A study of efficiency improvement of wireless power transfer by impedance matching

In wireless electric power transmission employing magnetic resonant coils, objects or debris in the vicinity of the coil cause impedance mismatching. The mismatching will decrease the transmission efficiency at the frequency for performing electric power transmission. We have investigated the efficiency improvement by impedance matching adjustment using variable lumped capacitors. In the present work, a loop is employed to excite the resonance coil, and a set of variable capacitors are added to the loop on the power transmission side to adjust the matching. For the test against a small object, a small aluminum plate was put close to the transmission coil, and the input impedance of the coil on the transmission side was adjusted by the variable capacitors. The test measurement showed that the adjustment of the input impedance substantially improved the efficiency at the power transfer frequency.