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				Penetration of a plane electromagnetic wave through the apertures on a perfectly conducting flat plate is a classical electromagnetic problem. In some practical applications like electromagnetic shielding, where only the fields far from the apertures are concerned and the aperture sizes are small compared with a wavelength, the role of apertures can be represented by the equivalent electric and magnetic dipoles located in the centers of the apertures. In principle, the penetration field can be expressed as the superposition of the radiation fields of the dipoles. However, the direct superposition leads to a double series with complex form and poor convergence. On the other hand, this problem may also be solved by full wave numerical simulations. Even so, finding analytical solutions is still desirable considering that it is clear in physical significance and easy to implement. In this paper, the analytical formula of the penetration fields are derived for both TE and TM polarization mode with different angles of incidence. The derivation is carried out firstly by averagely distributing each dipole moment within each periodic unit. As a result, the dipole array is replaced with a flat sheet with uniform magnetization and polarization intensity. Then, the equivalent surface current and charge distributions are obtained directly from the polarization intensity. Finally, the penetration fields are treated as the radiation fields of the surface sources. It is shown that the amplitude of the penetration field is proportional to aperture magnetic polarization coefficient and wave frequency, and it is inversely proportional to the area of a periodic unit. In regard to the effect of the incidence angle, the amplitude of the penetration field is proportional to the cosine of the incidence angle for TE polarization. However, for the TM polarization, the relationship is a little complicated due to the coexistence of electric and magnetic dipoles: the field is not rigorously inversely proportional to the cosine of the incidence angle due to the existence of a correction term involving both the polarization coefficient and the sine of the angle. The formula is used to calculate the shielding effectiveness for several different aperture shapes and different incidence angles. The results are in good agreement with those from the full wave simulation software.- 
										Keywords:
										
- electromagnetic shielding /
- aperture coupling /
- Bethe’s theory /
- polarizability coefficient
 [1] 阚勇, 闫丽萍, 赵翔, 周海京, 刘强, 黄卡玛 2016 物理学报 65 030702  Google Scholar Google ScholarKan Y, Yan L P, Zhao X, Zhou H J, Liu Q, Huang K M 2016 Acta Phys. Sin. 65 030702  Google Scholar Google Scholar[2] Mcdowell A J, Hubing T H 2014 IEEE Trans. Electromagn. Compat 56 1711  Google Scholar Google Scholar[3] 焦重庆, 牛帅, 李琳 2015 电工技术学报 30 1  Google Scholar Google ScholarJiao C Q, Niu S, Li L 2015 Transactions of China Electrotechnical Society 30 1  Google Scholar Google Scholar[4] 罗静雯, 杜平安, 任丹, 聂宝林 2015 物理学报 64 010701  Google Scholar Google ScholarLuo J W, Du P A, Ren D, Nie B L 2015 Acta Phys. Sin. 64 010701  Google Scholar Google Scholar[5] 段兴跃, 李小康, 程谋森, 李干 2016 物理学报 65 197901  Google Scholar Google ScholarDuan X Y, Li X K, Cheng M S, Li G 2016 Acta Phys. Sin 65 197901  Google Scholar Google Scholar[6] Nie B L, Du P A, Yu Y T, Shi Z 2011 IEEE Trans. Electromagn. Compat. 