MetaBioLiq: A Wearable Passive Metasurface Aided mmWave Sensing Platform for BioFluids

Human external biofluid (e.g., sweat, urine) contains vast health data that is readily harvestable. Currently, wearable sweat sensors require an electrochemical-based approach that is used in single use, creating environmental pollution as people track their exercise in the wild. Moreover, such solution relies on a battery-powered design, which brings battery health and thermal related issues. We present MetaBioLiq, a 3D printed wireless-readable sweat sensing system that offers continuous monitoring, featuring completely passive, environmentally friendly, and easily accessible. MetaBioLiq is developed upon sweat liquid's resonance upon high frequency RF interaction, with different sweat content driving RF resonance characteristics. To activate such resonance, we design 3D PolyLactic Acid (PLA) structures that capture e-field energy from the air, and tunneling it to the sweat. Once the resonance effect occurs, we analyze return signal from a wireless RF receiver to decouple the sweat's resonance. Lastly, we evaluate MetaBioLiq's performance with 24 artificial sweat samples containing different levels of glucose, electrolytes, and fat. MetaBioLiq proves its effectiveness with 95% liquid level detection performance, and 96% sweat liquid identification performance. We further investigate MetaBioLiq's robustness and reliability, as well as limitations. Overall, MetaBioLiq shows promising results to expand the realm of mobile continuous sensing to microscopic realm untangible in the past.