Apparatus for interrogating a magnetically coded tag

• US 6,323,769 B1
• Filed: 10/10/2000
• Issued: 11/27/2001
• Est. Priority Date: 04/04/1995
• Status: Expired due to Fees

• Current Assignee: Digital Magnetic Technologies, LLC
• Original Assignee: Flying Null, Ltd.
• Inventors: Dames, Andrew Nicholas
• Primary Examiner(s): MULLEN, THOMAS J
• Application Number:
  US09/685,249
• Time in Patent Office: 413 Days
• Field of Search: 340/572.2, 340/572.4, 340/505, 340/10.1, 340/5.8, 235/449, 235/450, 235/375, 235/380
• US Class Current: 340/572.2
• CPC Class Codes: G01V 15/00 Tags attached to, or associated with, an object, in order to enable detection of the object record carriers for use with machines having a detectable tag or marker G06K19/00
• CPC Class Codes: G06Q 10/0875 Itemisation or classification of parts, supplies or services, e.g. bill of materials
• CPC Class Codes: G08B 13/2417 having a radio frequency identification chip
• CPC Class Codes: G08B 13/2434 Tag housing and attachment details
• CPC Class Codes: G08B 13/2437 Tag layered structure, processes for making layered tags
• CPC Class Codes: G08B 13/2442 Tag materials and material properties thereof, e.g. magnetic material details
• CPC Class Codes: G08B 13/246 Check out systems combined with EAS, e.g. price information stored on EAS tag anti-theft systems in point of sale systems G07G3/003
• CPC Class Codes: G08B 13/2462 Asset location systems combined with EAS inventory, tracking, logistic G06Q10/00; entrance control systems G07C9/00
• CPC Class Codes: G08B 13/2471 Antenna signal processing by receiver or emitter
• CPC Class Codes: G08B 13/2474 Antenna or antenna activator geometry, arrangement or layout loop antennae H01Q1/22
• CPC Class Codes: G08B 13/2477 Antenna or antenna activator circuit
• CPC Class Codes: G08B 13/2485 Simultaneous detection of multiple EAS tags
• CPC Class Codes: Y10T 428/12465 having magnetic properties, or preformed fiber orientation coordinate with shape

Abstract

Magnetic tags or markers are disclosed, together with a variety of techniques by means of which such tags may be interrogated. In one aspect, the magnetic marker or tag which is characterized by carrying a plurality of discrete magnetically active regions in a linear array. In another aspect, the invention provides a method of interrogating a magnetic tag or marker within a predetermined interrogation zone, the tag comprising a high permeability magnetic material, for example to read data stored of the tag to detect its presence and/or to determine its position within the interrogation zone, characterized in that the interrogation process includes the step of subjecting the tag sequentially to: (1) a magnetic field sufficient in field strength to saturate the high permeability magnetic material, and (2) a magnetic null as herein defined. Applications of such techniques are described, inter alia, in relation to (a) identifying articles to which tags are attached; (b) accurate determination of position, as in the location of surgical probes; and (c) totalization of purchases, where each item carries a tag coded with data representing its nature and its place.

Claims

1. An apparatus for interrogating a magnetically coded tag, the apparatus comprising:

(a) means for generating a magnetic field, said magnetic field comprising a first region at which a component of the magnetic field resolved in a first direction is zero, wherein within regions contiguous with said first region the component of the magnetic field resolved in said first direction is sufficient to saturate at least a part of the magnetically-coded tag; and

(b) an electrical circuit having a signal source at frequency 2fand an output means for providing an electrical output, said signal source being coupled to said output means by (i) means for halving the frequency of said source signal, (ii) a first filter means arranged substantially to reject a signal at frequency 2f,(iii) a tuned circuit means tuned to energy at frequency f and including a transmitter coil adapted to radiate energy towards the magnetically coded tag positioned so as to be influenced by said radiated energy and a receiver coil for receiving energy radiated by the tag in response to the received energy, and (iv) a second filter means arranged substantially to reject energy at frequency f and to pass energy at frequency 2f, wherein said output means is arranged to provide an output which is a function of the amplitude of the output of said second filter means and the phase difference between the signal source and the output of said second filter means, wherein means for generating the magnetic field is associated with said transmitter and receiver coils such that, in use, a magnetically coded tag moving through the first region will also interact with said transmitter and receiver coils.

2. The apparatus as claimed in claim 1, wherein the first filter means comprises a capacitor connected in parallel to an inductor, the values of the capacitor and the inductor selected so as to reduce the signals of frequency 2f.

3. The apparatus as claimed in claim 1, wherein the tuned circuit means comprises a capacitor and an inductor connected in parallel to earth, the values of the capacitor and the inductor selected such that the capacitor resonates with the inductor at frequency f.

4. The apparatus as claimed in claim 1, wherein the second filter means comprises an inductor connected in parallel to a first capacitor, a second capacitor and an inductor, wherein the series combination of the second capacitor and the inductor is connected to earth.

5. The apparatus as claimed in claim 1, wherein the output means comprises a series combination of a low pass filter, an analog-to-digital converter and a digital processor.

6. The apparatus as claimed in claim 1, wherein a single coil acts as both the transmitter coil and the receiver coil.

7. The apparatus as claimed in claim 1, further comprising a second transmitter coil which is arranged so as to have its axis coincident with the transmitter coil.

8. The apparatus as claimed in claim 7, wherein the transmitter coil and the second transmitter coil are connected together such that their winding directions are opposite.

9. The apparatus as claimed in any one of the preceding claims, wherein the transmitter coil has a resistance of 6 ohms and an inductance of 100 mH.

10. The apparatus as claimed in claim 1, wherein the transmitter coil carries a direct current component and an alternating current component.

11. The apparatus as claimed in claim 10, wherein the direct current component is of the order of 3 A and the alternating current component is of the order of 50 mA.

12. The apparatus as claimed in claim 10, wherein the alternating current component has a frequency of 10 Hz to 100 kHz.

13. The apparatus as claimed in claim 10, wherein the alternating current component has a frequency of 50 Hz to 50 kHz.

14. The apparatus as claimed in claim 10, wherein the alternating current component has a frequency of 500 Hz to 5 kHz.

15. The apparatus as claimed in claim 10, wherein the alternating current component has a frequency of 2 kHz.

16. The apparatus as claimed in claim 10, wherein the alternating current component varies according to a predetermined cycle so as to generate an alternating magnetic field which causes the position of the magnetic field generated by said means for generating a magnetic field to oscillate in a predetermined manner.