BULK ACOUSTIC WAVE ACCELEROMETERS

• US 20090095079A1
• Filed: 10/10/2008
• Published: 04/16/2009
• Est. Priority Date: 10/11/2007
• Status: Active Grant

• Current Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Original Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Inventors: Ayazi, Farrokh
• Granted Patent: US 8,528,404 B2
• Time in Patent Office: Days
• US Class Current: 73/514.29
• CPC Class Codes: G01P 15/097 by vibratory elements
• CPC Class Codes: G01P 15/0975 by acoustic surface wave resonators or delay lines

Abstract

Accelerometers and associated techniques for detecting motion are described. For a resonant accelerometer, an externally-applied acceleration can cause a change in the electrical spring constant K_c of the electromechanical system. A resonant accelerometer can be driven to resonate in a bulk acoustic wave mode of vibration, which can have a high resonant frequency. Other accelerometers and associated techniques are disclosed.

Claims

1. An accelerometer, comprising:

a resonator element configured to vibrate along a first axis in a bulk acoustic wave mode at a resonant frequency; and

at least one electrode coupled to the resonator element to excite the resonator element to vibrate along the first axis in the bulk acoustic wave mode at the resonant frequency, and to detect a measurement signal.

2. The accelerometer of claim 1, wherein the resonator element has an electrical spring constant, and wherein the at least one electrode is further configured to detect a change in the resonant frequency of the electromechanical resonator, the change in the resonant frequency being caused by a change in the electrical spring constant.

3. The accelerometer of claim 1, wherein the resonator element has a mechanical spring constant that is a substantially fixed.

4. The accelerometer of claim 1, wherein the at least one electrode comprises a drive electrode displaced from the mechanical resonator element by less than 200 nm.

5. An accelerometer, comprising:

a resonator element having a resonant frequency of at least about 1 MHz, the resonator element being configured to vibrate along a first axis; and

at least one electrode coupled to the resonator element to excite the resonator element to vibrate along the first axis at the resonant frequency, and to detect a measurement signal.

6. The accelerometer of claim 5, wherein the resonator element has an electrical spring constant, and wherein the at least one electrode is further configured to detect a change in the resonant frequency of the electromechanical resonator, the change in the resonant frequency being caused by a change in the electrical spring constant.

7. The accelerometer of claim 5, wherein the resonator element has a mechanical spring constant that is a substantially fixed.

8. The accelerometer of claim 5, wherein the at least one electrode is displaced from the mechanical resonator element by less than about 200 nm.

9. The accelerometer of claim 5, having a quality factor of at least 1,000.

10. A method of measuring motion using an electromechanical resonator having a resonant frequency and an electrical spring constant, the electromechanical resonator comprising a resonator element, the method comprising:

driving the resonator element to vibrate along a first axis at the resonant frequency; and

measuring motion along the first axis based on a change in the electrical spring constant of the electromechanical resonator.

11. The method of claim 10, wherein motion is detected based on a change in the resonant frequency of the electromechanical resonator.

12. The method of claim 10, wherein the electromechanical resonator has a mechanical spring constant that is a substantially fixed.

13. The method of claim 10, wherein the resonant frequency is higher than about 1 MHz.

14. The method of claim 10, wherein the motion is measured according to the phase of a signal provided by the electromechanical resonator.

19. The accelerometer of claim 14, further comprising at least one electrode to capacitively sense motion of the proof mass, the at least one electrode being separated from the proof mass by no more than about 200 nm.

15. A accelerometer for measuring motion in any of a plurality of axes comprising an x-axis, a y-axis, and a z-axis, the accelerometer comprising:

a substrate defining a plane of the x-axis and the y-axis;

a proof mass suspended above the substrate by a suspension system, the suspension system comprising;

at least one first suspension member configured to allow motion of the proof mass along the z-axis; and

at least one second suspension member configured to allow motion of the proof mass along the x-axis and/or the y-axis, the at least one second suspension member being mechanically connected to the at least one first suspension member, wherein the at least one second suspension member is suspended from the at least one first suspension member.

16. The accelerometer of claim 15, wherein the at least one first suspension member is compliant in the z-axis direction and has no substantial mechanical compliance along the x-axis or y-axis.

17. The accelerometer of claim 16, wherein the at least one first suspension member extends in the plane of the x-axis and the y-axis in an L-shape.

18. The accelerometer of claim 15, wherein the at least one second suspension member has no substantial mechanical compliance along the z-axis.

20. The accelerometer of claim 15, wherein the at least one first suspension member comprises at least four first suspension members, and the at least one second suspension member comprises at least four second suspension members that are each mechanically connected to a respective one of the at least four first suspension members.

21. The accelerometer of claim 15, wherein the at least one second suspension member is configured to allow motion of the proof mass along both the x-axis and the y-axis.