Figure 5.

Dispersion relations ω=ω(k) of the standard Mindlin–Eringen model for the longitudinal waves with free micro-inertia η=10⁻³ and gradient micro-inertia ${\overline{\eta }}_3=(3\times {10}^{-4},\hspace{0.17em}3\times {10}^{-3},\hspace{0.17em}3\times {10}^{-2})$ kg m⁻¹ (a) and transverse waves with micro-inertia η=10⁻³ and gradient micro-inertia ${\overline{\eta }}_2=(2\times {10}^{-4},\hspace{0.17em}2\times {10}^{-3},\hspace{0.17em}2\times {10}^{-2})$ kg m⁻¹ (b). (Online version in colour.)