Piezeoelectric transducer having protuberances for transmitting acoustic energy and method of making the same

• US 20020036446A1
• Filed: 09/17/2001
• Published: 03/28/2002
• Est. Priority Date: 03/28/2000
• Status: Active Grant

• Current Assignee: Jeffrey D. Swan, Kyung-Tae Park, Minoru Toda
• Original Assignee: Jeffrey D. Swan, Kyung-Tae Park, Minoru Toda
• Inventors: Toda, Minoru, Park, Kyung-Tae, Swan, Jeffrey D.
• Granted Patent: US 6,504,289 B2
• Time in Patent Office: Days
• US Class Current: 310/328
• CPC Class Codes: B06B 1/0688 with foil-type piezoelectric elements, e.g. PVDF
• CPC Class Codes: H10N 30/098 Forming organic materials
• CPC Class Codes: Y10S 310/80 Piezoelectric polymers, e.g. PVDF
• CPC Class Codes: Y10T 29/42 Piezoelectric device making

Abstract

A method of forming an ultrasound transducer having thermoformed protuberances comprises providing a substrate having a plurality of perforations of a given dimension. The perforations or apertures are formed in the substrate and operate to determine the resonance frequency associated with the transducer. A film of polymeric material capable of showing piezoelectric properties when strained in its plane and electrically biassed by a field applied in a direction normal to its faces, is then laminated onto the substrate. The film is heated to a given temperature and a pressure differential is applied between the top and bottom surfaces of the film for a sufficient time to form protuberances in the film through the apertures in the substrate. The film is then cooled to a given ambient temperature while maintaining a pressure differential between the top and bottom surfaces of the film for a sufficient time until the ambient temperature is reached so as to cause the protuberances to maintain a substantially permanent curvature.

Claims

1. A method of forming protuberances in piezoelectric material for an acoustic device comprising:

providing a substrate having a plurality of perforations of a given dimension formed therein;

forming a laminate comprising a film of polymer piezoelectric material sandwiched between a first electrode layer on a top surface and a second electrode layer on a bottom surface;

securing the laminate to the substrate to form a composite assembly; and

treating the composite assembly to form protuberances in the film at the locations of the perforations.

2. The method according to claim 1, wherein the step of treating the composite assembly further comprises heating the film to a given temperature and applying a pressure differential between the top and bottom surfaces of the composite assembly to form the protuberances.

3. The method of claim 2, wherein the step of heating further comprises heating to a temperature of approximately 85 degrees C. for between 1 to 3 hours.

4. The method according to claim 2, wherein the step of applying a pressure differential comprises forming a vacuum at a bottom surface of the composite assembly and exposing the top surface to atmospheric air to form the pressure differential.

5. The method according to claim 4, wherein the pressure differential is approximately 13 psi.

6. The method according to claim 1, wherein the step of treating the composite assembly further comprises:

securing the bottom surface of the composite assembly to a vacuum chamber;

placing the composite assembly into a temperature chamber; and

activating a vacuum pump to cause a pressure differential between the top and bottom surfaces of the composite assembly (while applying heat to the assembly through the temperature chamber for a predetermined time interval) sufficient to form the protuberances in the film; and

after the predetermined time interval cooling the composite assembly to a given temperature while maintaining the pressure differential until the given temperature is reached to cause each of the protuberances to maintain a substantially permanent curvature.

7. The method according to claim 1, wherein the substrate comprises a metal.

8. The method according to claim 1, wherein the substrate comprises a printed circuit board.

9. The method according to claim 1, wherein the substrate comprises a plastic.

10. The method according to claim 1, wherein the perforations in the substrate are patterned in a periodic manner.

11. The method according to claim 10, wherein the perforations have a shape selected from the group consisting of a circle, rectangle and rhombus.

12. The method according to claim 1, wherein the first and second electrode layers are formed of silver ink.

13. The method according to claim 1, wherein the first and second electrode layers are formed of metal.

14. The method according to claim 1, wherein the step of securing the laminate to the substrate comprises applying a layer of adhesive material to the substrate.

15. The method according to claim 14, wherein the adhesive material is an epoxy.

16. The method according to claim 1, wherein the step of treating further comprises disposing a top plate layer at the top surface of the film and a bottom plate layer at a bottom surface of the substrate;

disposing a layer of pliable material between the top plate layer and top surface of the film; and

compressing the top and bottom plate layers toward one another to cause the layer of pliable material to forcibly engage the film to cause deformation of portions of the film through the perforations in the substrate thereby forming the protuberances.

17. The method according to claim 1, wherein the ultrasound transducer is an omnidirectional transducer.

18. The method according to claim 1, wherein the transducer is a substantially flat transducer.

20. The method according to claim 19, wherein the film is PVDF.

21. The method according to claim 19, wherein the pliable material is rubber.

22. The method according to claim 19, further comprising the steps of:

heating the film simultaneously with the compression step for a predetermined period; and

after the predetermined period, cooling the film to an ambient temperature to cause the protuberances to maintain a substantially permanent curvature.

25. The transducer according to claim 24, wherein the substrate is substantially flat.

26. The transducer according to claim 24, wherein the substrate is curved.

27. The transducer according to claim 26, wherein the curved substrate has a substantially cylindrical shape.

28. The transducer according to claim 24, wherein an output power is controllable as a function of the ratio of the active area to the total area of the substrate.

29. The transducer according to claim 24, wherein the apertures are circular.

30. The transducer according to claim 24, wherein the apertures are rectangular.

31. The transducer according to claim 26, wherein the transducer is an omnidirectional transducer having a frequency of over 100 KHz.

32. The transducer according to claim 24, further comprising first and second electrode layers disposed respectively, on a top and bottom surface of the piezoelectric material.

