Electroacoustic transducer

Abstract

An electroacoustic transducer comprises a pair of active piezo electric membranes and a sleeve closed at its ends by the membranes to a form an enclosed rear volume of air. A case accomodates the assembly of sleeve and membranes and provides an enclosed front volume of air between its inner wall and the assembly. An opening in the case to the outside forms a sound pressure output. Each membrane comprises a sandwich of two active piezo layers on a substrate material. Very small thicknesses of the substrate and active piezo layers provides for a correct impedance match to the acoustic load in the ear when used in hearing aids.

What is claimed is: 
     
       1. An electroacoustic transducer comprising at least one pair of active piezo electric membranes and a sleeve closed at its ends by said membranes to form an enclosed volume of air, a rear volume, a case accomodating said sleeve and said membranes and providing an enclosed volume of air, a front volume, between its inner wall and said sleeve and membranes, said case having an opening to the outside which provides a sound pressure output, wherein each active piezo electric membrane comprises a sandwich of two active piezo layers on either side of a substrate material, the thickness of said piezo layers and substrate material being less than 50 micrometers, respectively. 
     
     
       2. An electroacoustic transducer according to claim 1, wherein the thickness of said piezo layers and of said substrate is less than 10 micrometers. 
     
     
       3. An electroacoustic transducer according to claim 1, wherein said substrate material is electrically conductive. 
     
     
       4. An electroacoustic transducer according to claim 1, wherein said substrate material is electrically non-conductive, said piezo layers each being provided with an electrode on its side adjacent to the substrate. 
     
     
       5. An electroacoustic transducer according to claim 1, wherein the piezo layers are made of a ceramic material by one of a variety of specialized techniques which include: MOCVD (Metal Organic Chemical Vapour Deposition), Sol-Gel, Bulk Polishing, Vapour Phase Deposition and Physical Vapour Deposition, e.g. Sputtering. 
     
     
       6. An electroacoustic transducer according to claim 1, wherein each said membrane consists of a multiplicity of electrodes and active piezo layers on either side of the substrates. 
     
     
       7. An electroacoustic transducer comprising two active piezo electric membranes, a cylindrical case closed at its ends and divided by said two membranes into two end compartments and an intermediate compartment, each said end compartment forming an enclosed volume of air, a rear volume, and said intermediate compartment forming a front volume which is open to the outside through an opening in the case, said opening providing a sound pressure output, wherein each active piezo electric membrane comprises a sandwich of two active piezo layers on either side of a substrate material. 
     
     
       8. An electroacoustic transducer according to claim 7, wherein the thickness of said piezo layers and said substrate is less than 50 micrometers, respectively. 
     
     
       9. An electroacoustic transducer according to claim 7 wherein said substrate material is electrically conductive. 
     
     
       10. An electroacoustic transducer according to claim 7 wherein said substrate material is electrically non-conductive, said piezo layers each being provided with an electrode on its side adjacent to the substrate. 
     
     
       11. An electroacoustic transducer according to claim 7 wherein the piezo layers are made of a ceramic material by one of a variety of specialized techniques which include: MOCVD (Metal Organic Chemical Vapour Deposition), Sol-Gel, Bulk Polishing, Vapour Phase Deposition and Physical Vapour Deposition, e.g. Sputtering. 
     
     
       12. An electroacoustic transducer according to claim 7 wherein each said membrane consists of a multiplicity of electrodes and active piezo layers on either side of the substrates.