Piezoelectric actuator

Abstract

A piezoelectric actuator comprising a stack of piezoelectric layers formed from a piezoelectric material, a plurality of internal electrodes disposed throughout the stack to define active regions of the piezoelectric material therebetween which are responsive to a voltage applied across two or more groups of the internal electrodes in use, an insulating arrangement which at least partially covers at least one surface of the stack to define a piezoelectric/insulator interface, and two or more side electrodes to connect with the two or more groups of the internal electrodes. At least one bridging arrangement extends through the insulating arrangement and comprises a conductive material, so as to provide a connection between a side electrode and an internal electrode, wherein at least one first surface, defined by an interface between the conductive material and the insulating arrangement, and at least one second surface, defined by an internal boundary of a piezoelectric layer, are substantially continuous with one another in the vicinity of the piezoelectric/insulator interface.

Description

Reference has already been made to:

FIG. 1, which is a sectional drawing of a known piezoelectric actuator;

FIG. 2, which is a cross-section on R-S of the actuator of FIG. 1;

FIG. 3, which is a sectional drawing showing equipotential lines in part of the actuator of FIGS. 1 and 2, in use;

FIG. 4, which is a sectional drawing of part of a second known piezoelectric actuator; and

FIG. 5, which is a sectional drawing similar to that of FIG. 4, showing equipotential lines in the second known actuator, in use.

The present invention will now be described, by way of example only, with reference to the remaining drawings, in which:

FIG. 6 is a sectional drawing of part of an actuator according to a first embodiment of the present invention;

FIG. 7 is a sectional drawing similar to that of FIG. 6, showing equipotential lines in the actuator of the first embodiment, in use;

FIG. 8 is a sectional drawing of part of an actuator according to a second embodiment of the present invention;

FIG. 9 is a cross-section on P-Q of the actuator of FIG. 8;

FIG. 10 is a larger scale sectional drawing of part of the actuator of FIGS. 8 and 9;

FIG. 11 is a sectional drawing similar to that of FIG. 10, showing equipotential lines in the actuator of the second embodiment, in use;

FIG. 12 is a sectional drawing of part of an actuator according to a third embodiment of the present invention;

FIG. 13 is a sectional drawing similar to that of FIG. 12, showing equipotential lines in the actuator of the third embodiment, in use;

FIG. 14 is a sectional drawing of part of an actuator according to a fourth embodiment of the present invention;

FIG. 15 is a sectional drawing similar to that of FIG. 14, showing equipotential lines in the actuator of the fourth embodiment, in use;

FIG. 16 is a cross-sectional drawing of a fifth embodiment of the present invention;

FIG. 17 is a cross-sectional drawing of a sixth embodiment of the present invention;

FIG. 18( a) is a sectional drawing of a seventh embodiment of the present invention, and FIG. 18(b) is a cross-section on T-U of FIG. 18(a);

FIG. 19( a) is a sectional drawing of an eighth embodiment of the present invention, and FIG. 19(b) is a cross-section on V-W of FIG. 19(a);

FIG. 20 is a sectional drawing of an actuator according to the present invention, to illustrate a first construction method; and

FIG. 21 is a sectional drawing of an actuator according to the present invention, to illustrate a second construction method.

Claims

1. A piezoelectric actuator comprising: a stack of piezoelectric layers formed from a piezoelectric material,a plurality of internal electrodes disposed throughout the stack to define active regions of the piezoelectric material therebetween which are responsive to a voltage applied across two or more groups of the internal electrodes in use,an insulating arrangement which at least partially covers at least one surface of the stack to define a piezoelectric/insulator interface, andtwo or more side electrodes to connect with the two or more groups of the internal electrodes;wherein at least one bridging arrangement extends through the insulating arrangement, the bridging arrangement comprising a conductive material so as to provide a connection between a side electrode and an internal electrode,and wherein at least one first surface, defined by an interface between the conductive material and the insulating arrangement, and at least one second surface, defined by an internal boundary of a piezoelectric layer, are substantially continuous with one another in the vicinity of the piezoelectric/insulator interface.

2. The actuator of claim 1, wherein the first and second surfaces share a common tangent at the piezoelectric/insulator interface.

3. The actuator of claim 1, wherein the first and second surfaces intersect the plane of the piezoelectric/insulator interface at a perpendicular angle.

4. The actuator of claim 1, wherein the first and second surfaces intersect the plane of the piezoelectric/insulator interface at an oblique angle.

5. The actuator of claim 1, wherein a midplane of the or each bridging arrangement is aligned with respect to a midplane of the or each internal electrode.

6. The actuator of claim 1, wherein a midplane of the or each bridging arrangement is misaligned with respect to a midplane of the or each internal electrode.

7. The actuator of claim 1, wherein the or each bridging arrangement comprises a slot.

8. The actuator of claim 7, wherein the or each slot is a groove with parallel sides.

9. The actuator of claim 7, wherein the or each slot is a ‘v’ shaped groove.

10. The actuator of claim 7, wherein the or each slot has a rounded internal end.

11. The actuator of claim 7, wherein the or each slot has a part-cylindrical internal end.

12. The actuator of claim 8, wherein the or each slot has a sharp internal end.

13. The actuator of claim 7, wherein the or each slot traverses the piezoelectric/insulator interface.

14. The actuator of claim 7, wherein the or each bridging arrangement further comprises an internal electrode which extends into the insulating arrangement and the or each slot intersects the internal electrode within the insulating arrangement.

15. The actuator of claim 7, wherein the conductive material of the side electrode coats the surface of the or each slot.

16. The actuator of claim 7, wherein the conductive material of the side electrode fills the or each slot.

17. The actuator of claim 1, wherein the bridging arrangement comprises an internal electrode which extends through the insulating arrangement.

18. The actuator of claim 1, wherein the shape of the or each bridging arrangement is complementary to the shape of the perimeter of the respective internal electrode.

19. A method of constructing a piezoelectric actuator comprising a stack of piezoelectric layers formed from a piezoelectric material, an insulating arrangement, and two or more side electrodes, the method comprising: forming one or more slots in the insulating arrangement carried on the piezoelectric stack; andapplying a conductive material to the insulating arrangement and the or each slot so as to provide a connection between an internal electrode and one of the side electrodes,

20. The method of claim 19, wherein the or each slot is formed across the interface between the piezoelectric material of the stack and the insulating arrangement.

21. The method of claim 19, wherein the conductive material is coated on the surface of the or each slot.

22. The method of claim 19, wherein the conductive material fills the or each slot.

23. A piezoelectric actuator comprising: a stack of piezoelectric layers formed from a piezoelectric material,a plurality of internal electrodes disposed throughout the stack to define active regions of the piezoelectric material therebetween which are responsive to a voltage applied across two or more groups of the internal electrodes in use,an insulating arrangement which at least partially covers at least one surface of the stack to define a piezoelectric/insulator interface, andtwo or more side electrodes to connect with the two or more groups of the internal electrodes,