Piezoelectric speaker

1. A piezoelectric speaker comprising:

a diaphragm including a substrate and a plurality of piezoelectric elements arranged on said substrate; and

a frame supporting said substrate at an outer peripheral portion of said substrate,

wherein each of said plurality of piezoelectric elements includes at least one piezoelectric body and at least one electrode, the at least one piezoelectric body and the at least one electrode being stacked,

wherein said plurality of piezoelectric elements includes a first piezoelectric element having a first number of layers, and second and third piezoelectric elements, each having a second number of layers, the first number of layers being larger than the second number of layers,

wherein said first piezoelectric element has a first contribution ratio to amplitude, and said second and third piezoelectric elements each have a second contribution ratio to amplitude, the first contribution ratio to amplitude being larger than the second contribution ratio to amplitude such that a distortion of said first piezoelectric element is larger than a distortion of each of said second and third piezoelectric elements,

wherein said first piezoelectric element is arranged on said substrate in a portion having a first stress, said second piezoelectric element is arranged on said substrate in a portion having a second stress, and said third piezoelectric element is arranged on said substrate in a portion having a third stress equal to the second stress, the first stress being smaller than the each of the second and third stresses,

wherein the first, second, and third stresses are caused by a bending vibration of said substrate, and

wherein said second piezoelectric element and said third piezoelectric element are symmetrically arranged with respect to a center of said substrate.

2. The piezoelectric speaker according to claim 1 ,

wherein said second piezoelectric element and said third piezoelectric element are arranged farther from the center of said substrate than said first piezoelectric element.

3. The piezoelectric speaker according to claim 1 ,

wherein each at least one electrode includes a first electrode and a second electrode through each of which an electrical signal is applied to said respective piezoelectric element, and

wherein each of said plurality of piezoelectric elements has a face on which both said first electrode and said second electrode of said respective piezoelectric element are exposed.

4. The piezoelectric speaker according to claim 3 ,

wherein said substrate includes a third electrode and a fourth electrode which are formed by printing on a face on which said plurality of piezoelectric elements is arranged,

wherein said plurality of piezoelectric elements is arranged such that the face on which both said first electrode and said second electrode are exposed is in contact with the face of said substrate on which said third electrode and said fourth electrode are formed,

wherein said third electrode is connected to said first electrode included in each of said plurality of piezoelectric elements, and

wherein said fourth electrode is connected to said second electrode included in each of said plurality of piezoelectric elements.

5. The piezoelectric speaker according to claim 1 ,

wherein said substrate is made of polyethylene terephthalate.

6. The piezoelectric speaker according to claim 1 ,

wherein said substrate is made of paper.

7. The piezoelectric speaker according to claim 1 ,

wherein said substrate is made of foam.

8. The piezoelectric speaker according to claim 1 , further comprising

an edge portion which is provided between the outer peripheral portion of said substrate and said frame and which functions as a suspension.

9. The piezoelectric speaker according to claim 8 ,

wherein said edge portion has a rolled shape.

10. A television receiver comprising a piezoelectric speaker according to claim 1 .

11. A mobile phone device comprising a piezoelectric speaker according to claim 1 .

12. The piezoelectric speaker according to claim 1 ,

wherein said first piezoelectric element is arranged between said second piezoelectric element and said third piezoelectric element, and said first piezoelectric element is arranged over the center of said substrate.

13. The piezoelectric speaker according to claim 12 ,

wherein said first piezoelectric element includes two piezoelectric elements, and said two piezoelectric elements of said first piezoelectric element are symmetrically arranged with respect to the center of said substrate.

14. The piezoelectric speaker according to claim 1 ,

wherein each of said second piezoelectric element and said third piezoelectric element includes a three-layer structure comprising two electrode layers and one piezoelectric body layer, and

wherein said first piezoelectric element includes a five-layer structure comprising three electrode layers and two piezoelectric body layers.

15. The piezoelectric speaker according to claim 1 ,

wherein each of said plurality of piezoelectric elements comprises a surface having a rectangular shape, each of the surfaces being arranged on said substrate, and

wherein said first piezoelectric element and said second piezoelectric element are arranged such that a longitudinal side of the rectangular surface of said first piezoelectric element is in contact with a longitudinal side of the rectangular surface of said second piezoelectric element.

16. The piezoelectric speaker according to claim 1 ,

wherein, when a driving voltage is applied to said plurality of piezoelectric elements, a vibration mode occurs such that an amplitude in a central portion of said diaphragm is largest.

17. The piezoelectric speaker according to claim 16 ,

wherein said vibration mode is dome-shaped.