Eddy current probe having diagonal magnetic fields alternating between posts at corners of orthogonal solenoid coils

Abstract

An eddy current probe comprising two solenoid coils wound around a common rectangular wafer base of high permeability material extending beyond the coils at wafer corners with the wafer becoming the solenoid core. Posts also of high permeability material depend from a wafer front at its corners with coils crossing orthogonally on the wafer. The coils are connected to alternating current to produce magnetic fields that have like magnetic poles at wafer corners diagonally opposed across the wafer, the coils switching in phase to alternate the magnetic field between posts at base diagonal corners. With the posts at the wafer base corners, the combined magnetic fields generated from the orthogonal coils conduct through the posts and emanate from post ends. The post ends have a curvature matching that of a material to be tested for better coupling the magnetic field into the material. Thus, with posts ends positioned proximate a material to be tested, the combined magnet field is delivered to the test material without significant loss. A cap of high magnetic permeability can cover the base underside between posts in providing a guide to complete the magnetic circuit secondary magnetic fields that pass under the base instead of the primary magnetic circuit preferred between post ends.