PhD-Level Ultrasonic Engineering • Medical • Manufacturing • Consumer
Stop Using Fixed Boundary Conditions On Your Piezo Simulation
The question was poised to me:
I received a question from someone who was doing a basic piezoelectric simulation - they were applying a force, and they wanted to measure voltage
The values they calculated, however, were much smaller, just over half of the voltage he expected.
So, what was the problem? BOUNDARY CONDITIONS.
Here is a link to my youtube video explanation if you are into watching videos: https://youtu.be/uTLpeb2ooAs
If not, read on!
What's wrong with fixed boundary conditions?
The piezoelectric constitutive equations, and the definition of the voltage constant “g” assumes there is no restraining force on the piezo.
However, in order to do a static simulation you have to put a fixed constraint somewhere.
The constraint does not allow the piezo to deflect outward according to the Poisson's ratio, so this reduces the Z-axis strain and hence reduces the charge and voltage generated.
The easy solution
Upon reading this solution, you are going to say "Why didn't I think of that!"
The solution is to use a low frequency harmonic analysis to avoid the requirement for a fixed boundary condition to constrain the model. For example, specify the forces and supporting forces at 10 Hz, instead of doing a 0 Hz frequency static simulation. This way, you don't have to apply the fixed boundary condition constraint. If you think about it, DC or static is just a very low frequency. Thus, using 10 Hz or even 1 kHz will work.