Research On Shielding Effectiveness Of Cavity Based On Mode Matching Method

With the continuous development of science and technology and the wide application of electronic technology,electromagnetic environment becomes increasingly complex,so it is very important to shield the electronic system.Although completely sealed and shielded cavity has the good shielding effectiveness,cavity can not be totally shielded for some reasons,such as the necessary of transmission line connection.Its surface is inevitable to open some apertures.These apertures will reduce the shielding effectiveness of cavity,even will produce huge influence.So it has practical application value to study the shielding effectiveness of cavity with apertures on its surface.First of all,using the hybrid algorithm of equivalent circuit method and electromagnetic topology theory(Robinson-EMT algorithm)to calculate the shielding effectiveness of cavity is presented.Because the Robinson-EMT algorithm has a larger deviation compared with CST software simulation results when the frequency is higher than 1.7 GHz.In order to calculate the shielding effectiveness under high frequency,this paper uses the hybrid algorithm of mode-matching method and the electromagnetic topology theory(MMM-EMT algorithm).The MMM-EMT algorithm takes the higher order mode into account when calculates the distribution of electromagnetic field in the shielded cavity.It improves the precision of the electromagnetic topology algorithm theory.For the MMM-EMT algorithm,by using the mode-matching method to describe Maxwell's equation at the aperture surface and taking the series expansion to express the electromagnetic field beside the both side of discontinuous surface,this paper can solve the aperture coupling matrix.The aperture coupling matrix is applied to the electromagnetic topology theory,and finally we can get the electromagnetic field distribution inside the cavity.The MMM-EMT algorithm is used to solve the shielding effectiveness of cavity in the case of central opening apertures,non-central opening apertures and central opening apertures matrix.The calculation results show that the MMM-EMT algorithm is closer to the simulation results of the CST software than the Robinson-EMT algorithm.When the time domain finite difference method is applied to the shielding efficiency of the cavity,There are often problems with the boundaries of semi-open and open areas.Due to the limited computing resources,the region truncation of the time domain finite difference method has a significant influence on the calculation accuracy and speed.Therefore,a hybrid algorithm of the mode-matching method and the time domain finite difference method(MMM-FDTD algorithm)is proposed.The MMM-FDTD algorithm uses the mode-matching method to solve the boundary problem of the time-domain finite difference method which not only insure the calculation speed but also improve the accuracy,by overcoming the limitation of the pattern matching method which can only be used in regular waveguide.Finally,the MMM-FDTD algorithm is used to solve the shielding efficiency of the double layer cavity with center and non-center apertures,and the solution proves that the MMM-FDTD algorithm is feasible.