New metamaterials with macroscopic behavior outside that of continuum elastodynamics

Metamaterials are constructed such that, for a narrow range of frequencies, the momentum density depends on the local displacement gradient and the stress depends on the local acceleration. In these models the momentum density generally depends not only on the strain, but also on the local rotation, and the stress is generally not symmetric. A variant is constructed for which, at a fixed frequency, the momentum density is independent of the local rotation (but still depends on the strain) and the stress is symmetric (but still depends on the acceleration). Generalizations of these metamaterials may be useful in the design of elastic cloaking devices.