Eddy Current Testing Probe Based on Double-Coil Excitation and GMR Sensor

The development of eddy current nondestructive techniques and instruments is moving toward new challenges in detecting buried and smaller defects and minimizing the amplitude of excitation currents. The smaller the size of the detected defect, the greater is the diagnostic capability of these techniques. Moreover, the lower the excitation current required, the longer the battery discharge time of the portable instruments, the greater the possibility of implementing broadband excitation strategies with reliable results. This feature is also important when portable instruments with array of probes have to operate for a large amount of time. Following the actual trends based on the use of double-coil excitations, this paper proposes the investigation of the performance of these kinds of probes, when small and buried defects are involved, and low amplitudes of the excitation current are adopted. To allow these activities a suitable double-coil-based excitation probe has been assembled. The obtained performance has been also compared with a traditional single-coil excitation probe based on the same sensing element. The experimental analysis demonstrated the appreciable performance of the proposed solution in a number of test cases.