Modeling Light Propagation Through Finger Tissue for Sensor Alignment in Transmission Mode

Abstract Light propagation through biological tissues is crucial for non-invasive optical monitoring techniques, such as blood oxygen saturation or blood glucose sensing, due to the advantages of optical methods, including non-ionization, cost-efficiency, and non-invasive continuous monitoring capabilities. This study simulates light propagation at four wavelengths of 633, 735, 810, and 980 nm through a human finger model using COMSOL Multiphysics, with the objective of determining the optimal sensor placement angle relative to the vertical illumination axis to maximize photon fluence at the sensor. A five-layer finger model reconstructed from MRI data is employed in the simulation, and photon distribution is computed based on the Helmholtz Equation. The results indicate that sensor placement at a deflection angle of approximately 7° yields the highest light intensity beneath the tissue surface across all wavelengths. These findings provide practical guidance for the design and positioning of optical sensors in biomedical applications. Future work will focus on validating the simulation with experimental measurements and extending the model to incorporate inter-subject variability, such as differences in tissue thickness and optical properties.