Near-Field Magnetic Shielding in the Frequency Range from 20 Hz to 100 MHz

This work is part of our larger research activity that has as its ultimate goal the experimental validation of the theoretical predictions regarding the electromagnetic shielding of conductive materials, in the frequency range 20 Hz–18 GHz. The present article deals with electromagnetic shielding in the range of 20 Hz to 80 MHz, i.e., in a near, magnetically generated field. For this frequency range, there is currently no normative document or in-depth research regarding the experimental validation of theoretical predictions, so the works published to date do not have an adequate degree of confidence. The paper presents the theoretical basis, i.e., the equations that describe the phenomenology of electromagnetic shielding, equations that are unanimously accepted in the scientific community in the field. The employed methodology and laboratory equipment that allowed obtaining the experimental results are also presented. The main component is an adapted zero gauss chamber with three concentric layers (two of Mu-metal and one of steel). The experimental results are compared with the theoretical ones for analytically calculable materials: copper, aluminum, Monel, and graphite. The agreement of these data validates the experimental method, which can then be used also for materials that are not analytically calculable, like composite materials, multilayer materials, or textiles.