## 3 Experiments and Results
### Guideline for Fabricating Pressure Sensors for Individual Applications
#### 3.2.2 Experimental Participant Information
Figure 12: Determination of the pressure range inside the socket of the subject. Subject 2 showed a pressure range of around 100 kPa when the maximum pressure was applied due to their relatively small weight, and four sensor sizes were selected accordingly. Subject 3 showed a pressure range of 150 and 100 kPa at the top and bottom of the front, respectively, and the sensor size suitable for the maximum pressure of 180 kPa or more was selected at the lower and rear parts. Subjects 2 and 3 showed the same flexion radius at the attachment point because they used the same simple experimental prosthetic leg for non-amputated subjects. Compared with the lower part of the socket, the upper and rear parts of the front were cut at 8% of the lower part and 16% of the height to suit the gentle flexion radius of around 120. The cutting was performed by cutting the lower part at 14% and the height at 28% to prevent an unfastened state in the lower part, with a small bending radius of 60 or less. In the case of the rear lower limb of Subject 1, sufficient muscle mass did not occur compared with the initial pressure caused by the initial physical load. For this reason, in order to check the pressure change in a broadened area, an additional 60-mm-wide and 40-mm-long sensor with a different shape compared with the sensors selected for Subjects 2 and 3 was fabricated and applied to the upper and lower positions of the rear. It was designed to eliminate the unfastened state by performing cutting in a total of six locations, two in the horizontal direction and one in the vertical direction, to suit the broadened range. In this study, a Velostat-film-based pressure sensor system is proposed to solve the problems of the non-detection of pressure changes and pressure saturation identified in previous studies. In order to verify whether the proposed system solves these problems, the sensor of Subject 2 and the capacitive sensor applied in the method proposed in this study were applied inside the socket in order to compare the pressure change patterns according to locomotion movements. Figure 13 shows the results of comparing the pressure changes in the sensor according to the locomotion of two steps in Subject 2. Section (1) of Figure 13 represents the swing phase within the locomotion cycle, and section (2) represents the stance phase. Figure 13a shows the capacitive sensor presented in the locomotion, and Figure 13b presents the sensor proposed in this study. Capacitive sensors are vulnerable to the skin impedance, which changes when the temperature rises inside the socket and sweating occurs; they have slow recovery characteristics and are applied only to local areas with a size of 4 cm\({}^{2}\). In addition, the prosthetic user and the individual pressure range inside the socket were not considered. As a result, as shown in Figure 13a, it was verified that a discontinuous step occurred due to the slow recovery in the lower sensor of the rectus femoris in locomotion movement. In addition, at the lower part of the biceps femoris, since a small-sized sensor was applied to the area with less muscle mass after the saturation of the measured value, the load application points did not match, and thus no pressure change was confirmed. Figure 13: Comparative experiments to verify whether the proposed sensor system is improved: (**a**) pressure change patterns of locomotion in the capacitive sensor; (**b**) pressure change patterns of locomotion in the Velostat-based sensor considering individual pressure ranges. In comparison, the Velostat film sensor, considering the pressure range proposed in this study, did not show a discontinuous step in locomotion movement. It was confirmed that the measurement problem identified in Figure 13a was solved by fabricating a resistance-change-type sensor, rather than a capacitive type, to cover a wide area and by ensuring the consideration of the individual pressure range.