The Effect of Particle Shape on the Density of Acoustic Modes in Granular Materials

Most granular simulations and experiments are conducted using circular particles. We report on the effect of particle shape on the density of vibrational modes in a real two dimensional granular material. We acoustically excite static packings composed of one of four shapes: circles, ellipses, pentagons, and concave stars. Using embedded piezoelectric sensors we measure the particle-scale vibrational response. We observe shape-dependence in the acoustic spectra and density of modes, particularly at low frequency.