Biomedical Engineering Reference
In-Depth Information
Figure 2. Plot of log|
Z
| (solid circles) and I (solid triangles) against log
f
(Bode
plot) for a mercury-supported DPTL|DPhyPC bilayer incorporating gramicidin
from its 1u10
-7
M solution in aqueous 0.1 M KCl at -0.600 V vs. Ag|AgCl(0.1M
KCl).
2
The solid curve is the best fit of the equivalent circuit shown in the figure
to the impedance spectrum, with
C
s
=0.25 PF,
R
m
=106 k:,
C
m
=14 nF, and
R
:
=146 :. Drop area = 2.2u10
-2
cm
2
. Top: structure of DPTL in tail-to-tail con-
tact with a DPhyPC lipid molecule. The double-headed arrows mark the lipoic
acid residue (lar), spacer (s) and lipid bilayer (m) sections of the tBLM.
1
/(
Z
C
s
)
, is
<<R
:
; the same is true for the impedance of the
R
m
C
m
mesh, which is determined by the lowest of the impedances of
these two elements in parallel, i.e., 1
/(
Z
C
m
).
At the highest fre-
quencies, |
Z
| is therefore controlled by
R
:
,
which is independent of
frequency and is characterized by a phase angle I=0. With de-
creasing frequency, 1
/(
Z
C
m
)
becomes greater than
R
:
, while still
remaining lower than
R
m
, and it is also > 1
/(
Z
C
s
),
because
C
s
is >
C
m
. Hence, |
Z
| coincides with 1
/(
Z
C
m
),
and the log|
Z
| vs. log
f
plot
has a slope equal to -1, while the phase angle tends to 90°. With a
further decrease in frequency, 1
/(
Z
C
m
)
becomes comparable with
and ultimately less than
R
m
, and the Bode plot tends to become
Search WWH ::
Custom Search