Multichannel Reflective PPG Earpiece Sensor With Passive Motion Cancellation

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 ac/dc ratio of 0.001-0.01 and 10% relative strength (compared to finger-based approach) were recorded from the superior and posterior auricular skins. The integrity of PPG signal and accuracy of heart rate detection were evaluated and the results showed that with adequate optical shielding and the proposed passive motion cancellation, the device was able to 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.