2008 年 79 巻 4 号 p. 271-279
Eddy current probe to detect longitudinal discontinuities such as seams of wires and bars has been discussed. Conventional encircling coil is hard to detect the longitudinal discontinuities because of the fundamental principal restriction. Moreover, a system using a rotating probe hardly has an ability to support high-speed inspection. Therefore, a probe with array sensors has been developed to detect the longitudinal discontinuities without mechanical rotor. The spin-valve type giant magnetoresistance (SV-GMR) sensor was used as the detection sensor. It has advantages in high sensitivity, high frequency response characteristic up to 100 MHz, and the integration of the sensor element compared with coil or other magnetic sensors. The probe is constructed from two excitation coils and 36 detection sensors. The excitation coils are encircling type such as the conventional encircling coils and excited by opposite phase each other. The detection sensors are arranged in the directions of surrounding a rod for examination between excitation coils. The probe has the capabilities to detect the longitudinal notches by sequential scanning with detection sensors. In addition, a correction method for eccentric effect is proposed by taking the addition of signals at position of opposed sensor pair. The present study showed that the probe has the ability to detect the longitudinal notch that depth of 0.3 mm with 5 mm air gap.