33. The transducer according to claim 24, wherein the first and second electrode layers are uniformly disposed on the top and bottom surfaces.

34. The transducer according to claim 32, wherein the second electrode layer is patterned so as to form a gap between adjacent portions of the second electrode layer, such that the patterned electrode layer is formed substantially over only the apertures of the substrate.

35. The transducer according to claim 24, wherein the piezoelectric material comprises PVDF.

38. The transducer according to claim 37, wherein said curved substrate is cylindrically shaped, and wherein said transducer emits at ultrasonic frequencies.

39. The transducer according to claim 37, wherein the predetermined frequency is a function of the curvature of the protuberances as determined by at least one dimension of the apertures.

19. A method of forming a transducer having protuberances comprising:

providing a substrate including a plurality of perforations each of a given dimension formed therein and indicative of a resonance frequency associated with the transducer;

laminating a film of polymeric material onto the substrate, the polymeric material capable of exhibiting piezoelectric properties;

disposing a top plate layer at a top surface of the film and a bottom plate layer at a bottom surface of the substrate;

disposing a layer of pliable material between the top plate layer and the top surface of the film;

compressing the top and bottom plate layers toward each other to cause the layer of pliable material to forcibly engage the film to cause deformation of portions of the film through the perforations in the substrate thereby, forming the protuberances.

23. A method of forming an ultrasound transducer having thermoformed protuberances comprising:

providing a substrate having a plurality of perforations each of a given dimension formed therein;

laminating a film of polymeric material onto the substrate, the polymeric material capable of exhibiting piezoelectric properties when strained in its plane and electrically biased by a field applied in a direction normal to its faces;

heating the film to a given temperature and applying a pressure differential between top and bottom surfaces of the film to form protuberances in the film through the perforations in the substrate for a predetermined time interval; and

cooling the heated film to a given temperature while maintaining the pressure differential until the given temperature is reached to cause the protuberances to maintain a substantially permanent curvature.

24. An ultrasonic transducer apparatus comprising:

a substrate having an array of apertures respectively formed therein at predetermined positions on the substrate such that the array forms a given area within the substrate;

a layer of polymeric piezoelectric material disposed on the substrate, the layer of piezoelectric material having a plurality of protuberances each being defined by a respective portion of the piezoelectric material extending into a corresponding one the apertures, the plurality of protuberances being substantially permanently formed and defining an active area of the transducer corresponding to the given area of the substrate;

wherein a resonance frequency of the transducer is a function of a shape of the protuberances as determined by at least one dimension of the apertures, and wherein a vertical and horizontal beam angle associated with the transducer is controllable as a function of the dimensions of the active area of the transducer.

36. A flat ultrasonic transducer comprising:

a flat substrate having a plurality of apertures formed therein;

a layer of polymeric piezoelectric material disposed on the flat substrate, the layer of piezoelectric material including a plurality of protuberances defined by portions of the piezoelectric material extending into corresponding ones of the apertures, the plurality of protuberances defining an active area of the transducer;

wherein the resonance frequency of the transducer is a function of a curvature of each of the protuberances as determined by at least one dimension of the apertures, and wherein the output power is controllable as a function of the ratio of the active area to the total substrate area.

37. A transducer comprising:

a curved substrate having a plurality of apertures formed therein;

a layer of polymeric piezoelectric material disposed along the curved substrate, the layer of piezoelectric material including a plurality of protuberances of a given curvature, the protuberances each being defined by portions of the piezoelectric material extending into a corresponding one of the apertures, the plurality of protuberances defining an active area of the transducer;

contact means coupled to the piezoelectric material for providing an electrical input to cause vibration of said protuberances at a predetermined frequency which is independent of the radius of curvature of the curved substrate.

40. An ultrasonic transducer assembly comprising:

an ultrasound transducer including;

a substrate including top and bottom surfaces, the substrate formed of a conductive material and including a plurality of apertures formed therethrough;

a laminate comprising a film of a polymer piezoelectric material sandwiched between a first electrode layer on a top surface and a second electrode layer on a bottom surface, the laminate disposed on the top surface of the substrate, the laminate including a plurality of protuberances each of a given curvature and respectively extending into a corresponding one the apertures; and

a housing containing the ultrasound transducer, the housing including an open end and a closed end, the housing comprising;

a first contact in electrical communication with the first electrode layer;

a second contact in electrical communication with the second electrode layer;

means coupled to the first contact for providing a first electrical connection through the closed end to provide a first terminal for connection to a first electrical potential; and

,

means coupled to the second contact for providing a second electrical connection through the closed end to provide a second terminal for connection to a second electrical potential;

whereby the substrate is operative to provide mechanical protection to the transducer laminate and to electrically couple the first and second electrode layers each to a corresponding terminal.

41. A housing assembly for an ultrasound transducer comprising a substrate including top and bottom surfaces, the substrate formed of a conductive material and including a plurality of apertures formed therethrough;

a laminate comprising a film of polymer piezoelectric material sandwiched between a first electrode layer on a top surface and a second electrode layer on a bottom surface, the laminate disposed on the top surface of the substrate, the laminate including a plurality of protuberances each of a given curvature and extending into a corresponding one of the apertures;

the housing assembly comprising;

a first contact in electrical communication with the first electrode, the first contact having a first arm member;

a second contact in electrical communication with the substrate and having a second arm member;

an end cap member having a first slot for receiving the first arm member to provide a first terminal, and a second slot for receiving the second arm member to provide a second terminal, the first and second terminal operable to provide external connectivity thereto;

a front member disposed opposite the end cap member; and

means for securing the front member to the end cap member for retaining the transducer within the housing.