Single crystal piezo (SCP) apparatus and method of forming same

• US 20040154730A1
• Filed: 02/10/2003
• Published: 08/12/2004
• Est. Priority Date: 02/10/2003
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Clingman, Dan J., Jacot, A. Dean
• Granted Patent: US 6,994,762 B2
• Time in Patent Office: Days
• US Class Current: 156/160
• CPC Class Codes: B32B 37/144 using layers with different mechanical or chemical conditions or properties, e.g. layers with different thermal shrinkage, layers under tension during bonding constructional features for tensioning B32B38/1825
• CPC Class Codes: B32B 38/1866 conforming the layers or laminate to a convex or concave profile
• CPC Class Codes: H10N 30/073 by fusion of metals or by adhesives
• CPC Class Codes: H10N 30/204 using bending displacement, e.g. unimorph, bimorph or multimorph cantilever or membrane benders
• CPC Class Codes: H10N 30/30 with mechanical input and electrical output, e.g. functioning as generators or sensors
• CPC Class Codes: Y10T 29/42 Piezoelectric device making
• CPC Class Codes: Y10T 29/49863 with prestressing of part

Abstract

A single crystal piezo (SCP) apparatus and method of forming same. The apparatus is ideally suited for actuator and energy harvesting applications. The apparatus includes an SCP layer bonded to a surface of a flexible metal layer while the metal layer is held flattened within a press or other tool. Once the bonding process is complete, the metal layer, it imparts a compressive strain to the SCP layer bonded thereto. A layer of uniaxial graphite may also be bonded to the SCP layer to eliminate the poison'"'"'s ratio tension that would otherwise be created in the SCP layer.

Claims

1. A method for imparting a compressive strain to a single crystal piezo (SCP) material, comprising:

placing a flexible substrate on a support surface;

placing a layer of adhesive on a first surface of said flexible substrate;

placing a layer of single crystal piezo (SCP) material on said adhesive; and

bonding said SCP layer to said flexible substrate in a manner that causes said flexible substrate to impart a compressive stress into said SCP material.

2. The method of claim 1, wherein said step of placing said flexible substrate comprises placing a curved flexible substrate within a tool suitable for temporarily flattening said flexible substrate.

3. The method of claim 2, wherein said step of bonding comprises bonding said layer of SCP material to said flexible substrate while said flexible substrate is held in a flattened condition.

4. The method of claim 1, wherein said bonding step comprises:

applying a voltage to said SCP material to cause said SCP material to shorten in longitudinal length; and

allowing said adhesive to set before removing said voltage, said flexible substrate operating to impart said compressive stress as said voltage is removed.

5. The method of claim 4, wherein said bonding step comprises holding said SCP layer under pressure against said flexible substrate while said flexible substrate is held against a tool surface.

6. The method of claim 1, wherein said step of placing said flexible substrate against said support surface comprises placing a flat, flexible substrate against said support surface.

7. A method of imparting a compressive strain to a single crystal piezo (SCP) material, comprising:

placing a flexible substrate component having a predetermined curvature on a first surface;

placing a layer of adhesive on a concave contact surface of said substrate component;

placing a layer of SCP material on said concave contact surface of said substrate component;

applying a force to said SCP material from a side opposite to that which is in contact with said concave contact surface, so as to flatten said substrate component against said first surface;

maintaining said force applied to said SCP material and said substrate component for a time sufficient to allow said adhesive to bond said SCP material to said concave contact surface of said substrate component; and

removing said force to allow said substrate component to flex back to its said predetermined curvature to thus apply a compressive strain to said SCP material.

8. The method of claim 7, further comprising:

prior to applying said force, placing a layer of adhesive onto a surface of said SCP material which is opposite to said surface facing said substrate component;

placing a layer of uniaxial graphite against said surface of said SCP material opposite to said surface facing said substrate component; and

maintaining said force against said layer of uniaxial graphite, said SCP material and said substrate component for a time sufficient to bond said uniaxial graphite to said SCP material.

9. The method of claim 7, wherein the step of placing a substrate component on a first surface comprises placing a brass component against said first surface.

10. The method of claim 7, wherein the step of placing a substrate component on a first surface comprises placing a graphite epoxy composite component against said first surface.

11. The method of claim 7, wherein the step of placing a substrate component on a first surface comprises placing a glass epoxy composite component against said first surface.

