the driving techniques and circuits for WPT system started to appear. The examples listed below adopt magnetic resonance based on LC resonators. LL1 V1 i1 1994 A.W. Green and J. Boys presented their work in an inductively coupled power transmission system based on resonant power converter and well-tuned C2 i2 iM 1990 Bo Cho used a pair of magnetically coupled circuits operating at a resonance mode for a transcutaneous energy transmission system, as shown in Figure 6 [21]. The coupling was fairly loose, with a coupling coefficient of k = 0.1. For an output power of 48 W, an energy efficiency of 72% was achieved for an operating frequency of about 53 kHz. It should be noted that the impedance matching in the resonant tanks was implemented to reduce the effects of leakage inductance in the primary and secondary circuits. LL2 i'2 l:n VIEQ VL LoEQ (a) CoEQ LoEQ VIEQ i2 VL (b) fig 6 (a) The magnetically coupled resonant circuit and (b) its equivalent circuit (redrawn from [21]). (resonant) pickup coils (Figure 7). Resonant tanks are used in the primary circuit (C 1 and L1) and the secondary circuit (C 2 and L2) [22]. 1998 A small planar coreless transformer has been used for transferring power and signal. Energy was transferred from one planar spiral winding into another parallel planar winding without any magnetic core [23]. The diameter of the planar winding is 1 cm, and each planar winding has ten turns. The leakage inductances are the significant components of the equivalent circuit We engineer optimally designed custom magnetics, while offering thousands of part numbers standard, off the shelf. We can help you find one that meets your needs today. and it can be on your desk, tomorrow. Standard Products Custom Products Power Transformers Current Sense Transformers Wall Plug In Transformers Power Supplies & LED Drivers Switching Power Supply Alternative Energy Inductor Audio Transformers Inductors and Chokes Medical-Grade Isolated Sources Medical-Grade LowLeakageTransformers Power Supply Precision Toroidal Transformer Professional Audio Impedance Matching Transformer Triad Magnetics 460 Harley Knox Blvd, Perris, CA 92571 Tel: 951.277.0757 Fax: 951.277.2757 Email: info@triadmagnetics.com March 2016 www.triadmagnetics.com z IEEE PowEr ElEctronIcs MagazInE 21http://www.triadmagnetics.com