Source-Detector Geometry Analysis of Reflective PPG by Measurements and Simulations

Goal: We investigate the effect of source-detector geometry, including distance and angle, on the reflective photoplethysmography (PPG) signal. Methods: A porcine skin phantom was used for laboratory measurements and replicated by Monte Carlo simulations. Variations in sensor geometry were analysed. Results: Laboratory measurements and Monte Carlo simulations showed agreement for various geometry settings. With decreasing negative sensor angle, the differential path length factor and the average maximum penetration depth increases. Conclusions: Our analyses highlight the influence of source-detector geometry on the PPG DC signal. Based on our analysis of penetration depth and optical path length, the geometry effects can be transferred to the PPG AC signal too. MC simulations provide an important tool to optimise PPG performance.