Leveraged shear mode accelerometers

• US 20080072671A1
• Filed: 09/26/2006
• Published: 03/27/2008
• Est. Priority Date: 09/26/2006
• Status: Abandoned Application

• Current Assignee: Eldon Eller, Sarah Rhee
• Original Assignee: Eldon Eller, Sarah Rhee
• Inventors: Rhee, Sarah, Eller, Eldon
• Application Number:
  US11/535,364
• Publication Number:
  US 20080072671A1
• Time in Patent Office: Days
• US Class Current: 73/514.34
• CPC Class Codes: G01P 15/0915 of the shear mode type

Abstract

A single crystal based leveraged shear mode accelerometer includes a housing base portion with a base portion bottom surface that includes two base metallization areas. A housing top portion is coupled to the housing base portion. A subassembly includes a piezoelectric single crystal positioned between the housing base portion and the housing top portion. The piezoelectric single crystal is held vertical by the base portion and a shear plate bonded with a metal loaded electrical conductive epoxy. The base portion and the shear plate both have machined edges in a vertical direction. These machined edges pointing against an electrically insulating plate and form an active electrical connection at a top surface of the piezoelectric single crystal, and an electrical ground connection at a bottom surface of the piezoelectric single crystal. The subassembly is held to a mass construct with micromachined screws to the base portion, forming an accelerometer assembly in tension.

Claims

1. A single crystal based leveraged shear mode accelerometer, comprising:

a housing base portion with a base portion bottom surface that includes two base metallization areas;

a housing top portion coupled to the housing base portion; and

a subassembly that includes a piezoelectric single crystal positioned between the housing base portion and the housing top portion, the piezoelectric single crystal being held vertical by the base portion and a shear plate bonded with a metal loaded electrical conductive epoxy, the base portion and the shear plate both having machined edges in a vertical direction pointing against an electrically insulating plate and form an active electrical connection at a top surface of the piezoelectric single crystal and an electrical ground connection at a bottom surface of the piezoelectric single crystal, the subassembly being held to a mass construct with micromachined screws to the base portion forming an accelerometer assembly in tension.

2. The accelerometer of claim 1, wherein the mass construct is a two-piece tungsten construct.

3. The accelerometer of claim 1, wherein the housing base portion, crystal and shear plate assembly are held to the mass construct with the micromachined screws in tension.

4. The accelerometer of claim 1, wherein the mass construct is made of micromachined tungsten with threads and two fitted screws.

5. The accelerometer of claim 1, wherein the mass construct is isolated from the subassembly by an electrically insulating ceramic plate.

6. The accelerometer of claim 1, wherein the accelerometer assembly in tension is formed without epoxy flue lines.

7. The accelerometer of claim 1, wherein the piezoelectric single crystal is a shear mode (d ₁₅) relaxor single crystal.

8. The accelerometer of claim 1, wherein the piezoelectric single crystal is a PMN-PT (lead metaniobate—

lead titanate) or PZN-PT (lead zinc niobate—

lead titanate) crystal, electroded and poled in <

100>

direction, with electrodes removed and reapplied in perpendicular direction.

9. The accelerometer of claim 1, wherein the piezoelectric single crystals senses mechanical vibration in a z-axial direction.

10. The accelerometer of claim 1, wherein the base portion is formed of metallized ceramic.

11. The accelerometer of claim 1, wherein the accelerometer is a rectangular prismatic structure poled in perpendicular direction to the electrodes.

12. The accelerometer of claim 1, wherein the accelerometer has a high voltage output.

13. The accelerometer of claim 1, wherein the accelerometer has a high voltage output of greater than 200 mV/g.

14. The accelerometer of claim 1, wherein the accelerometer is included in a device that measures vibration.

15. The accelerometer of claim 1, wherein the accelerometer is configured to measure vibration at a frequency under resonance.

16. The accelerometer of claim 1, wherein the accelerometer is configured to measure vibration in a range of 100 Hz to 2,500 Hz.

17. The accelerometer of claim 1, wherein the accelerometer is included in a cardiac rhythm management device.

18. The accelerometer of claim 17, wherein the accelerometer is configured to measure vibration of about 200 Hz.

19. The accelerometer of claim 1, wherein the accelerometer is included in a cardiac monitoring device.

20. A method of measuring vibration, comprising:

providing a vibration measuring device with a single crystal based leveraged shear mode accelerometer that includes a sub-assembly with a piezoelectric single crystal positioned between a housing base portion and a housing top portion, the piezoelectric single crystal being held vertical by the base portion and a shear plate bonded with a metal loaded electrical conductive epoxy, the housing base portion and the shear plate both having edges in a vertical direction that points against an electrically insulating plate and form an active electrical connection at a top surface of the piezoelectric single crystal and an electrical ground connection at a bottom surface of the piezoelectric single crystal, the subassembly being held to a two-piece tungsten mass construct with micromachined screws to the base portion forming an accelerometer assembly in tension.

positioning the vibration measuring device in a position to measure vibration at a selected site; and

utilizing the vibration measuring device to measure vibration at the selected site.

21. The method of claim 20, wherein the vibration is measured at a frequency under resonance.

22. The method of claim 20, wherein the vibration is measured in a range of 100 Hz to 2,500 Hz.

23. The method of claim 20, wherein the vibration is measured in a range of 20 to 160 Hz range in a z-axial direction.

24. The method of claim 20, wherein the vibration measuring device is included in a cardiac rhythm management device.

25. The method of claim 20, wherein the selected site is a human chest cavity.

26. The accelerometer of claim 24, wherein the accelerometer is configured to measure vibration of about 200 Hz.

27. The method of claim 20, wherein the piezoelectric single crystal is a compression mode (d ₃₁) relaxor single crystal.

28. The method of claim 20, wherein the piezoelectric single crystal is a piezoelectric crystal, poled along <

110>

.

29. The method of claim 20, wherein the piezoelectric single crystal is a PMN-PT or PZN-PT crystal, poled along <

110>

to optimize the highest (d ₃₁) piezoelectric output.