  Anisotropic density-near-zero (ADNZ) acoustic metamaterials are investigated
theoretically and numerically in this letter and are shown to exhibit
extraordinary transmission enhancement when material loss is induced. The
enhanced transmission is due to the enhanced propagating and evanescent wave
modes inside the ADNZ medium thanks to the interplay of near-zero density,
material loss, and high wave impedance matching in the propagation direction.
The equi-frequency contour (EFC) is used to reveal whether the propagating wave
mode is allowed in ADNZ metamaterials. Numerical simulations based on
plate-type acoustic metamaterials with different material losses were performed
to demonstrate collimation enabled by the induced loss in ADNZ media. This work
provides a different way for manipulating acoustic waves.
