| 摘要 |
<p>An article surveillance system for detecting the presence of articles in a detection zone (18) has at least one transmitter means (11, 13) and at least one receiver means (12, 15) for transmitting and receiving, respectively, electromagnetic radio-frequence signals in the detection zone or in a proximity thereof. Each article is provided with a sensor or marker (20) operating as a transponder for transmitting an electromagnetic radio-frequent reply signal to the receiver means when receiving a signal from the transmitter means. Furthermore, the system has a coil arrangement (16) with driving means (17) for generating a low-frequent magnetic modulating field in the detection zone (18), and a controller (14) operatively connected to the transmitter means (11, 13), the receiver means (12, 15) and the coil arrangement (16, 17). Each sensor (20) is arranged to transmit a reply signal, the amplitude of which is modulated by the magnetic modulating field, and the receiver means is arranged to receive and to demodulate the amplitude-modulated reply signal. The controller (14) is arranged to supply modulating signals (imod) to the coil arrangement (16, 17), to receive the demodulated signals (idemod) from the receiver means (12, 15) and to use the demodulated signals (idemod) when determining the position of the sensor (20) in relation to the detection zone (18).</p> |
