Multi-frequency ECT with AMR sensor

Multi-frequency Eddy current testing (ECT) system with high sensitive AMR sensor was developed. By subtracting the signals of two frequencies, the influence of lift off variance could be reduced. As a testing, a specimen of copper plate with grooves and slits was used to simulate the combustion chamber of liquid rocket and the defects. Three defects, with the width of 0.2 mm, the length of 4 mm and the depth of 0.2, 0.5, and 0.8 mm were made in the bottom of the grooves. Multi-frequency ECT experiments were done and the defects with the depth of 0.8 and 0.5 mm could be successfully detected.