| With the wide application of electronic products as well as the electromagnetic environment pollution being aggravating, electromagnetic interference(EMI) is more and more serious, the electromagnetic compatibility design requirements are also increasing. As an effective means to restrain EMI, shielding has been widely used in electronic equipments. Electromagnetic shielding takes advantage of the good conductor reflection, absorption and guidance of electromagnetic wave to realize electromagnetic isolation, resulting in resonance phenomenon of the shielding cavity. When the electromagnetic resonance occurs, the shielding effectiveness of the shielding encolsure will be drastically reduced, causing severe electromagnetic radiation and coupling problems. In this paper, the electromagnetic resonance characteristics and calculation methods of the shielding enclosure were studied thoroughly, so as to achieve the purpose of inhibition of electromagnetic resonance. The specific work is as follows:(1)Electromagnetic resonance mechanism of the shielding enclosure is analyzed. Three resonant forms, which are aperture resonance, cavity resonance and aperture-cavity coupling resonance, are studied based on the generalized network method, combining the waveguide theory and resonant cavity theory. And the occurrence conditions of resonances are obtained. Taking the aperture parameters into account, generalized formulas for resonant frequencies calculation are deduced. This part lays a theoretical foundation for the research process behind.(2)Research on calculation method of electromagnetic resonance of the cavity with slots. According to the condition of resonance, a fast computational scheme for resonant frequencies of a cavity with a slot on its wall is proposed based on the impedance of cavity backed slot antenna. Then the effects of structure parameters such as cavity size, slot length and slot offset on the resonant frequency are discussed. This part provides a theoretical basis and technical guidance for reducing the harm of electromagnetic resonance in structure design of the shielding enclosure.(3)Research on calculation method of electromagnetic resonance of the cavity with an aperture array. Through the analysis of the Transmission characteristics of a periodic aperture array on the infinite plate, a method to calculate the shielding properties of the cavity with an aperture array is proposed based on the periodic boundary condition, the method of moments and mode-matching technique. In this method, the Floquet theory is used to deal with the periodic aperture array by taking an unit cell into account, resulting in considerably savings in computation resources and simplification in computational complexity. Then the resonance phenomenon of the cavity is analyzed from the viewpoint of transmission coefficient, and the effects of the incident angle, array element spacing and aperture dimension on the shielding properties are discussed.(4)Analysis of influencing factors on resonance mode. The structural parameters such as polarization parameters, aperture position, the number of apertures and the apertures on differential cavity walls which may excite differential cavity resonant modes have been investigated by theoretical analysis and simulations. And the rules of influence of these parameters on resonant modes have been obtained which is beneficial to judge the resonant modes of cavity with apertures in engineering practice. |
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