Measurement-based modeling of dual loop magnetic near-field probe

Magnetic near-field probes consisting of dual ferrite-core coils have been experimentally evaluated and their frequency characteristics have been theoretically calculated. The two coils are connected in series, but they have opposite winding directions so as not to generate a uniform magnetic field from a distant source, which is considered a disturbance in near-field measurements. The frequency dependencies of two different probes were measured using a microstrip line for frequencies in the range 30 kHz to 0.1 GHz. They were also calculated using the effective permeability, which was derived from the measured probe inductances and a theoretical expression for the inductance that considers the different flux paths for different probe structures. The calculation results agreed well with the measurement results for frequencies up to 0.1 GHz.