Ultra-Miniaturized Antenna for Deeply Implanted Biomedical Devices

Abstract

A small antenna system plays a vital role in wireless communication and monitoring of key-signs through information collected by implantable devices. Therefore, this study presents an ultra-miniaturized antenna for deeply medical implants, operating at 2.45 GHz industrial, scientific, and medical (ISM) band. To achieve a miniaturized geometry, slotted ground plane and patch, a thin substrate, and a superstrate are used. A liquid crystalline polymer material (Rogers ULTRALAM; tan $\delta =0.0025$ and $\epsilon _{r} =2.9$ ) is used as the substrate and superstrate. The proposed antenna has a surface area of 6 $\times $ 6.5 mm2 and a thickness of 0.2 mm. A realistic device-like environment and analysis in different implantation (homogeneous and heterogeneous + in different organs) sites are used to check and extend the applicability in realistic multiple implanted applications. To ensure the reliability of the communication, link budget is analyzed, which shows that the antenna can successfully communicates up to twenty meters. The proposed antenna has an impedance (10-dB) bandwidth of 480 MHz and peak realized gain of -16.5 dBi in homogeneous phantom. Further, to check the compliance with IEEE C905.1-2005 safety limits, the specific absorption rate is analyzed and found 185.56, 170.24, 134.5, and 124.2 W/kg., which limits with the radiated powers of the antenna to 9.21, 8.56, 10.54, and 12.48 mW in small intestine, large intestine, stomach, and heart, respectively. Finally, the antenna is fabricated and performed in-vitro measurements by placing the integrated antenna inside minced pork. The measured results confirm the trends of the simulated results. The proposed antenna exhibits quasi-omnidirectional radiation patterns in both planes. The analysis confirm that the proposed antenna is suitable for deeply implanted biomedical devices such as leadless pacemakers and wireless capsule endoscopes.