Solid-Liquid Transition in a Highly Dense 3D Vibro-Fluidized Granular System

The fluidization process of a vibro-fluidized granular system is studied using diffusing-wave spec-troscopy. A container filled with granular particles is sinusoidally forced by a vertical vibra-tion of A sin(2pift) in a vacuum state. The control parameter is the dimensionless acceleration Γ = A(2pif)2/g. At small Γ, the correlation function shows periodic echoes in time with a period of 1/f. As Γ increases, however, the height of the echoes decays. Therefore, the degree of fluidization can be characterized by the decaying property of the echo height. Fluidization occurs at Γ ∼ 1 near the free surface of the system. Also, the fluidization point Γc increases linearly with the distance from the free surface