Experimentally Validated Implant-to-Implant Communication at ISM Bands using Compact Loop Antennas

Reliable wireless connectivity among deeply implanted medical devices is essential for advancing next-generation wireless implantable systems. While most previous studies have focused on implant-to-external communication, the feasibility of direct implant-to-implant (I2I) communication under realistic tissue conditions remains largely unexplored. This paper presents an experimentally validated compact loop antenna designed to enable robust I2I links at the 915 MHz and 2.45 GHz ISM bands. Full-wave simulations using a seven-layer human head model and experimental validation in liquid phantoms were conducted to assess antenna performance and link reliability. The proposed antennas demonstrate stable performance with radiation efficiencies of 0.025% and 0.02%, maintaining positive link margins up to 15 cm at data rates of 25 Mbps. This work provides one of the first comprehensive experimental validations of I2I communication in brain-equivalent media, highlighting its potential as a low-power, short-range solution for future distributed biomedical implant networks.