A digitally assisted repeater antenna for implant communications

The wireless link between an implant and an off-body gateway may be difficult to secure due to the fact that electromagnetic waves quickly attenuate as they propagate through human tissues. Depending on the depth of the implant within the body, the signal strength may be quite weak by the time the waves reach the skin. In order to address this problem, a digitally assisted repeater antenna has been designed to be located outside of the patient's body, which can detect the signals radiated by the implant and relay those signals to the off-body gateway. The radiation pattern of the antenna is switched between two modes depending on the link it is forming: in-body link or off-body link. With an overall size of 30 × 30 × 3.15 mm, the antenna operates in the 2.4 GHz ISM band. The repeater is aimed to be used to secure wireless communications with a smart orthopaedic hip implant. Therefore, for a typical depth of such an implant of 4 cm, the repeater has been shown to enable a decrease of more than 40 dB in the transmit power level while the distance between the implant and the off-body gateway is kept constant.