Lecture of Graeme Milton, University of Utah on

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Lecture of Graeme Milton, University of Utah on
"Metamaterials: high contrast composites with unusual
properties"
Publié le September 12, 2012
Date de l'évènement : September 14, 2012
Composite materials can have properties unlike any found in nature, and in this case they are
known as metamaterials. Recent attention has been focussed on obtaining metamaterials
which have an interesting dynamic behavior. Their effective mass density can be anisotropic,
negative, or even complex. Even the eigenvectors of the effective mass density tensor can
vary with frequency. Within the framework of linear elasticity, internal
masses can cause the effective elasticity tensor to be frequency dependent, yet not contribute
at all to the effective mass density at any frequency. One may use coordinate transformations
of the elastodynamic equations to get novel unexpected behavior. A classical propagating
wave can have a strange behavior in the new abstract
coordinate system. However the problem becomes to find metamaterials which realize the
behavior in the new coordinate system. This can be solved at a discrete level, by replacing
the original elastic material with a network of masses and springs and then applying
transformations to this network. The realization of the transformed network requires a new
type of spring, which we call a torque spring. The forces at the end of the torque spring are
equal and opposite but not aligned with the line joining the spring ends. We show how torque
springs can theoretically be realized.
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