53 73  Google Scholar Google Scholar[7] 任丹, 杜平安, 聂宝林, 曹钟, 刘文奎 2014 物理学报 63 120701  Google Scholar Google ScholarRen D, Du P A, Nie B L, Cao Z, Liu W K 2014 Acta Phys. Sin. 63 120701  Google Scholar Google Scholar[8] 焦重庆, 牛帅 2013 物理学报 62 114102  Google Scholar Google ScholarJiao C Q, Niu S 2013 Acta Phys. Sin. 62 114102  Google Scholar Google Scholar[9] Zhao Y L, Ma F H, Li X F, Ma J J, Jia K 2018 Chin. Phys. B 27 027302  Google Scholar Google Scholar[10] 彭强, 周东方, 侯德亭, 余道杰, 胡涛, 王利萍, 夏蔚 2013 强激光与粒子束 25 2355 Peng Q, Zhou D F, Hou D T, Yu D J, Hu T, Wang L P, Xia W 2013 High Power Laser and Particle Beams 25 2355 [11] Li B, Dong H, Huang X L, Qiu Y, Tao Q, Zhu J M 2018 Chin. Phys. B 27 020701  Google Scholar Google Scholar[12] 毛湘宇, 杜平安, 聂宝林 2009 系统仿真学报 21 7493 Mao X Y, Du P A, Nie B L 2009 Journal of System Simulation 21 7493 [13] Frikha A, Bensetti M, Duval F, Benjelloun N, Lafon F, Pichon L 2015 IEEE Trans. Magn. 51 1 [14] García-Pérez L G, Lozano-Guerrero A J, Blázquez-Ruiz J M, Valenzuela-Valdés J F, Monzó-Cabrera J, Fayos-Fernández J, Díaz-Morcillo A 2017 IEEE Trans. Electromagn. Compat. 59 789  Google Scholar Google Scholar[15] Benhassine S, Pichon L, Tabbara W 2002 IEEE Trans. Magn. 38 709  Google Scholar Google Scholar[16] Ali S, Weile D, Clupper T 2005 IEEE Trans. Electromagn. Compat. 47 367  Google Scholar Google Scholar[17] Wallyn W, De Zutter D, Rogier H 2002 IEEE Trans. Electromagn. Compat. 44 130  Google Scholar Google Scholar[18] 焦重庆, 李顺杰 2016 电工技术学报 31 112  Google Scholar Google ScholarJiao C Q, Li S J 2016 Transactions of China Electrotechnical Society 31 112  Google Scholar Google Scholar[19] Robinson M P, Benson T M, Christopoulos C, Dawson J F, Ganley M D, Marvin A C, Porter S J, Thomas D W P 1998 IEEE Trans. Electromagn. Compat. 44 240 [20] 焦重庆, 齐磊 2012 物理学报 61 134104  Google Scholar Google ScholarJiao C Q, Qi L 2012 Acta Phys. Sin. 61 134104  Google Scholar Google Scholar[21] Otoshi T Y 1972 IEEE Trans. Microwave Theory Tech. 20 235  Google Scholar Google Scholar[22] Hyun S Y, Jung I, Hong I P, Jung C, Kim E J, Yook J G 2016 IEEE Trans. Electromagn. Compat. 58 911  Google Scholar Google Scholar[23] Bethe H A 1944 Phys. Rev. 66 163  Google Scholar Google Scholar[24] Nitsch J B, Tkachenko S V, Potthast S 2012 IEEE Trans. Electromagn. Compat. 54 1252  Google Scholar Google Scholar[25] Tesche F M, Ianoz M V, Karlsson T 1997 EMC Analysis Methods and Computational Models(New York: John Wiley& Sons)pp208—211 [26] Cohn S B 1951 Proc. IRE 39 1416  Google Scholar Google Scholar
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表 1 常见开孔形状极化系数 Table 1. Polarization coefficients of typical opening shapes. 孔形状 ${\alpha _{\rm{e}}}$ ${\alpha _{{\rm{m}}x}}$ ${\alpha _{{\rm{m}}y}}$ 圆形(r为半径) $\frac{{2{r^3}}}{3}$ $\frac{{4{r^3}}}{3}$ $\frac{{4{r^3}}}{3}$ 椭圆(l为长轴,沿x方向,w为短轴) $\frac{{\text{π}}}{{24}} \cdot \frac{{{w^2}l}}{{{\rm{E}}(e)}}$ $\frac{{\text{π}}}{{24}} \cdot \frac{{{e^2}{l^3}}}{{K(e) - E(e)}}$ $\frac{{\text{π}}}{{24}} \cdot \frac{{{e^2}{l^3}}}{{{{(l/w)}^2}E(e) - K(e)}}$ 
