Abstract
The soil plate oscillator apparatus (SPO) consists of two circular flanges (5 inch ID, 8 inch OD, 2.5 inch thick) sandwiching and clamping a thin (1/8 inch) circular elastic acrylic plate. Granular media (soil, masonry sand, glass beads, or even edible granular material) is supported at the bottom by the plate and side walls of the upper flange. A magnetic disk (1 cm) fastened below the plate (on center) is driven by a swept sinusoidal current in a coil placed below the magnet. This electrodynamic SPO, placed in a Wheatstone bridge, was used to measure the on-axis motional electrical impedance Zmot with and without granular loading. Nonlinear tuning curves near resonance exhibit softening with increasing drive amplitude. Measurements of Real{Zmot} and Imag{Zmot} were used to predict the nonlinear mechanical point impedance (Zmech = constant / Zmot) behavior of the SPO system. A lumped element model (granular media and elastic plate system) help determine the mesoscopic nonlinear properties of the granular media alone. Nonlinear tuning curves of the magnet’s acceleration were also measured. A bilinear hysteresis model fits the tuning curve results. See I. T. Perez-Miravete et al., JASA 125, 1302 (2009) for a nonlinear mesoscopic analysis of a flexural bar.
Published Version
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