Simulated Lamb wave velocities and sensitivities for frequencies 150 and 300 Hz for wall thickness H = 12 mm and different combinations of μ1 and μ2. (a) Lamb wave velocities at 150 Hz, (b) Lamb wave velocities at 300 Hz, (c) Sμ1 at 150 Hz, (d) Sμ1 at 300 Hz, (e) Sμ2 at 150 Hz, (f) Sμ2 at 300 Hz. The black dashed lines in panels (c) and (d) depict when Sμ1 = 0.