was prepared,and CIP / PDMS flexible absorbing coating was formed by ink direct writing 3D printing technology(DIW).The high concentration ink was successfully prepared and the DIW printing process was studied.The CIP / PDMS samples were formed by DIW technology to test their electromagnetic parameters.Based on these electromagnetic parameters,the electromagnetic reflection loss of single component CIP / PDMS composites was calculated by electromagnetic simulation software.The results show that when the content of spherical carbonyl iron powder(SCI)is 80 wt%,the SCI /PDMS composite has the strongest absorption peak(﹣41.5 d B)at the thickness t = 2.4 mm and frequency f = 7.3 GHz,and the effective absorption bandwidth is3.6 GHz;When the content of flaky carbonyl iron powder(FCI)is 30 wt%,the FCI / PDMS composite has the strongest absorption peak at t = 1.8 mm and f =10.9 GHz,with a peak value of﹣34.8 d B and an effective absorption bandwidth of 4.8 GHz.The FCI has anisotropy,and the anisotropic structure will improve the permeability and resonance frequency of magnetic particles,and is conducive to reducing eddy current loss.Compared with SCI,FCI / PDMS composites still have excellent absorpting performance despite the lower concentration of FCI.(3)Based on the electromagnetic parameters of the above single component CIP / PDMS composites,the multilayer gradient structure absorbing material is designed by using the electromagnetic simulation software CST,and its electromagnetic reflection loss is calculated.The results show that for the concentration gradient structure: when the thickness of the CIP / PDMS composite is t = 2.2 mm,the effective absorption bandwidth is 8.3 GHz,and the maximum absorption peak is﹣34 d B;Foe the particle size gradient structure:when the thickness of the CIP / PDMS composite is t = 1.8 mm,the effective absorption bandwidth is 8.6 GHz and the maximum absorption peak is﹣60.1 d B;For the SCI / FCI / PDMS multilayer absorbing structure: when the thickness of composite material is t = 2 mm,the strongest absorption peak is﹣43.9 d B,and the effective absorption bandwidth is 3.62 GHz.Compared with single-layer absorbing material,the multi-layer gradient structure has better absorbing performance because the multi-layer gradient structure increases the number of reflections of electromagnetic waves between different layers.(4)In order to make the SCI lighter,Hollowing carbonyl iron(HC)is prepared by pitting etching.HC / PDMS composites were prepared by mixing the HC and PDMS,and the electromagnetic parameters were tested and the electromagnetic reflection loss were calculated.The experimental results show that the hollowing treatment can increase the electromagnetic parameters of SCI and enhance the attenuation ability of electromagnetic wave.This is because the HC weakens the skin effect of magnetic powder,thus improving the effective absorption of electromagnetic wave and improving the absorption performance.