  Pentamode metamaterials are a class of acoustic metafluids that are
characterized by a divergence free modified stress tensor. Such materials have
an unconventional anisotropic stiffness and isotropic mass density, which allow
themselves to mimic other fluid domains. Here we present a pentamode design
formed by an oblique honeycomb lattice and producing customizable anisotropic
properties. It is shown that anisotropy in the stiffness can exceed three
orders of magnitude, and that it can be realistically tailored for
transformation acoustic applications.
