Research On Electromagnetic Shielding Effectiveness Of The Conductor Plate With Periodic Apertures

With the continuous development of the power grid construction,the number and types of electrical and power electronic equipment are constantly being enriched.The use of these power electronic equipment not only facilitate our daily life,but also further aggravates the complexity of the electromagnetic environment,which may increase the possibility that other equipment is interfered.Electromagnetic shielding is one of the effective ways to prevent equipment from electromagnetic interference,which is always measured by the shielding effectiveness(SE).The purpose of electromagnetic shielding is to "cut off" the electromagnetic waves from the propagation path,which effectively weaken the interference electromagnetic waves.The shielding effect of the complete metal conductor plate is usually pretty well.Due to the needs of ventilation,observation,it is necessary to open more than one aperture for the conductor plate.At present,there have been many researches focus on the shielding plate with a single hole or slit,but the research on the periodic apertures structure is relatively lacking.This thesis focuses on the electromagnetic shielding effectiveness of a conductor plate with arrays of apertures.Firstly,based on the Bethe's theory,the analytical model of the shielding effectiveness is derived for different polarization mode with different angles of incidence.It is shown that the SE is proportional to the aperture magnetic polarization coefficient,the wave frequency,and is inversely to the area of a periodic unit.The results are in good agreement with those from full wave simulation software.Secondly,the SE prediction of the periodic aperture array of different size on an infinite conductor plate against a plane electromagnetic wave is analyzed.Especially,the existing analytical expressions of SE are combined to cover the entire range of the aperture rate,which is defined as the ratio of the side length of the aperture to that of the unit cell.The combination is carried out by bridging the small aperture model and the wire mesh model.Then,a multi-stage model based on the piecewise function of the aperture rate is presented to calculate the shielding effectiveness for any aperture rate.The model is also extended to consider different wave polarization and incident angles.The applicability of the model is discussed.Also,the upper-limit frequency at which the model is no longer applicable is analyzed.Furthermore,a theoretical model is established for the shielding effectiveness of the infinite PEC plate with the periodic circular apertures against the low frequency(?1 MHz)magnetic field resulted from a current loop parallel to the plate.Experiments were used to verify the theoretical model.The results show that the model has a critical frequency.The theoretical results are in good agreement with the measurement if the frequency is higher than a critical frequency.Finally,the magnetic field shielding effectiveness of the metal conductor wire mesh under the excitation of a current loop is studied,and the analytical model is derived by the separation variable method and the surface impedance boundary conditions.Combining experiments and models,it can be obtained that the shielding effectiveness first increases with frequency,then remains constant,and finally decreases.