A Study of Continuous Noninvasive RF Hydration Sensing on Human Forearm

In this work, a planar radio-frequency sensor is developed for noninvasive and efficient monitoring of water content variations in human body and tissues. The sensor operates on the principle of electromagnetic resonance, which is highly sensitive to changes in dielectric properties influenced by water content. Designed on a FR4 substrate, the planar loop resonator, tuned with an embedded metal pad, features enhanced resonance performance, compactness, sensitivity and wearability. Experiments conducted to monitor hydration processes on the forearm of a human subject at different days demonstrate the sensor ability to detect distinct trends as an individual's transition from dehydrated to hydrated states. The sensor's small, planar form factor offers promising potential for integration into a wearable device to be worn on the human forearm, enabling continuous and reliable hydration monitoring.