Research on visual detection technology using eddy current magnet excitation device

A visual method for detecting invisible and buried micro-flaws under fine metallic surface is described. A new magneto-optic microscope that has a laser source, a CCD camera, and an eddy current magnet excitation device is developed for this work. A pulse generator supplies an intermittent square pulse to induce the magnet excitation device, which can intensify eddy currents yet reduce the working temperature of the exciting coil and specimens. The magnetic field variation produced by the imbedded defect causes a rotation of the polarization plane of the reflected beam. Therefore the reflected beam carries an image of the defect, which is received by a CCD camera. Now the imperceptible flaws in subsurface of mental product are visually tested. Image edge processing approaches are designed to enhance the effect. Experimental tests have been done and the method presented is evaluated by the experimental results.