Locally resonant sonic materials*

Ping Sheng

Department of Physics
The Hong Kong University of Science and Technology
Clear Water Bay
Kowloon, Hong Kong, China

We have fabricated a new type of composites with a microstructure size in the millimeters to 2 cm range, which display localized sonic resonances at ~350 Hz to 2000 Hz.. Around the resonance frequencies the composite behaves as a material with effective negative elastic constants and as a total wave reflector---a 2 cm slab of this composite material is shown to break the conventional mass density law of sound transmission by order(s) of magnitude. When the microstructure is periodic, our composites exhibit large elastic wave bandgaps at the sonic frequency range, but with a lattice constant order(s) of magnitude smaller than the corresponding sonic wavelength in air. Good agreement is obtained between theory and experiment.

*Work done in collaboration with Zhengyou Liu, Yiwei Mao, Xixiang Zhang, Zhiyu Yang, and C. T. Chan