Eddy-current crack detection at frequencies approaching electrical resonance

The effect of operating an absolute eddy-current (EC) probe at frequencies around its electrical resonance was investigated. A defect signal enhancement phenomenon was observed and characterised. Experimental tests were performed on notch defects in typical aerospace superalloys. An absolute mode EC probe was operated by sweeping through a range of frequencies, in the MHz range, encompassing the electrical resonance of the system. Resonance decoupling above defects results in a signal-to-noise ratio (SNR) peak, within a band of frequencies approaching resonance, of up to 3.7 times that measured at 1MHz. This near electrical resonance signal enhancement (NERSE) phenomenon poses the possibility for a simple operational approach method for improving the sensitivity of conventional eddy-current testing.