radiation
absorption
attenuation
  
attenuation


Attenuation progression of enclosures without EMC seal:

Enclosures with slots and holes, no matter how small these may be, cannot possibly be "EMC sealed". The reason for this is the nature of electromagnetic waves. The relationship between slot length/hole diameter and the frequency passing through can be described as follows: the larger the aperture, the more radiation can pass through. This is also the reason fro the 0dB attenuation in the 500 - 700 Mhz range. Another important aspect is that apertures should be closed electronically i.e. that enclosure parts (lod, base) should have a good bonding over the entire bearing surface. For illustration of the above, take a look at the following drawing:

Values for attenation of enclosures with and without EMC seal

Frequency in MHz with enclosure lid with enclosure lid and EMC seal a in dB a in dB with EMC seal
30,00 1,20 1,40 20,00 23,34
54,25 1,60 1,80 26,67 30,01
78,50 1,80 1,90 30,01 31,67
102,75 2,00 2,10 33,34 35,01
127,00 2,10 2,40 35,01 40,01
151.25 2,00 2,40 33,34 40,01
175,50 2,00 2,60 33,34 43,34
199,75 1,80 2,50 30,01 41,68
224,00 1,40 2,10 23,34 35,01
248,25 1,00 1,90 16,67 31,67
272,50 1,20 2,10 20,00 35,01
296,75 1,70 2,40 28,34 40,01
312,00 1,70 2,80 28,34 46,68
345,25 2,10 3,10 35,01 51,68
369,50 1,60 3,10 26,67 51,68
393,75 1,20 3,00 20,00 50,01
418,00 1,00 2,90 16,67 48,34
442,25 0,80 2,70 13,34 45,01
490,75 0,40 2,60 6,67 43,34
515,00 0,00 2,50 0,00 41,68
539,25 0,10 2,30 0,00 38,34
563,50 0,10 2,20 1,67 36,67
587,75 0,00 2,10 1,67 35,01
612,00 0,00 2,00 0,00 33,34
636,25 0,00 1,90 0,00 33,34
660,50 0,20 1,90 0,00 31,67
684,75 0,40 1,90 3,33 31,67
709,00 0,30 1,70 0,00 28,34
733,25 0,90 2,50 5,00 41,68
757,50 1,60 2,40 15,00 40,01
781,75 1,90 2,60 26,67 43,34
806,00 2,00 2,90 31,67 48,34
830,25 2,00 2,90 33,34 48,34
854,50 1,90 3,10 31,67 51,68
878,75 1,70 3,20 28,34 53,34
903,00 1,40 3,20 23,34 53,34
927,25 0,90 3,10 15,00 51,68
951,50 1,10 3,00 18,34 50,01
975,75 1,00 3,00 16,67 50,01
1000,00 1,30 2,90 21,67 48,34
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