Characterizing Magnetic Shielding Effectiveness Below 30 MHz Using Time-Domain Techniques

This study uses time domain measurements to determine the magnetic field shielding effectiveness (SE) of materials at frequencies below 30 MHz. The setup, inspired by the IEEE 299, employs a shielded room and two loop antennas. To address the challenge of dynamic range compression, commonly encountered when measuring broadband signals, three waveform types —a single pulse, a multitone, and a chirp— are evaluated with respect to the signal-to-noise ratio and detection sensitivity. Validations are performed through comparisons with the existing frequency domain methods and numerical simulations. Using multitone excitation with optimized amplitudes allowed measuring magnetic field SE up to 65 dB. The findings indicate our proposal is a viable alternative for characterizing magnetic field SE in this frequency range, offering comparable results to the vector network analyzer-based method, with the added benefit of faster measurements.