Shoplifting detection system of the transmission type
First Claim
1. A shoplifting detection system of the transmission type, suitable in particular for the use of high frequency interrogating signals, in which system an electronic label provided with a resonance circuit can effect an electromagnetic coupling between at least two antenna coils, at least one of which is a transmitting antenna coil which, in operation, is fed with an A.C interrogating signal from a transmitter circuit, and at least one other of which is a receiving antenna coil which supplies a received signal to a receiver circuit, characterized in that said receiver circuit comprises a phase-sensitive synchronous detector to which the received signal is supplied, and to which a reference signal is supplied of such a phase that a component in the received signal, caused by an electronic label, provides a maximum output signal of said synchronous detector, and a signal phase-shifted through 90°
- relatively to said component provides a minimum output signal of said synchronous detector.
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Accused Products
Abstract
The invention relates to a shoplifting detection system of the transmission type, suitable in particular for the use of high-frequency interrogating signals, in which system an electronic label provided with a resonance circuit can effect an electromagnetic coupling between at least two antenna coils, at least one of which is a transmitting antenna coil which, in operation, is fed with an A.C. interrogating signal from a transmitter circuit, and at least one other of which is a receiving antenna coil which supplies a received signal to a receiver circuit. According to the invention said receiver circuit comprises a phase-sensitive synchronous detector to which the received signal is supplied, and to which a reference signal is supplied of such a phase that a component in the received signal, caused by an electronic label, provides a maximum output signal of said synchronous detector, and a signal phase-shifted through 90° relatively to said component provides a minimum output signal of said synchronous detector.
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Citations
14 Claims
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1. A shoplifting detection system of the transmission type, suitable in particular for the use of high frequency interrogating signals, in which system an electronic label provided with a resonance circuit can effect an electromagnetic coupling between at least two antenna coils, at least one of which is a transmitting antenna coil which, in operation, is fed with an A.C interrogating signal from a transmitter circuit, and at least one other of which is a receiving antenna coil which supplies a received signal to a receiver circuit, characterized in that said receiver circuit comprises a phase-sensitive synchronous detector to which the received signal is supplied, and to which a reference signal is supplied of such a phase that a component in the received signal, caused by an electronic label, provides a maximum output signal of said synchronous detector, and a signal phase-shifted through 90°
- relatively to said component provides a minimum output signal of said synchronous detector.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
Specification