Biomedical Engineering Reference
In-Depth Information
with flat top and bottom surfaces, changed when affected by an electric field. The
top surface became curved and the sense of the curvature (whether concave or
convex) depended on the polarity of the applied electric field. The curvature of the
surface changed from concave to convex and vice versa by changing the polarity of
the electric field. By the use of an optical apparatus, focusing capability of the curved
surface was verified and the focal length of the deformed gel was measured.
The effect of the intensity of the applied electric field on the surface curvature
and thus on the focal length of the gel is tested. Different mechanisms are discussed;
either of them or their combination may explain the surface deformation and cur-
vature. Practical difficulties in the test procedure and the 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. This area of research has only recently been
explored and is projected to be a major driver in future biotechnology as well as
industrial optics applications.
5.4.2
T
M
HEORETICAL
ODEL
In order to describe the electrically induced deformation of ionic polymeric gels,
we consider the process of symmetrical deformation of a cylindrical segment of
ionic polymeric gels in a transverse electric field. Suppose a cylindrical sample of
an ionic gel of radius
is deformed into a convex lens (fig.
5.1) by an imposed voltage gradient across its radius
r
and thickness
t
* = 2
C
. It is assumed that initially
the gel is in a natural stress-free state equilibrated with a pH = 7.
Due to the presence of an electrical voltage gradient across the radius
r
of the
gel, the gel cylindrical sample is deformed nonhomogeneously into a convex (fig.
5.2a) or a concave (fig. 5.2b) lens by a nonuniform distribution of fixed as well as
r
FIGURE 5.1
PAMPS muscle shown in bent state after applying a 30-V DC field. There are
two gold-plated electrodes at each side of the Teflon (polytetrafluoroethylene, PTFE) container.
