Meaning
Inductive loops designed to detect local magnetic fields are used to identify high frequency currents on circuit boards and cables. Technicians use h field probes to trace noise sources to their origin, such as a specific integrated circuit or connector pin. These probes generate a voltage proportional to the rate of change of the magnetic flux passing through the loop.
Loop Architecture
Small loop diameters provide excellent spatial resolution but lower sensitivity. Many h field probes are shielded with a balanced balun to suppress electric field pickup. The choice of loop size is a trade-off between the amplitude of the signal and the accuracy of the location.
Localized Scan
Moving the loop parallel to traces on the board allows the engineer to map the current density. This localized scan shows where high speed currents are concentrated and where they might be radiating.
Component Selection
Commercial probing kits include several sizes of loops to cover different frequency bands and physical constraints. When a specific trace is suspected of radiating, the smallest probe is used to confirm the exact location of the current peak. This systematic approach reduces debug time during pre compliance failures.
Engineers use the diagnostic data to design targeted shielding or filtering.
