An Electromagnetic Sensor Platform with Passive Implant-Target and Wearable Patch for Monitoring Deep-Tissue...

This paper presents an electromagnetic sensor platform for monitoring deep-tissue biomarkers, utilizing tuning circuit principles. The implant-target (I-tag) includes a biomarker sensing frontend, diodes, and a spiral coil-based inductor-capacitor resonant coil. Compared to solutions with integrated active chips, the I-tag improves size, safety, and power consumption. The sensing frontend converts electrochemical signals into voltage signals applied across the diodes. In the resonant circuit, coupling between the patch system's coil and the implanted coil, aided by the diodes, translates potential changes into resistance modulation, resulting in a quantifiable offset. Unlike traditional interrogation techniques using vector network analyzers, this paper introduces a simple patch system employing a coherent demodulation technique, implemented with printed circuit board technology and commercially available components. The platform's performance was validated through experiments, achieving an RMSE of 0.1764 and a detectable distance of up to 12 mm.