High-frequency characterization of Fe-based nanocrystalline cores

Fe-based nanocrystalline alloys like Fe _73.5Si _15.5Cu ₁Nb ₃B ₇ are commonly used in variable frequency drive systems as electromagnetic interference (EMI) noise absorbers. We study the high frequency magnetic properties of such magnetic alloys employing a well-controlled VNA-based reflectometric method. Our focus is on the dynamic magnetic susceptibility. We developed a coaxial probe head for measuring the magnetic properties of toroid cores up to 1 GHz in addition to a more conventional wired approach. We observe a single-exponential magnetic relaxation in most cases, which obey the Snoek’s limit, i.e. the product of the initial permeability and the cut-off frequency is constant. We show that the coaxial probe-head-based approach provides reliable dynamic susceptibility data without the effects of the ill-reproducible wired approach.