Theoretical and experimental analysis of the diffusion of light generated by a light emitting diode inside tissue-like media

The knowledge of the spatial distribution of light within a biological tissue exited by a light source (LASER or LED) is fundamental to achieve optimal photodynamic treatment. In this paper, we develop an analytical model relative to the diffuse fluence rate within a tissue-like medium irradiated by a continuous-wave light emitting diode (LED). The model is based on the two dimensional Fourier transform and applied to a homogeneous tissue slab. The total fluence rate along the axis of the medium was computed by adding the collimated and the diffuse components. The analytical solution was also used to study the depth evolution of the photon fluence rate as functions of the finite source beam size and the tissue optical parameters. Measurement results were performed using a tank filled with a liquid-simulating turbid medium (milk) illuminated with a LED beam. The experimental behaviour results agree with the theoretical predictions

Theoretical and experimental analysis of the diffusion of light generated by a light emitting diode inside tissue-like media

The knowledge of the spatial distribution of light within a biological tissue exited by a light source (LASER or LED) is fundamental to achieve optimal photodynamic treatment. In this paper, we develop an analytical model relative to the diffuse fluence rate within a tissue-like medium irradiated by a continuous-wave light emitting diode (LED). The model is based on the two dimensional Fourier transform and applied to a homogeneous tissue slab. The total fluence rate along the axis of the medium was computed by adding the collimated and the diffuse components. The analytical solution was also used to study the depth evolution of the photon fluence rate as functions of the finite source beam size and the tissue optical parameters. Measurement results were performed using a tank filled with a liquid-simulating turbid medium (milk) illuminated with a LED beam. The experimental behaviour results agree with the theoretical predictions

Bleustein-Gulyaev waves in a finite piezoelectric material loaded with a viscoelastic fluid

A generalized analytical approach for the propagation of Bleustein–Gulyaev wave in a piezoelectric material loaded on its surface with a viscoelastic fluid is established in this paper. The Bleustein–Gulyaev waveguide surface is subjected to various glycerol concentrations. The Maxwell and Kelvin–Voigt models are used to describe the viscoelasticity of this fluid. Exact dispersion equation is obtained in the cases of both electrically short circuit and open circuit by solving the equilibrium equations of piezoelectric materials and the Stokes equation of viscoelastic fluid. The effect on the phase velocity and attenuation for several frequencies is highlighted. The influence of key parameters such as substrate thickness and fluid thickness is also studied. These investigations can serve as benchmark solution in design of Bleustein–Gulyaev wave sensors

Surface wave in a Maxwell liquid-saturated poroelastic layer

An analytical approach of the propagation and attenuation of Love waves in a viscoelastic liquidsaturated poroelastic layer has been considered in this paper. The equations of motion have been formulated separately for different media under suitable boundary conditions at the interface of viscoelastic liquid, poroelastic layer and elastic substrate. Following Biot’s theory of poroelasticity, a new accurate and simple generalized dispersion equation has been established to design Love wave liquid sensors. The effect of liquid shear viscosity on the Love waves velocity has been studied. The influence of thickness and porosity of the waveguide layer has also been shown on the Love waves velocity and attenuation. The various investigations results can serve as benchmark solutions in design of liquid sensors and nondestructive testing

Correlation between the toroidal modes of an elastic sphere and the viscosity of liquids

Vibration characteristics of elastic nanostructures embedded in fluid medium have been used for biological and mechanical sensing and also to investigate materials and mechanical properties. An analytical approach has been developed in this paper to accurately predict toroidal vibrations of an elastic nanosphere in water–glycerol mixture. The Maxwell and Kelvin–Voigt models are used to describe the viscoelasticity of this fluid. The influence of key parameters such as glycerol mass fraction, sphere radius, and angular mode number are studied. We demonstrate that the sphere radius plays a significant role on the quality factor. Results also highlight three behavior zones: viscous fluid, transition, and elastic solid. In addition, these investigations can serve as benchmark solution in design of liquid sensors

Correlation between the toroidal modes of an elastic sphere and the viscosity of liquids

Vibration characteristics of elastic nanostructures embedded in fluid medium have been used for biological and mechanical sensing and also to investigate materials and mechanical properties. An analytical approach has been developed in this paper to accurately predict toroidal vibrations of an elastic nanosphere in water–glycerol mixture. The Maxwell and Kelvin–Voigt models are used to describe the viscoelasticity of this fluid. The influence of key parameters such as glycerol mass fraction, sphere radius, and angular mode number are studied. We demonstrate that the sphere radius plays a significant role on the quality factor. Results also highlight three behavior zones: viscous fluid, transition, and elastic solid. In addition, these investigations can serve as benchmark solution in design of liquid sensors

