  In this work, a recent theoretically predicted phenomenon of enhanced
permittivity with electromagnetic waves using lossy materials is investigated
for t he analogous case of mass density and acoustic waves, which represents
inertial enhancement. Starting from fundamental relationships for the
homogenized quasi-static effective density of a fluid host with fluid
inclusions, theoretical expressions are developed for the conditions on the
real and imaginary parts of the constitutive fluids to have inertial
enhancement, which are verified with numerical simulations. Realizable
structures are designed to demonstrate this phenomenon using multi-scale sonic
crystals, which are fabricated using a 3D printer and tested in an acoustic
impedance tube, yielding good agreement with the theoretical predictions and
demonstrating enhanced inertia.
