Figure 2.

Bulk, surface and hybrid acoustic waves. Dispersion curves (top) and finite element simulations (bottom) showing the distinction between (I) a bulk (e.g., Lamb) wave, obtained for h/λ < 1; (II) a hybrid wave (i.e, a surface reflected bulk wave; SRBW), obtained for h/λ ≈ 1; and, (III) a Rayleigh surface wave (e.g., a surface acoustic wave; SAW), obtained for h/λ > 1. Here, the fundamental symmetric and asymmetric wave modes, denoted by S ₀ and A ₀, respectively, can be seen to asymptotically approach the SAW phase velocity c _SAW with decreasing wavelength λ (or increasing frequency) compared to the piezoelectric (in this case, lithium niobate (LiNbO₃)) substrate thickness h. In the simulations, t denotes time. Reproduced with permission.^{[ 40 ]} Copyright 2016, Wiley‐VCH.