US 5,353,010 AGranted

Device and a method for detecting a magnetizable marker element

AssigneeMinnesota Mining and Manufacturing Company

InventorJuergen Sanetra

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Abstract

To detect a marker element, a transmitter generates an alternating magnetic field. A receiver arranged in this field generates an electrical signal having a waveform corresponding to the magnetic flux density of the alternating magnetic excitation field superimposed by peaks produced upon reversal of the magnetic state of the marker element. The position of these peaks, relative to the alternating magnetic excitation field, is determined, and if different from half the period duration of the alternating magnetic excitation field by less than a predetermined value, a first state of the marker element may be detected. Otherwise, it may be determined that, either, no marker element is present in the alternating magnetic excitation field, or that the marker element is in a second state different from the first state.

Claims11

Dependent claims

A device for detecting a magnetizable marker element, adapted to be attached to an object to be protected against unauthorized removal, comprising:

(a) a transmitter for generating a periodically alternating magnetic excitation field for reversing the magnetic state of the marker element;
(b) a receiver arranged in said alternating magnetic excitation field for generating an electrical output signal corresponding to a signal received upon a said magnetic state reversal;
(c) a signal processing means including a band pass filter for filtering said output signal of said receiver, the resultant filtered output signal having a superimposition of signal components, the frequencies of which are integral multiples of the fundamental frequency of the excitation field;
(d) means for comparing the time interval between two successive maximum signal values of different polarities of the filtered output signal to a predetermined tolerance range associated with half the period duration of the excitation field, and for generating a first output signal when the time interval is within said predetermined tolerance range;
and
(e) an indicator generating a first indication signal upon receiving a first output signal from said comparing means.

3 more elements

Dependencies are inferred from the claim text.

Facts

Application: 07/990,442Filed 15 Dec 1992
Priority: DE 42000823 Jan 1992
Granted: 4 Oct 1994
Term ends: Not estimatedThe source records don’t support an estimate.

Classification8 codes

G08B 13/2408
Characterised by the tag technology used: using ferromagnetic tags
G06K 7/087
Using inductive or magnetic sensors: flux-sensitive, e.g. magnetic, detectors
G08B 13/2442
Tag layered structure, processes for making layered tags: tag materials and material properties thereof, e.g. magnetic material details
G08B 13/2445
Tag layered structure, processes for making layered tags: tag integrated into item to be protected, e.g. source tagging

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