Steady state versus time-resolved photoplethysmography (PPG): the effect of epidermal thickness (Conference Presentation)

The photoplethysmography (PPG) sensors commonly used in wearable devices rely on changes in the diffuse reflection of light on the skin to detect heart rate. These changes are primarily due to the varying volume of blood in the tissue throughout the cardiac cycle. In this study, we consider three different epidermal thicknesses and study their effects on PPG signal. This is accomplished by using Monte Carlo eXtreme (MCX) to evaluate the photon path length in the tissue. We will study the phenomenon using both continuous wave (steady state) PPG which is a standard format in common wearables, and time-of-flight (time-resolved) PPG. Experimental validation on hemoglobin phantoms will be performed at common wavelengths (between 500 and 900 nm) for steady state cases whereas TOF-PPG will be studied using a system consisting of a pulse laser with wavelength at 780 nm, single-photon avalanche diodes, and a multi-channel time-correlated single photon counter.