Mihai Bădic

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.

Mechanical antennas with rotating permanent magnets are a relatively new type of transmitting antenna in low- and ultralow-frequency (LF/ULF) ranges. The perspectives of the applications are encouraging, especially in the field of non-destructive defectoscopy and communications through conductive media (underwater communications), which is reflected in the articles published in the last decade. This article describes the experimental setup, results, harmonic analysis, and simulation validation for two configurations of mechanical antennas with rotating NdFeB permanent magnets. The emphasis is placed on the known analytical equations, specifically on the matching of the measurement results with the analytical data as well as with the results given by the numerical analysis. Also, several means of measurement are used to validate the results through replicate testing. Through analytical analysis and the performed measurement, this article establishes the basics for designing mechanical antennas with rotating permanent magnets for the considered configurations based on a single static magnetic field measurement. Finally, we explore prospects for future research in this domain as well as the advantages and disadvantages compared to other types of LF/ULF antennas.