The loosely coupled transformer is the key component of an inductive power transmission(IPT)system. In order to reduce the size of the loosely coupled transformer

mixed winding arrangement containing planar winding and vertical winding is proposed. However

since the vertical winding is adopted

the proposed transformer has a large part of leakage flux at the back of the core

resulting in low coupling coefficient k. An aluminium sheet is attached to the back area as electromagnetic shielding to avoid this problem and improve the coupling coefficient. Then

the length of the aluminium sheet is optimised. A loosely coupled transformer with mixed winding and shielding is fabricated in the lab. The optimization of the length of the shielding is found by experimental measurement to be very accurate. A loosely coupled transformer with k of 0. 583 and length of 73 mm is achieved. Compared with the previous transformer having k of 0. 523 and length of 90 mm

the proposed transformer is smaller size and higher k. This work is supported by National Natural Science Foundation of China(No. 51377081).