Magnetic field sensor using microelectromechanical system

• US 20030020472A1
• Filed: 09/27/2001
• Published: 01/30/2003
• Est. Priority Date: 07/30/2001
• Status: Active Grant

• Current Assignee: Longitude Licensing Limited (Vector Capital Corporation)
• Original Assignee: Rockwell Automation Technologies Incorporated (Rockwell Automation, Inc.)
• Inventors: Kretschmann, Robert J., Harris, Richard D.
• Granted Patent: US 6,664,786 B2
• Time in Patent Office: Days
• US Class Current: 324/259
• CPC Class Codes: G01R 15/20 using galvano-magnetic devices, e.g. Hall-effect devices , i.e. measuring a magnetic field via the interaction between a current and a magnetic field, e.g. magneto resistive or Hall effect devices
• CPC Class Codes: G01R 33/028 Electrodynamic magnetometers
• CPC Class Codes: G01R 33/0286 comprising microelectromechanical systems [MEMS] MEMS devices in general B81B

Abstract

A microelectromechanical systems (MEMS) Device manufactured on a microscopic scale using integrated circuit techniques provides a sensitive magnetic field sensor by detecting motion caused by the Lorentz force produced by a current through a MEMS conductor. The resulting MEMS may be used as a component in a variety of devices including current sensors and proximity sensors.

Claims

1. A microelectromechanical system (MEMS) sensor providing magnetic field measurement, the sensor comprising:

a substrate supporting a first and second terminal;

a flexible conductor extending between the first and second terminals and positionable within a crossing magnetic field, the flexible conductor providing a path of conduction of a current between the first and second terminals; and

a detector communicating with the flexible conductor for detecting the Lorentz force deflection of the flexible conductor, the detector generating an output signal dependent on this force and thus on the strength of the crossing magnetic field.

2. The MEMS detector of claim 1 further including a proof current source communicating with the first and second terminals to provide a predetermined proof current through the flexible conductor.

3. The MEMS detector of claim 1 wherein the flexible conductor is substantially straight.

4. The MEMS detector of claim 3 wherein the flexible conductor is less than one millimeter long.

5. The MEMS detector of claim 1 including further a beam connecting the flexible conductor to the detector for communication of displacement of the flexible conductor therebetween.

6. The MEMS detector of claim 5 wherein the flexible conductor is a conductive layer on an insulating material and wherein the conductive layer is interrupted on the beam passing to the detector.

7. The MEMS detector of claim 6 wherein the conductive layer is selected from the group consisting of a metal, a semiconductor and a combination of metal and semiconductor.

8. The MEMS detector of claim 1 wherein the substrate further supports integrated circuitry.

9. The MEMS detector of claim 1 wherein the detector is selected from the group consisting of:

variable gap capacitors, optical detectors, resistive detectors, piezoelectric detectors and inductive detectors.

10. The MEMS detector of claim 1 further including a bias means communicating with the flexible conductor and producing a bias force resisting the Lorentz force of the flexible conductor.

11. The MEMS detector of claim 1 further including a bias means communicating with the flexible conductor and producing a bias force augmenting the Lorentz force of the flexible conductor.

12. The MEMS detector of claim 10 wherein the bias means receives an electrical signal to control the bias source.

13. The MEMS detector of claim 12 wherein the bias source is selected from the group consisting of an electrostatic motor, a thermal motor, and a piezoelectric motor.

14. The MEMS detector of claim 10 wherein the bias source is a flexible element.

15. The MEMS detector of claim 1 further including a feedback circuit communicating with the bias means and responding to the output signal to vary the force resisting the Lorentz force of the flexible conductor.

16. The MEMS detector of claim 1 further including a feedback circuit communicating with the bias means and responding to the output signal to vary the force augmenting the Lorentz force of the flexible conductor.

17. The MEMS detector of claim 1 further including a compensation coil and a feedback circuit responding to the output signal to energize the compensation coil to oppose the crossing magnetic field.

18. The MEMS detector of claim 1 further including magnetic field biasing means and a feedback circuit wherein the feedback circuit modifies the current in the flexible conductor.

19. The MEMS detector of claim 1 further including:

a third and fourth terminal supported by the substrate;

a second flexible conductor extending between the third and fourth terminals and generally parallel with the first flexible conductor and positionable within the crossing magnetic field, the flexible conductor providing a path of conduction of a current between the third and fourth terminals;

a second detector communicating with the second flexible conductor for detecting Lorentz deflection force of the second flexible conductor, the second detector generating a second output signal dependent on this force and thus on the strength of the crossing magnetic field; and

a combiner circuit combining the first and second output signals to reject detector signals not related to the strength of the crossing magnetic field.

20. The MEMS device of claim 19 further including a proof current source communicating with the first, second, third and fourth terminals to provide for opposite currents in the first and second flexible conductors.

