Biomedical Engineering Reference
In-Depth Information
0
Without resistors
-20
With resistors
-40
1.5
2
2.5
Frequency (GHz)
3
3.5
FIGURE 5.37
Experimental matching characteristics.
conductive line part, the resistance and the inductance can be modified by
adjusting each length of a high- and a low-conductive part or their respective
areas. Capacitance is obtained by changing the adjacent space between the tips
of the unit-circuit elements in a cross shape. When a large capacitance is
needed, however, the adjacent space between the tips of the unit-circuit ele-
ments becomes too narrow. To avoid this inconvenience, a unit-circuit element
with a high conductivity at the tip of it is used as shown in Figure 5.36
a
.By
introducing these structures, the variable factors for each circuit constant
R
,
L
,
C
can be provided.
As an example of an experimental reflection coefficient, a matching char-
acteristic is shown in Figure 5.37. The solid line represents the matching char-
acteristic of the present case; the resistance value is 89
. When the microchip
resistors do not exist, that is, when the circuit is composed of only high-
conductive strip lines, matching cannot be obtained, as is shown in Figure 5.37
by a dotted line. The tendency of this broadband matching characteristic
agrees with the theoretical result obtained by FDTD analysis [13]. As an
example at 60 GHz, the whole size
b
and the width
a
of the unit-circuit element
are 2.85 and 0.6 mm, respectively (Fig. 5.38). Production of these fine unit-
circuit elements becomes possible by applying integrated-circuit technology to
the present absorber. This is why we call this an integrated-circuit EM wave
absorber.
W
5.7 METHOD FOR IMPROVING RF FIELD DISTRIBUTION
IN A SMALL ROOM
In the previous section, EM wave absorbers at high frequencies such as
microwaves or millimeter waves were described. However, these absorbers
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