A passive implantable relay module includes a first coupler arm configured to wirelessly receive electromagnetic energy radiated through electric radiative coupling from a transmitting antenna located outside a subject's body; a second coupler arm; and a connector portion comprising a first metal core and a first dielectric coating surrounding the first metal core, the connector portion configured to connect the first coupler arm to the second coupler arm such that when the passive implantable relay module is implanted inside the subject's body and the transmitting antenna initiates wireless energy transfer to the first coupler arm via non-inductive coupling, electromagnetic waves carrying the electromagnetic energy received at the first coupler arm propagate along the first metal core to arrive at the second coupler arm, where the electromagnetic energy arriving is wirelessly transferred, again via non-inductive coupling, to a receiving antenna on a passive wireless neural stimulator device.