Lumped and Distributed-Parameter Circuit Models of the Electromagnetic Clamp

Abstract

This paper presents two circuit models of the electromagnetic (EM) clamp defined in Standard IEC 61000-4-6 for conducted-immunity (CI) testing. First, a lumped-parameter circuit model is extracted from measurements of scattering parameters. This model is merely behavioral since it provides a valid representation of the EM clamp at external ports up to 1 GHz, whereas physical interpretation of the involved sources/impedances is possible under 10 MHz only. To extend physical insight at higher frequencies, a distributed-parameter circuit model is proposed, which is based on the description of the internal structure of the EM clamp as a three-conductor transmission line. Unknown model parameters (such as the magnetic permeability of ferrite rings) are identified by optimized fitting of ad hoc measurements. Both models are eventually validated by experiments performed in an idealized CI test setup. Several observations on the operating principles and features of the EM clamp are inferred from the two complementary modeling approaches