Members of the NEPTUN research group have recently published a peer-reviewed article in a special issue of tm – Technisches Messen entitled "Milestones of measurement technology research - past, present, and future". In their article "Measurement of multiphysical material parameters of piezoceramic components for high-power ultrasonic applications", Olga Friesen and her coauthors present an overview of results from the first phase of FOR 5208 NEPTUN, covering contributions from all subprojects of the research unit. The article demonstrates how impedance-based measurements under controlled thermal and mechanical conditions, combined with sensitivity-informed inverse identification procedures, enable the characterisation of piezoceramic material parameters under realistic operating conditions, and outlines first steps towards nonlinear material modelling for high-power ultrasonic applications.
Abstract
Simulation-based design of high-power ultrasonic systems depends on the accurate modelling of the electromechanical behaviour of piezoceramic materials. In practical transducer applications, the relevant operating points are influenced by mechanical preload and heating, both of which give rise to changes in the elastic, dielectric, and piezoelectric material properties. Material parameters identified under idealised, unloaded conditions are therefore insufficient to represent piezoceramic material behaviour under realistic operating conditions. To overcome this limitation, experimental setups are developed that enable the measurement of electrical impedance spectra under controlled thermal and mechanical conditions. The acquired impedance data are used in an inverse identification procedure, in which the behaviour of a finite element forward model is iteratively fitted to the measurements using a block coordinate descent optimisation strategy guided by a sensitivity analysis. This yields effective linear material parameters as a function of temperature and mechanical stress at varying operating points. The identified temperature-dependent parameters, for instance, can be employed in a coupled thermo-electromechanical simulation framework to predict the temperature-dependent material behaviour during operation. The linear identification based on varying operation points provides an initial approximation of the nonlinear material response, establishing a basis for the development of corresponding nonlinear material models.