Fully printed and flexible patch for real-time wireless monitoring of the sweating rate with physiological detection

The human sweating rate reflects body hydration status and holds intrinsic significance for monitoring physiological health. This work presents a fully printed sweat rate sensor architecture, where the internal sensing layer is fabricated via aerosol jet printing at micrometer resolution to detect nanoliter-scale sweat volume changes in microfluidic channels. The sensor transduces internal microstructural variations into radiofrequency (RF) signals through energy coupling, enabling wireless transmission to external terminals. Leveraging the RF sensor's wireless compatibility, a pulse wave sensor for monitoring physiological changes is integrated into the system. This allows simultaneous operation with the sweat rate sensor without wired connections, ultimately forming a wireless and battery-free wearable patch suitable for detecting the skin sweating rate and heart rate during human activities. By analyzing the patch's wireless signals and extracting parameters including resonant frequency and amplitude, we develop a dual-mode sensing patch. The system evaluates the effects of daily activities like resting, walking, exercising and environmental factors like temperature on skin perspiration and heart rate. In addition, the fully printed technology adopted in this work provides ideas for the lightweight and low-cost development of wearable sweat sensing systems.