THE TRANSMISSION OF A LONGITUDINAL-WAVE THROUGH A LAYER OF SPHERICAL INCLUSIONS WITH A RANDOM OR PERIODIC ARRANGEMENT

The transmission of a normally incident plane longitudinal wave throug h a single layer of spherical inclusions embedded in a polyester matri x is measured. Area fraction of inclusions is varied from 0.05 (a very dilute suspension) to 0.86 (densely packed). Two specimens are manufa ctured for each area fraction: in the first, the spheres are distribut ed in a random manner; in the second, they are arranged in a periodic (square) array; otherwise, the two are identical. The transmission spe ctra are measured at wavelengths that are large, equal or small compar ed to the two characteristic lengths of the composites, namely, the pa rticle radius and, in the case of the periodic composites, the inter-p article distance. The transmission spectra are characterized by severa l resonances; the first of these corresponds to the excitation of the rigid-body translation resonance. It also happens to be the most domin ant resonance for both the periodic and the random composites. In the case of the periodic composites, the transmission spectra are characte rized by at least one additional resonance that can be unambiguously a ttributed to the periodicity of the lattice. (C) 1997 Elsevier Science . All rights reserved.