Ultra-sensitive magnetic field receiver capable of operating in high noise environments

• US 6,476,719 B2
• Filed: 03/06/2001
• Issued: 11/05/2002
• Est. Priority Date: 03/07/2000
• Status: Expired due to Term

• Current Assignee: Zebra Technologies Corporation
• Original Assignee: Wherenet Corporation (Zebra Technologies Corporation)
• Inventors: Eisenberg, John A., Belcher, Donald K., Hash, Ronald J., Bowman, Douglas C.
• Primary Examiner(s): TWEEL JR, JOHN ALEXANDER
• Application Number:
  US09/800,079
• Publication Number:
  US 20020135479A1
• Time in Patent Office: 609 Days
• Field of Search: 340/572.1, 340/551, 340/539, 340/525, 342/450, 342/126
• US Class Current: 340/572.1
• CPC Class Codes: B60R 25/33 of global position, e.g. by providing GPS coordinates
• 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: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 5/73 for taking measurements, e.g. using sensing coils

Abstract

The unwanted influence a noise-source environment upon a modulated (e.g., FSK-encoded) magnetic field-based communication system is diminished by a non-modulated AC magnetic field communication scheme that uses a demodulatorless magnetic field detector. When installed in a tag to be tracked by a geolocation system, the demodulatorless detector responds when the tag comes within a prescribed proximity of the field generator producing the non-modulated AC magnetic field. The received signal is downconverted to baseband and processed to detect a valid AC magnetic field tone and indicate whether the tag is within a prescribed proximity of the AC magnetic field source.

Claims

1. A method of controlling the operation of a system for geolocating objects within a monitored environment, wherein RF transmissions from tags associated with said objects are detected at a plurality of spaced apart monitoring locations containing tag transmission readers, and outputs of said tag transmission readers are processed to geolocate said tags and thereby their associated objects within said monitored environment, said method comprising the steps of:

(a) generating, from at least a location of the monitored environment that is proximate to a region which a tagged object may enter, an unmodulated magnetic field having a constant frequency representative of information intended for a tag entering said region; and

(b) at a tag that has entered said region, detecting said unmodulated magnetic field and causing said tag to perform a prescribed function.

2. The method according to claim 1, wherein step (b) comprises processing a detected unmodulated magnetic field to determine whether said tag is within a prescribed proximity of said location.

3. The method according to claim 2, wherein step (b) comprises processing said detected unmodulated magnetic field to validate whether said detected magnetic field is a valid unmodulated magnetic field as generated in step (a).

4. The method according to claim 1, wherein step (b) comprises processing a detected unmodulated magnetic field to validate whether the detected magnetic field is a valid unmodulated magnetic field as generated in step (a).

5. The method according to claim 1, wherein step (b) comprises downconverting the frequency of a detected unmodulated magnetic field to baseband, and processing the downconverted baseband signal to determine whether the detected magnetic field is a valid unmodulated magnetic field as generated in step (a), and to determine whether said tag is within a prescribed proximity of said location.

6. The method according to claim 1, wherein step (a) comprises generating a plurality of unmodulated magnetic fields having respectively different constant frequencies representative of different information intended for a tag entering said region, and step (b) comprises detecting said unmodulated magnetic fields, so as to distinguish among the frequencies thereof.

7. An arrangement for controlling the operation of a system for geolocating objects within a monitored environment, wherein RF transmissions from tags associated with said objects are detected at a plurality of spaced apart monitoring locations containing tag transmission readers, and outputs of said tag transmission readers are coupled to an object location subsystem which processes outputs of said tag transmissions to geolocate said tags and thereby their associated objects within said monitored environment, said arrangement comprising:

at least one magnetic field generator located proximate to a region which a tagged object may enter, and being operative to generate an unmodulated magnetic field having a constant frequency representative of information intended for a tag entering said region; and

a magnetic field receiver installed on said tag and being operative to detect said unmodulated magnetic field and causing said tag to perform a prescribed function.

8. The arrangement according to claim 7, wherein said magnetic field receiver is operative to process a detected unmodulated magnetic field to determine whether said tag is within a prescribed proximity of said at least one magnetic field generator.

9. The arrangement method according to claim 8, wherein said magnetic field receiver is operative process said detected unmodulated magnetic field to validate whether said detected magnetic field is a valid unmodulated magnetic field as generated by said at least one magnetic field generator.

10. The arrangement according to claim 7, wherein said magnetic field receiver is operative to process a detected unmodulated magnetic field to validate whether the detected magnetic field is a valid unmodulated magnetic field as generated by said at least one magnetic field generator.

11. The arrangement according to claim 7, wherein said magnetic field receiver is operative to downconvert the frequency of a detected unmodulated magnetic field to baseband, and to process the downconverted baseband signal to determine whether the detected magnetic field is a valid unmodulated magnetic field as generated by said at least one magnetic field generator, and whether said tag is within a prescribed proximity of said at least one magnetic field generator.

12. The arrangement according to claim 7, wherein said at least one magnetic field generator comprises a plurality of magnetic field generators that generate a plurality of unmodulated magnetic fields having respectively different constant frequencies representative of different information intended for a tag entering said region, and said magnetic field receiver is operative to detect said unmodulated magnetic fields to distinguish among frequencies thereof.

13. An arrangement according to claim 7, wherein said magnetic field receiver is operative to cause said tag to change the repetition rate of RF transmissions therefrom.

14. A magnetic field receiver for use with a tag associated with an object to be tracked by a geolocation system containing at least one magnetic field generator, located proximate to a region which a tagged object may enter and being operative to generate an unmodulated magnetic field having a constant frequency representative of information intended for a tag entering said region, said magnetic field receiver comprising:

a magnetic field detector that is operative to detect said unmodulated magnetic field; and

a processing circuit, coupled to said magnetic field detector and being operative to validate whether said detected magnetic field is a valid unmodulated magnetic field as generated by said at least one magnetic field generator.

15. The magnetic field receiver according to claim 14, wherein said processing circuit is operative to determine whether said tag is within a prescribed proximity of at least one magnetic field generator.

16. The magnetic field receiver according to claim 14, wherein said processing circuit is operative to downconvert the frequency of a detected unmodulated magnetic field to baseband, and to process the downconverted baseband signal to determine whether the detected magnetic field is a valid unmodulated magnetic field as generated by said at least one magnetic field generator, and whether said tag is within a prescribed proximity of said at least one magnetic field generator.

17. The magnetic field receiver according to claim 14, wherein said at least one magnetic field generator comprises a plurality of magnetic field generators that generate a plurality of unmodulated magnetic fields having respectively different constant frequencies representative of different information intended for a tag entering said region, and said processing circuit is operative to detect said unmodulated magnetic fields to distinguish among frequencies thereof.

18. The magnetic field receiver according to claim 14, wherein said processing circuit is operative to generated an output that causes said tag to change the repetition rate of RF transmissions therefrom.

19. The magnetic field receiver according to claim 14, wherein said processing circuit is operative to generate an output that causes said tag to increase the repetition rate of RF transmissions therefrom while said tag is proximate to said region, and to cause said tag to revert to its previous repetition rate after said tag is no longer proximate to said region.