First prototypes of vortex retarders obtained by polarization holography

This paper will present the first prototypes of vortex retarders made of photo-orientable liquid crystals polymers recorded without mechanical action using only polarization holography. Vortex retarders are birefringent plates characterized by a uniform phase retard and a rotation of their fast axis along their center. Liquid crystals are anisotropic molecules possessing birefringent properties. They are locally orientable and their orientation defines the fast axis orientation of the retarder. Their alignment depends on the local orientation of the recording electric field. The superimposition of several polarized beams will be used to shape the electric field to achieve the recording of vortex retarders. The mathematical aspects of the superimposition process, as well as several numerical simulations are exposed. Finally, the first prototypes are presented, characterized and compared to the numerical simulations

Diffusion acoustique par des coques cylindriques. Etude des ondes axiales

The study of the propagation of the axial waves are necessary to interpret the experimental results obtained on objects constituted by a tube limited by two hemispherical shells. In this paper, we present the calculation of phase velocities of the waves which propagate in the length of a tube. These results are compared to ones obtained from a plate which is made of the same material and which has the same thickness. An experimental study is achieved on a tube of stainless steel. It consists of exciting the tube on one of its ends

Experimental determination of elastic constants of an orthotropic composite plate by using lamb waves

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Acoustic scattering from a finite plate: Generation of guided Lamb waves \textit S _\textrm0 , \textit A _\textrm0 and \textitA

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DIFFUSION ACOUSTIQUE PAR UN TUBE FERMÉ PAR DEUX COQUES HÉMISPHÉRIQUES

The acoustic scattering from infinite cylinders or spheres has shown the high influence of the surface wave propagation. We distinguish two types of surface waves: the Rayleigh or Whispering gallery waves and the Scholte-Stoneley waves. In this paper we present experimental results obtained from finite cylindrical shells bounded by two hemispherical endcaps. In our study, the insonification is in a parallel direction with the main axis of objects. We explain these experimental results by writting the stationary condition in the meridian plane of these objects, and by computing the phase velocity in the spherical shell and in the length of cylindrical shell

Etude Théorique et Expérimentale d’une Coque Mince Elastique Cylindrique Soumis à une Source Ponctuelle

International audienceLe rayonnement acoustique d’une coque élastique cylindrique immergée dans l'eau et excitée par une source ponctuelle est l'objet de la présente étude. L’objectif de ce travail a donc été d'étudier théoriquement etexpérimentalement le rayonnement acoustique d'une coque cylindrique élastique excitée par une source ponctuelle. Notre intérêt s'est porté dans un premier temps sur l’étude théorique d’une coque cylindriquerecevant une force ponctuelle de contact sous la forme d'une impulsion de Dirac et sur la pression acoustique rayonnée le long du tube en un point d'observation en champ lointain. Le modèle utilisé est basé sur la théorie de l'élasticité. Il a été de ce fait intéressant, dans un second temps, de mener des expérimentations afin de valider ces calculs théoriques et de réaliser des mesures complémentaires. Deux expériences ont ainsi été réalisées. La première expérience est basée sur une méthode bistatique, l’émission en position fixe est réalisée par un transducteur focalisant et la réception par un transducteur non focalisant se déplaçant le long de l'axe de l'objet. Pour la deuxième expérience, le transducteur récepteur est à une position axiale fixée et effectue une rotation pour une réception en oblique dans une gamme d'angle 0-30°. L'analyse de la propagation des ondes selon la direction axiale est réalisée

Implementacija in testiranje klepetalnika

This paper will present the first prototypes of vortex retarders made of photo-orientable liquid crystals polymers recorded without mechanical action using only polarization holography. Vortex retarders are birefringent plates characterized by a uniform phase retard and a rotation of their fast axis along their center. Liquid crystals are anisotropic molecules possessing birefringent properties. They are locally orientable and their orientation defines the fast axis orientation of the retarder. Their alignment depends on the local orientation of the recording electric field. The superimposition of several polarized beams will be used to shape the electric field to achieve the recording of vortex retarders. The mathematical aspects of the superimposition process, as well as several numerical simulations are exposed. Finally, the first prototypes are presented, characterized and compared to the numerical simulations

Application of orthogonality-relation for the separation of Lamb modes at a plate edge: Numerical and experimental predictions

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Nature de l'onde d'interface de Scholte sur une coque cylindrique

The theoretical and experimental studies of the ultrasonic scattering by cylindrical shells filled with air and immersed in water show, on the backscattering spectra, large amplitude variations. These variations are related to an interface wave called "A wave". The resonances of this wave are detected in a frequential window that depends on the radius ratio (inner radius b/outer radius a). They are observed for cylindrical shells with a radius ratio superior to 0.6. This wave that propagates in the water around the pipe is still not very well know in spite of the investigations which have been devoted to it. In this numerical study, it is proposed a study of the evolution of the frequency of different resonances for cylindrical shells with the radius ratio between 0.2 and 0.95. The interaction between the flexural wave A0 in the shell and the creeping wave in the fluid around the pipe is studied in greater detail. The dispersion curves of the phase velocity for these waves are presented. They show a repulse area between these two curves. This area is translated toward the high frequencies when the radius ratio tends toward 1. This phenomenon is related to the contact condition at the liquid/shell interface

Detection of a straight groove in a metal plate by acoustic scattering in water with applications to marine current turbines

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