EM Wave Absorbers Protecting Biological and Medical Environment - RF/Microwave Interaction with Biological Tissues - page 233

0

Ferrite thickness t: 6.25 mm

-20

With squares
c

Without
squares

a

Theory

b

c

-40

Experiment

a b

Width of line a: 0.9 mm

Adjacent space

Size of conductors
b: 5.5 mm c: 0.9 mm

-60

1 1.5 2

Frequency (GHz)

FIGURE 5.34 Comparison of theoretical values with measured values.

5.6.4 Integrated-Circuit-Type Absorber

In this section, we introduce a single-sheet broadband EM wave absorber
based on a new concept of the equivalent material constant transformation
method. This microwave absorber is composed of actual circuit elements of
resistance, capacitance, and inductance. It covers the microwave and
millimeter-wave regions. The three circuit elements are needed to finely
control resonant conditions in the microwave circuit, that is, to obtain an
optimum broadband matching condition. The structural concept of a
microwave integrated-circuit absorber is based on the methods used for
arranging three circuit constants, or resistance R , capacitance C , and induc-
tance L , on a circuit board. The principle of constructing this absorber follows.
Figure 5.35 a shows the equivalent circuit of a transmission line for the sim-
plest EM wave absorber with space d and a conductive plate at the back of
the absorber. To realize this circuit on a substrate backed with a conductive
plate, the method of arranging a unit-circuit element, which consists of differ-
ent conductive sections, is introduced as shown in Figure 5.35 b : A unit-circuit
element is composed of a high- and a low-conductive part to give resistance
and inductance. The cross-shape pattern consists of two parts. One is a high-
conductive part. The other is formed of low-conductive or low-resistive parts,
as shown in the figure. When microwave currents flow on the surface of the
high-conductive line part, this presents inductive characteristics. Since these
inductance and resistance values are proportional to the length of a