Magnetoresistive flux focusing eddy current flaw detection

An eddy current device resistant to conductive material edge effects for non-destructive evaluation of an electrically conductive material comprising:

• an excitation coil for inducing eddy currents within the electrically conductive material, the excitation coil having windings wherein the excitation coil's longitudinal axis is perpendicular to the surface of the electrically conductive material;
• a giant magnetoresistive sensor having a longitudinal axis perpendicular to the surface of the electrically conductive sample and surrounded by the windings of the excitation coil;
• a tubular flux focusing lens disposed between the excitation coil and the giant magnetoresistive sensor, composed of a conductive material having a high magnetic permeability, having a first opening opposite the surface of the electrically conductive material and having a second opening adjacent to the surface of the electrically conductive material and which prevents magnetic coupling between the excitation coil and the giant magnetoresistive sensor and which produces high flux density at the outer edge of the giant magnetoresistive sensor;
• a feedback source;
• a feedback coil electrically connected to the feedback source and positioned adjacent to the giant magnetoresistive sensor along the longitudinal axis thereof and surrounded by the windings of the excitation coil and the flux focusing lens, the feedback coil receiving a feedback current from the feedback source having the same frequency as the excitation coil frequency but 180 degrees out of phase with the output of the giant magnetoresistive sensor, such that leakage magnetic fields are canceled;
• and
• a flux focusing shield which surrounds the excitation coil.

A magnetoresistive flux focusing eddy current device for non-destructive evaluation of an electrically conductive material surrounding a circular inhomogeneity, comprising:

• an excitation coil for inducing eddy currents within the electrically conductive material, the excitation coil having windings wherein the excitation coil's longitudinal axis is perpendicular to the surface of the electrically conductive material;
• a giant magnetoresistive sensor having a longitudinal axis perpendicular to the surface of the electrically conductive sample and surrounded by the windings of the excitation coil;
• a tubular flux focusing lens disposed between the excitation coil and the giant magnetoresistive sensor, composed of a conductive material having a high magnetic permeability, having a first opening opposite the surface of the electrically conductive material and having a second opening adjacent to the surface of the electrically conductive material and which prevents magnetic coupling between the excitation coil and the giant magnetoresistive sensor and which produces high flux density at the outer edge of the giant magnetoresistive sensor;
• a feedback source;
• a feedback coil electrically connected to the feedback source and positioned adjacent to the giant magnetoresistive sensor along the longitudinal axis thereof and surrounded by the windings of the excitation coil and the flux focusing lens, the feedback cool receiving a feedback current from the feedback source having the same frequency as the excitation coil frequency but 180 degrees out of phase with the output of the giant magnetoresistive sensor, such that leakage magnetic fields are canceled;
• and
• rotator means for rotating the device about the circular inhomogeneity such that the center of the device remains a constant distance from the center of the circular inhomogeneity.