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In this paper, we propose an original method for the physical analysis of electromagnetic interactions between an inductive sensor and any homogeneous conducting plane target. In the first part of this paper, the basic principles of inductive sensors are recalled. Then, we solve Maxwell's equations in order to obtain an analytical model for the relationship between the target properties and the electrical signals for a U-shaped sensor. Next, we emphasize the fact that our analytical relations can be interpreted as an extension of the electrical image method, even in the most difficult case of conducting and magnetic targets. In the last part, we present some measurements illustrating this new electrical image concept.

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.