| With the development of modern signal processing technology and printed circuit board production technology, integrated circuits with high-density, multilayer, high speed signal processing ability and small size have been widely used. Increase of the density of printed circuit board can raise the information processing efficiency, this may also cause serious electromagnetic interference problems at the same time. Electromagnetic compatible problems in printed circuit boards have become one of the important factors which can determine whether the circuit board, even the whole system can function properly.In this thesis, we proposed a novel analyzing and prediction method of the electromagnetic interference in the printed circuit boards. The study object is high frequency printed circuit and the purpose of this research is to build the equivalent model of the electromagnetic interferences generated by printed circuit board under a certain working condition, which includes micro-strip line, components, dielectric layers etc. Then finite difference time domain (FDTD) algorithm is used to calculate the electromagnetic field generated by the equivalent dipole model, the location of interference source on the printed circuit board and the electromagnetic field distribution regularities on the surface of the printed circuit can be determined, thus can provide theoretical guidance and reference in practice.The main works in this thesis includes the following parts:(1) The near-field scanning technology and equivalent dipole modeling method are combined to build the equivalent model of the electromagnetic interference of the printed circuit board. The printed circuit can be replaced by an array of equivalent dipoles and the electromagnetic field generated by this equivalent model can replace that produced by the printed circuit. We deduced the relationship between the equivalent dipoles and the magnetic field obtained from near-field scanning. Magnetic field data gained by measuring the surface of the printed circuit board can be used to determine the parameters in the equivalent dipole model. In this part, the comprehensive model of the near-field electromagnetic interference of the target printed circuit board was built and the electromagnetic interference generated by the printed circuit in the open space was simulated.(2) FDTD algorithm and Yee cells were used to build the propagation space of the electromagnetic field generated by the equivalent dipole model. The iterative equations and the parameters of the electric and magnetic field in the FDTD calculation space were deduced.Based on the area of the under test printed circuit board, the characteristics of the medium, the size of the calculation space, the spatial step, the time step and the excitation source in the calculation space can be determined.(3) The boundary conditions of the equivalent dipole model's calculation space was studied, and uniaxial perfectly matched layer is used as the absorbing boundary, the parameters and the FDTD iterative equations in this material were calculated, then the thickness of the absorbing boundary was determined by theory analysis and numerical experiment.(4) To verify the analysis and prediction results of the electromagnetic interference prediction model of the printed circuit board. The equivalent model is built and calculated,finally we can realize our purpose to analyze and predict the electromagnetic interference over different height of the surface of the printed circuit board. In order to verify the universality of this model,the same method was used to build the equivalent dipole models of the area where resistances and capacitances are densely distributed and the power supply area to predict the electromagnetic interference over them. The near-field measuring result and the test result in the standard anechoic chamber verified the correctness and accuracy of the equivalent dipole model. The method proposed in this thesis has great potential applications and significance in science. |
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