Free vibration investigation of submerged thin circular plate

Free vibration of coupled system including clamped-free thin circular plate with hole submerged in three dimensional cylindrical container filled with inviscid, irrotational and compressible fluid is investigated in the present work. Numerical approach based on the finite element method (FEM) is performed using the Comsol Multiphysics software, in order to analyze qualitatively the vibration characteristics of the plate. Plate modeling is based on Kirchhoff-Love plate theory. Velocity potential is deployed to describe the fluid motion since the small oscillations induced by the plate vibration is considered. Bernoulli's equation together with potential theory are applied to get the fluid pressure on the free surface of the plate. To prove the reliability of the present numerical solution, a comparison is made with the results in the literature, which shows a very good agreement. Then, different parameters effect including fluid density, fluid height, free surface wave, hole radius and hole eccentricity on the natural frequencies of the coupled system is discussed in detail. Some three-dimensional mode shapes of the submerged plate are illustrated. Furthermore, the obtain results can serve as benchmark solutions for the vibration control, parameter identification and damage detection of plate

Analytical approach for predicting vibration characteristics of an embedded elastic sphere in complex fluid

Vibration characteristics of elastic nanostructures embedded in fluid medium have been used for biological and mechanical sensing, and also to investigate the materials mechanical properties. The fluid medium surrounding the nanostructure is typically modeled as a Newtonian fluid. A novel approach based on the exact theory has been developed in this paper, to accurately predict the various vibration scenarios of an elastic sphere, in a compressible viscous fluid. Then the analysis is extended to a viscoelastic medium using the Maxwell fluid model. To demonstrate the accuracy of the present approach, a comparison is made with the published theoretical results in the literature in some particular cases, which shows a very good agreement. The effects of fluid compressibility and viscoelasticity are discussed in details and we demonstrate that the fluid compressibility plays a signi cant role in the vibration modes of an elastic sphere. Results also show that the different vibration modes of a sphere triggers a viscoelastic response in water-glycerol mixtures similar to that of literature. In addition, the obtained results can serve as benchmark solution in design of liquid sensors

Mesure non invasive des paramètres optiques des tissus biologiques par spectroscopie résolue en fréquence (approche analytique par l'équation de diffusion et implications cliniques)

Le déplacement des photons dans un tissu biologique est décrit par un modèle basé sur l'approximation de la diffusion. Deux conditions frontières à l'interface air-tissu peuvent être utilisées pour résoudre l'équation de diffusion : "flux égal à zéro en tout point de la surface réelle" (ZSR) et "flux égal à zéro en tout point de la surface extrapolée" (ZSE). Nous considérons un tissu irradié par un faisceau laser. Pour une impulsion courte assimilée à une fonction de Dirac, la "reflectance" et la "transmittance" sont déduites de la théorie de la diffusion en utilisant la condition frontière la plus simple : la condition ZSR. La description du déplacement des photons dans le domaine temporel est complétée par une description équivalente dans le domaine fréquentiel. Au lieu d'une source lumineuse pulsée, une diode laser modulée en intensité, à la fréquence f est utilisée pour injecter les photons dans le tissu. Le flux de photons au niveau du détecteur varie aussi sinusoïdalement dans le temps...ANGERS-BU Médecine-Pharmacie (490072105) / SudocPARIS-BIUP (751062107) / SudocSudocFranceF

A novel generalized dispersion equation to design circumferential wave fluid sensors

A novel analytical investigation of circumferential (i.e. torsional) wave propagation in long anisotropic cylindrical rod (waveguide), surrounded by a viscoelastic fuid is proposed. The material is transversely isotropic, with its symmetry axis coincident with the axial axis of the cylindrical rod. In particular, a new form of the complex dispersion equation is presented. The aim of this paper is to study the correlation between the rheological properties of the fuid and the wave characteristics (phase and attenuation). The efect of the frequency and the waveguide radius on the wave characteristics are highlighted. The obtained results show that the measurements should be performed at high frequency using small rod radius. Accordingly, the results can be serve as benchmark solutions in design of torsional wave fluid sensor