| 主权项 |
1. A method of detecting near-surface defects in a test sample consisting at least partly of ferromagnetic material, wherein a test volume of the test sample is magnetized and scanned to detect magnetic leakage fields caused by defects, and the test volume is magnetized by a magnetic constant field and simultaneously by a magnetic alternating field superposed on the constant field,
wherein the constant field and the alternating field are coupled into the test volume such that the induced magnetic flux generated by the constant field and the induced magnetic flux generated by the alternating field have substantially the same orientation, a relative movement is produced between the test sample and the magnetic constant field acting on the test sample, and the relative movement has a relative speed component directed substantially in the direction of the magnetic field lines of the constant field within the test sample, a component of the relative speed that is measured in the direction of the field lines of the constant field is at least 0.3 m/s, and a magnetic alternating field is generated with an alternating field frequency of at least 1 kHz. |
