| 摘要 |
PURPOSE:To reduce a minor lobe to improve a directional pattern, by changing the distribution of the magnetic field density between the center and the peripheral part. CONSTITUTION:An iron core 6 around which a magnetic field generating coil 2 is wound consists of the mixture of narrow ferromagnetic wire rods W and nonmagnetic wire rods W', and the density of ferromagnetic wire rods is high in the center and is low in the peripheral part. When a current (i) is flowed to a coil 4 to flow a DC to the coil 2, a magnetic field B which is strong in the center and is weak in the peripheral part is generated near the surface of a material 5 to be examined. The density of the eddy current which is generated by flowing the current (i) to the eddy current generating coil 4 wound spirally at regular intervals is uniform. consequently, a force f generated on the surface of the material 5 to be examined is larger in an inside FI of the iron core 6 than in an outside Fphi, and a minor lobe becomes smaller than conventional lobes. |
