Transducers with improved impedance matching

Abstract

A transducer ( 140 ) having a mechanical impedance over an operative frequency range and having a desired power coupling ( 145 ) to a load over the operative frequency range comprises a piezoelectric device ( 141 ) having a frequency distribution of modes in the operative frequency range; and an overmould ( 143 ). The overmould ( 143 ) is arranged to surround at least part of the piezoelectric device ( 141 ); and the parameters of the overmould ( 143 ) are selected to provide a required impedance matching between the mechanical impedance of the transducer ( 140 ) and the mechanical impedance of the load. An alternative transducer comprises a mounting means for holding a discrete portion of at least a part of the periphery of the piezoelectric device 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.

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.