Experimental investigation of 2d rainbow phononic crystals for broadband vibration attenuation

Phononic crystals (PnCs) and metamaterials are nowadays widely investigated for vibration suppression owing to their stopbands that prohibit wave propagation. The application of PnCs and metamaterials is however limited by their narrow bandgaps especially for low frequencies. The recently introduced rainbow metamaterials composed of spatially varied oscillating unit cells are found to generate broader bandgaps than the periodic structures. 2D rainbow PnCs consisting of cubic blocks with internal voids connected by curved beam are proposed in the present paper. Masses of the cubic blocks differ due to different dimensions of internal voids. To prove the effects of rainbow design, two 2D block-beam lattice structures, with periodic and nonperiodic units respectively, were manufactured by additive manufacturing method. Frequency response functions of the manufactured PnCs were measured with a testing system containing a mechanical shaker, an impedance head and a laser Doppler vibrometer. Receptance functions of the PnCs in two directions were measured separately. The obtained experimental results show that the PnC with rainbow mass has extended bandgaps compared with the periodic one.