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