Mechanical metamaterials

Mechanical metamaterials derive their extraordinary effective properties primarily from architecture rather than from constituent chemistry. This Special Topic in Journal of Applied Physics assembles eleven contributions that span the contemporary breadth of the field, ranging from terahertz phononic bandgaps in van der Waals heterostructures to ventilated low-frequency acoustic absorbers, transient flexural-wave control, bistable lattices with negative stiffness under multi-modal loading, hierarchically porous lattices manufactured by foaming fused deposition modeling, culturally inspired unit cells, oxide ceramics with negative permittivity, and tunable microgel suspensions. Together, the works document a field in which geometric programming is increasingly coupled with multi-physics integration, accessible manufacturing, and application-driven engineering.