| 摘要 |
Apparatus for detecting magnetic and electrically conductive materials includes means for driving (3, 4) an excitation coil (1) with an alternating current at two or more frequencies simultaneously and means for detecting (5, 6) two or more coil (2) output signals of different frequencies from an output signal comprising two or more frequencies and means for subtracting (6) one detected signal from another. The apparatus enables improved elimination of background signals in the coil output signals, and thus enables detection of smaller particles of magnetic and conductive materials. The apparatus may include means for scaling and/or phase rotation of a detected coil output signal.
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