Elastodynamic response of ordered materials

The interaction of a normally incident plane longitudinal wave with an ordered or disordered single layer of spherical inclusions embedded in a polyester matrix was measured. Inclusions were arranged in a periodic (square or hexagonal) and random arrays with area fraction ranging from 0.07 to 0.65. Measurements were carried out at wavelengths that are large, equal, or small compared to the two characteristic lengths of the composites, namely, the particle radius and the interparticle distance. The transmission and reflection spectra for periodic layers are characterized by several resonances, the frequencies of which are close to the cut‐off frequencies of the appropriate shear lattice modes. The excitation of resonances is accompanied by the propagation of mode‐converted shear waves, which are propagated along certain symmetry directions within the plane of the particles. These waves were detected by the use of a shear wave transducer. At the first lattice resonance frequency, the reflection coefficient of a layer drops down to near‐zero value. The vibrations of an individual particle have been measured by a laser interferometer. Finally, a simple model of the elastodynamic event was constructed. In spite of its simplicity, the model captures the essential features of the experimental data.