Eddy Current Arrays for Defect Detection

What was originally an inspection technique for large-scale defects has become an increasingly miniaturized method. Originally, the use of eddy currents for nondestructive evaluation was limited to gross defects in massive structures such as railroads and ship hulls; today, eddy current techniques are routinely used to detect sub-millimeter cracks. Unfortunately, the trend towards miniaturization creates a practical dilemma. To achieve greater resolution and sensitivity, eddy current probes must be made smaller. As probes become smaller, the amount of time needed to completely cover an inspection area escalates. As with other NDE modalities, one solution proposed to resolve the conflict between productivity and sensitivity is the use of eddy current arrays. An array of many elements could easily decrease the required inspection time by an order of magnitude without sacrificing the high-resolution capabilities of smaller probes. The advantages of array inspection are thus quite attractive, and interest is increasing. However, practical implementation of eddy current arrays requires careful attention to a number of details, including elementto-element uniformity, size versus sensitivity, and electrical interactions (crosstalk).