Figure 7.

An inhomogeneous triangular lattice structure linked to a system of spinners. The elementary cell for this structure is shown, which contains three particles having displacements u^(p), v^(p) and w^(p). The lattice is composed of springs with stiffnesses c (solid lines) and c_ε (dashed lines), where c_ε≤c. Springs possessing stiffness c_ε form the internal connections of hexagon vertices in the lattice. Here, the lattice basis vectors are taken as t⁽¹⁾ = (3l, 0)^T and ${\mathit{t}}^{(2)}={(3l/2,\sqrt{3}l/2)}^{\mathrm{T}}$.