Piezoelectric element and an oscillation transducer with a piezoelectric element
There is put forward a piezolectric element for converting pressure signals into electrical signals and vice versa, with a porous homogeneous ceramic body and with at least two electrodes attached to the ceramic body. The porous ceramic body comprises open pores and is preferably hermetically sealed on the whole surface with an elastic coating. Furthermore there is suggested an oscillation transducer with the piezolement which is accommodated in a housing. The piezolectric element is with one end face rigidly connected to the base of the housing. The other end face represents a surface which is sensitive to oscillations, which preferably is not covered by the housing. The volume of the housing is filled with a casting compound, wherein the piezolectric element is mechanically decoupled from the casting compound.
1. An oscillation transducer comprising a piezoelectric element for converting pressure signals into electrical signals and vice versa, with a porous ceramic body and with at least two electrodes attached onto the ceramic body, wherein the porous ceramic body comprises open pores and at least on the surface which is not taken up by the electrodes is provided with an elastic coating for increasing the pressure gradient within the ceramic body;
said piezoelectric element being accommodated in a housing, wherein one end face of the piezoelectric element is rigidly connected to the housing base and the opposite end face represents a surface which is sensitive to the oscillations from the outer space, and the piezoelectric element in the housing is surrounded by a casting compound and is mechanically decoupled from this.
2. An oscillation transducer according to claim 1 , wherein the lateral circumferential surface of the piezoelectric element comprises a cover which is loosely connected to this, as a mechanic decoupling, which separates the casting compound from the piezoelectric element.
3. An oscillation transducer according to claim 1 , wherein the electrodes of the piezoelectric element are connected to an impedance converter circuit, which is cast into the casting compound.
4. An oscillation transducer according to claim 1 , wherein the sensitive end surface of the piezoelectric element projects beyond the housing.
5. An oscillation transducer according to claim 1 , wherein the sensitive end face is covered over by a metal foil or a wire fabric or a metallized plastic foil or an electrically conducting elastomer.
6. An oscillation transducer according to claim 1 , wherein the housing is placed onto a frame of oscillation-absorbing material and is connected to this.
7. An oscillation transducer according to claim 6 , wherein the frame comprises a sleeve at least partly surrounding the housing, and a base plate, wherein between the sleeve and the housing there is provided an intermediate space which is filled with an oscillation-damping medium.
8. An oscillation transducer according to claim 7 , wherein the sleeve is fastened on a flange of the housing and a base plate is a constituent part of a cover cap surrounding the housing.
9. An oscillation transducer according to claim 1 , wherein the elastic coating is formed hermetically sealing and covers the whole surface of the ceramic body with electrodes.
10. An oscillation transducer according to claim 1 , wherein the porous ceramic body is manufactured of a lead titanate zirconate mixture.
11. An oscillation transducer according to claim 1 , wherein the porosity is at least 10%.
12. An oscillation transducer according to claim 11 , wherein the porosity lies between 50 and 70%.
13. An oscillation transducer according to claim 1 , wherein the coating consists essentially of silicone rubber, isoprene rubber or polyurethane or likewise.
14. An oscillation transducer according to claim 1 , wherein the thickness of the coating lies in the region of 0.1 to 1.5 mm.
15. An oscillation transducer according to claim 1 , wherein the elasticity of the coating lies in the range of 10 to 50 Shore A.
16. An oscillation transducer according to claim 1 , wherein the porous ceramic body with open pores is essentially homogeneous.
17. An oscillation transducer according to claim 11 , wherein the porosity is more than 30%.
18. An oscillation transducer according to claim 14 , wherein the thickness of the coating lies in the region of 0.1 to 1.0 mm.
19. An oscillation transducer according to claim 18 , wherein the thickness of the coating lies in the region of 0.1 to 0.5 mm.
20. An oscillation transducer according to claim 15 , wherein the elasticity of the coating lies in the range of 10 to 30 Shore A.