title: Random acoustic metamaterial with a subwavelength dipolar resonance.
abstract: The effective velocity and attenuation of longitudinal waves through random dispersions of rigid, tungsten-carbide beads in an elastic matrix made of epoxy resin in the range of beads volume fraction 2%-10% are determined experimentally. The multiple scattering model proposed by Luppé, Conoir, and Norris [J. Acoust. Soc. Am. 131(2), 1113-1120 (2012)], which fully takes into account the elastic nature of the matrix and the associated mode conversions, accurately describes the measurements. Theoretical calculations show that the rigid particles display a local, dipolar resonance which shares several features with Minnaert resonance of bubbly liquids and with the dipolar resonance of core-shell particles. Moreover, for the samples under study, the main cause of smoothing of the dipolar resonance of the scatterers and the associated variations of the effective mass density of the dispersions is elastic relaxation, i.e., the finite time required for the shear stresses associated to the translational motion of the scatterers to propagate through the matrix. It is shown that its influence is governed solely by the value of the particle to matrix mass density contrast.
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, CNRS, UMR 7190, Institut Jean Le Rond d'Alembert (∂'Alembert), 4, Place Jussieu, F-75005, Paris, France.
authors.forename: Mickaël
authors.initials: M
authors.lastname: Duranteau
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, CNRS, UMR 7190, Institut Jean Le Rond d'Alembert (∂'Alembert), 4, Place Jussieu, F-75005, Paris, France.
authors.forename: Tony
authors.initials: T
authors.lastname: Valier-Brasier
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, CNRS, UMR 7190, Institut Jean Le Rond d'Alembert (∂'Alembert), 4, Place Jussieu, F-75005, Paris, France.
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Conoir
authors.affiliation: Université de Bordeaux, CNRS, UMR 5798, Laboratoire Ondes et Matière d'Aquitaine (LOMA), 351 Cours de la Libration, F-33400 Talence, France.
authors.forename: Régis
authors.initials: R
authors.lastname: Wunenburger