Ein modellbasiertes Messverfahren zur Charakterisierung der frequenzabh?ngigen Materialeigenschaften von Piezokeramiken unter Verwendung eines einzelnen Probek?rperindividuums

The process used to determine the complete material parameter set for piezoelectric ceramics currently is based on the measurement of five separate geometries that have been differently processed. Since the production process influences the material properties significantly, this procedure can result in an inconsistent parameter set. This partly results in rather large deviations between simulations and experiments. The current practice to use many specimens results from the fact that not every material parameter influences the measured characteristic in the same manner. For example the measured impedance of a piezoelectric disk with electrodes covering both sides shows very little sensitivity in the radial component of the permittivity tensor. The increasing application of simulation tools for the design of sensors as well as the preferred use for smaller elements make the characterization of all material parameters for the particular concrete geometry extremely necessary. The determination of such a consistent material parameter set is a key requirement for the design of optimized piezoceramic ultrasonic transducers (e.g. Sensor Arrays, Annular Arrays, Interdigital Transducers). A new measurement procedure shall be developed in the course of this research project, which will be able to determine all relevant material parameters in a consistent manner on one single material specimen. The project partners have already shown in cooperation with each other that the sensitivity of the material parameters can be increased significantly by using three ring shaped electrodes. Due to two concentric electrodes on the same surface an electric field can be generated in the radial directions also, which explains the increased sensitivity. Due to the high complexity of the measurement apparatus required, direct analytical computation of the material parameters from the measured data is not
possible. An inverse method will therefore be used, in which the frequency dependent impedance characteristic of the piezoceramics are compared with the results of FEM simulations. Using derivative based optimization algorithms the model parameters are then adjusted so long until the measured and simulated results match as best as possible.