A focused-field eddy current sensor for nondestructive testing

In this paper, we present an original structure of eddy current sensor meant for nondestructive testing of electrically conducting materials. Initially, the basic physical principles of the sensors are recalled, and afterwards we discuss the fact that it is generally impossible to design a sensor with a good spatial resolution and having at the same time a good range detection. Then, we propose an original idea, which consists of exploiting the good directivity of large cup sensors associated to a particular set of measurements, in order to extract relevant information only about the small part of the eddy currents induced in the target, below the centre of the sensor. The interest of this method is illustrated by scanning graphite composite plates containing small defects with this novel sensor. The comparison of the results obtained with actual sensors and our focused-field sensor demonstrates the efficiency of the structure.