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Simulating piezoelectric actuators

By Chloe Allison 08 January 2020

Piezoelectric actuators are electromechanical transducers that convert electrical excitation into mechanical displacement, they are widely used as controlling or regulating devices. Piezo benders that exist in both unimorph (one layer of PZT material) and bimorph (two layers of PZT) configurations are usually mounted on a passive flexing layer. The passive flexing layer is used to convert the longitudinal strain into a bending deflection.

Piezo benders with two piezo elements bonded together can produce contracting or expanding motion when the elements are driven together. These actuators use the transverse piezoelectric effect and produce motion in one direction. Contracting and expanding piezo actuators have small displacements – typically up to 20microns – but high force generation. When contracting actuators are mounted to a base or substrate, a bending actuator is created. In a bending actuator, the applied voltage causes one piezo element to expand while the other contracts. The result is a bending motion with relatively large displacements – typically several millimetres – but low force generation.

Why simulate piezoelectric actuators?

Piezoelectric structures are widely used as sensors, actuators and energy harvesting devices. Engineers must juggle multiple design variables in order to optimize the performance of a design. Inputs are design variables; Outputs are Key Performance Indicators (KPIs). OnScale enables you to quickly run massive parametric design sweeps to find optimums this can all be done in parallel using the power of the cloud.

Analysis

The bimorph example presented below has two identical pieces of piezoelectric material, stacked on top of each other. One side of the model is completely fixed and the other sides of the model are free to vibrate as a cantilever beam. The voltage source is connected to the two electrodes on the top and bottom surfaces of the model, the ground electrode is along the bondline which is assumed to be negligible in thickness and effect. This arrangement induces bending vibration in the bimorph. All 3 electrodes cover the entire length of the model.

electrodes

The voltage is applied to the electrodes via an electric source connected to a resistor in series. The resistor helps the voltage return to zero more quickly than if left to ringdown on its own.

Here we have shown an animation of how activation causes the device to flex:

piezoelectric

Here are a list of the types of outputs to expect from this model:

  • Time Histories (XY Graphs)
    • Drive input signal
    • Voltage and charge on electrodes
    • Y Displacement on free end of the model
  • Field Data
    • Maximum Y Displacement in Model
  • Mode Shapes (Harmonic Analysis) of base design
    • Requested at 0 and 180 degrees for plots

If you would like to run this model for yourself check out our example here!

If you have any questions regarding this example you can post a question to our forum.



Chloe Allison
Chloe Allison

Chloe Allison is an Application Engineer at OnScale. She received her MA in Electrical and Electronics Engineering from the University of Strathclyde. As part of our engineering team Chloe assists with developing applications, improving our existing software and providing technical support to our customers.