In supplying energy to a medical device implanted in a mammal patient a first coil system (20) external to the patient's body for wirelessly transferring energy can be used that inductively cooperates with a second coil system (12) that, when implanted in the patient's body, receives wirelessly transferred energy for supplying energy or control signals to the medical device, when implanted in the patient's body. The first and second coil systems comprise each at least two individual coils (50, 51； 60, 61) which are not directly electrically connected to each other and operate basically independently of each other. This may give a very efficient and versatile transfer of energy or control signals. The coils in each of the coil systems can be operating at different frequencies by being connected to respective electric circuits, where each of these respective electric circuits operate basically independently of each other generating e.g. alternating electric current of different frequencies.
