Acoustic metamaterial based on multi-split hollow spheres

We firstly present a kind of acoustic metamaterial (AM) with resonant microstructure of double split hollow sphere (DSHS). Simulation and experimental results show that the DSHS AM has a transmission dip and accompanied phase advance near the resonant frequency. Effective properties extracted by homogenized-media theory show that the negative modulus of the DSHS AM occurs near the dip frequency. With the increase of the diameter of the double holes in the DSHS, the resonant intensity will be stronger which leads to a greater negative modulus. By adjusting the double holes of DSHS structure with different diameter or angle, the negative-modulus band of the AMs with the modified unit cells will become tunable. Furthermore, we extend the DSHS AMs to the AMs with multi-split hollow sphere (MSHS), which still possess the property of negative modulus. This concept may pave a theoretical way to study the micro-sized and nano-sized MSHS AMs fabricated by chemical manufacturing techniques, which have potential application in the future.