“…It was shown that in the elastic plates, the backward acoustic waves can be polarized both in the sagittal plane (Lamb waves) and in the shear-horizontal direction (SH waves) [ 22 , 23 , 24 ]. The backward acoustic waves of higher orders in isotropic plates and multilayered structures were also considered in [ 25 , 26 , 27 , 28 ]. Active studies of backward acoustic waves in piezoelectric plates and structures with large piezoelectric constants (potassium niobate, lithium niobate, SOI/AlN) have been carried out recently [ 6 , 7 , 24 , 29 , 30 ].…”