Influence of Micro-Structural Parameters on Apparent Absorption Coefficient in Porous Structures Mimicking Cortical Bone

Ultrasound wave propagation in porous media is associated with energy loss and attenuation. Attenuation is caused by both scattering and absorption, and is influenced by the microstructure as well as the operating frequency. In the present simulation study, we calculate the attenuation coefficient in porous structures mimicking cortical bone both in presence and absence of absorption to isolate the effects of scattering and absorption on the total attenuation. A parameter called apparent absorption α
_app.abs
is defined as the difference between the total attenuation α
_total
and the attenuation exclusively due to scattering α
_scat
. α
_total
, α
_scat
and α
_app.abs
are estimated in porous structures with varying pore diameters (φ ∈ [40, 120] μm) and pore densities (ρ ∈ [5, 25] pore/mm
²
) at 5MHz and 8MHz. Results show that both scattering and absorption contribute to the total attenuation. They also illustrate that, although absorption only occurs in the solid matrix, the apparent absorption α
_app.abs
is a function of porosity, presumably due to the presence of multiple scattering. For large values of kφ, an increase in pore size or density does not lead to increase in α
_scat
and only results in an increase of the total attenuation as a result of increase in α
_app.abs
. On the other hand, in low/intermediate scattering regimes (kφ ≤ 1), an increase in either pore size or pore density results in increase in α
_scat
while α
_app.abs
remains constant.