EM Wave Absorbers Protecting Biological and Medical Environment - RF/Microwave Interaction with Biological Tissues - page 239

TABLE 5.5 Material Parameters

Conductivity Sm -1

Material Relative Permitivity

Human body (muscle) 0.62 81.0

Applicator (salt) 1.0 ¥ 10 2 70.0

Wall (concrete) 0 5.3

Window (glass) 1.0 ¥ 10 -5 8.5

Window frame (aluminum) 4.0 ¥ 10 3 10.0

Bed (cloth) 1.0 ¥ 10 -5 5.0

Ferroelectric material 1.0 ¥ 10 -5 3.0 ¥ 10 3 -1.0 ¥ 10 4

or conductive materials A , B , C , or D . The relative permittivity of the fer-
rodielectric material is assumed to take values from 3000 to 10,000. All these
material parameters are tabulated in Table 5.5.
Figure 5.41 a shows an example of visualized electric field distribution in the
room when the ferrodielectric material is not mounted and a worker is stand-
ing at position b in Figure 5.40. The frequency is 13.56 MHz and the height of
the ceiling is 3 m. Figure 5.41 b shows the magnification of the field in the vicin-
ity of the worker at position b . The solid line represents the vector electric
field in the presence of a worker in the room. The dotted line shows the case
when there is no worker in the room. This figure indicates that the direction
of the vector is changed toward the worker and the electric field is concen-
trated on a worker when the worker is standing near the applicator.
Next, Figure 5.42 a shows a visualized field distribution when ferrodielectric
materials are not mounted. This field distribution is calculated from the ratio
of the electric field for the cases when a worker is in the room and is not in
the room. Dark color means a strong electric field. It is found that the electric
field is concentrated on the worker. Figure 5.42 b shows the case when the fer-
rodielectric materials are mounted on the ceiling and left-side wall and a
worker is standing at the position b , as shown in Figure 5.40. The value of per-
mittivity of the ferrodielectric material is 6000 and the height of the ceiling is
3 m. It is found that the electric field has a tendency concentrated on the fer-
rodielectric material. This field distribution with the ferrodielectric materials
is compared to one without ferrodielectric materials. On the base of these
investigations, it is suggested that the electric field in the room can be con-
trolled by mounting ferrodielectric materials. This method can effectively
improve the field distributions in the room, particularly in the case where the
radiated field slightly exceeds the value in the guidelines.
Regarding the effect of the height of the ceiling, as the result of theoreti-
cal calculations taking the ceiling height as a parameter, the field intensity in
a room has a tendency to be proportionally decreased as the ceiling height
increases. Therefore, it is found that the suppressing effect of the electric field
on a worker decreases as the ceiling height increases. On the basis of these
investigations, it is suggested that the electric field in the room can be con-
trolled by mounting ferrodielectric materials or conductors.