I've read (I think on wikipedia, but I can't find the reference) that microwave oven leakage is often due to faulty seals on the door. Given that any gap in the door is going to be far smaller than 10% of the wavelength, how is it possible for the microwaves to leak through? Shouldn't the Faraday cage function perfectly?
[Physics] 2.4Ghz microwaves have a 12cm wavelength. How do microwave ovens leak radiation, since any gap in the shielding is much smaller than that wavelength
electromagnetic-radiationmicrowaves
Best Answer
Two things are going on. First - the conductivity of the shielding of the microwave oven is "only so good": the skin effect in particular results in the electrical currents running in only a very superficial layer of the conductor, and this means there is some phase lag (and incomplete reflection, i.e. some transmission of power).
Second, gaps do occur. In a well designed microwave the gaps have compliant conductive seals; but if these lose their springiness I can see how currents flowing around the gap will result in re-emission of microwave energy. You don't need a 2D opening: just a gap that is "long and thin" is sufficient to act as an antenna. Where "long" is a few cm (1/4 of a wavelength). See for example this diagram:
from http://www.interferencetechnology.com/in-situ-emc-testing-using-surface-current-sense-wires-1/ which describes some of the techniques behind using such an "antenna".