Patent ID: 6225905
Filing Date: 2001-05-01
Classification: G01V,G08B

Abstract:
A sensor for remote detection of objects in a surveillance zone (10), preferably for use in an article surveillance system, which further comprises at least one transmitter means (11, 13) and at least one receiver means (12, 15) for transmitting and receiving, respectively, electromagnetic radio-frequency signals in the surveillance zone, and at least one modulating means (16) for generating a modulation field in the surveillance zone, said sensor being arranged to transmit an electromagnetic reply signal at the reception of electromagnetic energy from said transmitter means, and said reply signal being dependent on said modulation field and being receivable by said receiver means, characterized bya magnetic element (23) arranged in a sensor body (21; 101, 102) and having a magnetic property, which is controllable by a magnetic field acting as said modulation field, so that the amplitude of the reply signal from the sensor is modulated by said magnetic modulation field.