Biomedical Engineering Reference
In-Depth Information
Fig. 13
Displacement profile along the square diaphragm using the trial function of (
2
)
where "
0
is the permittivity of free space (
8.8546 x 10-12 F/m
), "
r
is the relative
permittivity,
w
and
l
are the width and length of the capacitor electrodes, and
d
0
is
the gap between the electrodes.
Since the capacitive sensor uses diaphragm electrodes with a complex bending
profile, integration over the effective area of the electrodes is required to compute
the total capacitance:
ZZ
"
0
"
r
d
0
C
2
w
.x; y/
dxdy
C
D
(4)
where w(x,y) is the distance between electrodes due to the diaphragm bending at
position x, y. The integration in (
4
) can easily be solved numerically, enabling the
computation of the capacitance for a given pressure change.
9.2
Fabrication Process
Given the characteristics of the application (the sensor will be attached to the stent-
graft) the capacitive sensor must be foldable, extremely flexible and characterized by
a very small profile. In addition, the technology should be simple and biocompatible.
Silicon based micro technologies are widely used in implantable medical devices
[
24
], but due to the application specifications, there are other technologies that can
deliver better design approaches and results.
