A unit configured for implantation in a subject's body may include a carrier, an implantable circuit associated with the carrier, an antenna arranged on the carrier and configured to wirelessly receive energy from a location external to the subject's body and to provide at least a portion of the energy to the implantable circuit, and at least one component associated with the carrier for receiving energy from the implantable circuit. Wherein the implantable circuit and the antenna have an internal resonant frequency mismatched from an external resonant frequency of an external circuit, to account for resonance frequency variation as a result of implantation in the subject's body.