Abstract
Wireless inductive power transmission systems can potentially supply wearable devices. Power cables or batteries can be eliminated by implementing a wireless power transfer system, making the wearable devices less obtrusive to users. However, rigid coils can cause discomfort to users in wearable applications. The novel screen-printed flexible coils on textiles reported here are intended to be a low-cost and comfortable solution when integrated into clothing. A constant-width circular-spiral flat coil has been designed to minimize the detrimental effect of the low conductivity of the screen-printed flexible conductors on the efficiency of the wireless power transfer system. The coils are printed on 65/35 polyester/cotton textile with a screen-printed Fabink-UV-IF1 interface layer coating. The interface layer provides a relatively flat and smooth surface to prevent the permeation of the conductive paste into the textile and allows the printing of finer-profile coils. A 5 V 1.2 W DC output has been achieved by a wireless power transfer system using the printed flexible coils with Qi standard circuitry; a DC-DC efficiency of 37% has been measured.
Highlights
Wireless power transmission (WPT) using inductive coupling has been employed in numerous applications [1], in particular where cable-free devices are desired
Flexible printed electronics for e-textiles are fabricated by printing the conductive paste to form the electronic circuitry onto a substrate material, such as a polyimide film, which is attached to the host textile by a mechanical fixing method such as sewing, as such the printed electronics are not directly integrated with the actual textile
The profile of a printed conductive paste is poorly defined when printed onto a rough substrate. These factors lead to unpredictability and variation of the electrical properties which can cause the coils of the WPT system to diverge from their tuned operational frequency or cause the driver circuit to fail
Summary
Wireless power transmission (WPT) using inductive coupling has been employed in numerous applications [1], in particular where cable-free devices are desired. Most current research involves the use of coils fabricated either by winding copper wire or by using a track fabricated onto a PCB [3,4] These rigid inflexible coils are uncomfortable and so less suited to e-textile applications due to their impact on the user. Screen-printed flexible coils have been designed and fabricated for a WPT system. The profile of a printed conductive paste is poorly defined when printed onto a rough substrate These factors lead to unpredictability and variation of the electrical properties which can cause the coils of the WPT system to diverge from their tuned operational frequency or cause the driver circuit to fail.
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