| 摘要 |
A method of, and a system for, detecting articles containing or carrying magnetic markers is disclosed. The articles are passed through a surveillance zone in which a high frequency magnetic field is generated and in which the response of said magnetic markers is detected. Means for generating a high frequency field having quadrupole characteristics is provided. Such means generally comprises a transmitting coil and an electrically conductive screen placed behind said coil. This arrangement gives reduced interference from farfield sources, thus improving sensitivity and reliability of detection. It also permits the transmitting coil or part thereof to function as the receiving means. |
