ELECTROMAGNETIC NONDESTRUCTIVE EVALUATION: PRESENT AND FUTURE Keynote lecture

1. Introduction Eddy current examination has its origin with Michael Faraday's discovery of electromagnetic induction in 1831. Faraday was a chemist in England during early 1800's and is credited with the discovery of electromagnetic induction, electromagnetic rotations as the magneto-optical effect, diamagnetism and other phenomena [1]. Faraday discovered that when a magnetic field passes through a conductor or when a conductor passes through a magnetic field, an electric current will flow through conductor if there is a closed path through which the current can circulate. The phenomenon of eddy currents was discovered by French physicist Leon Foucault in 1851, and for this reason eddy currents are sometimes called Foucault currents. Foucault built a device that used a copper disk moving in a strong magnetic field to show that eddy currents are generated when a material moves within an applied magnetic field [2]. In the year that J.C. Maxwell died, 1879, at the time when many still doubted his theories and eight years before Hertz demonstrated the existence of the electromagnetic waves, D.E. Huges distinguished different metals and alloys from one another by means of induced eddy current. Locking an electronic oscillator, Huges used the ticks of a clock falling on a microphone to produce the exciting signal. The resulting electrical impulses passed through a pair of identical coils and induced eddy currents in conductive objects placed within the coils. Listening to the ticks with a telephone receiver (invented by A.G.Bell two years earlier), Huges adjusted a system of balancing coils until the sound disappeared [3]. Huges measured the conducting of various metals on his induction balance, using copper as a reference standard. This standard, " the International Annealed Copper Standard " (IACS) survives today as a common conductive measure; values are given as a percentage of the conductivity of copper. A relative scale, %IACS, appears in much of the literature on eddy current [4]. For the next fifty years, no significant advances in eddy current testing were reported. At the end of 1922s, eddy current devices begun to appear in the steel industry for measurements on billets, round stock and tubing. But the limitations of electronic instrumentation allowed no more than some simple sorting applications. Instrumentation and electromagnetic theories developed during the Second World War, primarily for the development and detection of magnetic mines, paved the way for the robust testing methods and equipments that allowed eddy current its entry …