Motion-Aware Low-Power Wearable Photoplethysmography System with Metamaterial-Enhanced Wireless Telemetry

In wireless photoplethysmography (PPG) systems, motion artifacts (MAs) and high-power consumption of PPG data acquisition are the critical bottlenecks. MAs induced by body movement during long-term wear significantly degrade PPG signal fidelity, thereby increasing post-processing power consumption. Although previous studies have investigated MA mitigation, power optimization, and wireless connectivity independently, their co-design and system-level integration remains largely unexplored. This paper presents a motion-controlled wearable (MCW) wireless PPG sensing system that features an autonomous motion-gated sampling technique, adaptive power management, and robust data transfer via a metamaterial-enhanced telemetry link. The MCW system autonomously employs motion-gated sampling to acquire heart rate (HR) and blood oxygen saturation (SpO₂) data under different physical activities. The motion-gated sampling algorithm reduces system power consumption by 55% from its active mode while ensuring robust physiological measurements accuracy. Experimental results demonstrate Mean Absolute Errors (MAEs) ranging from 1.5-6.2 BPM (HR) and 0.5-1.0 % (SpO₂) across sitting, standing, walking, and running motions, while maintaining PPG signal-to-noise ratio 10 dB under all evaluated activities. Additionally, integrating an electromagnetic bandgap (EBG) structured metamaterial enhances the on-body antenna's performance and decreases the specific absorption rate (SAR) from 4.36 W/kg to 1.677 W/kg. The proposed MCW system, encapsulated in silicone, provides a compact, energy-efficient platform for reliable long-term wearable cardiovascular monitoring.