Magnetic resonance imaging of vibrating granular beds by spatial scanning

Nuclear magnetic resonance is becoming an important experimental technique to study the behavior of moving granular materials because of its unique ability to measure concentration, velocity, and dissipation within the bulk granular materials rather than only on the surface. Of all the common motions of such assemblies of particles, the most difficult to measure is the vibrating bed because of the unsteady motion. This paper demonstrates a nuclear magnetic resonance imaging method to study highly energetic vibrating granular beds by spatial scanning. In contrast to Fourier imaging, spatial scanning prevents scattering of image intensities caused by unsteady motion. Two-dimensional images of a vibrating bed undergoing period doubling were obtained. A band of high shear was identified by reduced image intensity. It traveled back and forth across the bed with each cycle of up and down motion of the bed. Further studies of vibrating beds with the sequence modified for velocity encoding and velocity compensation should provide additional useful information. (C) 1997 American Institute of Physics. [S0034-6748(97)03411-4].