Ultrawide Bandgap Locally Resonant Sonic Materials

We prepare a class of locally resonant (LR) sonic materials. The experiments demonstrate that the resonant frequency decreases with the increasing density of the scattering unit cores or with the reducing elastic constants of the silicone rubber coating. By combining three LR layers of different resonant frequencies and choosing 10dB as the threshold of relative attenuation, we obtain an ultrawide bandgap (200--950Hz) sound material with an average transmission loss 22dB lower than that dictated by mass density law.