Research On Analytical Method For Shielding Effectiveness Of Perforated Shielding Enclosures

Metal shielding enclosure is one of the most common and effective shielding measures.Electronic equipments often need heat dissipation,external power supply,data transmission and so on,which lead to the complex apertures on the shielding enclosures of the electronic equipments.The apertures will reduce the shielding effectiveness of the shielding enclosures,and also bring challenges to the design and shielding characteristic analysis of the shielding enclosures.At present,numerical methods based on Maxwell's equations such as finite-difference time-domain method,method of moment,transmission line matrix modeling,finite element method and so on are the main method to analyze the shielding effectiveness of complex shielding enclosures.Based on numerical methods,mature commercial electromagnetic simulation software such as FEKO,CST and HFSS have been formed,which have certain dependence on the computer performance.Analytical method for shielding effectiveness of the perforated shielding enclosures has also been widely concerned due to its accuracy and efficiency.The equivalent circuit model of perforated enclosure is one of the representative analytical methods.In recent years,the equivalent circuit model has made remarkable progress in the calculation of shielding effectiveness of the enclosures under the conditions of regular enclosure,regular aperture,multi-faceted aperture and built-in metal structure.However,in practical engineering,the aperture structure of shielding enclosure may be complex and diverse,and there may be special structures such as penetrative conductor and cut-off waveguide at the aperture position.At the same time,we also need to face the problems of the arbitrariness of incident and polarized direction of plane wave and the complexity of higher order modes of shielding enclosure.It is of great theoretical and practical significance to further develop and improve the efficient calculation method of shielding effectiveness of perforated shielding enclosures.In this paper,the rectangular shielding enclosure is taken as the research object,around the problems such as complex apertures,penetrative conductors,external waveguide,based on the theory of transmission line,waveguide theory,theory of diffraction by holes and so on,we study the analytical method and analytical-numerical hybrid method of the shielding effectiveness of the perforated enclosure,which can provide guidance for electromagnetic compatibility design.The major innovation points of this dissertation are as follows.?1?We propose an analytical-numerical hybrid method based on Azaro's equivalent circuit model and full-wave numerical method to calculate the shielding effectiveness of the rectangular enclosure with circular aperture or rectangular aperture with arbitrary aspect ratio under the irradiation of plane wave.In the proposed hybrid method,the precise coupling voltage of apertures is calculated by TLM full-wave numerical method.The coupling voltage of the apertures is taken as the excitation source of the equivalent circuit model of the enclosure to calculate the equivalent voltage response of the enclosure analytically.The electric field components of higher order modes at any position inside the enclosure are calculated based on waveguide theory.The effects of incident plane wave elevation,azimuth,polarization angle and so on on the shielding effectiveness are simulated and analyzed.The simulation results show that the proposed hybrid method is in good agreement with TLM method,and can show higher computational accuracy compared with Azaro's model and Yin's model.The hybrid method requires much less simulation time than pure TLM full-wave numerical method on Windows platform.?2?We propose an analytical-numerical hybrid method based on Robinson's equivalent circuit model and full-wave numerical method to calculate the shielding effectiveness of the rectangular shielding enclosures with apertures of arbitrary shape or aperture arrays of arbitrary distribution under the irradiation of plane wave with arbitrary incident and polarization directions.In the proposed hybrid method,the S₂₁parameter of the perforated plate with apertures is calculated by TLM full-wave numerical method and used to estimate the aperture equivalent impedance.Based on the aperture equivalent impedance,the equivalent circuit model of the perforated enclosure is established,and the high-order mode equivalent voltage responses of the enclosure are calculated analytically.A modified Shim's plane wave decomposition technique is adopted to modify the equivalent voltage source and the position coefficient of the apertures using the magnetic field and electric field direction coefficient respectively,considering the effects of the electric field components perpendicular to the perforated plate.The simulation results show that the proposed hybrid method is in good agreement with TLM method,and can show higher computational accuracy compared with Shourvarzi's model,Shim's model and so on.The hybrid method requires much less simulation time than pure TLM full-wave numerical method on Windows platform.?3?We propose an analytical method based on the equivalent circuit of monopole antenna and dyadic Green's function of enclosure to calculate the shielding effectiveness at any position inside the rectangular shielding enclosures with cylindrical wire penetration under the irradiation of plane wave.In the proposed method,the wire is approximately equivalent to a pair of monopole antennas,and the four-element lumped-parameter equivalent circuit for monopole antenna is established.Based on dyadic Green's function of the rectangular enclosure and the eigenmode expansion of the electric field in the enclosure,the approximate solution of the electric field distribution in the enclosure is derived.Based on Bethe's theory and dyadic Green's function,the electric field leaking into the enclosure excited by the wire-penetrated aperture is derived.The effects of enclosure sizes,wire lengths,penetration positions,wire-penetrated aperture sizes and so on on the shielding effectiveness are simulated and analyzed.The simulation results show that the proposed method is in good agreement with TLM method and the simulation time of the proposed method is much less than TLM full-wave numerical method.?4?Based on Robinson's model,we propose an equivalent circuit model of the perforated enclosure with rectangular external waveguide to calculate the shielding effectiveness at any position inside the perforated rectangular enclosure with external waveguide under the irradiation of plane wave analytically.In the proposed model,the electromagnetic coupling process of the perforated enclosure with external waveguide is described by the equivalent circuit of the enclosure.The external waveguide is equivalent to a waveguide transmission line in which only the fundamental mode is excited,and the enclosure is modeled by a short-circuited waveguide.The influence of the position of the external waveguide on the shielding effectiveness of the enclosure is corrected by the aperture position coefficient.Based on waveguide theory,the high-order mode equivalent voltage responses at any position inside the enclosure are calculated.The effects of external waveguide positions,external waveguide lengths,cross section sizes of external waveguide and so on on the shielding effectiveness are simulated and analyzed.The simulation results show that the proposed model is in good agreement with TLM method and the simulation time of the proposed model is much less than TLM full-wave numerical method.