Biomedical Engineering Reference
In-Depth Information
1.12.
Repeat problem 1.11 for fat.
1.13.
A monopole antenna is fabricated by removing length
l
of the outer con-
ductor and the dielectric of a 2.2-mm Teflon-filled coaxial cable. For a
sufficiently small value of
l
, the impedance of the antenna in free space
is approximated as
[
(
) -
]
j
60
ln
2
l a
kl
1
2
()-
Z
=
10
kl
0
in
(
)
where is the wavenumber in free space and
a
is
the inner conductor radius (Fig. P1.13).
(a)
Use what is called Deschamps' theorem
k
=
2
pl w me
0
=
0
(
)
Y
(
wee
,
)
=
e
Y
w ee
,
i
0
in
0
0
to find a general relation for
Y
in
and
Z
in
, the admittance and imped-
ance of the monopole in the lossy medium, if the antenna is
immersed in a tissue with complex permittivity e.
(b)
For 915 MHz and 2.45 GHz, respectively, find the input impedance
and reflection coefficient of a monopole with
l
= 10 mm made from
a 2.2 mm coaxial cable immersed in muscle.
(c)
Repeat part (b) if the antenna is in a fat medium.
1.14.
Suppose that the available power in the input to the monopole of
Problem 1.13 is 2 W. Find the power absorbed in the tissue.
1.15.
An insulated dipole with half-length
h
and radius
a
is rounded by two
cylindrical concentric dielectric layers with radii
b
and
c
, and permittiv-
ity e
2
and e
3
, respectively. The antenna is inside a tissue medium with
complex permittivity e
4
. The dipole is fed by a source
V
e
placed at the
middle of it (Fig. P1.15
a
).
e
c
r
e
l
z
FIGURE P1.13
Coaxial probe monopole applicator immersed in lossy medium with
complex permittivity e.
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