12. The method of claim 7, wherein the step of maintaining said force applied to said SCP material comprises maintaining said force for a time period of at least about one hour.

13. The method of claim 7, wherein the step of placing a layer of adhesive on a contact surface of said substrate component comprises placing a layer of electrically conductive epoxy on said contact surface.

14. The method of claim 7, wherein the step of placing a flexible substrate comprises placing a flexible steel substrate on said first surface.

15. A method of forming an apparatus having a single crystal piezo (SCP) layer, comprising:

placing a first adhesive on a concave side of a flexible component having a predetermined curvature;

placing a layer of single crystal piezo (SCP) material having a first surface and a second surface against said first adhesive such that said second surface thereof is in at least partial contact with said first adhesive;

applying a force to said first surface of said SCP material sufficient to at least substantially flatten said flexible component;

maintaining an application of said force for a time sufficient to bond said SCP material to said flexible component; and

removing said application of force to allow said flexible component to flex back into said predetermined curvature, thereby generating a compressive strain in said SCP material.

16. The method of claim 15, further comprising:

prior to applying said force, placing a second adhesive on said first surface of said SCP material;

placing a layer of uniaxial graphite at least partially against said second adhesive; and

applying said force for a time sufficient to also bond said uniaxial graphite layer to said first surface of said SCP material.

17. The method of claim 15, wherein said step of placing a first adhesive on a concave side of a flexible component comprises placing said first adhesive on a length of spring steel.

18. The method of claim 15, wherein the step of placing a first adhesive on a concave side of a flexible component comprises placing an electrically conductive epoxy on said concave side.

19. The method of claim 15, wherein the step of maintaining said force comprises maintaining said force for a time period of at least about one hour.

20. The method of claim 15, wherein the step of placing a first adhesive on a concave side of a flexible component comprises placing an adhesive on a concave side of one of:

a brass component;

a graphite epoxy composite component; and

a glass epoxy composite component.

21. An energy harvesting apparatus comprising:

a metal layer having a predetermined curvature;

a layer of single crystal piezo (SCP) material bonded to a concave surface of said metal layer while said metal layer has been held in a flattened out orientation such that said metal layer, when allowed to flex back into its predetermined curvature, imparts a compressive strain to said SCP material.

22. The apparatus of claim 21, further comprising a layer of uniaxial graphite bonded to a surface of said SCP material facing away from said metal layer, while said metal layer is held in said flattened out orientation.

23. The apparatus of claim 21, wherein said metal layer comprises a spring steel layer.

24. The apparatus of claim 21, wherein said metal layer comprises a brass layer.

25. The apparatus of claim 21, wherein said metal layer comprises a composite material.

26. A method for forming an energy harvesting apparatus, comprising:

providing a flexible layer of material having a preformed curvature forming a concave surface;

providing a layer of single crystal piezo (SCP) material;

placing an adhesive on one of said flexible layer and said layer of SCP material;

placing said flexible layer and said SCP material into contact with one another such that said SCP material is in contact with said concave surface;

applying a force to one of said flexible layer and said SCP material sufficient to flatten said flexible layer;

maintaining an application of said force for a time sufficient to bond said flexible layer to said SCP material; and

removing said force to allow said flexible layer to flex back into said preformed curvature, thus providing a compressive strain to said SCP material.

27. The method of claim 26, further comprising:

bonding a layer of uniaxial graphite material to a surface of said SCP material.

28. The method of claim 27, wherein said bonding of said uniaxial graphite material, and said bonding of said flexible layer and said SCP material, are performed concurrently.

29. An actuator comprising:

a flexible layer of material having a predetermined curvature, thereby producing a concave surface;

a layer of single crystal piezo (SCP) material;

a layer of adhesive for bonding said SCP layer to said concave surface of said flexible layer while said flexible layer is held in a generally flat orientation, thus providing a compressive strain to said SCP material when said flexible layer is allowed to flex back into said predetermined curvature.

30. The actuator of claim 29, further comprising a layer of uniaxial graphite material boned to a surface of said SCP layer opposite that surface which is bonded to said flexible layer.

31. The actuator of claim 29, wherein said flexible layer comprises a layer of spring steel.

32. The actuator of claim 29, wherein said flexible layer comprises one of:

a graphite epoxy composite material;

a glass epoxy composite material; and

a layer of brass.