Abstract: An axial direction groove is formed in a high permeability toroidal core taking the form of a pot core half with a mounting hole, a high cross-section ratio copper casing being tightly fit around core circumference, having poly-phase excitation windings shuttled through the mounting hole to encompass both the copper casing and the pot-core, forming an integral driving-sensing eddy current probe. A naked pot-core is wound as an integral driving-sensing probe. Poly-phase excitation of the probe is mesh-connected as a gramme-ring.

Abstract: Oscillatory signal build-up is increased in the polar coordinates sensor by integrating the rotating driving flux with the resonating flux resulting from the series resonant pick-up coil current. The imbalance flux linking the pick-up coil is more dependent on radii proximate the z-axis and is more suitable for detection of cracks radial to an aircraft rivet.

Abstract: A single toroidal core is wound with excitation/detection windings for reciprocal-integral eddy current driving-detection means, the pick-up coil being wound around the circumference of the toroid core. The utilized fields being orthogonal for an inherent null. The preferred excitation is ramping sine-cosine currents generating a variable angular velocity driving dipole. A rotating field torus core having an excited poloidal winding for generating concentric n-s s-n diameter-wise dipoles on the plane of the torus for shifting the hemispherical sensing field eccentric in an orbital motion.