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[1] 阚勇, 闫丽萍, 赵翔, 周海京, 刘强, 黄卡玛 2016 物理学报 65 030702  Google Scholar Google ScholarKan Y, Yan L P, Zhao X, Zhou H J, Liu Q, Huang K M 2016 Acta Phys. Sin. 65 030702  Google Scholar Google Scholar[2] Mcdowell A J, Hubing T H 2014 IEEE Trans. Electromagn. Compat 56 1711  Google Scholar Google Scholar[3] 焦重庆, 牛帅, 李琳 2015 电工技术学报 30 1  Google Scholar Google ScholarJiao C Q, Niu S, Li L 2015 Transactions of China Electrotechnical Society 30 1  Google Scholar Google Scholar[4] 罗静雯, 杜平安, 任丹, 聂宝林 2015 物理学报 64 010701  Google Scholar Google ScholarLuo J W, Du P A, Ren D, Nie B L 2015 Acta Phys. Sin. 64 010701  Google Scholar Google Scholar[5] 段兴跃, 李小康, 程谋森, 李干 2016 物理学报 65 197901  Google Scholar Google ScholarDuan X Y, Li X K, Cheng M S, Li G 2016 Acta Phys. Sin 65 197901  Google Scholar Google Scholar[6] Nie B L, Du P A, Yu Y T, Shi Z 2011 IEEE Trans. Electromagn. Compat. 53 73  Google Scholar Google Scholar[7] 任丹, 杜平安, 聂宝林, 曹钟, 刘文奎 2014 物理学报 63 120701  Google Scholar Google ScholarRen D, Du P A, Nie B L, Cao Z, Liu W K 2014 Acta Phys. Sin. 63 120701  Google Scholar Google Scholar[8] 焦重庆, 牛帅 2013 物理学报 62 114102  Google Scholar Google ScholarJiao C Q, Niu S 2013 Acta Phys. Sin. 62 114102  Google Scholar Google Scholar[9] Zhao Y L, Ma F H, Li X F, Ma J J, Jia K 2018 Chin. Phys. B 27 027302  Google Scholar Google Scholar[10] 彭强, 周东方, 侯德亭, 余道杰, 胡涛, 王利萍, 夏蔚 2013 强激光与粒子束 25 2355 Peng Q, Zhou D F, Hou D T, Yu D J, Hu T, Wang L P, Xia W 2013 High Power Laser and Particle Beams 25 2355 [11] Li B, Dong H, Huang X L, Qiu Y, Tao Q, Zhu J M 2018 Chin. Phys. B 27 020701  Google Scholar Google Scholar[12] 毛湘宇, 杜平安, 聂宝林 2009 系统仿真学报 21 7493 Mao X Y, Du P A, Nie B L 2009 Journal of System Simulation 21 7493 [13] Frikha A, Bensetti M, Duval F, Benjelloun N, Lafon F, Pichon L 2015 IEEE Trans. Magn. 51 1 [14] García-Pérez L G, Lozano-Guerrero A J, Blázquez-Ruiz J M, Valenzuela-Valdés J F, Monzó-Cabrera J, Fayos-Fernández J, Díaz-Morcillo A 2017 IEEE Trans. Electromagn. Compat. 59 789  Google Scholar Google Scholar[15] Benhassine S, Pichon L, Tabbara W 2002 IEEE Trans. Magn. 38 709  Google Scholar Google Scholar[16] Ali S, Weile D, Clupper T 2005 IEEE Trans. Electromagn. Compat. 47 367  Google Scholar Google Scholar[17] Wallyn W, De Zutter D, Rogier H 2002 IEEE Trans. Electromagn. Compat. 44 130  Google Scholar Google Scholar[18] 焦重庆, 李顺杰 2016 电工技术学报 31 112  Google Scholar Google ScholarJiao C Q, Li S J 2016 Transactions of China Electrotechnical Society 31 112  Google Scholar Google Scholar[19] Robinson M P, Benson T M, Christopoulos C, Dawson J F, Ganley M D, Marvin A C, Porter S J, Thomas D W P 1998 IEEE Trans. Electromagn. Compat. 44 240 [20] 焦重庆, 齐磊 2012 物理学报 61 134104  Google Scholar Google ScholarJiao C Q, Qi L 2012 Acta Phys. Sin. 61 134104  Google Scholar Google Scholar[21] Otoshi T Y 1972 IEEE Trans. Microwave Theory Tech. 20 235  Google Scholar Google Scholar[22] Hyun S Y, Jung I, Hong I P, Jung C, Kim E J, Yook J G 2016 IEEE Trans. Electromagn. Compat. 58 911  Google Scholar Google Scholar[23] Bethe H A 1944 Phys. Rev. 66 163  Google Scholar Google Scholar[24] Nitsch J B, Tkachenko S V, Potthast S 2012 IEEE Trans. Electromagn. Compat. 54 1252  Google Scholar Google Scholar[25] Tesche F M, Ianoz M V, Karlsson T 1997 EMC Analysis Methods and Computational Models(New York: John Wiley& Sons)pp208—211 [26] Cohn S B 1951 Proc. IRE 39 1416  Google Scholar Google Scholar
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