A transcutaneous energy transfer system (TETS) that includes external and internal coils that have permeable cores is provided. According to one aspect, the TETS includes an external coil having disposed in proximity thereto, a first set of at least one permeable core that is wound by windings of the external coil. The TETS also includes an internal coil having disposed in proximity thereto, for each permeable core disposed in proximity to the external coil, a corresponding permeable core that is wound by windings of the internal coil.