TRANSDUCERS WITH IMPROVED IMPEDANCE MATCHING

1 . A transducer having a mechanical impedance over an operative frequency range and having a desired power coupling to a load over the operative frequency range, the transducer comprising:

a piezoelectric device having a frequency distribution of modes in the operative frequency range; and

an overmould, wherein

the overmould is arranged to surround at least part of the piezoelectric device; and

the parameters of the overmould are selected to provide a required impedance matching between the mechanical impedance of the transducer and the mechanical impedance of the load, whereby,

the desired power coupling between the transducer and the load is provided.

2 - 5 . (canceled)

6 . The transducer according to claim 1 , wherein the overmould comprises layer with a lateral dimension and a dimension perpendicular to the lateral dimension that defines a thickness of the layer, wherein the layer provides a relatively high stiffness in a direction perpendicular to the lateral dimension and the layer provides a relatively low stiffness in a direction parallel to the lateral dimension.

7 . (canceled)

8 . The transducer according to claim 1 , wherein the overmould is bonded to the whole of, or a substantial part of, the faces of the piezoelectric device.

9 . (canceled)

10 . The transducer according to claim 1 , wherein the overmould comprises coupling means for mounting the piezoelectric device to the load.

11 - 27 . (canceled)

28 . The transducer according to claim 1 , wherein

the piezoelectric device comprises at least one resonant element.

29 - 31 . (canceled)

32 . The transducer according to claim 1 , wherein the mechanical impedance of the transducer comprises,

the mechanical impedance of the piezoelectric device;

the mechanical impedance of the overmould; and

the mechanical impedance of the coupling means.

33 . A transducer having an operative frequency range, and having a desired power coupling to a load over the operative frequency range, the transducer comprising:

a piezoelectric device having a frequency distribution of modes in the operative frequency range;

a mounting means for holding a discrete portion of at least a part of the periphery of the piezoelectric device; and wherein,

the parameters of the mounting means are selected to provide a required boundary condition for the periphery of the piezoelectric device, whereby,

the desired power coupling between the transducer and the load is provided.

34 . The transducer according to claim 33 , wherein the mounting means comprises coupling means for holding a discrete portion of at least one periphery of the piezoelectric device.

35 . The transducer according to claim 33 comprising coupling means for coupling the piezoelectric device to the load.

36 . The transducer according to claim 33 , wherein the mounting means for holding a discrete portion of at least one periphery of the piezoelectric device comprises a mounting means for mounting the piezoelectric device to a mechanical ground.

37 - 40 . (canceled)

41 . The transducer according to claim 33 , wherein the mounting means is mechanically constrained, whereby the mechanical constraint inhibits the mounting means from changing its volume.

42 . The transducer according to claim 41 , wherein the mechanical constraint comprises, a non-compliant layer surrounding at least part of the periphery of the mounting means.

43 . The transducer according to claim 42 , wherein the non-compliant layer surrounds substantially all the free periphery of the mounting means.

44 - 59 . (canceled)

60 . The transducer according to claim 33 , wherein the transducer is configured to transition from a simply supported mode to an inertial mode with increasing frequency.

61 . The transducer according to claim 60 , wherein the transducer is configured to operate in a simply supported mode at low to mid frequencies, and in an inertial mode at mid to high frequencies.

62 . The transducer according to claim 33 , wherein the parameters of the mounting means are selected to provide a required boundary condition for the periphery of the piezoelectric device to tune an additional resonance in the operative frequency range.

63 . The transducer according to claim 62 , wherein the parameters of the mounting means selected to tune an additional resonance in the operative frequency range comprise the stiffness of the mounting means.

64 - 67 . (canceled)

68 . A transducer comprising;

a piezoelectric device in the form of a panel; and

a support,

the support comprising an elastomeric element and a mechanical ground, the elastomeric element supporting the device at least at a part of the periphery of the device and at least a part of the device extending through the elastomeric element into a recess in the mechanical ground.

69 - 71 . (canceled)

72 . A transducer as claimed claim 68 , in which the piezoelectric device comprises a vane extending at at least the part of the periphery supported by the elastomeric element and the vane extends through the elastomeric element into the recess.

73 . A transducer as claimed in claim 72 , in which the piezoelectric device comprises one or more piezoelectric elements attached to the vane and only the vane extends through the elastomeric element into the recess.