A MATLAB application has been developed for characterization of piezoceramic elements and transducers operating in the thickness-extensional mode. The input data is the impedance or admittance measured with Omicron BODE 100 analyzer. The ouptuts include real parameters of the equivalent RLC circuit, determined in the usual manner, using the so-called forward approach. Improvements to this method have been made and a reverse approach method has been defined for determining the values of the elements in the RLC circuit. The results show that the admittance of a piezoceramic element modeled with parameters obtained from the reverse approach is in better agreement with the actual measured admittance, thus justifying the proposed approach. Sherrit characterization with complex parameters has been implemented as well.
The admittance of a piezoceramic element can be simulated by determining the parameters of the equivalent RLC circuit, with real-valued parameters. The forward approach begins by finding the static capacitance and loss resistance at a chosen frequency far from resonance and continues with determining the parameters of the resonant part of the circuit, all from measured admittance or impedance. The agreement between the measured data and the data obtained from simulation greatly depends on the values of static capacitance and loss resistance, which are highly dependant on the chosen admittance point (and the corresponding frequency).
The reverse approach to the RLC equivalent circuit was devised to improve the agreement between the simulation and measured data. The real-valued parameters of the circuit are found in reverse order, in comparison with the classic forward approach. The admittance peak at serial resonance is reconstructed, and the parameters of the resonant part of the equivalent circuit are found. From this, the static capacitance can be determined and then a specific frequency is chosen, at which the loss resistance is calculated. The results show a significant improvement, regarding the agreement between the measured data and the simulations.
The Sherrit approach defines a series of complex-valued parameters to account for various types of losses that occur in the electro-mechanical-acoustical conversion in the piezoceramic element. The resulting simulation shows excellent agreement with measured data.