A wireless power transmitter (101) or power receiver (105) comprises a power transfer coil (103, 107) for receiving or generating a power transfer signal and a controller (201, 301) for controlling the device to perform power transfer during a power transfer phase. The power transfer phase comprises power transfer intervals where power is transferred and foreign object detection time intervals during which a power level of the power transfer signal is reduced. A magnetic shielding element (503, 505) is positioned between the power transfer coil (103, 107) and a power transfer coil of a complementary device. The magnetic shielding element (503, 505) comprises a magnetic shield material having a saturation point such that it operates in a saturated and non-saturated mode during respectively power transfer intervals and foreign object detection time intervals. The saturation point is above a magnetic field strength generated by the power transfer signal during the power transfer time intervals and below that generated during the foreign object detection time intervals.