Electroactive apparatus and methods

• US 6,847,155 B2
• Filed: 03/27/2002
• Issued: 01/25/2005
• Est. Priority Date: 04/24/2001
• Status: Expired due to Fees

• Current Assignee: Clemson University
• Original Assignee: Clemson University
• Inventors: Narayanan, Manoj, Schwartz, Robert W.
• Primary Examiner(s): BUDD, MARK OSBORNE
• Application Number:
  US10/108,203
• Publication Number:
  US 20020153807A1
• Time in Patent Office: 1,035 Days
• Field of Search: 310/328, 310330-332
• US Class Current: 310/328
• CPC Class Codes: H10N 30/204 using bending displacement, e.g. unimorph, bimorph or multimorph cantilever or membrane benders
• CPC Class Codes: H10N 30/886 Mechanical prestressing means, e.g. springs springs in general F16F1/00
• CPC Class Codes: Y10S 310/80 Piezoelectric polymers, e.g. PVDF

Abstract

High performance electromechanical devices suitable for a wide range of applications are described. The electroactive devices are capable of operating in a manner that offers enhanced mechanical displacement responses and increased load-bearing capabilities. In one embodiment, the device is capable of providing a significantly increased level of free displacement. The electroactive devices include an electroactive composite which includes at least one electroactive material that may comprise an electrostrictive or a piezoelectric material and a tensioning device which is adapted for inducing a mechanical pre-load to the electroactive composite structure. The tensioning device exerts a mechanical pre-load upon the electroactive material which alters stress profile, increases mechanical energy and increases stored elastic energy of the electroactive devices.

Claims

1. An electroactive device, comprising:

an electroactive composite comprising an electroactive material defining a first edge and an opposite edge; and

a tensioning device selected from the group consisting of a spring, a coil, or an elastic member located at a distance from the electroactive composite, wherein said tensioning device indirectly induces a mechanical pre-load comprising compressive forces between the first edge and the opposite edge to said electroactive material, said mechanical pre-load increasing lateral tensile stresses in the surface region of the electroactive composite when in static equilibrium.

2. The electroactive device of claim 1, wherein said electroactive composite comprises multiple layers, said electroactive material being one of said multiple layers.

3. The electroactive device of claim 2, wherein one of said layers is a support layer.

4. The electroactive device of claim 3, wherein said support layer is selected from the group consisting of metals, plastics, glass, cermets, carbon fiber composites, and ceramics.

5. The electroactive device of claim 2 further comprising one or more layers selected from the group consisting of polyimides and adhesives.

6. The electroactive device of claim 1 wherein said electroactive material is selected from the group consisting of ceramics and polymers.

7. The electroactive device of claim 1 wherein said electroactive material is selected from the group consisting of electrostrictive, ferroelectric, piezoelectric, electrooptic, pyroelectric, and magnetostrictive materials and combinations thereof.

8. The electroactive device of claim 1, wherein said electroactive material is a stress-biased electroactive material comprising a convex surface and a concave surface.

9. The electroactive device of claim 8 wherein said stress-biased electroactive material comprises a piezoelectric material having a pair of electrodes attached thereto, one electrode being attached to said convex surface, and the other electrode being attached to said concave surface.

10. The electroactive device of claim 1, wherein said electroactive composite comprises more than one electroactive material.

11. The electroactive device of claim 10, wherein at least one of said electroactive materials is selected from the group consisting of a piezoelectric material and an electrostrictive material.

12. The electroactive device of claim 1, wherein said tensioning device comprises an elastic member, the member being selected from the group consisting of silicone rubber, natural rubber, neoprene rubber, butyl rubber, chlorosulfonated polyethylene, and elastomers.

13. The electroactive device of claim 1, wherein said tensioning device is an elastomeric loop.

14. The electroactive device of claim 1, wherein said electroactive device comprises more than one electroactive composite.

15. An electroactive device, comprising:

an electroactive composite comprising an electroactive material;

a tensioning device, wherein said tensioning device induces a mechanical pre-load to said electroactive material; and

an applied mass, wherein the force of said applied mass to said electroactive device is counteracted by the force of said mechanical pre-load.

