Biomedical Engineering Reference
In-Depth Information
mechanical anisotropic characteristic, which affects the stress - strain relation, as well as
the non-equality, of
d
31
and
d
32
in electromechanical relations.
The response of the sensation and actuation modes varies as a function of the deviation
angle,
θ
which is the angle between the material coordinate system, in which all material
properties are defined, and the global coordinate system. In order to show the differences
between two types of PVDF films, a simple cantilever beam was selected as the host
structure.
Figure 3.8a shows the case where a PVDF film is adhered to a beam in such a way that
the material coordinate system and the global coordinate system have the same orientation,
while Figure 3.8b represents the case in which axis 1 of the PVDF is rotated by
θ
with
respect to the global coordinate system (
x, y, z
). As emphasized in Figure 3.8c, the edges
of the piezoelectric patches remain parallel to the global axes, that is, the drawn direction
(axis 1) rotates with respect to the global axis. The best sensing and actuation response is
achieved from a piezoelectric when axis 1 is aligned with the global
x
- axis. However, in
some cases, the orientation of the applied load might result in a two-dimensional stress
profile, making it even more important to find the best orientation in which to attach
the piezoelectric film. Rotation of the material relative to the global coordinate system
can also occur inadvertently during the manufacturing phase of a sensor. Evidently, by
simply considering PVDF as an isotropic material, no alteration in the responses in terms
of deviation angle would be observed.
3,
d
33
z
2,
d
32
y
1,
d
31
x
PVDF
Film
(a)
z
3,
d
33
y
1,
d
31
2,
d
32
q
x
(b)
q = 0°
q = 45°
q = 90°
(c)
Figure 3.8
The PVDF material coordinate system (1, 2, 3) versus the global coordinate system
(
x, y, z
)
