Flaw detection of alloys using the eddy-current method

Abstract

A subminiature transformer eddy-current transducer (ECT) that is intended for the study of different nonuniform materials, alloys, miniature parts, printed-circuit boards, and microscopic defects has been designed. A block diagram of the transducer is given and its basic technical characteristics ensuring localization of the magnetic field on areas of approximately 50 × 50 μm are stated. A scheme that uses a computer as a generator and receiver of signals from windings is proposed. It is capable of automatically changing the filtering cutoff frequency and operating frequency of the device. The designed measuring system eliminates the main drawback of eddy-current transducers (the small area of the electromagnetic field), simultaneously significantly reducing the noise level due to the use of high-quality amplifiers and filters, and searches for defects in printed circuit boards, metal–dielectric–metal-junctions, and alloys of different metals. A measurement procedure that allows one to perform high-accuracy monitoring of flaws in different alloys is described. The eddy-current transducer was successfully tested on several objects, e.g., a 5.5-μm thick Al–Mg alloy and welded seams of 5-mm thick titanium plates, as well as other objects. The dependences of the ECT signal on the flaws in these structures are given.