| 摘要 |
<p>A method and apparatus for detecting the presence of objects in a magnetic field, in particular, objects with a label (8) affixed thereto. The object with the affixed label (8) passes through a surveillance zone defined by a pair of coil housings (2, 4). The coil housings (2, 4) contain therein transmitting coils (48) which are periodically driven in-phase in one time period and out-of-phrase in an alternate time period to produce an alternating electromagnetic field between the coil housings (2, 4). The label (8) cuts or links the electromagnetic field regardless of the spacial orientation of the label (8), whereby the label (8) generates harmonic signals which in turn are coupled by a receiving coil (36) which is connected to electronic circuitry adapted to distinguish the harmonic signals and set off an alarm (14).</p> |
