Thermacoustic piezoelectric generator

• US 20070090723A1
• Filed: 07/25/2006
• Published: 04/26/2007
• Est. Priority Date: 03/31/2003
• Status: Active Grant

• Current Assignee: Penn State Research Foundation, United States Department Of Health And Human Services
• Original Assignee: Penn State Research Foundation
• Inventors: Keolian, Robert, Bastyr, Kevin, Wuthrich, John
• Granted Patent: US 7,772,746 B2
• Time in Patent Office: Days
• US Class Current: 310/311
• CPC Class Codes: H02N 2/18 producing electrical output from mechanical input, e.g. generators for measurement devices G01
• CPC Class Codes: H10N 30/30 with mechanical input and electrical output, e.g. functioning as generators or sensors

Abstract

An electroactive transducer converts between acoustical power and electrical power. The transducer includes a diaphragm and a perimeter member. The perimeter member includes at least one electroactive element and is mechanically coupled to the perimeter of the diaphragm such that displacement of the diaphragm stresses the electroactive element.

Claims

1. An electroactive transducer for converting between acoustical power, consisting of pressure and velocity, and electrical power, consisting of potential and current, the transducer comprising:

a diaphragm having a perimeter and a central portion, the diaphragm having a neutral position and at least one flexed position wherein the central portion is displaced axially relative to the neutral position, the perimeter and central portion disposed generally in a common diaphragm plane when the diaphragm is in the neutral position; and

a perimeter member including at least one electroactive element, the perimeter member generally defining a transducer plane and surrounding a central area, the perimeter member being mechanically coupled to the perimeter of the diaphragm such that displacement of the central portion from the neutral position to the flexed position stresses the electroactive element.

2. The electroactive transducer according to claim 1, wherein:

the diaphragm plane is generally coextensive with the transducer plane and the diaphragm is disposed in the central area defined by the perimeter member such that the perimeter member generally surrounds the diaphragm.

3. The electroactive transducer according to claim 1, wherein:

the at least one electroactive element comprises a plurality of electroactive elements disposed generally in a ring.

5. The electroactive transducer according to claim 3, wherein:

the perimeter member further comprises a plurality of supports, each support having a portion disposed between two adjacent electroactive elements and another portion interconnected with the perimeter of the diaphragm.

7. The electroactive transducer according to claim 3, wherein:

the plurality of electroactive elements is disposed such that a portion of each element is above the diaphragm plane and another portion of each element is below the diaphragm plane.

8. The electroactive transducer according to claim 1, wherein:

the diaphragm has a plurality of radial slots defined from the perimeter and extending partially into the central portion.

11. The electroactive transducer according to claim 1, further comprising:

a mounting structure for mounting the transducer, the mounting structure including a plurality of struts each having a first end interconnected with the diaphragm.

14. The electroactive transducer according to claim 1, wherein:

the at least one electroactive element comprises a first plurality of electroactive elements disposed generally in a first ring and a second plurality of electroactive elements disposed generally in a second ring, the first ring being disposed above the diaphragm plane and the second ring being disposed below the diaphragm plane.

4. (canceled)

6. (canceled)

9-10. -10. (canceled)

12-13. -13. (canceled)

15. (canceled)

16. An electroactive transducer for converting between acoustical power, consisting of pressure and velocity, and electrical power, consisting of potential and current, the transducer having a first face and an opposed second face, the transducer comprising:

a diaphragm having a first convex face defining at least a portion of the first face of the transducer and an opposed concave face defining at least a portion of the second face of the transducer, the diaphragm having a perimeter and a central portion, the diaphragm having a neutral position and at least one flexed position wherein the central portion is displaced axially relative to the neutral position; and

a perimeter member including at least one electroactive element, the perimeter member generally defining a transducer plane and surrounding a central area, the perimeter member being mechanically coupled to the perimeter of the diaphragm such that displacement of the central portion from the neutral position to the flexed position stresses the electroactive element.

17. The electroactive transducer according to claim 16, wherein:

the perimeter of the diaphragm is disposed in the transducer plane and the diaphragm is disposed in the central area defined by the perimeter member such that the perimeter member generally surrounds the diaphragm.

18. The electroactive transducer according to claim 17, wherein:

the at least one electroactive element comprises a plurality of electroactive elements disposed generally in a ring.

20. The electroactive transducer according to claim 18, wherein:

the perimeter member further comprises a plurality of supports, each support having a portion disposed between two adjacent electroactive elements and another portion interconnected with the perimeter of the diaphragm.

21. The electroactive transducer according to claim 20, wherein:

the diaphragm has a plurality of radial slots defined from the perimeter and extending partially into the central portion, each support being interconnected with the perimeter of the diaphragm between the slots.

