Broadband locally resonant sonic shields

We demonstrate a class of sonic shield materials based on the principle of locally resonant (LR) microstructures. Each local resonator is found to vibrate almost like an independent unit, and two layers of such resonators can even be regarded as a sonic crystal. By combining several LR layers of different resonant frequencies, a broadband (200-500 Hz) sound shield, with an average transmission intensity 11 dB lower than that dictated by mass density law, has been achieved. (C) 2003 American Institute of Physics.