*2.1. Textile Capacitive Pressure Sensing Insole (TCPSI)*

The textile capacitive pressure sensing insole (TCPSI) was designed based on Coulomb's law as shown in Figure 1. The capacitance is determined by how much electricity is collected between the two conductive plates. The wider the gap between the plates, the higher the capacitance. 1 Farad (F) is equal to the capacitor charged at 1 C when a voltage of 1 V is applied. Equation (1) is a formula for calculating the parallel capacitance value, and the C value is derived using the above formula.

$$\mathbb{C} = \mathbb{Q}/V = \varepsilon (A(\text{width} \times \text{length}))/d \tag{1}$$

where, *d* means the distance between two plates, *A* means the area of plates (width × length), ε is the permittivity material between the plates.

For TCPSI, a parallel capacitance measurement method was applied as illustrated in Figure 2a. The W-290-PCN model (Ajin Electronics, Gangseo, Busan, ROK) conductive textile was used and its characteristics have been described in Table 1. The textile consists of polyester, sequentially plated with nickel, copper, and nickel. Non-conductive rubber with a thickness of 3 mm was placed between a sensor layer and a ground layer, and another two layers of non-conductive woven textiles were placed on the top and bottom of all other layers as a cover and shock absorber. Figure 2b shows the size (2 × 2 cm2) and locations of the 10 channels in each insole. Sensor channel 1 was located in the medial upper corner of the insole to detect the pressure mainly under the big toe area (1st, 2nd distal phalanges) and channel 2 was located in the lateral upper corner of the insole to detect the pressure under the 3rd 4th, and 5th distal phalanges. These channels were to detect the plantar pressure in the forefoot during the pre-swing and toe-off phases. Channels 3 and 4 were located below the channels 1 and 2 to detect the pressure under the proximal interphalangeal joint area. Channels 5 and 6 were located in the metatarsal-phalangeal joint area. Channels 7, 8, 9 and 10 were located in the heel area.

**Table 1.** Characteristics of the W-290-PCN model.


(**a**) Textile capacitive pressure sensing insole

(**b**) Sensor location with anatomical reference

**Figure 2.** The structure of the textile capacitive pressure sensing insole (TCPSI) and sensor location, (**a**) textile capacitive pressure sensing insole, (**b**) sensor location.
