Effect of aperture on shielding performance of metal cavity under excitation of high-intensity electromagnetic pulse
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摘要: 核电磁脉冲和高功率微波等强电磁脉冲易造成电子设备功能失效甚至损毁，在实际工程实施中用金属腔体对电子设备进行屏蔽是常用的强电磁脉冲抑制手段。基于电磁仿真计算，对含矩形孔缝金属腔体的强电磁脉冲耦合特性进行了系统研究，阐述了孔缝宽长比、腔体尺寸等因素对多种不同类型强电磁脉冲（核电磁脉冲、宽带高功率微波、窄带高功率微波）作用下腔体内耦合场的影响；并以此为基础，重点分析了强电磁脉冲与含孔缝金属腔体之间的作用机制。研究结果表明：不同类型强电磁脉冲耦合信号差异明显，金属腔体对强电磁脉冲的响应是腔体谐振模式、孔缝谐振频率与强电磁脉冲共同作用的结果；当腔体谐振模式、孔缝谐振频率在强电磁脉冲的带内时，腔体内部的耦合场会出现增强效应；特别地，腔体与孔缝间的相互作用还可造成腔体与缝隙的谐振频率发生偏移。因此，在为电子设备设计金属屏蔽外壳时，应基于不同强电磁脉冲的频带范围，对腔体与孔缝的尺寸进行综合设计，抑制腔体、孔缝谐振及谐振频率偏移，提升其强电磁脉冲防护性能。Abstract: High-intensity electromagnetic pulses like high-altitude electromagnetic pulse (HEMP), high power microwave (HPM) are very harmful to electronic devices, which will cause malfunction or even damage to electronics. Using metallic cavity to isolate electronic systems from high-intensity electromagnetic pulse is an important and effective way to lessen the effect. Herein, we performed a systematic study on coupling property of metallic cavity with a rectangular aperture under the excitation of three types of high-intensity electromagnetic pulses, i.e., HEMP, wide-band HPM, and narrow-band HPM. The width/length ratio of aperture and cavity size were varied to investigate their effect on electromagnetic coupling. The interaction mechanism of high-intensity electromagnetic pulses and the metallic cavity was also carefully analyzed. The results demonstrate that the shielding property of metallic cavity is highly dependent on resonance mode of cavity, resonant frequency of aperture as well as the spectral characteristics of high-intensity electromagnetic pulse. When the resonance mode of cavity, and/or resonant frequency of aperture are within the bandwidth of high-intensity electromagnetic pulse, an enlarged coupling electromagnetic field in the metallic is always produced. Specifically, the interaction between the cavity and aperture can give rise to spectral shift of resonant frequency. Therefore, to obtain excellent shielding effect, we need to take into consideration the suppression of resonance mode of cavity, resonant frequency of apertureas well as the spectral shift when performing electromagnetic protection of electronic devices.
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图 1 典型的强电磁脉冲波形与频谱分布
Figure 1. Typical high-intensity electromagnetic pulses and their corresponding spectral distributions
图 3 三种强电磁脉冲辐照下典型腔体中心位置场强波形与频谱
Figure 3. Electric field and the corresponding spectral characteristics at the central position of metallic cavity
图 4 具有不同宽长比孔缝金属腔体强电磁脉冲耦合场波形
Figure 4. Coupling electric field of metallic cavity with different W/L under excitation of high-intensity electromagnetic pulse
图 5 孔缝宽长比对金属腔体强电磁脉冲耦合场峰值影响
Figure 5. Evolution of peak value of the coupling electric field with W/L of metallic cavity under the excitation of high-intensity electromagnetic pulse
图 6 腔体尺寸对场强峰值的影响
Figure 6. Influence of cavity size on the peak value of coupling electric field
图 8 不同尺寸腔体在核电磁脉冲作用下场强频谱随孔缝宽长比的变化
Figure 8. Electric field and the corresponding spectral characteristics at the central position of metallic cavity under the excitation of HEMP
图 9 不同尺寸腔体在宽带高功率微波作用下场强频谱随孔缝宽长比的变化
Figure 9. Electric field and the corresponding spectral characteristics at the central position of metallic cavity under the excitation of WB-HPM
图 10 不同尺寸腔体在窄带高功率微波作用下场强频谱随孔缝宽长比的变化
Figure 10. Electric field and the corresponding spectral characteristics at the central position of metallic cavity under the excitation of NB-HPM
图 11 孔缝宽长比对金属腔体强电磁脉冲屏蔽效能影响
Figure 11. Evolution of the shielding effectiveness of metallic cavity with W/L under the excitation of high-intensity electromagnetic pulse
表 1 典型金属腔体强电磁脉冲耦合性能
Table 1. Electromagnetic coupling of metallic cavity to different high-intensity electromagnetic pulses
electromagnetic pulse peak value of electromagnetic field/（kV·m−1） time domain shielding effectiveness/dB HEMP 3.2 23.9 WB-HPM 47.8 0.4 NB-HPM 22.8 6.8 
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表 2 具有不同宽长比孔缝的金属腔体
Table 2. Metallic cavity having aperture with different width to length ratio (W/L)
No. W/cm L/cm W/L note 1 2 30 ～0.07 polarization direction is identical to the aperture direction 2 8 7.5 1.07 nearly a square aperture 3 20 3 6.67 polarization direction is orthogonal to the aperture direction
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表 3 孔缝最小谐振频率
Table 3. Minimum resonant frequency of aperture
No. W/cm L/cm W/L estimated fmin/MHz simulation fmin/MHz 1 2.0 30.0 ～0.07 500 449 2 2.8 21.4 0.13 700 606 3 3.2 18.75 0.17 800 680 4 4.0 15.0 0.27 1000 832 5 4.4 13.6 0.32 1103 911 6 6.0 10.0 0.60 1500 1198 7 8.0 7.5 1.07 2000 1654
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