https://ujm.hal.science/ujm-00628784Mottin, StéphaneStéphaneMottinLHC - Laboratoire Hubert Curien - IOGS - Institut d'Optique Graduate School - UJM - Université Jean Monnet - Saint-Étienne - CNRS - Centre National de la Recherche ScientifiquePanasenko, GrigoryGrigoryPanasenkoLAMUSE - Laboratoire de Mathématiques de l'Université de Saint-Etienne - UJM - Université Jean Monnet - Saint-ÉtienneGanesh, S SivajiS SivajiGaneshIIT Bombay - Indian Institute of Technology BombayMultiscale modeling of light absorption in tissues: limitations of classical homogenization approach.HAL CCSD2010[SDV.NEU] Life Sciences [q-bio]/Neurons and Cognition [q-bio.NC][MATH.MATH-AP] Mathematics [math]/Analysis of PDEs [math.AP][PHYS.PHYS.PHYS-OPTICS] Physics [physics]/Physics [physics]/Optics [physics.optics]Mottin, Stephane2011-10-13 03:53:552023-03-24 14:52:542011-10-13 09:04:54enJournal articleshttps://ujm.hal.science/ujm-00628784/document10.1371/journal.pone.0014350application/pdf1In biophotonics, the light absorption in a tissue is usually modeled by the Helmholtz equation with two constant parameters, the scattering coefficient and the absorption coefficient. This classic approximation of "haemoglobin diluted everywhere" (constant absorption coefficient) corresponds to the classical homogenization approach. The paper discusses the limitations of this approach. The scattering coefficient is supposed to be constant (equal to one) while the absorption coefficient is equal to zero everywhere except for a periodic set of thin parallel strips simulating the blood vessels, where it is a large parameter ω. The problem contains two other parameters which are small: ε, the ratio of the distance between the axes of vessels to the characteristic macroscopic size, and δ, the ratio of the thickness of thin vessels and the period. We construct asymptotic expansion in two cases: ε --> 0, ω --> ∞, δ --> 0, ωδ --> ∞, ε2ωδ --> 0 and ε --> 0, ω --> ∞, δ --> 0, ε2ωδ --> ∞, and and prove that in the first case the classical homogenization (averaging) of the differential equation is true while in the second case it is wrong. This result may be applied in the biomedical optics, for instance, in the modeling of the skin and cosmetics.