Reflective Photoplethysmograph Earpiece Sensor for Ubiquitous Heart Rate Monitoring

This paper addresses the design considerations of a novel earpiece photoplethymograph (PPG) sensor and its

in-situ

evaluation results. The device is encapsulated with multiple LEDs and photodiodes based on a reflective PPG design. A compact and low power circuitry was developed for signal control and conditioning. PPG signals with an averaged a.c./d.c. ratio of 0.001–0.01 and 10% relative strength (compared to finger-based approach) were recorded from the superior and posterior auricular skins. PPG signal integrity and heart rate detection accuracy were evaluated and the results showed that with adequate optical shielding and motion cancellation, the device could reliably detect heart rate both during rest and moderate exercise. The proposed sensor design is low power, easy to wear compared to conventional earlobe PPG devices.