History of Eddy Current Testing
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 (magnetic fields) are generated when a material moves within an applied magnetic field.
Eddy current testing began largely as a result of the English scientist Michael Faraday's discovery of electromagnetic induction in 1831. Faraday discovered that when a magnetic field passes through a conductor (a material in which electrons move easily)-or when a conductor passes through a magnetic field-an electric current will flow through the conductor if there is a closed path through which the current can circulate. In 1879, another breakthrough was made when another English
scientist, David Hughes, demonstrated how the properties of a coil change when placed in contact with metals of different conductivity and permeability. However, it was not until the Second World War that these developments in the transmitting and receiving of electromagnetic waves were put to practical use for materials testing.
Beginning in 1933, in Germany, while working for the Kaiser-Wilhelm-Institute, Professor Friedrich Förster adapted eddy current technology to industrial use, developing instruments for measuring conductivity and for sorting mixed-up ferrous components. In 1948, Förster founded his own company in Reutlingen, a business based on eddy current testing that continues to this day. Other companies soon followed. Many advances were made throughout the 1950s and 1960s, especially in the aircraft and nuclear industries. There have been many recent developments in eddy current testing, leading to improved performance and the development of new applications. Eddy current testing is now a widely used and well-understood inspection technique for flaw detection as well as for thickness and conductivity measurements.
