# Textile-Based Coils for Inductive Wireless Power Transmission
## 2 Materials and Methods
### Sample Production
#### 2.2.1 Embroidered Coils with Conductive Yarns  
The first coils were embroidered onto a ground textile using a zigzag stitch (test series Z). The difficulty in processing the Shielddex yarns is to design the templates in such a way that a high stitch density can be achieved (Figure 1). At the same time, we have to ensure small gaps between the turns of a coil. However, due to the fact that Shielddex yarns do not have any insulation, the windings must not touch each other, otherwise there would be a short circuit at this point. We examined if there are any short circuits between the windings. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Material**} & \multicolumn{1}{c}{Shieldex} & \multirow{2}{*}{Shieldex} & \multirow{2}{*}{ELITEX I} & \multirow{2}{*}{} & \multirow{2}{*}{} \\  & 117/17 dex 2 ply & & & & \\  & HC+B & & HC+B & & f34x4\_PA/AG & \\ \hline
**Raw material** & polyamide 6.6 & polyamide 6.6 & polyamide & wrapped yarn & 100\% copper \\
**coating** & 99\% silver & 99\% silver & \(>\)99\% silver & \(>\)99\% Silber & lacquered copper & polyurethane. \\
**Yarn count** & 295 dtex & 605 dtex & 4000 dtex \(\pm\) 20 dtex & & 0.236 mm\({}^{2}\) \\
**Electrical resistance** & 80 \(\Omega\)/m & \(<\)300 \(\Omega\)/m & \(5\)\(\Omega\)/m \(0.5\) A at 30 \({}^{\circ}\)C & 20 \(\Omega\)/m & \\ \hline
**Picture** & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Material data of the conductive wire/yarn. For initial trials five different coil sizes have been stitched, which had a varying number of turns. We also used different yarns and yarn combinations. The first embroidered coil (Z175) made out of Shieldex 235 has an outer diameter of 75 mm and consists of 10 turns. Both, upper thread and lower thread were made of the yarn. The track width of the windings was 2 mm each. The second coil (Z275) out of Shieldex 235 had a diameter of 75 mm and also 10 turns, the track width was 2 mm. The next bobbin (Z375) had an outer diameter of 75 mm, 10 turns. It consisted of Shieldex 117 in the upper thread, a non-conductive polyester yarn of similar fineness was used as the lower thread. The last bobbin (Z455) of this type has a diameter of 55 mm and seven turns with a track width of 1.5 mm. Both the upper thread and the lower thread are made of Shieldex 235. Table 2 provides an overview of all embroidered bobbin geometries made of Shieldex 235 and 117. They are called Z series (Table 2). The distance between the windings differs between 0.5-0.2 mm. The coils were stitched with an outer diameter of 40, 50, and 60 mm, with the three different conductor materials: ELITEX (E), wrapping yarn (U), and copper strand (L). The first two coils 60E12 and coil 60U12 had an outer diameter of 60 mm and an inner diameter of 11 mm. They each had 12 turns and a space of 1.5 mm between the turns. ELITEX and the wrapping yarn were used as conductor materials. The third stitched coil 60L12 had the same shape, size and number of turns as the previous coils, only the conductor material was replaced by the copper strand. Due to the larger wire diameter, the distance between turns was 0.5 mm and the inner diameter was 9 mm. An overview of the coils is shown in Table 3.  
The coils: 50E15, 50U15, and 50L15 had an outer diameter of 50 mm (Figure 3). Coils 50E15 and 50U15 had an inner diameter of 15 mm and their turns had a distance of 0.5 mm to each other. Coil 50L15 had an inner diameter of 11 mm and there was no distance between the windings. The remaining three coils--40E9, 40L9, and 40U9--had an outer diameter of 40 mm (Figure 4). The inner diameter of 40E9 and 40U9 was 15 mm, for 40L9 it was 12 mm. ELITEX was used as the conductor material (Table 3).