Electrically-Small Antenna With Low SAR for Scalp and Deep Tissue Biomedical Devices

An ultra-miniaturized implantable antenna for scalp and deep tissue implants operating in the Industrial, Scientific, and Medical (ISM) frequency band is proposed in this communication. The proposed antenna has a compact size of only 4.422 mm3 ( $3.45\times 3.4\times0.377$ mm3). A meandered patch backed by a full ground plane was used to implement the proposed ultra-miniaturized antenna. The full ground plane does not allow backward energy flow, thus ensuring patient safety. The performance of the proposed antenna was evaluated in three different simulation environments: homogeneous skin phantom (HSP), skin implant multilayer phantom (SIMP), and muscle implant multilayer phantom (MIMP) models with and without a dummy implantable wireless device (IMD). These models were considered to evaluate the performance of the proposed antenna in more realistic complex human body environments. The proposed antenna demonstrated excellent impedance matching performance at the ISM band with a measured −10 dB impedance bandwidth of 260 MHz (2,249–2,511 MHz). The effects of coaxial cable on antenna performance were also studied. The proposed antenna exhibited a maximum measured peak gain of −26.54 dBi. Furthermore, the 1-g and 10-g specific absorption rate (SAR) values were calculated and satisfied the safety guidelines. A reliable communication link up to distances of 15, 4, and 1.3 m for bit rates of 7 kbps, 100 kbps, and 1 Mbps, respectively, can be established between the implantable device and external base station. Finally, a sensitivity analysis of the proposed antenna was conducted showing that the proposed implantable antenna can efficiently work under varying tissue conditions.