## 2 Materials and Methods
### Hardware  
The sensory systems used for data collection in this study included FSR sensors from Tangio Printed Electronics (North Vancouver, Canada), model TPE-502 round sensors with the diameter of approximately 2 cm. FSRs were connected to an Arduino model Pro Mini that would register their responses through a voltage divider circuit where the FSR sensors were connected between \(V_{dd}\)--that was provided by the Arduino--and \(V_{out}\), and a base resistor (327 \(\Omega\)) was connected between \(V_{out}\) and ground. All sensors were connected to the same resistor on one side, and a separate Arduino output on the other side. The voltage at the Arduino side of each sensor was raised to \(V_{dd}\) when the other sensors were not supplied with a voltage. As a result, only one sensor was activated at each point in time. Analog sensor readings obtained through this method were converted to digital values to be read by the Arduino. Sensor readings were transferred to a computer by the Arduino board wirelessly using a Bluetooth module. The system was powered using a 3.7 V Lithium Polymer (LiPo) battery. The main components of the system are shown in Figure 1.  
Placement of the sensors used in the three-ply phase was done to ensure coverage of the main areas from which we expected to be able to retrieve information about fluctuations in the volume of the residual limb. In this phase, four sensors were placed in the distal, anterior distal, medial distal, and lateral distal locations inside the prosthetic sockets that participants used on a daily basis. The distance between locations of the anterior distal, medial distal, and lateral distal sensors from the distal end of the socket was approximately 6 cm. The distal end of the socket was selected since it was expected that an increase in the volume of the residual limb would cause the limb to be pushed upward inside the socket. This would lead to a decrease in the interface pressure at the distal end of the socket. This hypothesis was based on the literature and the experience of the collaborating prosthetist [22]. The other three locations were also selected based on evidenc  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Phase** & **Participant** & **Amputation Side** & **Cause** & **Weight Range (kg)** & **Prosthesis** \\ \hline
**Three-ply** & & & & & \\
**Phase** & & & & & \\  & & & & & \\  & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Summary of participants’ information. Prosthesis: Total Surface Bearing (TSB), Thermoplastic Elastomer (TPE), Patellar Tendon Bearing (PTB).  
the expertise of the collaborating prosthetist [23]. These locations were expected to experience greater pressure/force changes as they were areas of the limb with bony prominences. Posterior distal pressure was not considered as less pressure variation was expected at this location compared to the other distal locations due to higher ratios of soft tissue at this location in most individuals. Placement of sensors inside the prosthetic socket in the three-ply phase is shown in Figure 1. Out of the four positions that were tested in the three-ply phase, the distal location was selected and the other three were removed form experiments of the one-ply phase based on results of the three-ply phase.