| 摘要 |
The testing head has a transmission coil (2) coupled to a HF voltage for providing a magnetic HF field and a pre-magnetisation device providing a quasi-static magnetic field superimposed on the HF field. A detection coil (3) detects the induced voltage, fed to an evaluation stage. The transmission and detection coils (2,3) are associated with a partially closed magnetic circuit provided by a core (1) which abuts the surface of the workpiece at its free ends. The pre-magnetisation device is positioned between the latter, with linearly polarised transversal waves provided by using a soft magnetic cylinder with its axis perpendicular to the plane of the core. |
