Figure 2
From: Cloaking, trapping and superlensing of lamb waves with negative refraction
Forward and backward Lamb modes. Dispersion curves of the symmetric Lamb modes in duralumin plates of \(d_1=1\) mm (light grey) and \(d_2=0.9\) mm thickness (dark grey). Among all the symmetric modes supported by plate, the forward \(S_2\) mode (red) in the thick part and the backward mode \(S_{2b}\) (blue) in the thin part are of special interest for negative refraction. Their phase velocity coincide at crossing frequency \(f_c\).
