A wireless power transfer device comprising: a first coil having a first portion, and configured to generate a magnetic field; a second coil having a second portion, and positioned with respect to the first coil such that the first portion of the first coil overlaps the second portion of the second coil in an overlap region; characterised by further comprising a flux concentrator aligned with the overlap region and configured to concentrate a magnetic flux of the magnetic field; a power amplifier electrically couplable, via a selectively controlled switch network in response to an impedance parameter of the first coil or the second coil, to one selected from a group consisting of the first coil and the second coil, the power amplifier configured by the switch network, to output a drive signal under one of four switched network configurations, the four switched network configurations comprising: a first configuration, in which the power amplifier is electrically coupled (300, fig 4A) to the first coil, the first coil receiving the drive signal to behave as a transmitter coil for transferring power to an external device, while the second coil is detuned (325, fig 4A); a second configuration, in which the power amplifier is electrically coupled (305, fig 4B) to the second coil, the second coil receiving the drive signal to behave as a transmitter coil for transferring power to the external device, while the first coil is detuned (320, fig 4B); a third configuration, in which the power amplifier is electrically coupled (300, fig 4C) to the first coil, the first coil receiving the drive signal and behaving as a transmitter coil while the second coil is magnetically coupled to the first coil to behave as a repeater coil, both the transmitter coil and repeater coil transferring power to the external device; a fourth configuration, in which the power amplifier is electrically coupled (305, fig 4D) to the second coil, the second coil receiving the drive signal to behave as a transmitter coil while the first coil is magnetically coupled to the second coil to behave as a repeater coil, both the transmitter coil and the repeater coil transferring power to the external device. a first coil having a first portion, and configured to generate a magnetic field; a second coil having a second portion, and positioned with respect to the first coil such that the first portion of the first coil overlaps the second portion of the second coil in an overlap region; characterised by further comprising a flux concentrator aligned with the overlap region and configured to concentrate a magnetic flux of the magnetic field; a power amplifier electrically couplable, via a selectively controlled switch network in response to an impedance parameter of the first coil or the second coil, to one selected from a group consisting of the first coil and the second coil, the power amplifier configured by the switch network, to output a drive signal under one of four switched network configurations, the four switched network configurations comprising: a first configuration, in which the power amplifier is electrically coupled (300, fig 4A) to the first coil, the first coil receiving the drive signal to behave as a transmitter coil for transferring power to an external device, while the second coil is detuned (325, fig 4A); a second configuration, in which the power amplifier is electrically coupled (305, fig 4B) to the second coil, the second coil receiving the drive signal to behave as a transmitter coil for transferring power to the external device, while the first coil is detuned (320, fig 4B); a third configuration, in which the power amplifier is electrically coupled (300, fig 4C) to the first coil, the first coil receiving the drive signal and behaving as a transmitter coil while the second coil is magnetically coupled to the first coil to behave as a repeater coil, both the transmitter coil and repeater coil transferring power to the external device; a fourth configuration, in which the power amplifier is electrically coupled (305, fig 4D) to the second coil, the second coil receiving the drive signal to behave as a transmitter coil while the first coil is magnetically coupled to the second coil to behave as a repeater coil, both the transmitter coil and the repeater coil transferring power to the external device. a first configuration, in which the power amplifier is electrically coupled (300, fig 4A) to the first coil, the first coil receiving the drive signal to behave as a transmitter coil for transferring power to an external device, while the second coil is detuned (325, fig 4A); a second configuration, in which the power amplifier is electrically coupled (305, fig 4B) to the second coil, the second coil receiving the drive signal to behave as a transmitter coil for transferring power to the external device, while the first coil is detuned (320, fig 4B); a third configuration, in which the power amplifier is electrically coupled (300, fig 4C) to the first coil, the first coil receiving the drive signal and behaving as a transmitter coil while the second coil is magnetically coupled to the first coil to behave as a repeater coil, both the transmitter coil and repeater coil transferring power to the external device; a fourth configuration, in which the power amplifier is electrically coupled (305, fig 4D) to the second coil, the second coil receiving the drive signal to behave as a transmitter coil while the first coil is magnetically coupled to the second coil to behave as a repeater coil, both the transmitter coil and the repeater coil transferring power to the external device.