Electric field proximity detector for floating and grounded targets

• US 6,859,141 B1
• Filed: 12/08/1999
• Issued: 02/22/2005
• Est. Priority Date: 12/08/1999
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Van Schyndel, Andre J., Clayton, Diane J.
• Primary Examiner(s): Lee, Benjamin C.
• Application Number:
  US09/456,567
• Time in Patent Office: 1,903 Days
• Field of Search: 379/420, 340/854.8, 340/870, 340/856.3, 340/854.6, 340562-564, 340/686.6, 341/33, 361/271, 324/658, 324/659, 324/661, 324/662, 324/663, 324/679, 324/681, 324/683, 324/686, 324/687, 324/688, 324/690
• US Class Current: 340/562
• CPC Class Codes: G01S 13/04 Systems determining presence of a target based on relative movement of target G01S13/56
• CPC Class Codes: G08B 13/187 by interference of a radiation field
• CPC Class Codes: G08B 13/2491 Intrusion detection systems, i.e. where the body of an intruder causes the interference with the electromagnetic field
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 2217/960775 Emitter-receiver or "fringe" type detection, i.e. one or more field emitting electrodes and corresponding one or more receiving electrodes

Abstract

An electric field proximity detector capable of detecting partially conductive or conductive objects regardless of their impedance to circuit ground. The detector has a sensor with a transmitting electrode, a receiving electrode, and at least one circuit ground electrode preferably arranged in a bulls-eye configuration with the ground electrode between the transmitter and receiver electrodes. With appropriate sizing, upon the approach of an object, a signal received by the receiving electrode decreases, at least until the object is within a threshold distance of the sensor. The size and positioning of the ground electrode further reduces the effects of stray capacitance.

Claims

1. A transmit-receive type electric field proximity detector suitable for detecting partially conductive or conductive objects regardless of their impedance to circuit ground, said detector comprising:

a transmitting electrode;

a receiving electrode; and

at least one ground electrode,

arranged and sized such that, upon the approach of an object, independent of the impedance to circuit ground of said object a signal received by said receiving electrode des at least until said object is within a threshold distance of one of said transmitting electrode, receiving electrode, and at least one ground electrode.

2. The proximity detector of claim 1, further comprising a signal generator electrically coupled to the committing electrode.

3. The proximity detector of claim 2, wherein the signal generator is a low frequency oscillator.

4. The proximity detector of claim 1, wherein one of the transmitting electrode and receiving electrode is a generally circular disk of conductive material, and the other of the transmitting electrode and receiving electrode is a generally circular annular ring of conductive material, said transmitting and receiving electrodes being arranged concentrically in substantially the same plane.

5. The proximity detector of claim 4, wherein said at least one ground electrode comprises a first ground electrode being a generally circular annular ring of conductive material interposed between, and lying in substantially in the same plane as, the transmitting electrode and the receiving electrode.

6. The proximity detector of claim 5, wherein said at least one ground electrode further comprises a second ground electrode being a plate of conductive material having an extent at least equal to an extent of said other of said transmitting electrode and receiving electrode, said second ground electrode being positioned behind, and substantially parallel to, the transmitting electrode, receiving electrode, and first ground electrode.

7. The proximity detector of claim 6, wherein the first ground electrode is electrically coupled to the second ground electrode.

8. The proximity detector of claim 7, wherein the first ground electrode and second ground electrode are electrically insulated from said transmitting electrode and said receiving electrode.

9. The proximity detector of claim 8, wherein said transmitting electrode is said generally circular disk, and said receiving electrode is said surrounding generally circular annular ring.

10. The proximity detector of claim 5, wherein a relative diameter of the electrode disk is greater than 0 and less than 30, a relative inner diameter to outer diameter width of the annular ring ground electrode is greater than 0 and less than 15, and a relative inner diameter to outer diameter width of the outermost annular ring electrode is greater than 5 and less than 25.

11. The proximity detector of claim 8, further comprising detector circuitry coupled to said receiving electrode and being responsive to the induced electrical signal therefrom for generating an output signal indicative of the approach of an intruding object.

12. The proximity detector of claim 11, wherein said first ground electrode and said second ground electrode are electrically coupled to circuit ground of said detector circuitry.

13. The proximity detector of claim 12, wherein said second ground electrode is physically interposed between said detector circuitry and both the transmitting electrode and the receiving electrode.

14. The proximity detector of claim 13, wherein said detector circuitry further comprises a signal detector, an amplifier, and a rectifier, the input of said signal detector being electrically coupled to said receiving electrode, the input of said amplifier being electrically coupled to the output of said signal detector, and the input of said rectifier being electrically coupled to the output of said amplifier.

