Review on Noninvasive Radio-Frequency Sensing for Closed-Loop Body Health Management

In this presentation, non-invasive microwave and millimeter-wave sensing techniques are reviewed. The main discussion focuses on the needs and methods for wearables that are suitable for high-frequency electromagnetic-wave sensing in the applications of continuous, feedback-based closed-loop health management systems. First, the scheme and benefits of closed-loop health management systems, which consist sensors, actuators and wireless body networking are introduced. Current wearable sensors are limited in functionalities due to the constraints in their sensing modalities. Then high-frequency electromagnetic-wave sensing and imaging methods are reviewed. Based on spectral characteristics on reflectivity and power absorption, radar and wave scattering principles, and resonance shifts by tissue dielectric properties, these techniques enable internal interrogation of physical and biochemical variations in tissues due to health condition changes. Because of the strict physical and electrical requirements for wearable devices on body, implementing electromagnetic-wave sensing to accomplish non-invasive sensing faces technical challenges. Nonetheless, emerging designs and demonstrations manifest the advantages of microwave and millimeter-wave non-invasive sensing and promising future.