An Energy-Aware, Self-Adaptive, Battery-Free Smart Wristband for Long-Term Health Monitoring

Continuous monitoring of physiological parameters, including heart rate and oxygen saturation, is important in healthcare applications. Modern wearables are expected to support wireless connectivity, be small and lightweight, and offer long-term use. These features introduce challenges in power consumption and management. As a result, battery-powered wearables often face trade-offs between size, energy storage, performance, and operating time. This research presents a self-sustainable, battery-free smart wristband for continuous heart rate monitoring. The wristband extends operational life by integrating solar energy harvesting with supercapacitor technology in an environmentally sustainable design. Power consumption is minimized through onboard processing, which reduces inefficient data transmission, and adaptive sensor sampling, which dynamically allocates energy based on heart rate, supercapacitor voltage, and harvesting conditions. Benefiting from hardware and software co-design, the proposed wearable device achieves self-sustainability at a sensor sampling rate of 50 Hz with only 1.45 hours of indoor light exposure (1000 lux) per day and at 200 Hz with 4.74 hours. The in-field experiments show that onboard processing reduces Bluetooth Low Energy (BLE) data transmission to essential information, saving about 2 J of energy. The system shortens supercapacitor charging time by 17 minutes per hour through its ability to automatically reduce the sampling frequency from 200 Hz to 50 Hz when harvesting energy is scarce. The proposed system can even operate effectively in around 200 lux of light, equivalent to a dimly lit living room. These results underscore the system’s ability to dynamically balance power-performance trade-offs, offering a promising long-term solution for continuous health monitoring in various environments.