Spread spectrum baseband modulation of magnetic fields for communications and proximity sensing

• US 6,393,045 B1
• Filed: 09/24/1998
• Issued: 05/21/2002
• Est. Priority Date: 09/26/1997
• Status: Expired due to Term

• Current Assignee: Zebra Technologies Corporation
• Original Assignee: Wherenet Corporation (Zebra Technologies Corporation)
• Inventors: Belcher, Donald K., Boyd, Robert W., Hash, Ronald J.
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): AL BESHRAWI, TONY
• Application Number:
  US09/159,553
• Time in Patent Office: 1,335 Days
• Field of Search: 340/10.2, 340/825.54, 340/151, 340/152, 340/10.41, 340/10.1, 250/566, 342/44, 370/69.1, 375/130
• US Class Current: 375/130
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G06K 7/083 inductive G06K7/10336 takes precedence

Abstract

A magnetic field-based tagged object information storage and retrieval system employs a spread spectrum modulated magnetic field for identifying each of a plurality of tagged objects to which spread spectrum modulation magnetic field transponders are attached. When interrogated by a tag reader, transponders embedded in plural tags generate spread spectrum modulated magnetic fields that are correlated with a reference spreading sequence in a tag reader signal processor to both detect and identify each responding tag.

Claims

1. A method of conducting a magnetic field communication comprising the steps of:

(a) controllably emitting from a transponder a magnetic field modulated with a spreading signal indicative of object data that had been read from a transponder memory in a read mode of operation and previously written to the transponder memory in a write mode of operation; and

(b) detecting said magnetic field modulated with said spreading signal by a magnetic field detector of a reader, and processing an output of the magnetic field detector using a signal representative of one of a derivative or integral output of a replica of the spreading signal.

2. A method according to claim 1, wherein step (b) comprises receiving said magnetic field modulated with said spreading signal in step (a) to produce an electrical signal representative thereof, and processing said electrical signal using a replica of said spreading signal.

3. A method according to claim 1, wherein said spreading signal contains object identification information, and wherein step (b) comprises detecting said emitted magnetic field emitted and recovering said object identification information.

4. A method according to claim 1, wherein step (a) comprises stimulating a transponder by means of a coil coupled in circuit with a plurality of energy storage devices that extract and store power to operate said transponder, and provide for emission from said coil of said spreading signal modulated magnetic field from energy contained in an excitation magnetic field signal.

5. A method according to claim 4, wherein step (a) comprises allowing a predetermined transponder circuit settling time to elapse after receipt of said excitation magnetic field signal, before causing said transponder to emit said spreading signal modulated magnetic field.

6. A method according to claim 3, wherein step (a) comprises stimulating plural magnetic field emitters associated with plural objects into emitting magnetic fields modulated with said spreading signal containing information representative of at least one characteristic of respective ones of said plural objects, wherein step (b) comprises detecting plural spreading signal modulated magnetic fields emitted by said plural emitters and generating plural electrical signals representative thereof, and processing said plural electrical signals to recover information associated with respectively different ones of said objects.

7. A system comprising:

a transponder having a magnetic field emitter that is operative to emit a magnetic field modulated with a spreading signal indicative of object data that had been read from a transponder memory in a read mode of operation and previously written to the transponder memory in a write mode of operation; and

a detector that is operative to detect said spreading signal modulated magnetic field emitted by said magnetic field emitter and operative to process an electrical signal representative of said magnetic field with one of a derivative or integral output of a replica of said spreading signal.

8. A system according to claim 7, wherein said magnetic field emitter comprises a tag that is attachable to an object and containing a normally unpowered transponder having memory for storing information representative of at least one characteristic of said object, said normally unpowered transponder being powered from energy contained in a magnetic field excitation signal incident thereon, and being operative to controllably emit said magnetic field modulated with said spreading signal.

9. A system according to claim 7, wherein said detector is operative to process an electrical signal representative of said detected magnetic field using a replica of said spreading signal.

10. A system according to claim 8, wherein said spreading signal contains object identification information, and wherein said detector operative to detect said magnetic field emitted by said transponder and recover said object identification information.

11. A system according to claim 7, wherein said transponder coil is coupled in circuit with a plurality of energy storage devices that extract and store power to operate said transponder, and provide for emission of said spreading signal modulated magnetic field from energy contained in said magnetic field excitation signal.

12. A system according to claim 11, wherein transponder is operative to allow a predetermined settling time to elapse after receipt of said magnetic field excitation signal, before emitting said spreading signal modulated magnetic field.

13. A system for storing and retrieving information representative of at least one character of an object comprising:

a transponder supported at said object and including a magnetic field emitter that is operative to emit a magnetic field modulated with a spreading signal containing said information representative of at least one characteristic of said object, said transponder having a memory and a write mode of operation for writing object data into memory and a read mode of operation for reading object data and emitting a response message based object data in memory;

a reader that is operative to detect said spreading signal modulated magnetic field emitted by said magnetic field emitter and to generate an electrical signal representative thereof wherein said transponder is operative in a read or write mode of operation based on a signal from the reader; and

electrical signal to recover said information, using a signal representative of said magnetic field with one of a derivative or integral output of a replica of said spreading signal.

14. A system according to claim 13, wherein said reader is operative to generate a magnetic field signal that stimulates said transponder into emitting said magnetic field modulated with said spreading signal containing said information.

15. A system according to claim 13, said processor is operative to process said electrical signal with a signal associated with a replica of said spreading signal.

16. A system according to claim 13, wherein said reader is operative to generate a magnetic field signal that stimulates plural ones of said transponder into emitting magnetic fields modulated with said spreading signal containing information representative of at least one characteristic of respective objects with which said plural ones of said transponder are attached, and is operative to detect plural spreading signal modulated magnetic fields emitted by said plural ones of said transponder and to generate plural electrical signals representative thereof, and wherein said processor that is operative to process said plural electrical signals to recover information associated with respectively different ones of said objects.