| 摘要 |
<p>In order to locate, trace, and identify hidden elongated objects (12), such as buried fiber optic cables, the objects (12) are provided with elongated permanent magnet identifier devices having magnetic fields that may be detected at a distance from the objects. In one embodiment, the identifier device comprises an elongated strip (10) magnetized in the direction of its width and formed into a long-pitch helix, producing a characteristic 'magnetic field signature' that enhances detection and identification of the object, as by a portable gradiometer (14) that is moved over the surface of the earth along a line generally parallel to the length of the object. This embodiment may provide a magnetic field that diminishes as the square of the distance from the identifier device (rather than the usual cube of the distance), thereby enabling detection at substantial distances. In a second embodiment distinctive magnetic field signatures are produced by arrays of spaced permanent magnets (M), the fields of which add and subtract to provide resultant magnetic fields with peaks and valleys along a line generally parallel to the length of the object.</p> |
