A l'invitation de l'Ecole Doctorale de l'ENIT et en collaboration avec le Laboratoire de Modélisation Mathématique et Numérique dans les Sciences de l'Ingénieur (LAMSIN), le Professeur Andrew Norris (Rutgers University, USA) donnera le mercredi 25 Juin à
l'amphi Mokhtar Laatiri de l'ENIT une conférence intitulée:

Mirage, Cloaks and the Theory of Invisibility

Abstract: An acoustic cloak envelopes an object so that sound incident from all directions passes through and around the cloak as though the object were not present. A theory of acoustic cloaking is developed using the transformation or change-of-variables method for mapping the cloaked region to a point with vanishing scattering strength. We show that the acoustical parameters in the cloak must be anisotropic: either the mass density or the mechanical stiffness or both. If the stiffness is isotropic, corresponding to a fluid with a single bulk modulus, then the inertial density must be infinite at the inner surface of the cloak. This requires an infinitely massive cloak. We show that perfect cloaking can be achieved with finite mass through the use of anisotropic stiffness. The generic class of anisotropic material required is known as a pentamode material. If the transformation deformation gradient is symmetric then the pentamode material parameters are explicit, otherwise its properties depend on a stress like tensor which satisfies a static equilibrium equation. For a given transformation mapping the material composition of the cloak is not uniquely defined, but the phase and wave speeds of the pseudo-acoustic waves in the cloak are unique. Examples are given from 2D and 3D.

Dans ce seminaire, Prof. Norris exposera sa nouvelle théorie sur le masque acoustique (Acoustic cloak theory) qui a fait la une des journaux:

Acoustic cloaking in the news

- Acoustic cloaking material 'is inevitable' Daily Telegraph 4/28/08
- Invisibility Rules the Waves Physics World 2/29/08
- Steps Towards Warship Invisibility Science Daily 2/28/08
- Scientists Create the Sound of Silence Daily Telegraph 2/15/08
- Acoustic ``Invisibility" Cloaks Possible, Study Says National Geographic 1/23/08
- How to Make a Submarine Disappear Science/AAAS 1/14/2008
- Acoustic metamaterials: Silence all around Nature/China 11/14/07
- Hiding in Plain Sound ONR/NRE Navigator 10/19/07
- How to Build an Acoustic Invisibility Cloak New Scientist 8/31/07
- The mathematics of cloaking Physorg Dec. 2006

http://rci.rutgers.edu/~norris/
http://rci.rutgers.edu/~norris/cloaking.php

Professeur Norris est l'auteur de plus de 150 articles dans des journaux
internationaux

http://rci.rutgers.edu/~norris/papers_all.html

Ses activités editoriales et consultatives sont :

Editor: Wave Motion (Associate Ed.), Proc. R. Soc. London A (ed.board), Q. J. Mech. Appl. Math. (ed. board), J. Appl. Math. IMA (ed. board), J. Acoustical Society Am. (1995-2005) , Acoustics Research Letters Online (-2005), J. Elasticity

Member: Acoustical Society of America, American Society of Mechanical Engineers US National Committee/Theoretical and Applied Mechanics

Fellow of the Acoustical Society of America

Visiting Fellowships, Royal Irish Academy; Royal Society Fellowship

Consulting: Exxon, Schlumberger