Biomedical Engineering Reference
In-Depth Information
2.1
1.9
1.7
1.5
0
0.2
0.4
Friction coefficient
0.6
0.8
1.0
Figure 3.18
The total output voltage of a biaxial PVDF film compressed between two plates in
the presence of friction
Since all the piezoelectric coefficients of biaxial PVDF film have the same polarity,
compared with the results of the previous simulations, it is expected that the friction-
induced components cause an increase in total output. Figure 3.18 demonstrates the
relationship between the output voltage of the biaxial piezoelectric PVDF film and the
friction coefficient for a constant normal load. It can be seen that this behavior is differ-
ent to that of uniaxial film. For the biaxial film the friction-induced components cause an
increase in total output.
These results could provide some guidance on the proper selection of PVDF film type
(between uniaxial and biaxial) for a particular application. The extreme sensitivity of the
output voltage in the low friction-coefficient range is again evident. Similar to the analysis
of the uniaxial film, the whole length of the biaxial PVDF film is formed into 10 side-by-
side discrete electrodes which make 10 independent sensors. As shown in Figure 3.19,
voltage of each segment depends on the location of the sensing element, as well as the
friction coefficient. In this simulation, the PVDF bottom surface was taken as common
ground of all the sensing elements. In accordance with classical theory, and also with
the results obtained for uniaxial PVDF film, the performance of all 10 sensing elements
is similar when
μ
= 0. However, in the presence of friction, the outputs of sensing
elements are different and depend on the friction coefficient as well as the location of the
elements.
3.9 Experiments
In order to validate the results from the simulations of the influence of surface friction
on the output of a PVDF film compressed between two plates, a set of experiments were
performed. Prior to conducting the main experiment, the friction coefficients of the sample
