Proximity monitoring apparatus employing encoded, sequentially generated, mutually orthogonally polarized magnetic fields

• US 5,661,459 A
• Filed: 09/20/1995
• Issued: 08/26/1997
• Est. Priority Date: 04/30/1993
• Status: Expired due to Term

• Current Assignee: North South Holdings Incorporated (Spherix Incorporated)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Belcher, Donald K.
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): Lee, Benjamin C.
• Application Number:
  US08/530,653
• Time in Patent Office: 706 Days
• Field of Search: 340/573, 340/572, 340/539, 340/531, 340/825.34, 340/568, 324/207.26
• US Class Current: 340/573.4
• CPC Class Codes: G08B 21/0247 System arrangements wherein the alarm criteria uses signal strength
• CPC Class Codes: G08B 21/0263 System arrangements wherein the object is to detect the direction in which child or item is located

Abstract

A proximity detector includes a low frequency magnetic field generator, located with an individual being monitored, the generator sequentially generating a plurality of encoded, time varying magnetic fields having mutually orthogonal polarizations. A magnetic field sensor unit is provided within a second device, carried by another individual. The magnetic field sensor unit is operative to detect encoded magnetic field energy associated with one or more of the magnetic fields generated by the magnetic field generator. Preferably, the magnetic field sensor unit includes a plurality of magnetic field sensors having respective magnetic field polarization sensitivities that are oriented mutually orthogonal with respect to one another. Each of the magnetic field sensors produces a respective first output signal in response to detecting encoded magnetic field energy generated by the magnetic field generator of at least a predefined level and containing an code pattern corresponding to that stored by the magnetic field sensor unit. A time-out circuit is coupled to each of the magnetic field sensors, and generates an alarm signal in response to a prescribed failure to receive a first output signal from any of the magnetic field sensors within periodic time intervals, thereby indicating that the monitored individual is beyond a prescribed range or distance from the monitoring individual.

Claims

1. An arrangement for detecting whether a first entity is physically separated by more than a specified distance from a second entity comprising:

a magnetic field generator unit located at said first entity and being operative to generate a plurality of encoded, time varying magnetic fields; and

a magnetic field detector unit which is located at said second entity and is operative to detect magnetic field energy associated with said time varying magnetic fields generated by said magnetic field generator unit, but, upon failing to detect a predefined threshold level of magnetic field energy, generates a first output signal representative that said first entity is physically separated by more than said specified distance from said second entity.

2. An arrangement according to claim 1, wherein said magnetic field generator unit is operative to generate a plurality of encoded, time varying magnetic fields having respectively different magnetic field polarizations.

3. An arrangement according to claim 2, wherein said magnetic field generator unit is operative to generate a plurality of encoded, time varying magnetic fields having magnetic field polarizations that are substantially mutually orthogonal to one another.

4. An arrangement according to claim 3, wherein said magnetic field generator unit is operative to generate respective ones of said plurality of encoded, time varying magnetic fields in sequence.

5. An arrangement according to claim 2, wherein said magnetic field detector unit comprises a plurality of magnetic field sensors having magnetic field polarization sensitivities that are oriented differently from one another, each of said magnetic field sensors being operative to produce a respective magnetic field detection signal in response to detecting a predefined level of magnetic energy.

6. An arrangement according to claim 5, wherein said magnetic field generator unit comprises a plurality of magnetic field generators which generate respective ones of said plurality of time varying magnetic fields in sequence.

7. An arrangement according to claim 1, wherein said magnetic field generator unit includes an encoder which is operative to generate said plurality of encoded time varying magnetic fields, and wherein said magnetic field detector unit includes a decoder which is operative to decode detected magnetic field energy that has been encoded by said encoder.

8. An arrangement according to claim 7, wherein said magnetic field generator unit is operative to sequentially generate a plurality of digitally encoded magnetic fields of respectively different magnetic field polarizations, each of said digitally encoded magnetic fields being digitally encoded with a prescribed multi-bit digital code pattern, and wherein said magnetic field detector unit is operative to detect magnetic field energy associated with one or more of the digitally encoded magnetic fields sequentially generated by said magnetic field generator and to produce a first output signal in response to detecting a predefined level of digitally encoded magnetic field energy generated by said magnetic field generator, and includes a digital decoding circuit, which is operative to compare digital code contents of said first output signal with a replica of said prescribed multi-bit digital code pattern and to generate a second output signal in response to the digital code contents of said first output signal containing said prescribed multi-bit digital code pattern.

9. An arrangement according to claim 8, wherein said magnetic field generator is operative to sequentially generate a plurality of digitally encoded magnetic fields having magnetic field polarizations that are substantially orthogonal to one another, and wherein said magnetic field detector unit includes a plurality of magnetic field detectors having respective magnetic field polarization sensitivities that are oriented differently from one another, and wherein each of said magnetic field detectors is operative to produce a respective first output signal in response to detecting a predefined level of digitally encoded magnetic energy generated by said magnetic field generator.

10. An arrangement according to claim 9, wherein said magnetic field detector unit is operative to produce a third output signal in response to said second output signal not being repeatedly produced within prescribed periodic time intervals.

11. An arrangement according to claim 9, wherein each of said magnetic field detectors is operative to produce a respective third output signal in response to failing to detect magnetic field energy generated by said magnetic field generator of at least said predefined level.

12. An arrangement according to claim 8, wherein said magnetic field generator is operative to generate a plurality of digitally encoded on-off keyed oscillating magnetic fields.

13. An arrangement according to claim 12, wherein said plurality of digitally encoded on-off keyed oscillating magnetic fields have a frequency in a range on the order of multiple tens to several hundred KHz.

