First-in-human evaluation of a microwave impedance-matching metasurface to improve transmission for non-invasive electromagnetic sensing of blood analytes

Non-invasive biosensing faces major challenges due to impedance mismatch at the skin interface, which causes significant signal reflection and limits power transmission through biological tissues. In this paper, we propose and evaluate a novel, subwavelength-thick impedance-matching metasurface (MTS) designed for direct skin contact to enhance electromagnetic (EM) wave transmission in the Ka-band. Our evaluation includes controlled laboratory experiments and a first-in-human study. Using an in-house developed benchtop system, we performed transmission measurements through aqueous glucose solutions and, most importantly, through the hands of six human volunteers. Our results show that the MTS significantly enhances signal transmission into human skin tissue, yielding an average improvement of up to 5 dB in the 36-37 GHz frequency range compared to the bare-skin condition, thereby improving sensitivity for analyte detection without increasing system size or power consumption. These findings demonstrate the potential of MTS-based impedance-matching layers as practical, integrable solutions to overcome key hardware limitations in wearable biomedical sensing devices. The study represents the first human investigation of an impedance-matching MTS designed to improve microwave signal penetration for non-invasive sensing applications.