15. The proximity detector of claim 1, wherein send threshold distance is about 10 millimeters.

16. The proximity detector of claim 1, wherein one of the transmitting electrode and receiving electrode is a first plate of conductive material having a first polygonal outline, and the other of the transmitting electrode and receiving electrode is a second plate of conductive material having a second polygonal outline, said second plate having a concentric aperture, said aperture having a third polygonal outline, said transmitting and receiving electrodes being arranged concentrically in substantially the same plane.

17. The proximity detector of claim 16, wherein said at least one ground electrode comprises a first ground electrode being a third plate of conductive material having a fourth polygonal outline, said third plate having a concentric aperture, said aperture having a fifth polygonal outline, said first and electrode being interposed between, and lying in substantially in the same plane as, the transmitting electrode and the receiving electrode.

18. The proximity detector of claim 17, wherein said at least one ground electrode further comprises a second ground electrode being a fourth plate of conductive material having a sixth polygonal outline, said second ground electrode having an extent at least equal to an extent of said other of said transmitting electrode and receiving electrode, said second ground electrode further being positioned behind, and substantially parallel to, the transmitting electrode, receiving electrode, and first ground electrode.

19. The proximity detector of claim 18, each of said first, second, third, fourth, fifth and sixth polygonal outlines is a regular polygonal shape with sides of equal length.

20. The proximity detector of claim 19, wherein the first ground electrode is electrically coupled to the second ground electrode.

21. The proximity detector of claim 20, wherein the first ground electrode and second ground electrode are electrically isolated from said transmitting electrode and said receiving electrode.

22. The proximity detector of claim 21, wherein said transmitting electrode is said first plate, and said receiving electrode is said sounding, apertured second plate.

23. A sensor suitable for use in a transmit-receive type electrode field proximity detector, said sensor having a circuit ground and comprising:

a transmitting electrode;

a receiving electrode; and

at least one circuit ground electrode,

arranged and sized such that, upon the approach of an object, independent of the impedance to circuit ground of said object, the effective impedance between the receiver electrode and the at least one circuit ground electro decreases more quickly than the sum of the impedance between the receiver electrode and the at least one circuit ground electrode and the impedance between the transmitting electrode and the receiving electrode, at least until said object is within a threshold distance of one of said transmitting electrode, receiving electrode, and at least one ground electrode.

24. The sensor of claim 23, wherein one of the transmitting electrode and receiving electrode is a generally circular disk of conductive material, and, and the other of the transmitting electrode and receiving electrode is a generally circular annular ring of conductive material, said transmitting and receiving electrodes being arranged concentrically in substantially the same plane.

25. The sensor of claim 24, wherein said at least one ground electrode comprises a first ground electrode being a generally circular annular rin of conductive material interposed between and lying in substantially in the same plane as, the transmitting electrode and the receiving electrode.

26. The sensor of claim 25, when said at least one ground electrode further comprises a second ground electrode being a plate of conductive material having an extent at least equal to an extent of said other of said transmitting electrode and receiving electrode, said second ground electrode being positioned behind, and substantially parallel to, the transmitting electrode, receiving electrode and first ground electrode.

27. The sensor of claim 26, wherein the first ground electrode is electrically coupled to the second ground electrode.

28. The or of claim 27, wherein the first ground electrode and electrode ground electrode are electrically insulated from said transmitting electrode and said receiving electrode.

29. The sensor of claim 28, wherein said transmitting electrode is said generally circular disk, and said receiving electrode is said surrounding generally circular annular ring.

30. The seer of claim 25, wherein a relative diameter of the electrode disk is greater than 0 and less than 30, a relative inner diameter to outer diameter width of the annular ring ground electrode is greater than 0 and less than 15, and a relative inner diameter to outer diameter width of the outermost annular ring electrode is greater than 0 and less than 25.

31. A sensor suitable for use in a transmit-receive type electric field proximity detector, said sensor having a circuit ground and comprising:

a transmitting electrode driven with a low impedance;

a receiving electrode actively held at circuit ground potential; and

at least one circuit ground electrode connected to an earth ground,

arranged and sized such that, upon the approach of an object, independent of the impedance to circuit around of said object, the capacitance between the object and circuit ground increases more quickly than the product of the capacitance between the object and the transmitting electrode and the capacitance between the object and the receiving electrode, at least until said object is within a threshold distance of one of said transmitting electrode, receiving electrode and at least one ground electrode.