  The phenomenon of selective diffraction is extended to in-plane elastic waves
and we design surface corrugated periodic laminates that incorporate crystal
momentum transfer which, due to the rich physics embedded within the vector
elastic system, results in frequency, angle and wave-type selective
diffraction. The resulting devices are elastic grating couplers, with
additional capabilities as compared to analogous scalar electromagnetic
couplers, in that the elastic couplers possess the ability to split and
independently redirect, through selective negative refraction, the two body
waves present in the vector elastic system: compressional (P) and
shear-vertical (SV) elastic waves. The design paradigm, and interpretation, is
aided by obtaining isofrequency contours via a non-dimensionalised transfer
matrix method.
