An Exploration of Blue PPG Signal Using a Novel Color Sensorbased PPG System

Reflectance photoplethysmography is a widely employed method in personal health assessment devices. We developed a remote PPG system for obtaining the signal from palm skin. For the handle-mounted design, it is crucial to ensure accurate measurements under a range of skin temperatures. Under lower temperatures, green PPG was proven to provide superior signal quality in comparison to infrared PPG. However, since hemoglobin has maximum absorption in both green and blue parts of the spectrum, to ensure a stable performance of handle-mounted PPG system under different temperature conditions, it is worth exploring the PPG signal in both wavelengths. In our PPG system, TCS3472 Color Sensor was chosen as a photodetector. In distinction from video cameras with Bayer pattern, the TCS3472 has an equal number of R, G, and B sensing elements, thereby allowing the comparison of these wavelengths performance. Using the developed system, we compared green and blue PPG signals from six subjects in terms of amplitude and accuracy of heartbeat intervals estimation under two temperature conditions. According to our preliminary results, the performance of blue PPG was comparable to green PPG under both temperature conditions, suggesting further investigation with our system is worth conducting.