Electromagnetic detection system, as well as a responder for such a system

• US 4,742,341 A
• Filed: 06/13/1986
• Issued: 05/03/1988
• Est. Priority Date: 06/14/1985
• Status: Expired due to Fees

• Current Assignee: N.V. Nederlandsche Apparatenfabriek "Nedap"
• Original Assignee: N.V. Nederlandsche Apparatenfabriek "Nedap"
• Inventors: Hogen Esch, Johannes H. L.
• Primary Examiner(s): Swann, III, Glen R.
• Application Number:
  US06/874,005
• Time in Patent Office: 690 Days
• Field of Search: 340/572, 343/894, 343/895
• US Class Current: 340/572.2
• CPC Class Codes: E05B 73/0017 Anti-theft devices, e.g. tags or monitors, fixed to articles, e.g. clothes, and to be removed at the check-out of shops
• CPC Class Codes: G08B 13/2414 using inductive tags
• CPC Class Codes: G08B 13/2417 having a radio frequency identification chip
• CPC Class Codes: G08B 13/2425 Tag deactivation
• CPC Class Codes: G08B 13/2431 Tag circuit details
• CPC Class Codes: G08B 13/2434 Tag housing and attachment details
• CPC Class Codes: G08B 13/2442 Tag materials and material properties thereof, e.g. magnetic material details

Abstract

An electromagnetic detection system comprising transmission unit for producing in at least one first detection zone an electromagnetic interrogation field. The system includes a plurality of responders having attachment element for attachment to articles to be protected, each including a resonant circuit and when present in a detection zone, in response to the interrogation field, producing a signal. The system further includes a first detection adapted to detect a responder and, on detection of a responder, to produce a warning signal. According to the invention, the responders are designed in such a manner that when the attachment elements are removed or when a responder is damaged, at least one frequency determining parameter of the responder is changed in a predetermined manner. At least one second detection zone is provided wherein responders with the at least one changed frequency determining parameter can be detected.

Claims

1. An electromagnetic detection system comprising transmission means producing in at least one first detection zone an electromagnetic interrogation field;

a plurality of responders having attachment means for attachment to articles to be protected, each including a resonant circuit and an electric circuit and which, if present in said first detection zone, in response to the interrogation field, produce a signal; and

detection means associated with said first detection zone adapted to detect the responder and, on detection of the responder to produce a warning signal, characterized in that the responders are designed in such a manner that when the attachment means are removed or when the responder is damaged, at least one frequency determining parameter of the responder is changed in a predetermined manner and that at least one second detection zone is provided wherein responders with the at least one changed frequency determining parameter can be detected;

each of said plurality of responders having at least one connection wire extending along the edge of each responder, said wire forming an electric connection between a frequency determining component of the electric circuit of the responder and other frequency determining components of the resonant circuit; and

said resonant circuit includes at least two parallel-connected coils and that the connection wire forms a connection between the two coils and that the connection wire also forms one of the coils.

2. A electromagnetic detection system according to claim 1, characterized in that at least one of the second detection zones coincides at least partly with at least one of the first detection zones.

3. An electromagnetic detection system according to claim 2, characterized in that the detection means associated with the first detection zones are adapted to also detect said responder when a frequency determining parameter has been changed.

4. An electromagnetic detection system comprising transmission means producing in at least one first detection zone an electromagnetic interrogation field;

a plurality of responders having attachment means for attachment to articles to be protected, each including a resonant circuit and an electric circuit and which, if present in said first detection zone, in response to the interrogation field, produce a signal; and

detection means associated with said first detection zone adapted to detect said responder and, on detection of said responder to produce a warning signal, characterized in that the responders are designed in such a manner that when the attachment means are removed or when the responder is damaged, at least one frequency determining parameter of the responder is changed in a predetermined manner and that at least one second detection zone is provided wherein responders with the at least one changed frequency determining parameter can be detected;

each of said plurality of responders having at least one connection circuit forming an electric connection between a frequency determining component of the electric circuit of the responder and other frequency determining components of the responder, with said at least one connection circuit being closed by at least a part of the attachment means, and a lock adapted to receive an end of a conductive pin, the free end of the pin being connected to the responder by means of a flexible strip, characterized in that the connection circuit comprises a conductor extending through the flexible strip, which conductor is connected to the free end of the conductive pin, the connection circuit further comprising at least one contact member disposed in the lock and being adapted to coact with the pin.

