A Flexible, Low Noise Reflective PPG Sensor Platform for Ear-Worn Heart Rate Monitoring

This paper presents a novel ear-worn reflective photoplethysmography (PPG) sensor that addresses the mechanical complexities of coupling the sensor to the surface of the skin and a detection circuit that minimises ambient noise artefacts. The flexible optoelectronic transducer structure can adapt to a variety of skin surface contours. Light emitting diode (LED) modulation and a unique integrating photocurrent demodulator reduce susceptibility to wideband noise and allow subtraction of ambient light from the desired PPG signal. Experimental results demonstrate that the sensitivity is robust to sensor location and application pressure variations. Simulations also show that the photodetection method is resilient against high levels of wideband noise.