Abstract — 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.