Magnetofluidic accelerometer with capacitive sensing of inertial body position

• US 7,143,648 B2
• Filed: 11/21/2005
• Issued: 12/05/2006
• Est. Priority Date: 09/29/2004
• Status: Expired due to Fees

• Current Assignee: InnaLabs Limited
• Original Assignee: FerroLabs, Inc.
• Inventors: Pristup, Alexander G.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): Hanley, John C.
• Application Number:
  US11/282,727
• Publication Number:
  US 20060070443A1
• Time in Patent Office: 379 Days
• Field of Search: 735/140.8
• US Class Current: 73/504.08
• CPC Class Codes: G01P 15/0888 for indicating angular acceleration
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/18 in two or more dimensions

Abstract

An accelerometer includes an inertial body; a magnetized fluid holding the inertial body in suspension; and a plurality of capacitive elements, each forming a capacitor with the inertial body. A displacement of the inertial body produces a change of capacitance of the capacitive elements that is indicative of acceleration. The capacitive elements include at least two capacitive elements per side of the accelerometer. A housing encloses the inertial body and the magnetized fluid, and the plurality of capacitive elements are mounted on the housing. The housing can be cylindrical shaped, rectangular shaped and tetrahedral-shaped. The inertial body can include a disk-shaped magnet, an annular-shaped magnet, or be non-magnetic, or be weakly magnetic. The acceleration can be linear acceleration, angular acceleration, or three components of angular acceleration and three components of linear acceleration. A plurality of magnets magnetize the magnetic fluid.

Claims

1. A method of measuring acceleration comprising:

suspending an inertial body using a magnetized magnetic fluid, wherein the inertial body is disk-shaped and includes two electrodes that cover substantially the entire upper and lower surfaces of the disk respectively, and additional electrodes on a curved side surface of the disk that have the shape of a curved surface,

wherein the magnetic fluid is magnetized using a plurality of magnets oriented generally along an axis of symmetry of the inertial body;

measuring a change in capacitance generated by displacement of the inertial body due to acceleration; and

calculating the acceleration based on the capacitive voltage change between the two electrodes and the additional electrodes, and external electrodes.

2. The method of claim 1, wherein the calculating step calculates linear acceleration.

3. The method of claim 1, wherein the calculating step calculates angular acceleration.

4. The method of claim 1, wherein the calculating step calculates three components of angular acceleration and three components of linear acceleration.

5. The method of claim 1, further comprising driving current through a plurality of magnets for generating a magnetic field for magnetizing the magnetic fluid.

6. The method of claim 1, wherein the inertial body is non-magnetic.

7. The method of claim 1, wherein the inertial body is weakly magnetic.

8. The method of claim 1, wherein the two electrodes and the additional electrodes are formed by a conductive coating on portions of a surface of the inertial body.

9. The method of claim 1, wherein the inertial body is annular shaped.

10. A method of measuring acceleration comprising:

suspending a non-magnetic object using a fluid, wherein the non-magnetic object is disk-shaped and includes two electrodes that cover substantially the entire upper and lower surfaces of the non-magnetic object respectively, and additional electrodes on a curved side surface of the non-magnetic object that have the shape of a curved surface;

generating a magnetic field within the fluid using a plurality of magnets oriented generally along an axis of symmetry of the non-magnetic object;

detecting a capacitance change between the two electrodes and the additional electrodes and external electrodes due to a change in position of the object as a result of acceleration; and

calculating the acceleration as a function of the control of the magnetic field.

11. An accelerometer comprising:

an inertial body that is disk-shaped and includes two electrodes that cover substantially the entire upper and lower surfaces of the disk respectively, and additional electrodes on a curved side surface of the disk that have the shape of a curved surface;

a magnetized fluid holding the inertial body in suspension, wherein the fluid is magnetized using a plurality of magnets oriented generally along an axis of symmetry of the inertial body; and

a plurality of external electrodes, each forming a capacitor with the electrodes of the inertial body,

wherein a displacement of the inertial body produces a change in capacitance of the capacitors, the change being indicative of acceleration.

12. The accelerometer of claim 11, wherein the plurality of capacitors comprises at least three capacitive elements per side of the accelerometer.

13. The accelerometer of claim 11, further comprising a housing enclosing the inertial body and the magnetized fluid, wherein the plurality of external electrodes are mounted on the housing.

14. The accelerometer of claim 13, wherein the housing is any of cylindrical shaped, rectangular shaped and tetrahedral-shaped.

15. The accelerometer of claim 11, wherein the inertial body comprises a disk-shaped magnet.

16. The accelerometer of claim 11, wherein the inertial body comprises an annular-shaped magnet.

17. The accelerometer of claim 11, wherein the acceleration comprises linear acceleration.

18. The accelerometer of claim 11, wherein the acceleration comprises angular acceleration.

19. The accelerometer of claim 11, wherein the acceleration comprises three components of angular acceleration and three components of linear acceleration.

20. The accelerometer of claim 11, wherein the inertial body is non-magnetic.

21. The accelerometer of claim 11, wherein the inertial body is weakly magnetic.

22. The accelerometer of claim 11, further comprising a plurality of magnets that magnetize the magnetic fluid.

23. The accelerometer of claim 11, further comprising a housing enclosing the magnetic fluid and the inertial body, wherein the housing includes a stretchable membrane.

24. The accelerometer of claim 11, further comprising a housing enclosing the magnetic fluid and the inertial body, wherein the magnetic fluid partially fills the housing.

25. The accelerometer of claim 11, wherein the inertial body is annular shaped.

26. An accelerometer comprising:

a magnetic inertial body that is disk-shaped and includes conductive coatings that cover substantially the entire upper and lower surfaces of the disk respectively, and additional separate conductive coatings on a curved side surface of the disk that have the shape of a curved surface;

a magnetic fluid in contact with the inertial body, wherein the magnetic fluid is magnetized using a plurality of magnets oriented generally along an axis of symmetry of the inertial body; and

a plurality of external electrodes arranged around the inertial body, each forming a capacitor with the respective conductive coating on the inertial body,

wherein a displacement of the inertial body changes a capacitive reactance of the capacitors, the change being indicative of acceleration.

27. An accelerometer comprising:

a housing incorporating a stretchable membrane;

an inertial body within the housing, the inertial body being disk-shaped and includes conductive coatings that cover substantially the entire upper and lower surfaces of the disk respectively, and additional separate conductive coatings on a curved side surface of the disk that have the shape of a curved surface;

a magnetic fluid in contact with the inertial body, wherein the magnetic fluid is magnetized using a plurality of magnets positioned generally around an axis of symmetry of the inertial body;

a plurality of sensors sensing a change in position of the inertial body due to acceleration, the sensors sensing a change in capacitance of capacitors formed by the conductive coatings and external electrodes.