  Negative mass phenomena occurring below a cut-off frequency is examined by
both theoretical and experimental methods. The paper begins with the
investigation on a mass-spring structure, the effective mass of which is shown
to be negative below a specific frequency. Due to the decaying nature of
lattice waves in the negative-mass system, the transmission drop induced by
negative effective mass is demonstrated experimentally. Further investigation
is conducted for a rectangular solid waveguide with clamped boundary
conditions. It is shown that the lowest bandgap mode of the clamped waveguide
can be attributed to negative effective mass below a cut-off frequency. Based
on this observation, elastic metamaterials made of the steel grid filled by
styrene butadiene rubber are designed and fabricated. Both simulation and
experimental analyses demonstrate that the designed metamaterial have negative
effective mass below a cut-off frequency.
