Measurement of the Biot structural factor δ for sintered bronze spheres Free

The Biot structural factor δ of a porous solid [M. A. Biot, J. Acoust. Soc. Am. 28, 168 (1956)] can be extracted from measurements of sound speed and attenuation when the solid is saturated with superfluid helium [S. Baker et al., J. Acoust. Soc. Am. Suppl. 1 74, S59 (1983)]. The results of such measurements made in sintered bronze spheres (nom. diam. 75, 110, and 500 μ) yield values of δ from 3.3 to 4.5. [We take δ to be defined by κ = δ(αωk/vP)^1/2, where κ is the argument of Biot's high‐frequency correction function F(κ), α is the tortuosity, ω is the angular frequency, k is the permeability, v is the kinematic viscosity, and P is the porosity.] If δ_visc is the normal fluid viscous penetration depth and a is a characteristic pore size, then the range of(δ_visc/a) covered by these measurements is approximately 10⁻² to 1. The values of δ reported here are about $112$ to 2 times larger than has been estimated for typical marine sediments [R. Stoll, in Physics of Sound in Marine Sediments (Plenum, New York, 1974)]. [Work supported by ONR.]