16. An electroactive device, comprising:

a stress-biased electroactive composite comprising a pre-stressed, domed electroactive material layer defining a first edge and an opposite edge; and

a tensioning device, wherein said tensioning device contacts said electroactive composite at at least two points such that said two points are in opposed relation to each other across said electroactive composite thereby inducing a mechanical pre-load comprising compressive forces between the first edge and the opposite edge to said electroactive material layer, said mechanical pre-load increasing lateral tensile stresses in the surface region of the electroactive composite when in static equilibrium.

17. The electroactive device of claim 16, wherein said electroactive composite further comprises a support layer selected from the group consisting of metals, plastics, glass, cermets, carbon fiber composites, and ceramics.

18. The electroactive device of claim 16 wherein said electroactive material is selected from the group consisting of electrostrictive, ferroelectric, piezoelectric, electrooptic, pyroelectric, and magnetostrictive materials and combinations thereof.

19. The electroactive device of claim 16, wherein said electroactive composite comprises more than one electroactive material.

20. The electroactive device of claim 19, wherein at least one of said electroactive materials is chosen from the group consisting of a piezoelectric material and an electrostrictive material.

21. The electroactive device of claim 16 further comprising one or more layers selected from the group consisting of polyimides and adhesives.

22. The electroactive device of claim 16, wherein said tensioning device is selected from the group consisting of an elastomeric material, a spring, and a vise.

23. The electroactive device of claim 16, comprising more than one stress-biased electroactive composite.

24. A method for improving the electromechanical response of an electroactive device comprising:

providing an electroactive composite comprising an electroactive material defining a first edge and an opposite edge; and

indirectly inducing a mechanical pre-load comprising a compressive force between said first edge and said opposite edge to said electroactive composite by use of a tensioning device selected from the group consisting of a spring, a coil, or an elastic member, wherein said tensioning device does not contact said electroactive composite, said mechanical pre-load increasing lateral tensile stresses in the surface region of the electroactive composite when in static equilibrium.

25. The method of claim 24, wherein inducing said mechanical pre-load increases the mechanical energy of said electroactive device.

26. The method of claim 24, wherein inducing said mechanical pre-load increases the stored elastic energy of said electroactive device.

27. The method of claim 24, wherein inducing said mechanical pre-load alters the stress profile of said electroactive device and increases the surface tensile stress of said electroactive material.

28. The method of claim 24, wherein said electroactive composite is a domed, pre-stressed electroactive composite, and wherein inducing said mechanical pre-load increases the static equilibrium dome height of said electroactive composite.

29. The method of claim 28, wherein inducing said mechanical pre-load increases the static equilibrium dome height of said electroactive composite by at least about 10%.

30. The method of claim 28, wherein inducing said mechanical pre-load increases the static equilibrium dome height of said electroactive composite by about 25%.

31. The method of claim 24, wherein inducing said mechanical pre-load increases the deformation resistance of said electroactive device.

32. A method of increasing the stored elastic energy of an electroactive device comprising:

providing a stress-biased electroactive device comprising a pre-stressed, domed electroactive composite defining a first edge and an opposite edge; and

connecting a tensioning device placed under a tension to said electroactive device such that said electroactive composite is deformed with an increased curvature and a mechanical pre-load comprising compressive forces between said first edge and said opposite edge is induced to said electroactive composite, wherein said tensioning device contacts said electroactive composite at at least two points such that said two points are in opposed relation to each other across said electroactive composite, said mechanical pre-load increasing lateral tensile stresses in the surface region of the electroactive composite when in static equilibrium.

33. The method of claim 32, wherein said stored elastic energy is partially released during operation of said electroactive device.

34. An electroactive device, comprising:

a stress-biased electroactive composite comprising a pre-stressed, domed electroactive material layer;

a tensioning device, wherein said tensioning device induces a mechanical pre-load to said electroactive material layer; and

a movable sled, wherein said tensioning device is located at a distance from said electroactive composite, such that said mechanical pre-load is indirectly induced to said electroactive composite through said moveable sled.

35. The electroactive device of claim 34, further comprising added weight, wherein said added weight increases the inertia of said movable sled.