Transducers for Sound and Vibration - FEM Based Design

Design of transducers for measurement of vibration (piezoelectric accelerometers) and sound (condenser microphones) is a very labour intensive work. The design work is mostly based on experience and on simple analogies to electrical circuit design. Often a time consuming itterative loop is used: Specification of the transducer, production of a physical prototype, measurements on the prototype, changed specification of the transducer etc. Furthermore are many transducers made based on customer requirements which also increases the amount of required design work. For these reasons there is a need for methods that can reduce the design time consumption and the number of itterations. The present work proposes to use finite element based programs for simulating the behaviour of a transducer with a given set of specifications. A simulation program for accelerometers was developed and has been tested on a number of existing transducers. The program has also been used to design new accelerometers which was then tested. In both cases the procedure shows good results. A similar simulation program was then developed for microphones. The program shows good results for the open-circuit sensitivity and the diaphragm collapse voltage for the microphones. Conclusions are that the FEM programs can be used to simulate the transducers to the degree of precision required in development of existing transducers. The programs also represent a virtual prototype that gives a better understanding of the behaviour of the transducers. Furthermore does the programs make it easier to optimise the transducers. The work is made in close collaboration with and financed by Brüel & Kjær who is one the internationally leading producers of transducers.