The Difference Between "Terminal Charge" and "Integration of Surface Charge Density" in Modeling Pre-stressed Piezo Film?

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I'm working on a Piezo Film as microphone in 2-D axisymmetric model. I want to apply an input pressure and get the cumulative charge of the piezo layer.

The film is based on a Diaphragm (Silicon nitride), and the piezo layer (AlN) is deposited on it. For the piezo layer, I apply "terminal" boundry condition (V=0) at top surface and specifying the bottom surface as "ground". The "Bundary load" condition of Harmonic Perputation (Pressure = 1Pa) is at the bottom surface of diaphragm. After "Compute", the charge on the voltage layer can be derived by two methods:

(1) Use "es.Q0_1". (2) Use "Integration of Surface Charge Density (es.nD)"

There are two cases I tested. One is the film without pre-stress, and the other is the film with pre-stress. For the without pre-stress case, it seens fine that the charge value to the two methods is very close (Error < 0.2%). Strange thing appears in the case with pre-stress, the charge value obtained by the two methods have obvious differences (Error > 140%).

Can one tell me what causes this difference, and which one is a more correct method ?

Thanks in advance!

Regards,

Peng



0 Replies Last Post Jul 3, 2024, 2:22 p.m. EDT
COMSOL Moderator

Hello Tzu-huan Peng

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