5. An electromagnetic detection system according to claim 4, characterized in that said at least one connection circuit comprises the at least one connection wire.

6. An electromagnetic detection system according to claim 4, characterized in that at least one of the second detection zones coincides at least partly with at least one of the first detection zones.

7. An electromagnetic detection system according to claim 6, characterized in that the detection means associated with the first detection zones are adapted to also detect said responder at a frequency determining parameter of which has been changed.

8. An electromagnetic detection system comprising transmission means producing in at least one first detection zone an electromagnetic interrogation field;

a plurality of responders having attachment means for attachment to articles to be protected, each including a resonant circuit and an electric circuit and which, if present in said first detection zone, in response to the interrogation field, produce a signal; and

detection means associated with said first detection zone adapted to detect said responder and, on detection of said responder to produce a warning signal, characterized in that the responders are designed in such a manner that when the attachment means are removed or when the responder is damaged, at least one frequency determining parameter of the responder is changed in a predetermined manner and that at least one second detection zone is provided wherein responders with the at least one changed frequency determining parameter can be detected;

each of said plurality of responders having at least one connection circuit forming an electric connection between a frequency determining component of the electric circuit of the responder and other frequency determining components of the responder, with said at least one connection circuit being closed by at least a part of the attachment means, and a lock adapted to receive the end of a conductive pin, characterized in that the pin is designed as a plug member having two isolated portions, each adapted to coact with an associated contact member in the lock and to form an electrical connection adjacent the free end of the pin.

9. An electromagnetic detection system according to claim 8, characterized in that the pin is designed as a coaxial plug.

10. An electromagnetic detection system according to claim 8, characterized in that at least one of the second detection zones coincides at least partly with at least one of the first detection zones.

11. An electromagnetic detection system according to claim 10, characterized in that the first detection means associated with the first coinciding detection zones are adapted to also detect said responder at a frequency determining parameter of which has been changed.

12. An electromagnetic detection system comprising transmission means producing in at least one first detection zone an electromagnetic interrogation field;

a plurality of responders having attachment means for attachment to articles to be protected, each including a resonant circuit and an electric circuit and which, if present in said first detection zone, in response to the interrogation field, produce a signal; and

detection means associated with said first detection zone adapted to detect said responder and, on detection of said responder to produce a warning signal, characterized in that the responders are designed in such a manner that when the attachment means are removed or when the responder is damaged, at least one frequency determining parameter of the responder is changed in a predetermined manner and that at least one second detection zone is provided wherein responders with the at least one changed frequency determining parameter can be detected;

each said plurality of responders having at least one connection wire extending along the edge of the responder, said wire forming an electric connection between a frequency determining component of the electric circuit of the responder and other frequency determining components of the resonant circuit; and

said attachment means having a magnet and that the connection wire includes a reed switch disposed with the responder, the position of said switch being adjacent to the magnet when the attachment means are in the closed position.

13. An electromagnetic detection system according to claim 12, characterized in that the resonant circuit comprises at least two parallel-connected coils and that the connection wire forms a connection between the two coils.

14. An electromagnetic detection system according to claim 13, characterized in that the connection wire also forms one of the coils.

15. An electromagnetic detection system according to claim 12, characterized in that the resonant circuit comprises at least two serially connected coils and that the connection wire bypasses one of the coils.

16. An electromagnetic detection system according to claim 12, characterized in that the resonant circuit comprises at least two parallel capacitors and that the connection wire forms a connection between the two capacitors.

17. An electromagnetic detection system according to claim 12, characterized in that the resonant circuit comprises at least two series-connected capacitors and that the connection wire bypasses one of the capacitors.

18. An electromagnetic detection system according to claim 12, characterized in that the resonant circuit comprises a non-linear element and that the connection wire connects the non-linear element to the rest of the circuit.

19. An electromagnetic detection system according to claim 12, characterized in that at least one of the second detection zones coincides at least partly with at least one of the first detection zones.

20. An electromagnetic detection system according to claim 19, characterized in that the first detection means associated with the first coinciding detection zones are adapted to also detect said responder at a frequency determining parameter of which has been changed.

21. An electromagnetic detection system according to claim 16, characterized in that the responder circuit comprises a non-linear element and that the connection wire bypasses the non-linear element.