FMR Probe method utilizing main and spurious resonance modes for detecting surface flaws

摘要

In ferromagnetic resonance (FMR) probe apparatus for detecting surface flaws in a metal surface, probe impedance changes resulting from flaws are distinguished from impedance changes resulting from probe lift-off from the metal surface. A constant magnitude dc magnetic field and a constant frequency and constant magnitude rf magnetic field are applied to the ferromagnetic crystal and the real and imaginary components of probe impedance are detected. The impedance changes due to flaws are at least partially orthogonal to the impedance changes due to lift-out, and by observing probe impedance on an oscilloscope the presence of a flow or the occurrence of lift-off are readily identified.