| 摘要 |
<p>The present invention relates to an induction head (2) for sensing a magnetic strip or other magnetically permeable security structures. The induction head includes an exciting coil (18) associated with an electrically conductive concentrator (4), which produces a primary field and induces a responsive secondary field in the concentrator. The concentrator has an endwall (8) and sidewalls (6) defining a central cavity. The endwall has a narrow measuring gap dividing the endwall into two opposed sections. The sidewalls are also interrupted adjacent the measuring gap (10) to cause a concentrated current of the secondary field to pass along the gap. This concentrated current can be monitored for a change in induction due to the presence of an elongate magnetic strip or other magnetically permeable security structure which is moved past the measuring gap.</p> |
