# Piezoelectric coefficient modes 31 and 33 - What's the difference?

#### Luiz Fernando Vieira

Joined Aug 24, 2015
60
I'm having a hard time understanding the difference between model 31 and 33. I understood it as follows:

These terms are ratio of strain with applied field, whereas the indices represent the direction of stress which causes strain in one direction and direction electrodes.

In 31-mode the external vibration force or stress working on X axis, normally labeled as (1 direction) while the output voltage is measured from z axis normally labeled as (3 direction).

I did not understand the explanation was: in this case, the voltage output should not be on the axis at the ends of the part? (referring to model 31).

me reading about the material of the subject it was not clear that. if anyone can make a better explanation.

Souce: There are two prominent modes of operations applicable for MEMS piezoelectric micro power generator, which are 33 and 31 modes. In 31-mode the external vibration force or stress working on X axis, normally labeled as (1 direction) while the output voltage is measured from z axis normally labeled as (3 direction). On the other hand, within 33-mode of operation, the external vibration force or stress and output voltage is measured on the same z axis normally labeled (three direction) as shown in Fig. 2. In a PMPG design, a cantilever beam with 33 mode of operation is preferred due to its bigger open circuit voltage leading to maximum power generated in comparison with the same device material, dimensions, and thicknesses on the 31 mode of operation (Jeon et al. 2005).

TECHNICAL PAPER : Design and optimization of cantilever based piezoelectric micropower generator for cardiac pacemaker.

#### Delta Prime

Joined Nov 15, 2019
1,326
Hello there.Sir a pleasure to finally meet you...so to speak.
I did not understand the explanation was: in this case, the voltage output should not be on the axis at the ends of the part? (referring to model 31).
A comparison of both modes d33 Vs d31 Open Circuit Voltage where the output is taken.Page 2 figure 2.
Off topic: why is this in homework?

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