Abstract
New coreless transmitting (Tx) coils with a conductive material plate for wide-range ubiquitous inductive power transfer (IPT) zones, i.e., U-IPT zones, where electric devices can be wirelessly charged during operation, are proposed in this paper. Because commercialized IPT systems are only available for short distances of several centimeters and one-to-one charging, the demand is increasing for U-IPT zones in which long-distance wireless charging with three-dimensional (3-D) free-positioning and simultaneous charging of multiple receiving (Rx) coils can be achieved. To satisfy this demand, U-IPT zones should be constructed to have a uniform magnetic field distribution in a wide space, which also poses no risk to the human body. In addition, to generate a uniform magnetic field in a wide 3-D space, such as a single room, the system requires the installation of many Tx coils above the ceilings and behind the walls of the room, and these coils should be capable of high electrical performance to support the efficiency of the entire IPT system and should be of excellent mechanical quality. Therefore, a U-IPT zone should meet the following four criteria: human safety, free-positioning of Rx coils, magnetic field uniformity, and economization. By virtue of a conductive material plate that cancels out the undesired direction of magnetic flux generated from the return wires, the proposed coreless Tx coil does not need any heavy ferromagnetic cores, which can cause nonuniformity of the magnetic field distribution and difficult construction. A prototype coreless Tx coil with the dimensions of 1 m × 1 m × 10 cm was fabricated and experimentally verified for a 1 m × 1 m U-IPT zone. The experimental results showed that 74%, 83%, and 76% high magnetic field uniformity could be achieved for z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> = 25 cm, 50 cm, and 75 cm, respectively, and a 3-D omnidirectional wireless power delivery was achieved, while the guideline of the International Commission on Non-Ionizing Radiation Protection for human safety was satisfied throughout the entire U-IPT zone. Moreover, the weight of the entire system was only 9 kg, enabling easy installation. In the multiple wireless charging experiments, 47 W of power was consumed in total by load resistors, each of them connected to nine Rx coils, respectively, with 32% power efficiency at z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> = 20 cm.
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