Acoustic metamaterial with negative modulus

We present experimental and theoretical results on an acoustic metamaterial that exhibits a negative effective modulus in a frequency range from 0 to 450Hz. A one-dimensional acoustic metamaterial with an array of side holes on a tube was fabricated. We observed that acoustic waves above 450Hz propagated well in this structure, but no sound below 450Hz passed through. The frequency characteristics of the metamaterial has the same form as that of the permittivity in metals due to the plasma oscillation. We also provide a theory to explain the experimental results.