same as with the square sample.These patterns were observed not only in the single-layer sample,but also in the double-layer sample, and it was possible to detect the weld area in sidethe shielding tube.At frequency of 1 kHz,the intensity of the normal magnetic field strength changed periodically with the observed phase, and the in tensity change of the tangential magnetic field
strength was observed at the weld area.The in tensity of the