Magnetofluidic accelerometer with capacitive sensing of inertial body position

• US 20060070443A1
• Filed: 11/21/2005
• Published: 04/06/2006
• Est. Priority Date: 09/29/2004
• Status: Active Grant

• Current Assignee: InnaLabs Limited
• Original Assignee: InnaLabs Technologies, Inc.
• Inventors: Pristup, Alexander G.
• Granted Patent: US 7,143,648 B2
• Time in Patent Office: Days
• US Class Current: 73/514.80
• 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;

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.

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 inertial body has a conductive coating on portions of its surface.

9. The method of claim 1, wherein the inertial body is made of a conductive material.

10. The method of claim 1, wherein the change in capacitance is measured on two capacitive elements per side of the sensor.

11. The method of claim 1, wherein the change in capacitance is measured by measuring a change in capacitive voltage.

12. A method of measuring acceleration comprising:

suspending a non-magnetic object using a fluid;

generating a magnetic field within the fluid;

detecting a capacitance change 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.

13. An accelerometer comprising:

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,

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

14. The accelerometer of claim 13, wherein the plurality of capacitive elements comprises at least two capacitive elements per side of the accelerometer.

15. The accelerometer of claim 13, further comprising a housing enclosing the inertial body and the magnetized fluid, wherein the plurality of capacitive elements are mounted on the housing.

16. The accelerometer of claim 15, wherein the housing is any of cylindrical shaped, rectangular shaped and tetrahedral-shaped.

17. The accelerometer of claim 13, wherein the inertial body comprises a disk-shaped magnet.

18. The accelerometer of claim 13, wherein the inertial body comprises an annular-shaped magnet.

19. The accelerometer of claim 13, wherein the acceleration comprises linear acceleration.

20. The accelerometer of claim 13, wherein the acceleration comprises angular acceleration.

21. The accelerometer of claim 13, wherein the acceleration comprises three components of angular acceleration and three components of linear acceleration.

22. The accelerometer of claim 13, wherein the inertial body is non-magnetic.

23. The accelerometer of claim 13, wherein the inertial body is weakly magnetic.

24. The accelerometer of claim 13, further comprising a plurality of magnets that magnetize the magnetic fluid.

25. The accelerometer of claim 13, further comprising a housing enclosing the magnetic fluid and the inertial body, wherein the housing includes a stretchable membrane.

26. The accelerometer of claim 13, further comprising a housing enclosing the magnetic fluid and the inertial body, wherein the magnetic fluid partially fills the housing.

27. An accelerometer comprising:

a magnetic inertial body;

a magnetic fluid in contact with the inertial body; and

a plurality of electrodes arranged around the inertial body, each forming a capacitor with a 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.

28. An accelerometer comprising:

a housing incorporating a stretchable membrane;

an inertial body within the housing;

a magnetic fluid in contact with the inertial body;

a plurality of sensors sensing a change in position of the inertial body due to acceleration.