title: 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 2000s. One of the challenges at present is to extend that field beyond electromagnetism by realizing three-dimensional (3D) media with negative acoustic indices. 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.
authors.affiliation: University of Bordeaux, CNRS, I2M-APY, UMR 5295, 33405 Talence, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Brunet
authors.affiliation: University of Bordeaux, CNRS, CRPP, UPR 8641, 33600 Pessac, France.
authors.forename: Aurore
authors.initials: A
authors.lastname: Merlin
authors.affiliation: University of Bordeaux, CNRS, I2M-APY, UMR 5295, 33405 Talence, France.
authors.forename: Benoit
authors.initials: B
authors.lastname: Mascaro
authors.affiliation: University of Bordeaux, CNRS, CRPP, UPR 8641, 33600 Pessac, France.
authors.forename: Kevin
authors.initials: K
authors.lastname: Zimny
authors.affiliation: University of Bordeaux, CNRS, Solvay, LOF, UMR 5258, 33608 Pessac, France.
authors.forename: Jacques
authors.initials: J
authors.lastname: Leng
authors.affiliation: University of Bordeaux, CNRS, I2M-APY, UMR 5295, 33405 Talence, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Poncelet
authors.affiliation: University of Bordeaux, CNRS, I2M-APY, UMR 5295, 33405 Talence, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Aristégui
authors.affiliation: University of Bordeaux, CNRS, CRPP, UPR 8641, 33600 Pessac, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Mondain-Monval