Differential Koch Planar Eddy Current Probe Sensitivity Boosting by Iron Particulate Sheet.

Improving the performance of flexible eddy current (EC) probes (FECPs) is a current research hotspot. Thus, a novel FECP, fractal EC sensor technology is proposed. This FECP can enhance the consistency of the probe for detecting short cracks in different orientations by changing the coil structure of the probe, thereby reducing the probability of missing the particular direction cracks. However, due to the limit of the wires' layout space, an issue remains: the fractal probe's signal output is weak. To break through this limitation, this study proposes a method to achieve the passive amplification of the output signal of FECPs. A layer of homemade flexible sheet doped with pure iron particles is covered on a flexible Koch differential pick-up fractal EC probe. First, the manufacturing details of the flexible sheet and probe are provided; then, the influence of the probes with and without sheet on the amplification of the crack detection signals is compared via finite element analysis and experiment. The results show that the probe with the sheet can realize the passive amplification to the crack signals in C-scan experimental results of 28 kinds of cracks, and under the excitation frequencies of 50, 100, and 1000 kHz, the signal amplitudes output from the probe with sheet increase by at least 12.8%, 27.6%, and 40.4%, respectively.