Spatial anisotropy of the backscattered acoustic field from fiber reinforced composites

The spatial anisotropy of the backscattered acoustic field from fiber reinforced composites are studied experimentally and theoretically. These composites are formed from elementary layers composed of a unidirectional distribution of carbon fibers impregnated with resin. By stacking these basic building blocks, with a given sequence in predetermined directions, defining a superperiod, three materials have been manufactured: two periodic cross-ply composites, exhibiting a fourfold and an eightfold axis of rotation, and a unidirectional composite. The autocorrelation function of the echo is equal to the autocorrelation of the transducer aperture, except for the unidirectional composite. This means that the cross-ply composites behave, from the point of view of backscattering, like media where the scatterers are randomly distributed (biological tissues)