Highly tunable acoustic metamaterials based on a resonant tubular array

Recent theoretical studies demonstrated that waves can be steered in any desired fashion by using a suitable distribution of material parameters. However, the required parameters for acoustic transformations often surpass the ranges available from the metamaterials developed so far. We introduce a class of acoustic metamaterials based on standing waves in a tubular array and experimentally demonstrate continuous tuning of the compressibility in an unprecedentedly wide range from $\ensuremath{-}8$ to 6 relative to air at audio frequencies. Potential applications include the acoustic Luneburg lens and cloaking.