The lift-off effect analysis of flexible differential pick-up koch fractal eddy current probe

This study utilized finite element simulation and experimental methods to investigate the evolution of crack detection performance of a flexible differential fractal Koch eddy current probe at different excitation frequencies as the lift-off distance increases. As the lift-off distance increased, the distribution shape of induced eddy currents changed, leading to reduced similarity in the shape of the excitation coil and an expanded distribution range of induced eddy currents, ultimately resulting in weakened output signal strength. The experimental results showed that for excitation frequencies of 10 kHz, 20 kHz, 50 kHz, 100 kHz, 200 kHz, 500 kHz, and1 000 kHz, the maximum lift distances of the real part of the output signal when cracks were detected were 5.0 mm, 7.0 mm, 8.0 mm, 8.0 mm, 8.0 mm, 6.5 mm, and 4.0 mm, respectively. The imaginary parts were 6.5 mm, 6.5 mm, 7.5 mm, 5.5 mm, 8.0 mm, 6.5 mm, and 6.5 mm, respectively.