Research On Shielding Effectiveness Of Double Layer Enclosure

With the rapid development of electronic technology, electronic systems have become highly complex, and often the shielding cavities are divided into a number of spaces. In addition, massive electronic equipment is designed to be in the same compact and tiny space due to the highly integrated and complex systems. Although they are distributed to different areas, the electromagnetic interference (EMI) among electronic equipment, especially the near-field EMI, cannot be ignored due to the increasingly complexity of electromagnetic environment and the universal existence of the apertures. Unlike the far-field EMI, the near-field EMI is more fluctuated and variable, which increases difficulties in studying electromagnetic aperture coupling problems and designing complex enclosures.In this paper, the electromagnetic leakage from the adjacent enclosures is considered as the near-field EMI, and the near-field shielding effectiveness (SE) of double layer metallic enclosures is studied. First, an analytical formulation has been developed for the SE of a double layer metallic enclosure against the near-field electromagnetic waves. The near-field EMI is represented by an electric dipole in the external layer of the enclosure, and then the equivalent magnetic and electric dipole moments in the center of the aperture are calculated according to the Bethe’s small aperture coupling theory, and finally the electromagnetic field of the internal layer of the enclosure is calculated by using the equivalent magnetic dipole field, the electric dipole field and the cavity Green’s function for the SE of the target point. In this formulation, the SE can be expressed as a function of the target point, the source point, the position and the shape of the aperture, and the conductivity of the enclosure. The formulation then is employed to analyze the influences of the above factors on the SE. Then, a hybrid formulation has been developed for the SE of a double layer metallic enclosure with capacitive window structures against the near-field electromagnetic waves. The capacitive windows are regarded as rectangular apertures. Apertures can be divided into narrow apertures and wide apertures, and then the electromagnetic field of the internal layer of the enclosure is calculated by using the method of equivalent magnetic dipoles and the method of moments (MoM) respectively for the SE of the target point. In this formulation, the SE can be expressed as a function of the target point, the opening width of the capacitive windows and the center point of the capacitive windows. The formulation then is employed to analyze the influences of the above factors on the SE. Finally, an analytical formulation has been developed for the SE of a double layer metallic enclosure with an inner strip-shaped metallic plate against the near-field electromagnetic waves based on the first analytical formulation above. The model is also based on the Bethe’s small aperture coupling theory to calculate the equivalent magnetic and electric dipole moments in the center of the aperture, and then the electromagnetic field of the internal layer of the enclosure is calculated by using the equivalent magnetic dipole field, the electric dipole field and the generalized cavity Green’s function for the SE of the target point. In this formulation, the SE can be expressed as a function of the position and the angle of the strip-shaped metallic plate. The formulation then is employed to analyze the influences of the above factors on the SE. Comparison with the full wave simulation software CST(Computer Simulation Technology)has verified the important formulation over a very broad frequency range, which provides a theoretical reference for the rapid calculation of the SE of complex enclosures.