Opening leakage for enclosures at low and high frequencies

Opening leakage for shielded enclosures is reviewed for low and high frequencies. Empirical formulas based on quasi-static approximations are presented for low frequencies corresponding to wavelengths greater than six times the enclosure dimensions. Modal resonances that occur at high frequencies are discussed for single isolated modes, overlapping modes, and very dense modal spectra. Lower and upper bounds are defined for shielding effectiveness. Values of shielding effectiveness calculated by modal analysis are compared to approximate values calculated by the black-hole principle