An antenna system is provided that is capable of transmitting and receiving using near-field magnetic induction (NFMI). The antenna system includes a non-magnetic metallic core, a ferrite shield, and at least one electrically conducting winding. The ferrite shield is positioned between the non-magnetic metallic core and the electrically conducting winding. The non-magnetic metallic core may be a battery. The ferrite material forms a low impedance path for the magnetic field lines and increases inductance, thus providing increased energy efficiency and transmission quality. The antenna system is suitable for use in space constrained battery powered devices, such as hear instruments including hearing aids and earbuds.