| 摘要 |
An electronic article surveillance tag comprises a reradiator element, a nonlinear element connected electrically to the reradiator element, and an electrical ground plane member connected electrically to the nonlinear element. The reradiator element, the nonlinear element and the ground plane member are in electrical series circuit connection. The reradiator element and the ground plane member define a monopole antenna upon incidence on the tag of high frequency energy for reradiation of the high frequency energy and further define a dipole antenna upon incidence on the tag of energy of frequency substantially lower than the high frequency energy. An electronic article surveillance system in accordance with the invention comprises a transmitter-receiver arrangement disposed aside an area to be controlled for transmitting a first high-frequency signal into the area, a transmitter disposed aside the area and generating a second frequency signal of substantially lower frequency than the first frequency for establishing in the area an electrostatic field, a tag for attachment to an article to be subject to surveillance, the tag being responsive to the incidence thereon of energy of both the first and second frequencies to transmit a composite thereof and receiver apparatus disposed aside the area for receipt and detection of such composite signal and for generation of an output signal indicative of such detection.
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