Design And Realization Of Hard Foam Millimeter-wave Absorber Based On Electromagnetic Mixing Law

As mentioned in the white paper of the fifth generation of mobile communications(5th Generation,5G)development,5G commercial operation will be carried out in China by 2020,and the performance of the millimeter-wave mobile terminal testing needs Imminent.Being the wireless terminal testing equipment,millimeter-wave anechoic chamber needs to provide the clean environment without electromagnetic noise reflection.Its performance depends mainly on the absorptive capacity of millimeter-wave absorber.However,due to the increase of the communication frequency,the simulation calculation of the absorbing material become more demanding,and the electromagnetic wave is more sensitive to the dimensional accuracy and material uniformity,which forces the designer to face the new demand and challenge from the design method,the processing technology and the testing method.In this paper,a new kind of millimeter-wave absorbing material with foamed polypropylene as the base material is developed.Compared to the polyurethane sponge absorbing material that widely used in the anechoic chamber,the foamed polypropylene has advantages on moisture absorption,creeping and stable performance.The relative permittivity and dielectric loss of the material samples were measured by transmission/reflection method in the paper,and the characteristic parameters of samples were calculated by Nicolson-Ross-Weir(NRW)method from scattering parameters.The improvement of the accuracy in the measurement process is introduced and gives the method of measuring the relative electromagnetic parameters of the material.A kind of millimeter-wave absorber is designed with operating frequency over 20 to 40 GHz,which can achieve the performance below-40dB.In this paper,the mathematical model is used to analyze and optimize the design.And the finite element simulation software is used to solve the simulation model in high precision frequency domain,and the validity of the theoretical model is proved.The simulation software can use the periodic boundary conditions to simulate the performance parameters of the absorbing material and predict the performance indicators under various shapes and sizes.In the experimental part,mold injection molding process is employed to produce foam polypropylene millimeter wave absorbing material to control the processing of the size and shape of the accuracy.The performance parameters of the sample material are measured by the swing arm device.Comparing the results of the theoretical model,the simulation results of the simulation software and the actual measured data,we can find that the results are in good agreement.Because the theoretical model relies on the matrix operation of MATLAB,the calculation speed is far superior to the finite element simulation software,which can reduce the time cost in the early stage of millimeter wave absorbing material design,and hopefully become a high efficiency absorbing material design tool which can replace part numerical simulation in the future.