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Soft 3D acoustic metamaterial with negative index

Abstract : Many efforts have been devoted to the design and achievement of negative-refractive-index metamaterials since the 2000s1, 2, 3, 4, 5, 6, 7, 8. One of the challenges at present is to extend that field beyond electromagnetism by realizing three-dimensional (3D) media with negative acoustic indices9. We report a new class of locally resonant ultrasonic metafluids consisting of a concentrated suspension of macroporous microbeads engineered using soft-matter techniques. The propagation of Gaussian pulses within these random distributions of ‘ultra-slow’ Mie resonators is investigated through in situ ultrasonic experiments. The real part of the acoustic index is shown to be negative (up to almost − 1) over broad frequency bandwidths, depending on the volume fraction of the microbeads as predicted by multiple-scattering calculations. These soft 3D acoustic metamaterials open the way for key applications such as sub-wavelength imaging and transformation acoustics, which require the production of acoustic devices with negative or zero-valued indices.
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Thomas Brunet, Aurore Merlin, Benoit Mascaro, Kevin Zimny, Jacques Leng, et al.. Soft 3D acoustic metamaterial with negative index. Nature Materials, Nature Publishing Group, 2014, 14, pp. 384-388. ⟨10.1038/nmat4164⟩. ⟨hal-01146463⟩

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