Flute-model acoustic metamaterials with simultaneously negative bulk modulus and mass density

• We presented a three-dimensional double-negative acoustic metamaterial (AM).
• The AM consists of flute-model meta-molecule of perforated hollow steel tubes.
• The effective bulk modulus and mass density of the AM were calculated to be negative.
• The AM experimentally exhibits acoustic focusing properties.

We experimentally constructed a three-dimensional flute-model meta-molecule structure acoustic metamaterial (AM) from a periodic array of perforated hollow steel tubes (PHSTs) and investigated its transmission and reflection behaviors in an impedance tube system. The AM exhibited a peak and dip, and an inverse phase, thus exhibiting the local resonance of the PHSTs. Based on the homogeneous media theory, the effective bulk modulus and mass density of the AM were calculated to be simultaneously negative; the refractive index was also negative. PHST AM slab focusing experiments showed that the medium with a resonant structure exhibited a distinct metamaterial property.