Coercivity Measurement from Analysis of the Tangential Magnetic Field

Abstract

Coercivity, H_c, is one of the most useful magnetic parameters which can be used to nondestructively characterize the microstructure or mechanical properties of ferromagnetic materials (1–2). However, for in-the-field applications it is generally not possible or practical to have materials of ideal geometry, i.e. slender cylinders around which one can wind coils to measure magnetic induction and deduce H_c. Other techniques must therefore be devised. The most useful are based on locally magnetizing the material studied, while monitoring either eddy current response or Barkhausen noise (BN) (3, 4). These techniques, however, are limited to thin layers because of skin depth effects. Recently Dobmann and Pitsch⁵ have shown empirically that from analysis of the harmonic content of the surface tangential field, H(t), it is possible to obtain a field, H_CO which is strongly correlated to H_c. This technique, which is based solely on analysis of the tangential field, has the advantage of probing much greater depths than is practical using eddy currents or BN.