Acoustic signature of dispersive and orthotropic composites using a focused microscope

Abstract

This paper presents a theoretical investigation of the reflection of focused acoustic beams from a viscoelastic orthotropic composite. The reflection coefficients taking the anisotropy of the composite into account are expressed in terms of nine complex elastic constants. Using a classical Fourier optical method, the reflected beams by an anisotropic and absorbing medium are obtained theoretically for various defocus positions of the lens and for different line focus directions. In agreement with the Snell’s laws, any waves generated in the specimen are bulk heterogeneous plane waves. In addition, for a unidirectional carbon fiber/epoxy matrix composite the oscillations due to the generation of lateral wave in the medium are compared with the critical angle associated with these waves at various azimuthal angles. Conclusions are drawn regarding the use of focused beams in the inverse problem to recover elastic constants of composite materials.