ELASTIC WAVES IN PERIODIC COMPOSITE MATERIALS

M. KAFESAKI and E. N. ECONOMOU

Research Center of Crete-FORTH, P.O. Box 1527, 711 10 Heraklion Crete, Greece and Department of Physics, University of Crete, 714 09, Crete, Greece

and M. M. SIGALAS

Ames Laboratory and Department of Physics and Astronomy Iowa State University, Ames IA 50011

Abstract

The study of the elastic and acoustic wave scattering by a single sphere is used to analyze and to predict band structure results in composites consisting of periodically placed spheres in a host material. It was found that classical wave propagation in a composite can be understood by considering two idealized channels: the first is using the host and the second is by hopping coherently from sphere to sphere using the resonances of the single scattering cross-section - in analogy with the LCAO in solids and molecules. Thus, widely separated strong resonances with a strong background in between (attributed to a rigid or soft sphere) in the single sphere scattering cross-section implies a wide gap in the periodic composite. It was found that a high density sphere embedded in a plastic produces cross-sections favorable for gaps. Detailed band structure results confirm this prediction.