# Textile-Based Coils for Inductive Wireless Power Transmission
## 5 Conclusions  
The value of the transmission quality is always based on ideal conditions at the input and output. The efficiency of a coil system depends on the power electronic which supplies electric current to the coil. In this paper, coil systems can only be qualitatively compared based on their transmission characteristics. We can compare the suitability of a coil system for energy transmission. The results have proven the possibility of contactless power transmission using various textile materials.  
This paper shows and compares inductive energy transfer with textile receiver coils. The achievable transmission efficiencies are comparatively low. The samples show realization possibilities of textile coils, but they are not able to achieve the same results of a copper coil system in terms of efficiency. A lower efficiency can be accepted for low output powers, such as supplying some LEDs or a small sensor. Otherwise, the coils would probably heat up strongly and could cause burns to the user in the worst case. There are some difficulties in processing textile materials and in observing the electrical properties. For example, it is difficult to measure the electrical resistances of textile materials, because there is a lot of variation in the textile material. Selecting a suitable textile coil material, it should be decided whether the textile properties or the electrical properties are more important for the application. We recommend using insulated wires for inductive wireless power transmission. In either case, a ferrite foil should be used. Furthermore, not all coils had the same geometry. Further adjustments could be made in the measurement setup. That might have a positive effect on the transmission characteristics. In addition, the measurements could be carried out with a lateral offset in the x- and y-directions to determine how this affects the achievable efficiency and transmission quality. Before the textile coils can be integrated, further optimization is required. Follow-up investigations should be carried out for this purpose. In addition to the practical construction of actual transmission systems and the maximization of the actual overall efficiency, mechanical load and washability tests must be carried out.  
In addition, a way to protect the receiving coil from moisture or dirt should be worked out. Electromagnetic compatibility poses a particular challenge, and it must be examined whether the transmission systems need special shielding.  
For the transmission of larger amounts of energy we recommend using copper conductors. They show significantly higher efficiencies than textile conductive yarns, in any configuration. In addition, copper conductors are not significantly inferior to textile conductive yarns in terms of haptics and drapability. Textile conductive yarns can also be used as coil material, when transmitting small amounts of energy and focusing a purely textile setup.  
Conceptualization, S.M. and L.P.; Investigation, L.P.; Writing--original draft preparation, S.M.; Writing--review and editing, M.H.; Supervision G.T.G. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors declare no conflict of interest.