Quantcast Screens and Perforated Metal Shields -Cont. - hdbk419a_vol10269

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MIL-HDBK-419A
The multi-reflection correction term is
The number of openings correction factor is
The skin depth correction factor is
Finally, the hole-coupling correction factor is given by
The screen's shielding effectiveness, SE, is the sum of the six factors:
SE = 13.5 + 33.2 - 0.4 + 3.5 - 4.2 + 0.8
= 46.4 dB.
Figure 8-18 presents both calculated and measured values of shielding effectiveness for several types of copper
Representative non-solid sheet shielding effectiveness
screen located 1.75 inches from a loop antenna.
measurements are shown in Tables 8-12 and 8-13. The two tables provide data on a variety of material forms,
including meshes, perforated sheets, and cellular structures against low-impedance, high-impedance, and plane
waves.
Figures 8-19 and 8-20 illustrate how the effectiveness of perforated sheet material changes with
changes in hole size and hole separation. Table 8-14 contains both calculated and measured values of shielding
effectiveness for the No. 22, 15 mil copper screen of the example for magnetic, plane, and electric waves of
The shielding effectiveness of the screen is seen to increase with the frequency for
several frequencies.
magnetic fields, to decrease with increasing frequency for plane waves, and to be largely independent of
frequency for electric fields.
8-36





 


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