An electrostatic transducer, such as a loudspeaker or microphone, comprises a multi-layer panel (1) incorporating an electrically insulating middle layer (2) sandwiched between first and second electrically conducting outer layers (3, 4). At least one of the layers has a profiled surface (6) where i
An electrostatic transducer, such as a loudspeaker or microphone, comprises a multi-layer panel (1) incorporating an electrically insulating middle layer (2) sandwiched between first and second electrically conducting outer layers (3, 4). At least one of the layers has a profiled surface (6) where it contacts the surface of another of the layers. Furthermore a signal generator is provided for applying an alternating electrical voltage across the first and second layers (3, 4) to initiate vibration due to variation of the electrostatic forces acting between the layers, thereby serving as a loudspeaker (or for detecting variation of such electrostatic forces due to received vibration in the case of a microphone). Such a transducer can serve as a low cost audio loudspeaker which can be made lightweight and flexible so as to render it suitable for a wide range of applications, for example to provide sound reproduction in a home environment without requiring any bulky enclosure, or in a notebook computer or mobile telephone.
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The invention claimed is: 1. An electrostatic loudspeaker comprising a multi-layer panel incorporating an electrically insulating middle layer (2,2',2") sandwiched between first and second electrically conducting outer layers (3,3',3";4,4',4"), at least one of the layers (2,2',2";3,3',3";4,4 ',4")
The invention claimed is: 1. An electrostatic loudspeaker comprising a multi-layer panel incorporating an electrically insulating middle layer (2,2',2") sandwiched between first and second electrically conducting outer layers (3,3',3";4,4',4"), at least one of the layers (2,2',2";3,3',3";4,4 ',4") having a profiled surface where it contacts the surface of another of the layers, the three layers (2,2',2";3,3',3";4, 4',4") being separately formed so as to be capable of vibrating relative to one another, the profiled surface being an uneven surface and signal means (11) for applying an alternating electrical voltage across the first and second layers (3,3',3";4,4',4") to initiate vibration of the first layer (3,3',3") relative to the middle layer (2,2',2") due to variation of the electrostatic forces acting between the layers (2,2',2";3,3',3";4,4 ',4"). 2. A loudspeaker according to claim 1, wherein the multi-layer panel is flexible. 3. A loudspeaker according to claim 1, wherein the middle layer (2,2', 2") is made of a permanently electrostatically charged material. 4. A loudspeaker according to claim 1, wherein the middle layer (2,2', 2") is made of a material which does not remain permanently electrostatically charged, and biasing means (10) is provided for applying a steady-state bias potential across the first and second layers (3,3', 3"; 4,4', 4"). 5. A loudspeaker according to claim 1, wherein the middle layer (2, 2') is made of a polymeric material. 6. A loudspeaker according to claim 1, wherein the middle layer (2") is made of a porous material. 7. A loudspeaker according to claim 1, wherein the first layer (3,3', 3") comprises an electrically conducting film (8,8', 8") applied to the outer surface of an electrically insulating membrane (7,7', 7"). 8. A loudspeaker according to claim 7, wherein the membrane (7,7',7") is made of a polymeric material. 9. A loudspeaker according to claim 1, wherein the middle layer (2, 2") has a profiled surface in contact with the first layer (3,3"). 10. A loudspeaker according to claim 9, wherein the middle layer (2) is provided with pits (5) over which the first layer (3) extends. 11. A loudspeaker according to claim 1, wherein the first layer (3') has a profiled surface (6) in contact with the middle layer (2'). 12. A loudspeaker according to claim 1, wherein the second layer (4,4', 4") comprises a layer of metallisation applied to a back surface of the middle layer (2, 2', 2") by a metallisation process. 13. A loudspeaker according to claim 1, wherein the multi-layer panel has a thickness of less than 0.5 mm. 14. A loudspeaker according to claim 1, wherein the multi-layer panel is flat. 15. A loudspeaker according to claim 1, wherein the multi-layer panel is curved. 16. A loudspeaker according to claim 1, wherein the multi-layer panel is at least partly transparent. 17. A loudspeaker according to claim 1, wherein a plurality of loudspeakers are provided on a single panel.
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