| 摘要 |
<p>A method and apparatus for non-destructively examining cylindrical material by electromagnetic induction uses primary coils (14,16) separated by an annular gap. The primary coils are excited oppositely so that the respective magnetic fields thereby generated are in boosting relationship in the gap. Close electromagnetic coupling of the primary coils with the material under examination is effected, and detector means, such as secondary coils (18a,18b, etc) are disposed in the gap to detect flux perturbations caused by variation in the properties of the material under examination.</p> |