21. The MEMS device of claim 19 wherein the first and second output signals are of opposite polarity with Lorentz deflection force of the first and second flexible conductors.

22. The MEMS detector of claim 1 wherein the output signal is an analog signal.

23. The MEMS detector of claim 1 wherein the output signal is a digital signal.

24. The MEMS detector of claim 1 further including a measurement conductor for conducting a current to be measured therethrough, the measurement conductor position adjacent to the flexible conductor whereby the crossing magnetic field is a magnetic field produced by the current to be measured;

whereby the output signal provides an indication of the current to be measured.

25. The MEMS detector of claim 24 further including a magnetic core concentrating the flux from the measurement conductor to impinge on the flexible conductor.

26. The MEMS detector of claim 25 further including a compensation coil and a feedback circuit responding to the output signal to energize the compensation coil to oppose the crossing magnetic field wherein the compensation coil couples to the magnetic core.

27. The MEMS detector of claim 1 further including a magnet providing a predetermined crossing magnetic field.

28. The MEMS detector of claim 1 further including a switch operator movable to vary the crossing magnetic field;

whereby the output signal may provide a switch signal indicating movement of the switch operator.

29. The MEMS detector of claim 28 wherein the operator is attached to a permanent magnet.

30. A microelectromechanical system (MEMS) sensor providing magnetic field measurement, the sensor comprising:

a substrate supporting a set of pylons;

a beam supported above the substrate by at least two pairs of opposing flexible arms extending transversely to the pylons on opposites sides of the beam;

a flexible conductor supported by one pair of opposing flexible arms to extending between a first and second terminals on corresponding opposed pylons, the flexible conductor positionable within a crossing magnetic field to provide a path of conduction of a current between the first and second terminals; and

a detector attached to the beam to the flexible conductor but insulated therefrom for detecting movement of the beam to produce an output signal dependent on a Lorentz force acting on the flexible conductor and thus on the strength of the crossing magnetic field.

31. A method of sensing a magnetic field using a microelectromechanical system (MEMS) comprising the steps of:

positioning a flexible MEMS conductor between a first and second terminal within a crossing magnetic field;

applying a proof current to the flexible MEMS conductor; and

detecting a Lorentz force induced deflection of the flexible MEMS conductor to generate an output signal dependent on the Lorentz force and thus on the strength of the crossing magnetic field.

32. The method of claim 31 wherein the proof current is constant.

33. The method of claim 31 wherein the flexible conductor is substantially straight.

34. The method of claim 31 wherein the step of detecting a Lorentz force deflection employs a beam connecting the flexible conductor to a detector for communication of displacement of the flexible conductor to the detector.

35. The method of claim 34 wherein the beam includes an insulating portion.

36. The method of claim 31 wherein the step of detecting a Lorentz deflection of the flexible conductor employs a detector is selected from the group consisting of variable gap capacitors, optical detectors resistive detectors, inductive detectors and piezoelectric detectors.

37. The method of claim 31 further including the step of imposing a bias force on the flexible conductor resisting the Lorentz force.

38. The method of claim 31 further including the step of imposing a bias force on the flexible conductor augmenting the Lorentz force.

39. The method of claim 38 wherein the bias force is proportional to the Lorentz force.

40. The method of claim 38 wherein the bias force is proportional to deflection of the flexible conductor.

41. The method of claim 31 further including a compensation coil and including the step of energizing the compensation coil to neutralize the crossing magnetic field at the flexible conductor.

42. The method of claim 31 further including the steps of

positioning a second flexible MEMS conductor between a third and fourth terminal within the crossing magnetic field;

applying a proof current to the second flexible MEMS conductor;

detecting a Lorentz force induced deflection of the second flexible MEMS conductor to generate a second output signal dependent on the Lorentz force and thus on the strength of the crossing magnetic field; and

combining the first and second output signals to reject detector signals not related to the strength of the crossing magnetic field.

43. The method of claim 42 wherein the step of applying the proof current to the first and second flexible MEMS conductors applies the proof currents in opposite directions.

44. The method of claim 42 wherein the first and second output signals are of opposite polarity with Lorentz deflection force of the first and second flexible MEMS conductors.

45. The method of claim 31 wherein the output signal is an analog signal.

46. The method of claim 31 wherein the output signal is a digital signal.

47. The method of claim 31 further including the step of positioning a measurement conductor for conducting a current to be measured therethrough adjacent to the flexible conductor whereby the crossing magnetic field is a magnetic field produced by the current to be measured;

whereby the output signal provides an indication of the current to be measured.

48. The method of claim 42 further including the step of concentrating the flux from the measurement conductor to impinge on the flexible conductor through a magnetic core.

49. The method of claim 48 further including the step of coupling a compensation coil to the magnetic core and using a feedback circuit responding to the output signal to energize the compensation coil.