Fabrication And Microwave Absorbing Properties Of Polymer-based Composites

Due to the development of the communications industry and electronic devices,electromagnetic radiation has become a new pollutant.Electromagnetic radiation not only affects the proper functioning of a variety of electronic equipment but also is harmful to health.Therefore,the study of electromagnetic radiation protection has become a hot spot.The traditional electromagnetic shielding materials achieve the purpose of shielding mainly through the reflection of electromagnetic waves.However,the reflected electromagnetic waves still affect human health and the proper functioning of the external electronic devices.Therefore,it is necessary to develop an electromagnetic shielding material with high absorption and low reflection loss to electromagnetic waves.Because of their excellent electromagnetic properties,polymer-based composites are widely used as microwave absorbing materials.In this paper,six kinds of polymer-based composites were fabricated.A variety of analytical testing methods were used to characterize and test various properties and characteristics of the material.The relationship between reflection loss and matching thicknesses was discussed by Matlab simulation,and the microwave absorbing principle for materials was analysised.(1 The conductivity and Ms of Ni-Zn ferrite/hollow glass microsphere/polythiophene comosites(Ni0.7Zn0.3Fe204/HMG/PTh comosites)is 6.87×10-5 S/cm and 11.627 emu/g,respectively.As-prepared composites have good microwave absorbing properties(RL=-13.79 dB at 10.51 GHz)and the bandwidth less than-10 dB can reach 2.6 GHz(from 9.4 to 12.0 GHz)in X band(8.2-12.4 GHz).(2)The conductivity,Ms and He of Ag-coated Nd-doped strontium ferrite hollow microspheres with polypyrrole composites(Ag/SFHM/PPy composites)were 2.87 S/cm,17.946 emu/g and 1.64 Koe.Compared to PPy(RL=-4.58 dB at 9.94 GHz)and Ag/SFHM composites(RL=-10.25 dB at 10.36 GHz),Ag/SFHM/PPy composites(RL=-14.12 dB at 10.76 GHz)show better electromagnetic absorption properties.(3)Porous nickel ferrite hollow nanospheres/helical carbon nanotubes/polypyrrole nanowires(PNFHSs/HCNTs/PNWs)composites exhibit strong microwave absorption capacity(RL=-33.94 dB at 11.39 GHz)and the effective absorption bandwidth is 3.22 GHz(9.18?12.4 GHz)at the thickness of 2.1 mm.(4)The Ms,Mr and He of porous cobalt ferrite hollow nanospheres/carbon nanofibres/polypyrrole nanowires(PCFHSs/CNFs/PNWs composites)composites are 37.02 emu/g,15.53 emu/g and 445.23 Oe,respectively.The minimum reflection loss of composites(RL=-43.71 dB at 11.25 GHz)is obtained at the thickness of 2.1 mm.The reflection loss is different with different thicknesses.(5)The Ms,Mr and He of Cobalt ferrite hollow microspheres with protrusions/polythiophene composites(CFHMP/PTh composites)is 566.4 Oe,40.8 emu/g and 17.6 emu/g,respectively.The dielectric property of CFHMP/PTh composites is better than that of CFHMP,but the magnetic property of CFHMP/PTh composites is worse than that of CFHMP.At the thickness of 3.0 mm,CFHMP/PTh composites exhibit strong electromagnetic dissipation ability(RL-33.8 dB at 9.5 GHz),and the absorption bandwidth(RL<-10 dB)is 3.1 GHz(8.2-11.3GHz).(6)Porous nickel ferrite core-shell hollow microspheres/chiral polyaniline composites(PNFCSHM/CPANIs composites)exhibit strong microwave absorption capacity(RL=-33.75 dB at 10.93 GHz)and the effective absorption bandwidth is 4.52 GHz(8.52?12.94 GHz)with material thickness(2.3 mm).The minimum reflection loss of the microwave absorption or matching condition occurs when the thickness of the absorber approximates an odd number multiple of a quarter of the propagating wavelength.The matching frequency for minimum reflection loss decreases and the RL cuves shift to the lower frequency with increasing thicknesses of composites.Therefore,the purpose of improving the microwave absorbing performance can be improved by adjusting the matching thicknesses of composites.