## 3 Results
### Distribution of Electric Field
#### 3.2.2 Electric Field Vector Distribution  
Figure 5 shows the vector distribution of the electric field when the one-electrode transmitter was used. The plane shown in Figure 5a,b is a vertical cross-section passing through the feed point of the transmitter as viewed from the right side of the human body model. This distribution was obtained when the maximum received voltage was recorded. The direction of each arrow represents the vector of the electric field at that point, and the color of the arrows and stream lines represents the  
Figure 4: Electric field distribution in a vertical cross-section containing the transmitter, the receiver, and the human arm viewed from right side of the model. (**a**) Configuration of the simulation model. (**b**) Electric field distribution for the one-electrode transmitter. (**c**) Electric field distribution for the two-electrode transmitter.  
strength of the electric field. Figure 5a shows that the electric field in the one-electrode case travels from the surface of the arm through the space around the arm to the circuit board and is distributed symmetrically around the transmitter. Figure 5b shows a wider view of the same distribution as in Figure 5a, including the human body and the receiver. The electric field excited in the human body and under the arm was weaker than that above the arm. The signal path was concentrated locally in the space above the arm because the only return path is through the capacitive coupling of the floating ground.  
Figure 6 shows the vector distribution of the electric field when the two-electrode transmitter was used. A strong electric field was distributed in the space above and below the arm, as shown in Figure 6a. In the space above the arm, the electric field traveled in two directions; coupling occurred from the arm to the circuit board of the transmitter and from the arm to the surface of the receiver frame. In the space below the arm, the electric field from the surface of the arm was directed to the upper arm and the surface of the receiver frame. In the case of the two-electrode transmitter, both the electrical current inside the arm and the capacitive coupling via the air contributed to signal transmission. The distribution in a wider area is shown in Figure 6b. This figure shows that there was a relatively strong electric field distribution between the surface of the receiver frame and the torso. This electric field represents the capacitive coupling between the human body and the receiver frame.  
In order to evaluate the influences of realistic objects such as clothes, torso and legs were covered with sheet that had relative permittivity \(\varepsilon_{\mathrm{r}}\) of 3 and electric conductivity \(\sigma\) of 0 S/m, and thickness of 5 to 10 mm. The electric properties are the same as that of polyester. There were no noticeable differences in the direction and strength of the electric field, and the received signal amplitudes.  
Figure 5: Direction and strength of the electric field in the one-electrode transmitter case. (**a**) Distribution around the transmitter and the arm. (**b**) Distribution in a wider area including the whole human body.