Design of miniaturized triple-band implantable antenna sensor through characteristic mode analysis

This paper presents a miniaturized triple-band implantable antenna system operating in the ISM band (2.4–2.48 GHz) and midfield bands (1.45–1.6 GHz and 1.824–1.98 GHz) for sensing and biotelemetry applications. Characteristic mode analysis (CMA) is used during the design process to develop the antenna based on its modal behavior, while conventional full-wave simulations validate the analysis. The antenna achieves impedance bandwidths of 14.19% and 13.58% in the midfield bands and 23.31% in the ISM band. Despite its compact size of 0.000005λg3, the antenna maintains linear polarization. Triple-band operation is realized through open-ended slots etched on the radiating patch and ground plane, while metallic vias enhance overall performance. In addition, the link margin supports reliable wireless biotelemetry with an external control unit, and the estimated specific absorption rate satisfies IEEE human safety standards. Finally, measurements from the fabricated prototype show good agreement with the simulated results.