I am about to give a short seminar to our Mechanical Engineers and Designers
on enclosure design for EMC compliance. There is only one problem - I have
no faith in the theory I have for the attenuation through openings. The
following formula is from the "EMC Handbook", Vol 3, by Don White. Assuming
the frequencies of interest are below the waveguide cutoff frequency, the
formula is
A(dB) = KL/G - 20 log N where,
K = 32 for round holes or 27 for square holes
L = thickness of panel
G = hole diameter
N = number of holes.
According to this formula, one 1/4 inch hole in a 0.090 inch panel would
have an attenuation of 11 dB, and ten holes would have no attenuation
whatsoever. This does not match my experience in typical ITE. Does anyone
have any usable "rules of thumb" for Mechicanical types?
Richard Woods
Sensormatic Electronics
[email protected]
Views expressed by the author do not necessarily represent those of
Sensormatic.
