Circuit Modeling of Injection Probes for Bulk Current Injection

In this paper, two procedures are developed for lumped-parameter circuit modeling of injection probes for bulk current injection (BCI). Both procedures are based on frequency-domain scattering-parameter measurements, and refer to a clamped wiring composed of a single-ended interconnection. One procedure exploits a black-box approach, requires a calibration fixture, and is suited for practical implementation. The other is based on circuit interpretation of coupling and propagation effects, and is aimed at a theoretical analysis of injection. The former procedure requires an accurate deembedding of fixture-related effects, and the latter requires a detailed knowledge of the geometry of the probe interior parts. The two procedures lead to probe circuit models topologically equivalent, with lumped-Pi structure, performing well in the frequency band of interest for BCI. In the derivation, it is shown that the probe input impedance is the central quantity for the characterization of the frequency-dependent properties of the ferrite core, and for the modeling of inductive coupling (dominant effect). The probe circuit models developed in this paper go over the frequency limitations of previous models, and allow for accurate description of the frequency-dependent voltage transfer ratio and series impedance of the probe.