Multitextile and Multiband UHF RFID Antenna-Based Sensor for Noninvasive eHealth Hydration Monitoring

Continuous monitoring of body fluids is essential to maintain health and prevent critical issues such as dehydration, especially among those engaged in physical activities, living in harsh environments such as warm climates, or belonging to vulnerable populations. Traditional hydration monitoring solutions often involved complex measurements, required body-worn devices, or relied on batteries, making them impractical for widespread use among the general population. However, the development of low-cost, noninvasive hydration monitoring technology that can be integrated into textiles, together with the generalization of the digital product passport (DPP), could play a crucial role in democratizing and enhancing eHealth. Building upon previous studies, this work delves into the use of ultrahigh-frequency (UHF) radio frequency identification (RFID) antennas as hydration sensors on various fabrics and frequency bands. After dielectric characterization of different fabrics when mixed with synthetic euhydrated and dehydrated sweat, we developed and evaluated different prototypes compatible with different fabrics, achieving a read range four times larger compared with previous works. In a controlled laboratory environment, we achieved 100% accuracy classifying between euhydrated and dehydrated sweat in fabrics with liquid concentrations greater than 50%. Furthermore, the improved classification method ensures compatibility with both the Federal Communications Commission (FCC) and European Telecommunications Standards Institute (ETSI) bands.