Attenuation of surface acoustic waves (SAWs) by a disordered monolayer of polystyrene microspheres is investigated. Surface acoustic wave packets are generated by a pair of crossed laser pulses in a glass substrate coated with a thin aluminum film and detected via the diffraction of a probe laser beam. When a 170 μm-wide strip of micron-sized spheres is placed on the substrate between the excitation and detection spots, strong resonant attenuation of SAWs near 240 MHz is observed. The attenuation is caused by the interaction of SAWs with a contact resonance of the microspheres, as confirmed by acoustic dispersion measurements on the microsphere-coated area. Frequency-selective attenuation of SAWs by such a locally resonant metamaterial may lead to reconfigurable SAW devices and sensors, which can be easily manufactured via self-assembly techniques.
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The authors would like to thank Ryan Duncan for his help in the analysis of the results. The contribution by J.K.E., A.V.-F., K.A.N, and A.A.M. was supported by NSF Grant No. CHE-1111557. A.V.-F. appreciates support from CINVESTAV and CONACYT through normal, mixed and PNPC scholarships. A.K. and N.B acknowledge support by the NSF through Grant No. CMMI-1333858. M.H. was supported through the NSF Graduate Research Fellowship Program.