Miniature Triple-Band Capsule Antenna With Reverse Current Technique for Biomedical Implants With Optimized SAR Performance

This letter presents a first-of-its-kind ultra-compact triple-band implantable antenna optimized for biomedical applications that leverages a reverse current mechanism to redistribute currents within a unified resonator, enabling excitation of three distinct resonant modes without multiple resonators or additional stubs. With physical dimensions of just 6 mm × 6 mm × 0.25 mm, the proposed antenna is among the smallest reported to support triple-band operation, maintaining a simple structure with no ground plane slots or perturbations. The design incorporates a compact F-shaped radiating element. The antenna covers three key medical frequency bands: 915 MHz Industrial, Scientific, and Medical (ISM) band (28.5% BW, 787 1049 MHz), 1470 MHz Wireless Medical Telemetry Service (WMTS) band (18.5% BW, 1282–1544 MHz), and 2400 MHz Industrial, Scientific, and Medical (ISM) band (16.5% BW, 2097 2475 MHz). A peak gain of -31.8 dB at 915 MHz is achieved, suitable for in-body telemetry systems. Simulated and measured results show strong agreement, validating the design. Link budget analysis confirms its effectiveness for Medical Implant Communication System (MICS) applications, while Specific Absorption Rate (SAR) evaluations demonstrate compliance with safety standards. The antenna achieves one of the lowest SAR values reported for similar sizes, ensuring safe, efficient, and reliable operation within human tissue.