22. The electroactive transducer according to claim 18, wherein:

the plurality of electroactive elements is disposed such that a portion of each element is above the transducer plane and another portion of each element is below the transducer plane.

19. (canceled)

23-29. -29. (canceled)

30. A thermoacoustic generator, refrigerator or heat pump comprising:

a housing containing a working volume of gas with a pressure;

a thermoacoustic engine supported in the housing and having a first heat exchanger and a second heat exchanger, the thermoacoustic engine being operable to introduce acoustical power into the housing or to remove acoustical power from the housing; and

an electroactive transducer supported in the housing, the transducer comprising;

a diaphragm having a perimeter and a central portion that is movable when acted on by acoustical power, the diaphragm having a neutral position and at least one flexed position wherein the central portion is displaced axially relative to the neutral position; and

a perimeter member including at least one electroactive element, the perimeter member generally defining a transducer plane and surrounding a central area, the perimeter member being mechanically coupled to the perimeter of the diaphragm such that displacement of the central portion from the neutral position to the flexed position stresses the electroactive element.

31. The thermoacoustic generator, refrigerator or heat pump according to claim 30, wherein the diaphragm divides the housing into a first portion and a second portion that are generally sealed from each other.

32. An acoustic device comprising:

a housing having a volume defined therein, the housing being filled with a gas having a mean density ρ

₀, and an adiabatic sound speed C_a;

an electroactive transducer at least partially disposed in the housing, the transducer comprising;

a diaphragm having a perimeter and a central portion, the diaphragm having a neutral position and at least one flexed position wherein the central portion is displaced axially relative to the neutral position; and

a perimeter member including at least one electroactive element, the perimeter member generally defining a transducer plane and surrounding a central area, the perimeter member being mechanically coupled to the perimeter of the diaphragm such that displacement of the central portion from the neutral position to the flexed position stresses the electroactive element;

the diaphragm dividing the housing such that a first volume is defined on one side of the diaphragm and a second volume is defined on the other side of the diaphragm, the diaphragm having an effective radius a;

the diaphragm having a tensile force per length of edge T, given by T=F_R/(2π

a)+T₀, wherein F_R is the arithmetic sum of all radial time dependent tensile forces that the perimeter member applies to the diaphragm and T₀ is a bias tension, present when the diaphragm is in the neutral position;

the diaphragm being configured such that χ

is in the range of 7 to 34, inclusive, wherein χ

is defined as

χ

=π

ρ

₀c_a²a⁴/(V_oT)

Z wherein V₀ is the effective volume of the gas spring compressed by the diaphragm.

33. The acoustic device of claim 32, wherein V₀=1/(V₁⁻

1+V₂<sup>−

1</sup>), wherein V₁ and V₂ are the two nearest effectively closed mean volumes of gas on either side of the diaphragm.

34. The acoustic device of claim 32, further comprising a thermoacoustic engine supported in the housing and having a first heat exchanger and a second heat exchanger, the thermoacoustic engine being operable to introduce acoustical power into the housing or to remove acoustical power from the housing.

35-36. -36. (canceled)

37. A piezoelectric transducer for converting between acoustical power, consisting of pressure and velocity, and electrical power, consisting of potential and current, the transducer comprising:

a perimeter member including at least one portion of piezoelectric material, the perimeter member configured such that compression of the perimeter member causes compression of the portion of piezoelectric material, the perimeter member surrounding a central area;

a hub disposed in the central area, the hub being movable relative to the perimeter member along an axis; and

a plurality of spokes interconnecting the hub and the perimeter member such that relative movement of the hub along the axis compresses the perimeter member and thereby compresses the piezoelectric material.

38-46. -46. (canceled)

47. A piezoelectric transducer for converting between acoustical power, consisting of pressure and velocity, and electrical power, consisting of potential and current, the transducer comprising:

a perimeter support member generally defining a transducer plane, the member surrounding a central area;

a hub disposed in the central area, the hub being movable relative to the perimeter support member along an axis generally perpendicular to the plane; and

a plurality of piezoelectric bimorph members each having an inner end in mechanical communication with the hub and an outer end supported by the perimeter support member such that relative movement of the hub along the axis flexes the bimorph members.

48-50. -50. (canceled)

51. A thermoacoustic device comprising:

a housing containing a working volume of gas with a pressure;

a piezoelectric transducer separating the housing into a first area containing a first volume of gas and a second area containing a second volume of gas, the transducer comprising a perimeter wall having at least one portion of piezoelectric material and at least one spring in series;

a first thermoacoustic core supported in the first area of the housing and including a pair of heat exchangers; and

a second thermoacoustic core supported in the second area of the housing and including a pair of heat exchangers.