Low power RFID photoplethysmography (PPG) monitoring

This paper introduces a Battery-Assisted Passive (BAP), ring-shaped Radiofrequency Identification (RFID) tag that streams photoplethysmography (PPG) signals from an on-tag PPG sensor to a remote reader via UHF. Unlike Bluetooth or Wi-Fi based real-time systems, this wearable tag consumes sub 10 mW and requires no connection or pairing protocol, beginning to stream automatically when a reader is detected. The ring tag also transmits tri-axial accelerometer data (ADXL363) that used to compute a Motion Quality Index (MQI) at the reader-PC, which preserves signal integrity and identifies user activity states (for example, walking or stationary) and to mitigate motion artifacts (MA). Experimental validation with a ThingMagic M7E reader demonstrates reliable heart-rate calculation up to 300 bps with high data integrity at a 5 m read range in low noise laboratory environments.