  We experimentally demonstrate a simple micro-electro-mechnical systems (MEMS)
approach to acoustic metamaterials and have observed the average increase of
nearly 6 dB beyond the classic law for sound attenuation at low frequencies
from 200 Hz to 1200 Hz. Here, we have also found that the MEMS metastructure,
especially the cavity-backed micromembrane, contributes to 22.3% gain of sound
transmission loss (STL) with a fill factor of perforation of less than 7.6%.
