Modelling a piezoelectric actuatorTransport and microelectronics
Modelling a piezoelectric actuator through a modal and a frequency analyses require the simulation of coupled electrostatics and mechanical phenomena. These simulations are essential to choose and confirm the right frequency mode for the structure actuated by the piezoelectric ceramic.
Objectives from modelling a piezoelectric actuator
Piezoelectric devices are part of many appliances at home and in industry. As probes for medical imaging, pressure and flow sensors, or harvesting energy systems. As actuators for inkjet printers, nebulisers used for desinfection or micromotors in automotive and electronics. Their main advantage is robustness and low energy consumption.
Optimising the configuration of piezoelectric ceramics that will make the device vibrate is a way to reduce its development and operational costs. These ceramics are a good definition of multiphysics phenomena. When subject to an electric potential at their electrodes, they will deform and vibrate at a certain frequency. The model helps to find the frequency of the operational mode that will have the best energy conversion.
Results from simulation and information extracted
One carries the simulation in two steps:
Modal Eigenfrequency analysis of the piezoelectric actuator
This analysis can be fast to run and it uses less RAM memory during simulation (unless the frequency spectrum is very large). It provides information about EMCC (Electromechanical Coupling Coefficient) of the device and thus the efficiency of the different Eigenmodes.
Depending on the deformation mode that one wants to actuate the device (bending, shear), it helps to select a few frequencies that are worth investigating further.
Frequency analysis of the actuator
Following the modal analysis, one can run a frequency harmonic analysis to better understand the mechanical behaviour of the device for each pre-selected frequency. It will give information about the stresses and displacements of the structure.
A calculation of the impedance over the frequency spectrum will also confirm or not the frequencies that are selected in the first step.
Modal Eigenfrequency analysis and EMCC calculation
In this figure one can see the piezoelectric ceramic in grey. It vibrates at a certain frequency and it deforms the structure (green to purple colours) glued to its ends. The resonance of the structure is a bending mode with a high EMCC value that can be used, for example, on a inkjet system.
One can now investigate this frequency further and optimise the actuator shape and configuration.
Frequency impedance analysis
The graphs shows the admittance as a function of frequency. This analysis can confirm at which modes the EMCC is high.
One also needs to be cautious if running this analysis directly without the first step: the graph may miss a resonant mode with a high EMCC value. This is why the Eigenfrequency analysis as a first step is important.
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