A focused-field eddy current sensor for nondestructive testing

An original structure of an eddy current sensor meant for nondestructive testing of electrically conducting materials is presented. The basic physical principles of the sensors are recalled, and the fact that it is generally impossible to design a sensor with good spatial resolution and good range detection is discussed. An original idea is proposed, which consists of exploiting the good directivity of large cup sensors associated with a particular set of measurements in order to extract relevant information about the small part of the eddy currents induced in the target, below the center of the sensor. This method is illustrated by scanning graphite composite plates containing small defects. The comparison of the results obtained with actual sensors and the authors´ focused-field sensor demonstrates the efficiency of the structure