At recent symposium in Santa Clara, I talked to some length with one of the speakers about round holes in shielding for ventilation. For all the equations I've seen and tried to verify, they really don't pose a problem with the work I've done. But, that's strictly my experience and that in itself is limited to some others here.
Slots are the things to watch out for because in my experience they have caused alot of problems. Now, mechanical types I find are the best to teach EMI issues. Why? Because they aren't all cluttered up with Maxwell and integral vs. differential forms ... Just remember: Slots are wires incognito. Regards, Doug WOODS, RICHARD wrote: > > 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.
