| 摘要 |
<p>Ferromagnetic material of an elongated object, such as a fiber optic cable (12), is permanently magnetized in a manner that results in a substantially cylindrically symmetric radial external magnetic field around the object. The radial external magnetic field varies periodically along the length of the object. If the wavelength of the periodic variations is long compared to the width (diameter) of the object, the strength of the radial external magnetic field decreases approximately inversely with distance from the object for distances that are small compared to the wavelength. Magnetization of the ferromagnetic material is achieved by a magnetizer having pairs (10) of counter-rotating mirror-image magnets adjacent to an object that is moved longitudinally relative to the magnets. By virtue of the magnetization, buried objects, such as pipes and cables can be detected magnetically at substantial distances from the objects.</p> |
