New Technique for the Determination of the Integrity of Shielded Enclosures by the Measurement of the Perpendicular Magnetic Field

A solution of electromagnetic field equations with appropriate boundary conditions shows that at the surface of a material with infinite conductivity, no parallel electric field or perpendicular magnetic field exists. As conductivity decreases, there are large relative increases in the parallel electric field and perpendicular magnetic field at the surface. A reduction in permeability lowers the parallel electric field while increasing the perpendicular magnetic field. For most practical shielded enclosures of room size, the shielding effectiveness is determined largely by the quality of the seams between panels, along door edges, or filter mountings. Hence an investigation is presented of results of an evaluation of a method developed by the government for finding faults in a shielded enclosure by detecting changes in the perpendicular component of magnetic field along the surface of the conducting wall emphasizing continuity of all types of seams of shielded enclosures.