Nondestructive Testing of Back-Side Local Wall-Thinning by Means of Low Strength Magnetization and Highly Sensitive Magneto-Impedance Sensors

A nondestructive testing method is presented for inspection and evaluation of back-side local thinning in ferromagnetic structures. It is shown that the change of initial magnetic leakage reluctivity is correlated with a local thinning's reduced thickness and thinning area; a thinning's transversal length is more significant than the longitudinal length in terms of thinning area. The faint magnetic flux leakage excited from back-side local thinning can be detected by highly sensitive magneto-impedance sensors. Validation tests were carried out by moving a probe over a local thinning in the transversal and longitudinal directions, respectively. Results show the feasibility of inspecting and evaluating back-side local thinning by using small magnetization force and highly sensitive magneto-impedance sensors.