Biomedical Engineering Reference
In-Depth Information
By the use of an optical apparatus, focusing capability of the curved surface is
verified and the focal length of the deformed gel is measured. A more exact method
(thermal) to measure the focal length of the gel is also discussed. The effect of the
intensity of the applied electric field on the surface curvature and thus on the focal
length of the gel are tested. Two different mechanisms, based on ion mobility and
interaction forces, are discussed; either of them or their combination may explain
the surface deformation and curvature. Practical difficulties in the test procedure and
the future potential of the electrically adaptive and active optical lenses are also
discussed. These adaptive lenses may be considered as smart adaptive lenses for
contact lenses or other optical applications requiring focal point undulation.
5.4.4
E
XPERIMENTAL
R
ESULTS
: PAMPS
Experimental gel was cut in a cylindrical piece with a height of about 7 mm and a
diameter of about 25 mm. It was placed in the middle of a copper ring with a diameter
of about 40 mm. NaC1 solution was added such that the gel and the copper ring
were partially immersed in the electrolyte solution. A platinum wire of 1 mm in
diameter was inserted into the center of the cylindrical gel. The copper ring and the
platinum wire were connected to the positive and negative terminals of a power
source, respectively. A schematic of this setup is shown in figure 5.4.
When the electric voltage was applied, liquid exudation started from the upper
surface of the gel accompanied by swelling at the center. The swelling zone stretched
towards the edges of the gel. The speed at which the swollen zone stretched towards
the edges of the gel varied with the applied electric voltage. A higher applied electric
voltage caused a higher speed of stretching out of the swollen zone towards the outer
edges of the cylindrical gel. Figure 5.5 indicates the stretching of the swollen zone
as it was observed.
At all the applied electric voltages (10, 15, 20, 25, and 30 V), the swollen zone
eventually reached the outer edge. However, this was achieved at different stretching
speeds. The gel also was deformed at its circumferential wall, where it was immersed
in the electrolyte. The gel was photographed before (cylindrical sample with flat top
surface) and after (deformed with the convex top surface) applying the electric
voltage. These two configurations are indicated in figures 5.5 and 5.6.
The polarity of the electric field was reversed in a different test by connecting
the platinum wire and the copper ring to the positive and negative terminals, respec-
tively. This resulted in a concave upper surface. These observations were noticed
for PAMPS and PAAM gels. The convex gel was placed on a stationary glass below
which a screen was attached to a laboratory jack.
Figures 5.7a and 5.7b clearly depict an experimental set showing how PAMPS
optical lenses can be electrically controlled in terms of their power and focal length
under the action of a small electric field.
The distance between the stationary glass and the screen could be adjusted. A
light source was placed on top of the glass. With the light on and the convex gel on
the stationary glass, the distance between the screen and the glass was adjusted to
place the screen at the focal length of the convex PAMPS gel. This distance was
measured as about 65 mm for both PAAM and PAMPS lenses.
