| 摘要 |
<p>This invention relates to a deactivating device for deactivating shoplifting detection labels of an electronic shoplifting detection system. These labels comprise a resonant circuit with a coil and a capacitor and the deactivating device comprises an antenna circuit comprising an antenna coil tuned with at least one capacitor to the resonant frequency of the resonant circuit. By means of this arrangement, sufficient energy can be induced in a resonant circuit of a label to effect electrical breakdown in the capacitor thereof. According to the invention, the antenna coil of the deactivating device is coupled, on the one hand, to a supply source and, on the other, to earth via a switching means. Means are provided for supplying at intervals control pulses to the switching means in order to bring the switching means into the conductive state. The duration of each control pulse is chosen such that at the end of a control pulse, when the switching means returns to the blocking state, the energy necessary for deactivation is stored as magnetic energy in the antenna coil. This energy is subsequently converted into an electromagnetic oscillation when the switching means is in the blocking state. <IMAGE></p> |
