Biomedical Engineering Reference
In-Depth Information
20
Experimental data corresponding to
d
31
Data corresponding to
d
32
15
10
5
0
0
2
4
6
Force (N)
Figure 3.7
The results obtained for the piezoelectric coefficients
d
31
and
d
32
of uniaxial piezo-
electric PVDF in direction 1 as well as direction 2, respectively
3.5 The Anisotropic Property of Uniaxial PVDF Film and Its
Influence on Sensor Applications
As previously mentioned, the mechanical process on uniaxial and biaxial PVDF films
differ insofar as the behavior of uniaxial PVDF film is quite similar to orthotropic materi-
als, whereas biaxial PVDF film exhibits the properties of transversely isotropic materials.
In addition, there is no standard process for preparation of PVDF film that causes par-
ity in its mechanical and electrical properties. One of the obstacles encountered during
the studies of the anisotropic properties of the piezoelectric PVDF, was the discrepancy
observed between the few reported values of orthotropic PVDF due to the fact that it has
its roots in dissimilar mechanical and electrical production processes. Various electrical
and mechanical properties for uniaxial and biaxial PVDF films are reported by different
manufacturers [19 - 21] and are given in Table 3.2. In this table, piezoelectric and elastic
coefficients are given in pC N
-1
and GPa, respectively. The symbol
d
3
h
, represents the
hydrostatic piezoelectric coefficient.
This section elaborates on the effects of anisotropic behavior of uniaxial PVDF on
the output voltage of uniaxial PVDF and comparing it with the performance of biaxial
PVDF in the sensory mode. The behavior of PVDF films can be attributed to their
Table 3.2
PVDF properties reported by manufacturers
Uniaxial PVDF
Biaxial PVDF
d
31
d
32
d
33
d
3
h
E
11
E
22
E
33
d
31
=
d
32
d
33
E
11
=
E
22
Piezoflex
14
2
−
34
−
18
2.5
2.1
0.9
-
-
-
Goodfellow
18/20
2
−
20
−
6
1.8/2.7
1.7/2.7
-
8
15/16
2
Piezotech
18
3
−
20
-
-
-
-
7
−
24
-
