## 2 Materials and Methods
### Individual Application Method according to User Attachment of the Fabricated Sensor  
This section describes a customized application method according to the user of the Velostat-film-based pressure sensor. Table 1 shows the process of its application. First, it is necessary to check the individual pressure range inside the socket and select the fabrication size of the sensor. When the size is selected, it is necessary to cut the outer part to prevent wrinkles caused by the flexion of the attachment area. The cut sensor is attached to a position where the movement of the lower limb can be checked. The user intention is detected according to the lower limb movement in the attached sensor. The process of these four steps is described in detail below. 2.1 Check the Individual Pressure Range inside the Socket and Select the Fabrication Size of the Sensor  
The range of pressure changes occurring inside the socket varies depending on the user and the sensor attachment position. Sensors that do not consider the pressure range carry \begin{table}
\begin{tabular}{l} \hline
1. Check the individual pressure range inside the socket and select the fabrication size of the sensor \\ \hline
2. Cut the outer part of the sensor in accordance with the flexion of the attachment area \\ \hline
3. Attach the sensor and wear the prosthetic leg \\ \hline
4. Detect the user intention according to the movement of the lower limb \\ \hline \end{tabular}
\end{table} 
Table 1: Fabrication and application method of the Velostat-film-based customized sensor. Figure 1: Velostat-film-based pressure sensor: (**a**) pressure sensing principle; (**b**) resistance change according to the applied pressure of the Velostat film; (**c**) fabricated sensor structure; (**d**) voltage distribution circuit for measurement of the applied pressure, and the Wheatstone bridge circuit. problems such as undetected pressure changes and the saturation of pressure measurements. Therefore, when applying a pressure sensor inside the socket, the individual pressure range at the application position must be verified. The Velostat film has different resistance change characteristics depending on the size. The process of selecting an appropriate sensor size by checking the pressure range is as follows. Figure 2a shows the pressure range inside the socket. The value when the maximum load is applied in the direction of the ground after wearing the prosthetic leg is \(P_{max}\), and the value when the load is removed by raising the lower limb is \(P_{min}\). It is possible to consider the pressure range by selecting the size showing linear pressure change characteristics within the range above \(P_{min}\) and below \(P_{max}\). Since the pressure value is measured by A/D conversion, it is based on the reference voltage of 3.3 V.  
For pressure discrimination, a range of 2.8 V to 3.3 V is set as the maximum pressure and a range of 0.5 V to 1 V is set as the minimum range. The pressure change due to the movement of the lower limb is verified to be a change that can be distinguished only when a voltage change of 1 V or more occurs. The size and shape of the sensor for application are presented as a production guideline through pressure measurement experiments in Section 3. In a standing state, there is an initial pressure value inside the socket due to the load of the body [34]. Therefore, whether the pressure changes due to the movement of the lower limb should be determined based on the initial pressure. Figure 2b shows how to convert the change in pressure based on the initial pressure. It is necessary to set the initial pressure \(P_{init}\) presented by the body load in the standing state to the reference value of 0% and convert the maximum pressure \(P_{max}\) to 100%, and the minimum pressure \(P_{min}\) to a percentage of \(-\)100%. The conversion value of the pressure change during the lower limb movement follows Equation (2).