The high-frequency behavior of the shield in the magnetic-field probes

Shielded loops are commonly used for magnetic-field emission and susceptibility experiments. The shield is demonstrated to play a role which changes from low to high frequencies. In the lower frequency range it operates as an electrostatic shield while at higher frequencies it carries the field-generating/sensing currents. The consequences are discussed for the probe equivalent circuit, terminal impedance and calibration, and the relevant formulas are given, along with the expressions defining the frequency limits. Experiments accurately confirm the shield's HF behavior.