Magnetic and electric force sensing method and apparatus

• US 5,036,286 A
• Filed: 03/12/1990
• Issued: 07/30/1991
• Est. Priority Date: 06/03/1988
• Status: Expired due to Fees

• Current Assignee: University of Hawai'i
• Original Assignee: Research Corporation of The University of Hawaii
• Inventors: Umemoto, Donald K., Holm-Kennedy, James W.
• Primary Examiner(s): Weider, Kenneth A.
• Assistant Examiner(s): EDMONDS, WARREN
• Application Number:
  US07/501,296
• Time in Patent Office: 505 Days
• Field of Search: 324/207.11, 324/207.12, 324/207.13, 324/207.14, 324/661, 324/690, 324/684-686, 324/71.5, 324/72, 324/260, 324/252, 73/780, 73/862.63, 73/862.64, 73/862.69, 73/718-727, 340/870.37, 307/309, 307/320, 310/327, 310/311, 357/27, 357/51, 361/383, 338/3, 338/4, 338/42, 338/47, 338/114
• US Class Current: 324/661
• CPC Class Codes: G01R 33/038 using permanent magnets, e.g. balances, torsion devices

Abstract

A magnetic and electric force sensing method uses a force responsive transducer made of a micromachined, solid state magnetic sensor consisting of a central silicon platform surrounded and supported by a thin silicon membrane. The silicon substrate is placed over an aluminum pad recessed into a well on a supporting glass substrate. The magnetic sensor responds to a static method of measuring force whereby the Earth'"'"'s magnetic field or magnetic field or other origin acts as an attractive or repulsive force towards the magnetic material placed onto the silicon platform. The magnetic force mechanically displaces the silicon platform and diaphragm membrane which is transduced to an electrical signal where a change in capacitance is measured. Geometry of the silicon platform, diaphragm membrane and glass well depth are used to affect the linearity, sensitivity and range of measurements of the magnetic sensor.

Claims

1. A method of measurement of electric and magnetic force comprising:

etching a well and a channel within a supporting substrate, mounting a fixed capacitive plate within said well, attaching a dynamic substrate having a membrane portion serving as a displaceable capacitive plate to the supporting substrate, thereby suspending the displaceable capacitive plate portion of the dynamic substrate over the etched well and fixed plate, mounting a field responsive material on the displaceable capacitive plate, such that the membrane is in between the fixed plate and the material, displacing the capacitive plate by a field responsive force vector, transducing the plate thereby displacing the plate and producing an electrical capacitive change and sensing the change.

2. The method of claim 1 wherein the sensing comprises sensing magnetic force through the transduced electrical capacitive change.

3. The method of claim 1 wherein the transducing comprises changing capacitance by moving the displaceable plate in relation to a fixed plate.

4. The method of claim 1 further comprising mounting a similar but non-responsive material on a second similar displaceable capacitive plate, transducing the second plate, and displacing the second plate and producing electrical capacitance change and sensing the change, comparing the first capacitance change with the reference capacitance change.

5. The method of claim 1 further comprising mounting second and third similar responsive material on second and third displaceable capacitive plates arranging the first, second and third plates on XYZ orthogonal axis, separately transducing the plates and separately displacing the plates and producing separate electrical capacitive changes and separately sensing the changes thereby determining three components of the field.

6. The method of claim 5 wherein the mounting comprises mounting a magnetic responsive material.

7. The method of claim 1 wherein the mounting comprises mounting a magnetic responsive material.

8. The method of claim 7 further comprising indicating earth magnetic direction with the sensed change.

9. Magnetic and electric force vector sensing apparatus comprising a field reactive sensor having a supporting substrate with a well, means for mounting a fixed capacitance plate on the bottom of the well in the substrate, a dynamic substrate having a mounting means for mounting the dynamic substrate on the supporting substrate, a diaphragm membrane attached to the mounting means, a movable capacitive plate means on the diaphragm membrane, a platform attached to the diaphragm membrane, a magnetic material attached to the platform, such that the membrane is in between the fixed plate and the material, channeling port means for channeling air flow to and from the well, sensing means for sensing movement of the platform in response to a magnetic force vector acting on the magnetic material.

10. The apparatus of claim 9 wherein the diaphragm membrane and the platform are machined out of a monolithic element.

11. The apparatus of claim 10 wherein the monolithic element is silicon.

12. The apparatus of claim 10 wherein the mounting means is machined out of the same monolithic element.

13. The transducer apparatus of claim 9 wherein the magnetic sensor is produced through batch processing technology and micromachining methods.

14. The transducer apparatus of claim 9 wherein the dynamic substrate is etched from a single material.

15. The transducer apparatus of claim 14 wherein the single material is a semiconductor of crystalline structure.

16. The magnetic and electric force vector apparatus of claim 9 wherein the dynamic substrate is a silicon block.

17. The magnetic and electric force vector sensor apparatus of claim 9 wherein the means for fixing a capacitance plate comprises a well in the supporting substrate and further comprising a port means in the supporting substrate for flowing fluid into and out of the well.

18. The magnetic sensor apparatus of claim 17 wherein the port means comprises means for flowing gas.

19. The magnetic sensor apparatus of claim 17 wherein the port means comprises a damping means having a length and cross section for providing a specific amount of damping of motion of the movable plate displacement.

20. The magnetic sensor apparatus of claim 19 wherein the damping means comprises a critical damping means for providing critical damping.

21. The apparatus of claim 17 wherein a depth of the well determines sensitivity and measurement range of the sensor apparatus.

22. The apparatus of claim 9 wherein the geometry and dimension of the membrane may be changed to affect the magnetic sensor'"'"'s sensitivity and measurement range.

23. The apparatus of claim 9 wherein the supporting means for holding the second capacitive plate in a fixed position is formed of silicon.

24. Magnetic and electric force vector sensor apparatus comprising a block having a recess, a displaceable membrane positioned over the recess, means for holding the membrane on the block over the recess, means for channeling fluid to and from the recess, magnetic means on the membrane such that the membrane is in between the recess and the magnetic means, measuring means for measuring displacement of the membrane and indicating means for indicating force related to the mass as a function of the measuring.

25. The apparatus of claim 24 wherein the measuring means comprises strain gauge means attached to the membrane.

26. The apparatus of claim 24 wherein the measuring means comprises piezoresistive film resistors on the membrane.

27. The apparatus of claim 24 wherein the measuring means comprises piezoresistive elements diffused in the membrane.

28. The apparatus of claim 24 wherein the measuring means comprises a first conductive means on the membrane.

29. The apparatus of claim 28 wherein the measuring means further comprises a second conductive means in the recess and electrical means for measuring changes between the first and second conductive means.

30. The apparatus of claim 29 wherein the measuring means further comprises driving means connected to the first and second conductive means for returning the conductive means to a null position and wherein the electrical means comprises means measuring potential in the driving means.

31. The apparatus of claim 30 wherein the measuring means further comprises means for measuring resistive changes in the first conductive means.