Methods of manufacture of sonar and ultrasonic transducer devices and composite actuators

Abstract

The present invention provides a method of manufacturing piezoelectric transducers that improves performance by reducing the mechanical losses in the component interfaces. The method involves the epoxy impregnation and encapsulation of the components within the piezoelectric stack assembly. Impregnation is achieved by capillary action that results in a chemical bond. The encapsulation method results in an epoxy conformal coating that provides a high degree of protection from harsh operational environments and reduces the risk of high voltage electric breakdown.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating the components within a typical Langeven style ultrasonic transducer that is generally representative of those used for medical and industrial applications.

FIG. 2 is a diagram of an assembly fixture that is used to manufacture piezoelectric subassemblies prior to assembly within the transducer.

FIG. 3 is a diagram of one type of shim electrode that can be sandwiched between the piezoelectric rings within a stack assembly. The shim electrode provides an electrical connection between the pairs of rings within the stack. A separate electrode is used for the high potential and ground connection.

FIG. 4 is a diagram illustrating part of the assembly procedure.

FIG. 5 is a diagram of a standard symmetrical dumbbell shaped Langeven style transducer that has historically been used to characterize material properties of piezo elements within a stack assembly.

FIG. 6 is a block diagram showing the connection of a transducer to a system for the purposes of high power testing of the transducer.

Claims

1. A method of manufacturing a joint between two piezo elements within a pre-stressed transducer assembly comprising the steps of: a) forming a metal coating on one or more surfaces of each of the piezo elements;b) melding a shim electrode to the metal coating; andc) impregnating the piezo elements with a low viscosity epoxy.

2. The method of claim 1, wherein the metal coating is silver.

3. The method of claim 1, wherein the metal coating is a screen printable thick film silver.

4. The method of claim 3, wherein the shim electrode is beryllium-copper.

5. The method of claim 4, wherein the shim electrode is coated with a layer of metal.

6. The method of claim 5, wherein the layer of metal is tin.

7. The method of claim 6, wherein the layer of tin is less than 5 microns.

8. The method of claim 1, wherein the impregnating is by capillary action.

9. The method of claim 1, further comprising the step of heating the transducer assembly and the epoxy prior to impregnating the piezo elements.

10. The method of claim 9, further comprising the step of applying the heated epoxy to a heated exterior surface of the transducer assembly.

11. The method of claim 1, further comprising the step of encapsulating the piezo elements and shim electrodes by using a combination of a low viscosity epoxy and a filled encapsulant epoxy.

12. The method of claim 11, wherein the step of encapsulation is prior to curing.

13. A method of manufacturing a transducer comprising the steps of: a) forming a silver coating on piezo elements within the transducer using print screening;b) melding a tin coated beryllium-copper shim electrode to the silver coating;c) heating the piezo elements with the melded shim electrode;d) impregnating the piezo elements by capillary action with a hot low viscosity epoxy;e) coating exterior surfaces of the piezo elements with the epoxy; andf) curing the epoxy.

14. The method of claim 13, wherein the silver coating has a surface finish of less than 1 micron.

15. The method of claim 14, wherein the tin coating is less than 5 microns.

16. A pre-stressed transducer assembly comprising: a) two or more piezo elements, wherein each piezo element has a silver surface formed from a silver electrode of screen printable thick film silver;b) a shim electrode coated with a metal coating and embedded into the silver surface of the piezo element; andc) a low viscosity epoxy between the piezo elements.

17. The transducer of claim 16, wherein the shim electrode is a beryllium-copper electrode.

18. The transducer of claim 17 wherein the metal coating is tin.

19. The transducer of claim 18, wherein the metal coating is less than 5 microns thick.

20. The transducer of claim 19, further comprising an epoxy coating on exterior surfaces of the transducer.