EXTERNAL CHARGER FOR AN IMPLANTABLE MEDICAL DEVICE FOR DETERMINING POSITION AND OPTIMIZING POWER TRANSMISSION USING RESONANT FREQUENCY AS DETERMINED FROM AT LEAST ONE SENSE COIL

The present invention relates to an external charger for wirelessly providing energy to an implantable medical device, IMD, comprising a charging coil configured when energized to produce a magnetic field to wirelessly provide energy to the IMD as a coupled system, wherein the charging coil is energized by a drive signal with a frequency, a sense coil, wherein the sense coil is configured to be induced by the magnetic field with an induced signal affected by a position of the charging coil with respect to the IMD, and control circuitry configured to determine a resonant frequency of the coupled system using the induced signal, and adjust the frequency of the drive signal to the determined resonant frequency.