Detection and Distinction of Conductive and Magnetic Security Markers Using Eddy-Current Inspection

摘要

??A printed magnetic marker is used effectively on bills or check for security. In securing of valuable documents, a further improvement in the degree of security is always indispensable. The addition of a conductive marker as well as a magnetic marker enhances the value of information and the reliability of these markers. We applied an eddy-current testing (ECT) technique by using the micro ECT probe with a giant magneto-resistance element (GMR) to detect both markers. Two markers can be detected and also distinguished by recognizing both the amplitude and phase of the ECT signal. This paper describes the method of detection and the results for these markers printed by a magnetic and conductive ink.