Granular crystals are artificially structured materials consist of closely packed arrays of elastic particles. This type of metamaterials can manipulate and control elastic waves in ways that are not possible in conventional solid materials. It is an exciting and rapidly expanding topic in the field of physical acoustics that, more than 20 years now offered a perfect test bed for fundamental studies of nonlinear dynamics including solitary waves, breathers, nonlinear energy transfer and chaos as well as different engineering applications like tunable waveguiding, shock- and energy-absorbing layers and acoustic diodes.

The main objectives of this talk are :

(1) on the one hand to present our current better understanding of the wave physics of granular crystals. Emphasis will be placed on the role of particle rotations that has been ignored in many studies and which lead to richer wave dynamics.

(2) Secondly, to present you novel wave phenomena coming from the interplay of geometry and nonlinearity.

Our experimental vehicle for the study of the above will be magnetogranular metamaterials, namely granular-based structures/devices composed of stainless steel spherical beads in contact, under a suitable designed magnetic field. The wave dynamics of one-dimensional and L-shaped waveguides will be presented in details while some preliminary results for two-dimensional magnetogranular structures will be also described.