14. A method for detecting whether a first entity is physically separated by more than a specified distance from a second entity comprising the steps of:

(a) generating a plurality of time varying magnetic fields from a first device located at said first entity; and

(b) sensing, by way of a second device located at said second entity magnetic field energy associated with said time varying magnetic fields generated from said first device in step (a), but, in response to failing to detect a prescribed threshold level of magnetic field energy, providing a first output signal indicating that said first entity is physically separated by more than said specified distance from said second entity.

15. A method according to claim 14, wherein step (a) comprises generating a plurality of time varying magnetic fields, which have magnetic field polarizations that are substantially mutually orthogonal to one another.

16. A method according to claim 14, wherein step (a) comprises sequentially generating a plurality of encoded, time varying magnetic fields having respectively different magnetic field polarizations.

17. A method according to claim 16, wherein said second device includes a plurality of magnetic field sensors having magnetic field polarization sensitivities that are oriented differently from one another, and wherein step (b) comprises causing each of said magnetic field sensors to produce a respective magnetic field detection signal in response to detecting a predefined level of magnetic energy.

18. A method according to claim 14, wherein step (a) comprises generating respective ones said plurality of time varying magnetic fields in sequence.

19. A method according to claim 18, wherein step (a) comprises generating said plurality of time varying magnetic fields, such that said plurality of time varying magnetic fields have respectively different magnetic field polarizations.

20. A method according to claim 14, wherein step (a) comprises generating a plurality of encoded time varying magnetic fields, and step (b) comprises decoding detected magnetic field energy that has been encoded in step (a).

21. A method according to claim 20, wherein step (a) comprises sequentially generating a plurality of digitally encoded magnetic fields of respectively different magnetic field polarizations, each digitally encoded magnetic field being digitally encoded with a prescribed multi-bit digital code pattern, and step (b) comprises detecting magnetic field energy associated with one or more of said digitally encoded magnetic fields, and producing a first output signal in response to detecting a predefined level of digitally encoded magnetic field energy, comparing digital code contents of said first output signal with a replica of said prescribed multi-bit digital code pattern, generating a second output signal in response to the digital code contents of said first output signal containing said prescribed multi-bit digital code pattern, and issuing an alarm signal, representative that said first entity is physically separated by more than said specified distance from said second entity, in response to a failure of said second output signal to be produced at at least a prescribed periodic repetition rate.

22. A method according to claim 21, wherein step (b) further includes providing at said second entity an encoded radio wave transmitter, which is controllably operative to emit an encoded radio wave signal, and wherein step (a) comprises providing at said first entity an encoded radio wave receiver, which is operative to generate an humanly perceivable signal in response to detecting an encoded radio wave signal emitted by said encoded radio wave transmitter, and further including the step of:

(c) in response to the issuance of said alarm signal, causing said encoded radio wave transmitter at said second entity to emit said encoded radio wave signal, and thereby causing said encoded radio wave receiver at said first entity to generate said humanly perceivable signal in response to detecting said encoded radio wave signal emitted by said encoded radio wave transmitter.

23. A method for detecting whether a first entity has become separated entity by more than a specified distance from a second entity comprising the steps of:

(a) providing said first entity with a magnetic field generator unit which is operative to sequentially generate respective ones of a plurality of encoded, time varying magnetic fields; and

(b) providing said second entity with a magnetic field detector unit which is operative to detect magnetic field energy associated with said encoded time varying magnetic fields sequentially generated by said magnetic field generator unit with which said first entity has been provided, said magnetic field detector unit being operative, upon failing to detect a predefined threshold level of magnetic field energy, to generate a first output signal representative that said second entity has become physically separated by more than said specified distance from said first entity.

24. A method according to claim 23, wherein said magnetic field generator unit is operative to generate a plurality of encoded, time varying magnetic fields, which have magnetic field polarizations that are substantially mutually orthogonal to one another.

25. A method according to claim 23, further including an encoded radio wave transmitter, which is located at said second entity and is controllably operative to emit an encoded radio wave, and further including an encoded radio wave receiver, which is located at said first entity and is operative to generate a humanly perceptible output in response to detecting an encoded radio wave signal emitted by said encoded radio wave transmitter at said second entity.

26. A method according to claim 23, wherein said magnetic field detector unit comprises a plurality of magnetic field sensors having magnetic field polarization sensitivities that are oriented differently from one another, each of said magnetic field sensors being operative to produce a respective magnetic field detection signal in response to detecting a predefined level of magnetic energy.

27. A method according to claim 26, wherein said magnetic field detector unit is operative to perform the steps of combining magnetic field detection signals generated by said plurality of magnetic field sensors and comparing the resultant combination of said magnetic field detection signals with a value representative of said predefined threshold level of magnetic field energy.

28. A method according to claim 27, wherein said value representative of said predefined threshold level of magnetic field energy is adjustable.

29. A method arrangement according to claim 23, wherein said magnetic field generator unit is operative to digitally encode sequentially generated magnetic fields with a prescribed multi-bit digital code pattern, and wherein said magnetic field detector unit is operative to detect magnetic field energy associated with digitally encoded magnetic fields sequentially generated by said magnetic field generator and to produce a first output signal in response to detecting a predefined level of digitally encoded magnetic field energy generated by said magnetic field generator, and includes a digital decoding circuit, which compares digital code contents of said first output signal with a replica of said prescribed multi-bit digital code pattern and to generate a second output signal in response to said first output signal matching containing said prescribed multi-bit digital code pattern.

30. A method according to claim 29, wherein said magnetic field detector unit is operative to produce a third output signal in response to said second output signal not being repeatedly produced within prescribed periodic time intervals.

31. A method according to claim 30, wherein each of said magnetic field detectors is operative to produce a respective third output signal in response to failing to detect magnetic field energy generated by said magnetic field generator of at least said predefined level.