| Low-frequency magnetic shielding is frequently adopted to prevent electromagnetic interference in many practical applications,such as electric vehicles,wireless power transfer,power converters,ultrasensitive atomic sensors,resistance spot welding,magnetic resonance imaging,power transformers and high-power power electronic equipment.Shielding is the main technical means to weaken the magnetic field.Depending on specific requirements and the working environment,different shielding configurations are selected,such as enclosures,wire meshes,solid plates,and perforated plates.This thesis focuses on wave impedance calculations employed in the transmission line analogy for the low-frequency magnetic shielding problem.Firstly,for the current loop of any shape parallel to the shielding plate,the frame solution of the electromagnetic field distribution in the form of infinite integral is derived by using the method of separation of variables,and a unified formula for the calculation of wave impedance is derived by theoretical analysis.The unified formula for wave impedance calculations is distinct from traditional definitions of the transverse E-field to H-field ratio,which is related to the ratio of the H-field components to its longitudinal derivative.The formula is relatively simple in terms of mathematical complexity when applied to derive a concrete wave impedance expression.For a circular loop,the formula produces the same wave impedance expression as the traditional definition for field points on the central axis of the loop.For field points off the axis,the formula more accurately predicts the shielding effectiveness relative to traditional definitions,and the formula is applicable in a wide range of covering typical practical applications.Based on the proposed formula,we also obtain wave impedance expressions for rectangular,elliptical,and regular polygon loops under quasi-static assumptions.The effectiveness of these expressions is verified through comparisons with finite element simulations.Secondly,the field formulas of the electric dipole in free space and the presence of the metal plate were deduced.According to the field formula of free space and field formulas after shielding,the wave impedance formula of the transmission line calculation model for the electric field shielding effectiveness when the electric dipole vertical conductor plate is arranged was deduced,and the effective verification was carried out.Finally,a preliminary calculation and analysis of the relationship between the shielding effectiveness of the electric dipole and the shielding effectiveness of the magnetic dipole and the shielding effectiveness of the plane wave are carried out. |
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