MEMS inertial sensor and method of inertial sensing

• US 9,551,576 B2
• Filed: 11/22/2012
• Issued: 01/24/2017
• Est. Priority Date: 11/23/2011
• Status: Active Grant

• Current Assignee: Silicon Microgravity Ltd.
• Original Assignee: Cambridge Enterprises Limited
• Inventors: Thiruvenkatanathan, Pradyumna, Seshia, Ashwin
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US14/360,182
• Publication Number:
  US 20140305208A1
• Time in Patent Office: 1,524 Days
• Field of Search: 735/142.9
• US Class Current: 1/1
• CPC Class Codes: G01C 19/5712 the devices involving a micromechanical structure
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• CPC Class Codes: G01P 15/097 by vibratory elements

Abstract

The invention comprises an inertial sensor comprising a frame, a proof mass, a first resonant element, the first resonant element being fixed to the frame and electrostatically coupled to the proof mass, and a second resonant element, the second resonant element being fixed to the frame, adjacent to the first resonant element such that there is substantially no electrostatic coupling between the second resonant element and the proof mass. A coupling is provided between the first resonant element and the second resonant element. A drive means is coupled to the first and second resonant elements for vibrating the first and second resonant elements and a sensor assembly is provided for detecting the amplitude of vibration of at least one of the resonant elements.

Claims

1. An inertial sensor comprising:

a frame;

a proof mass suspended from the frame by at least one flexure;

a first resonant element, the first resonant element being fixed to the frame and electrostatically coupled to the proof mass;

a second resonant element, the second resonant element being fixed to the frame, adjacent to the first resonant element such that there is substantially no electrostatic coupling between the second resonant element and the proof mass;

a coupling between the first resonant element and the second resonant element;

a drive means coupled to the first and second resonant elements for vibrating the first and second resonant elements; and

a sensor assembly for detecting the amplitude of vibration of at least one of the resonant elements.

2. An inertial sensor according to claim 1, wherein the first and second resonant elements are bulk acoustic resonators.

3. An inertial sensor according to claim 1, wherein the means for coupling the first resonant element to the second resonant element is an electrostatic coupling means.

4. An inertial sensor according to claim 3, wherein the electrostatic coupling means is a pair of plates, one plate in the pair of plates coupled to or forming part of the first resonant element and the other plate in the pair of plates coupled to or forming part of the second resonant element, and a voltage source connected to the pair of plates for applying a voltage difference between the plates.

5. An inertial sensor according to claim 1, wherein the means for coupling is a mechanical linkage between the first resonant element and the second resonant element coupled to the first resonant element at a position between the proximal and distal ends of the first resonant element and coupled to the second resonant element at a position between the proximal and distal ends of second resonating element.

6. An inertial sensor according to claim 1, wherein the means for coupling has an effective stiffness of less than half of the stiffness of both the first and second resonant elements.

7. An inertial sensor according to claim 1, wherein the first and second resonant elements are of substantially the same dimensions and material properties.

8. An inertial sensor according to claim 1, wherein the sensor assembly comprises electrical sensors positioned adjacent the first and second resonant elements.

9. An inertial sensor according to claim 1, wherein the drive means comprises a first drive electrode coupled to the first resonant element for exciting the first resonant element.

10. An inertial sensor according to claim 9, wherein the drive means further comprises a second drive electrode coupled to the second resonant element for exciting the second resonant element.

11. An inertial sensor according to claim 1, wherein the drive means includes a feedback loop to maintain an amplitude of vibration of one of the first or second resonant elements at a constant level, and wherein the sensor assembly is configured to detect the amplitude of vibration of the other of the first and second resonant elements.

12. An inertial sensor according to claim 1, further comprising at least one lever to amplify displacement of a portion of the proof mass relative to the first resonant element.

13. An inertial sensor according to claim 1, further comprising at least one additional resonant element fixed to the frame, and an additional coupling means coupling the additional resonant element to the first resonant element or the second resonant element.

14. An inertial sensor according to claim 1, further comprising a third resonant element fixed to the frame and electrostatically coupled to the proof mass;

a fourth resonant element having a proximal end and a distal end, the fourth resonant element being fixed to the frame, adjacent to the third resonant element; and

a second means for coupling the third resonant element to the fourth resonant element;

wherein the third resonant element extends from the proof mass in the same direction or an orthogonal direction orthogonal to the direction at which the first resonant element extends from the proof mass.

15. An inertial sensor according to claim 1, wherein the inertial sensor is configured as an accelerometer.

16. An inertial sensor according to claim 1, wherein the inertial sensor is configured as a gyroscope and wherein the proof mass is coupled to the first resonant element by an intermediate frame, the intermediate frame being coupled to the first resonant element by flexures that transmit movement resulting from a Coriolis force on the proof mass orthogonal to a drive direction.

17. A method of inertial sensing using a sensor comprising a proof mass coupled to a first resonant element, wherein a second resonant element is coupled to the first resonant element but not to the proof mass, comprising the steps of:

oscillating the first and second resonant elements with a drive signal of the same frequency and amplitude;

detecting an amplitude of oscillation of one of the first or second resonant elements at resonance;

adjusting the drive signal to maintain the amplitude of oscillation of one of the first and second resonant elements at a constant amplitude;

detecting an amplitude of oscillation of the other of the first and second resonant elements at resonance; and

determining the displacement of the proof mass based on the amplitude of the other of the first and second resonant elements.

18. A method according to claim 17, wherein the means for coupling the first resonant element to the second resonant element is an electrostatic coupling, further comprising the step of applying a different DC voltage to the first resonant element than to the second resonant element to provide the electrostatic coupling.