| 摘要 |
A preferred reader circuit for energizing the coils and detecting loading variations is shown in FIGS. 3A and 3B. It was designed for tabletop operation at relatively low frequencies; the amplitudes, frequencies, and time constraints listed below can be shifted as desired for other applications. The depicted schematic includes driver circuitry for three coils, it being understood that further drivers can be added as indicated in the figure. Each driver circuit includes an inductive bridge wherein a search coil 3051, 3052, 3053 is balanced against a series of reference inductors 3071, 3072, 3073; 3091, 3092, 3093; and 3311, 3112, 3113 (the latter being variable to trim residuals in the search coil's inductance). A representative pair of search coils 3051, 3052 are identically wound and driven together, and the sensing volume between them is once again indicated at 200. Coil 3053 may be one of another coil pair, or may instead be a non-aligned search coil used to resolve orientation-related ambiguities with respect to coils 3051, 3052.
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