Transducer

1. An electromechanical force transducer having an intended operative frequency range and comprising:

an active resonant element having a periphery and having a frequency distribution of modes in the operative frequency range with the parameters of the resonant element selected to enhance the distribution of modes in the resonant element,

a simple support coupled to the periphery of the resonant element, the support having a substantially restraining nature in relation to bending wave vibration of the resonant element so as to extend the operative frequency range of the transducer, and

a coupler on the resonant element, located away from the periphery of the resonant element, for mounting the transducer to a site to which force is to be applied.

2. A transducer according to claim 1 , wherein the support is coupled to at least two discrete portions of the periphery of the resonant element.

3. A transducer according to claim 2 , wherein the discrete portions are located about opposed positions on the periphery of the resonant element.

4. A transducer according to any preceding claim, wherein the support extends along at least part of the periphery of the resonant element.

5. A transducer according to claim 4 , wherein the resonant element is planar.

6. A transducer according to claim 5 , wherein the support is adapted to ground the transducer.

7. A transducer according to claim 6 , wherein the support is integral with the resonant element.

8. A transducer according to claim 7 , wherein the resonant element is a piezo-electric device.

9. A transducer according to claim 8 , wherein the resonant element is a bi-morph piezo-electric device with a central vane which is adapted to form the support.

10. A transducer according to claim 9 , wherein the resonant element is modal along two substantially normal axes, each axis having an associated fundamental frequency.

11. A transducer according to claim 1 , comprising a plurality of resonant elements each having a distribution of modes, the modes of the resonant elements being arranged to interleave in the operative frequency range to enhance the distribution of modes in the transducer as a whole.

12. A transducer according to claim 11 , wherein the resonant elements are coupled together by connectors and are arranged in a stack with axially aligned coupling points.

13. A transducer according to claim 11 or claim 12 , wherein the support is coupled to the periphery of each resonant element.

14. A transducer according to claim 11 or claim 12 , wherein at least one resonant element is unrestrained.

15. A loudspeaker comprising an acoustic radiator and a transducer as claimed in claim 11 , the transducer being coupled via the coupler to the acoustic radiator to excite the acoustic radiator to produce an acoustic output.

16. A loudspeaker according to claim 15 , wherein the resonant element is acoustically substantially inactive.

17. A loudspeaker according to claim 15 or claim 16 , wherein the mechanical impedance of the transducer is matched to the mechanical impedance of the acoustic radiator.

18. A loudspeaker according to claim 17 , wherein the transducer is mounted to a second load which ensures impedance matching between the acoustic radiator and the transducer.

19. Electronic apparatus having a body and comprising a loudspeaker according to claim 15 mounted in the body.

20. Electronic apparatus according to claim 19 , wherein the support is mounted to the body.

21. Electronic apparatus according to claim 19 or claim 20 , in the form of a portable cellular telephone.

22. A transducer according to claim 1 , wherein the resonant element is planar.

23. A transducer according to claim 1 , wherein the support is adapted to ground the transducer.

24. A transducer according to claim 1 , wherein the support is integral with the resonant element.

25. A transducer according to claim 1 , wherein the resonant element is a piezo-electric device.

26. A transducer according to claim 25 , wherein the resonant element is a bi-morph piezo-electric device with a central vane which is adapted to form the support.

27. A transducer according to claim 1 , wherein the resonant element is modal along two substantially normal axes, each axis having an associated fundamental frequency.

28. A loudspeaker comprising an acoustic radiator and a transducer as claimed in claim 1 , the transducer being coupled via the coupler to the acoustic radiator to excite the acoustic radiator to produce an acoustic output.

29. A loudspeaker according to claim 28 , wherein the resonant element is acoustically substantially inactive.

30. A loudspeaker according to claim 28 or claim 29 , wherein the mechanical impedance of the transducer is matched to the mechanical impedance of the acoustic radiator.

31. A loudspeaker according to claim 30 , wherein the transducer is mounted to a second load which ensures impedance matching between the acoustic radiator and the transducer.

32. Electronic apparatus having a body and comprising a loudspeaker according to claim 28 mounted in the body.

33. Electronic apparatus according to claim 32 , wherein the support is mounted to the body.

34. Electronic apparatus according to claim 32 or claim 33 , in the form of a portable cellular telephone.

35. A loudspeaker according to claim 15 , wherein the coupler is located away from the centre of the resonant element.

36. A loudspeaker according to claim 28 , wherein the coupler is located away from the centre of the resonant element.

37. A transducer according to claim 2 , wherein the resonant element is in the form of a beam, the discrete portions are located at the ends of the beam, and the coupler is located between the ends of the beam.