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Ch83-I044963.fm Page 411 Monday, August 7, 2006 11:30 AM
11:30 AM
Monday, August 7,2006
Ch83-I044963.fm
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surrounding environment. In order to minimize these undesired couplings, signal generator, amplifier,
and oscilloscope are all battery-powered. Separate power supplies are used for the transmitter and the
0 0
-10
-10
d -20
-20
B
3
n -30
-30

i
a
G to -40
-40
-50
-50
-60
-60
15
10
0 0 5 5 10 15 20 25 30 35 40
20
30
35
40
25
Frequency
MHz
Frequency MHz
Figure 2: Comparison of transmission gain with frequency
In the experiments, a human equivalent phantom was also used. The conductivity and relative
permittivity of the phantom was adjusted to the same value as the human body. Its size was 500 x 500
x 4500 mm , the average size of the human arm. Phantoms improve reproducibility of experiments. Its
simple shape makes computer based calculations easier.
Four-terminal circuit model
In the kHz range, the effect of electromagnetic waves is considered negligible. A common analysis
model of intra-body communication in such frequencies is a combination of capacitive coupling
among the electrodes attached to the human body, the devices, and the environment. Figure 3 shows a
four-terminal circuit model based on Hachisuka, et al. (2003) and Terauchi, et al. (2003).
Transmitter side Receiver side
Receiver side
Transmitter side
electrode
electrode
electrode Z b Z b Z b Z b electrode
Arm
Arm
Z a Z a Z a Z a Z c Z c Z c Z c Z a Z a Z a Z a
(Phantom)
(Phantom)
Z b Z b Z b Z b
Figure 3: Four-electrode model
Transmission gains calculated from this four-electrode model match the experimental results in the
kHz range. It is calculated by the following equation.
[dB] (1)
7 7
z az c
It can be seen from Eqn. 1 that the difference between the horizontal impedance element (Zj) and the
diagonal impedance element (Z c) has to be large to obtain a large gain. However, it can also be
understood that the difference between the two elements becomes small as the distance between the
transmitter and the receiver increases. Also, since the relative permittivity of the human muscle is
more than 20,000 at 10 kHz, it is difficult to enlarge the difference between Zj and Z c.
In this research, a similar four-terminal circuit model was investigated for a new form of transmission.