Abstract: A plurality of eddy-current generators are angularly grouped about an axis within an inspection tool or probe. Each eddy-current generator presents a circumferentially extending test segment. Collectively, the test segments form a discontinuous test gap which extends circumferentially about the probe. In some embodiments, adapted for inspecting from the inside of tubing or fastener holes, the test gap is at the outer periphery of a probe. In other embodiments, adapted for inspecting from the outer surface portions of tubing, rods, etc., the test gap region extends around the inside of a central passageway formed through a support body. The eddy-current generators are supported for limited radial movement, enabling the tool or probe to adapt to differences in shape and dimension of the material being inspected.

Abstract: A coil of insulated wire surrounds a low reluctance core. A combination of low reluctance and high reluctance materials positioned adjacent said coil: (1) control the spatial extent of the magnetic flux and, (2) concentrate the total reluctance of the magnetic circuit of the exciting coil into a volume of controlled size and shape within the material being tested. The magnetic flux is controlled, and the reluctance is concentrated, in such a manner as to optimize the sensitivity of the eddy-current generator to variations in the material being tested; at the same time, the coil impedance is maintained at a value which is optimum for the performance of any selected precision electrical impedance measuring device.