SPECTRAL GREENS-FUNCTION FOR WAVE EXCITATION AND PROPAGATION IN A PIEZOELECTRIC, CONTINUOUSLY TWISTED, STRUCTURALLY CHIRAL MEDIUM

A continuously twisted, structurally chiral medium (CTSCM) is a recipr ocal medium whose constitutive properties vary helicoidally along its axis of spirality (say, the z axis), and the corresponding piezoelectr ic medium is abbreviatedly called the PCTSCM. Very recent progress in thin-film research is presented here to show that technologically sign ificant CTSCM's and PCTSCM's an waiting in the wings and calling for t heoretical advances in the understanding of wave excitation and propag ation in these novel materials. A spectral Green's function is obtaine d as a bilinear composition of two matrices, after implementing a spat ial Fourier transform in the xy plane as well as the Oseen transformat ion. As a result, multilayered media problems as well as grating probl ems utilizing CTSCM's and PCTSCM's become accessible to theoretical ex ploration leading to novel transducers, sensors, and other devices. (C ) 1997 Acoustical Society of American.