A wideband technique for measuring sound dispersion and frequency-dependent attenuation in granular media is presented. The measurements were done on a mono-disperse medium of 2-cm solid polypropylene balls, over the frequency range of 500 Hz-20 kHz, enough to cover both weak and strong scattering regimes. A horn driver was used to launch sound into a foam-lined bucket containing the granular medium. The latter was mechanically isolated from the driver so as to minimize direct-contact coupling. The foam isolation was not enough, especially at resonances of the bucket-granular system. In the effort to simulate a free-granular medium, the bucket was replaced with a mesh bag hanging in free space. The frequency-dependent wavenumber of the granular is obtained by a filter-correlation method. After successive bandpass filtering, the phase speed and attenuation are obtained within each band, respectively, by signal alignment and amplitude log ratio. The attenuation coefficient yielded reasonable results, illustrating the transition from ``piston-like" dynamics to the strong scattering regime, as the frequency increased. The phase speed results where more sporadic, qualitatively there is a decrease in sound speed as the frequency increases.
|Advisor:||Petculescu, Andi G.|
|Commitee:||Dent, James B., Petculescu, Gabriela L.|
|School:||University of Louisiana at Lafayette|
|School Location:||United States -- Louisiana|
|Source:||MAI 54/06M(E), Masters Abstracts International|
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