This work develops and validates a unified multiphysics framework for Rayleigh wave propagation in human skin, treating the dermis as a functionally graded fibrous composite of collagen fibrils in a viscoelastic proteoglycan matrix. For the first time, we simultaneously incorporate nonlocal elasticity (capturing scale-dependent stress interactions), micropolar (Cosserat) theory (accounting for fiber–matrix rotational coupling), fractional-order thermoelasticity (describing power-law thermal memory), and the three-phase-lag bioheat equation (encompassing non-Fourier heat transfer). The governing equations are derived for a graded half-space and solved analytically. Results show that local continuum theories are inadequate: nonlocal and micropolar effects significantly alter dispersion, attenuation, penetration depth, and specific heat loss, while the fractional order α ( 0 < α ≤ 1 ) quantifies sub-diffusive thermal transport arising from the tissue’s multiple relaxation scales. A global sensitivity analysis identifies the dominant parameters—elastic nonlocality ϵ 1 , fractional order α , vortex viscosity κ , and inhomogeneity α ∗ - providing a roadmap for model reduction. The study offers (i) a physically realistic foundation for non-destructive skin diagnosis and thermal therapy planning, and (ii) establishes skin as a paradigm fibrous composite whose wave dynamics inform the design of biomimetic materials. • A unified multiphysics model is developed for Rayleigh wave propagation in human skin, explicitly framed as a natural fibrous composite of collagen fibrils within a proteoglycan matrix. • The framework innovatively integrates nonlocal elasticity, micropolar theory, fractional thermoelasticity, and a three-phase-lag bioheat model to capture skin’s scale-dependent and microstructurally-coupled behavior. • Analytical solutions for a functionally graded half-space reveal how composite micro-architecture governs wave dispersion, attenuation, penetration depth, and specific heat loss . • A Global Sensitivity Analysis (GSA) objectively identifies the thermal nonlocal parameter, fractional order ( α ), and micropolar vortex viscosity ( κ ) as the dominant factors controlling wave dissipation in the composite tissue. • The study establishes skin as a benchmark model system for understanding wave dynamics in complex composites, providing fundamental insights for non-destructive tissue evaluation and the design of biomimetic, wave-tailored materials .
Khan et al. (Fri,) studied this question.