Magnetic-Sphere-Based Phononic Crystals

Periodic arrays in one, two, and three dimensions, made of magnetic spheres embedded in a fluid matrix, are considered in this study and utilized as phononic structures. The propagation of acoustic waves through these structures is analyzed experimentally, in low- and high-frequency region, via laser vibrometry, as well as standard underwater acoustic measurements. A first comparison to theoretical calculations obtained through multiple-scattering techniques and multipole models reveals a distinct behavior depending on the immersion fluid and/or frequency regime. Our results show that the elastodynamic response of these systems can be, under conditions, simply described by classical elastic theory without taking directly (ab initio) into account the magnetic character of the spherical particles. The structures considered above could offer several possibilities including facility of construction and use in filtering applications, but they are also of interest from a theoretical point of view, as a means to investigate the validity of several approximate theoretical descriptions.