Ultrasonic transducer and method of joining an ultrasonic transducer
The invention concerns an ultrasonic transducer, which is assembled from several parts. These parts are a protecting plate, a piezoelectric disc and a housing. Joining of the parts for transducers are normally done by means of TIG welding or laser welding, but these are relatively costly processes, which also has an impact on the transducer, especially the piezoelectric disc, due to the heat. In order to reduce the heat load and simultaneously simplify manufacturing an ultrasonic transducer is suggested, in which the protecting plate and the housing consists of electrically conducting materials of different kinds and where joining of housing and plate is done by using a mechanical force influence and an electrical current which flows through plate and housing. Also, a method for joining the parts of an ultrasonic transducer is described.
1. An ultrasonic transducer for use in transmitting sound in a gas or a liquid where the transducer comprises a housing containing a piezoelectric disc which acts as an oscillation element, and which is placed in contact with a protecting plate characterized in that the protecting plate and the housing are manufactured of electrically conducting materials, and the protecting plate comprises one or more electrically conducting projecting noses on a side of the plate that faces the piezoelectric disc.
2. The ultrasonic transducer according to claim 1 , wherein the noses have a height which gives an optimum sound transmission to the liquid or the gas.
3. The ultrasonic transducer according to claim 1 , wherein an acoustic coupling layer is placed between disc and plate.
4. The ultrasonic transducer according to claim 3 , wherein the acoustic coupling layer is mixed with metal particles which have a size of 1–50 μm is placed between the piezoelectric disc and the protecting plate.
5. The ultrasonic transducer according to claim 1 wherein the plate and the housing are joined in a thermal process through the action of a mechanical force and an electrical current which is conducted through the plate and the housing after the piezoelectric disc is attached to the protecting plate.
6. The ultrasonic transducer according to claim 5 , wherein the thermal process comprises resistance welding, and the piezoelectric disc is attached to the protecting plate by grease prior to the thermal process.
7. An ultrasonic transducer for use in transmitting sound in a gas or a liquid, comprising:
a protecting plate;
a housing containing a piezoelectric disc which acts as an oscillation element, and which is placed in contact with the protecting plate, wherein
the protecting plate and the housing are manufactured of electrically conducting materials, and wherein
the protecting plate on the side that faces the piezoelectric disc comprises an electrically conducting projection that spaces the piezoelectric disc from the protecting plate and provides electrical conduction between the piezoelectric disc and the protecting plate.
8. The ultrasonic transducer according to claim 7 , wherein the plate and the housing are joined in a the thermal process accomplished by a mechanical force and an electrical current which is conducted through the plate and the housing, and wherein the piezoelectric disc is attached to the protecting plate prior to the thermal process.
9. The ultrasonic transducer according to claim 8 , wherein the piezoelectric disc is attached to the protecting plate by glue or grease prior to the thermal process.
10. The ultrasonic transducer according to claim 7 , wherein an acoustic coupling layer is placed between disc and plate.
11. The ultrasonic transducer according to claim 10 , wherein the acoustic coupling layer is mixed with metal particles which have a size of 1–50 μm is placed between the piezoelectric disc and the protecting plate.