  The possibility of shifting sound energy from lower to higher frequency bands
is investigated. The system configuration considered is a segmented structure
having non-linear stiffness characteristics. It is proposed here that such a
frequency-shifting mechanism could complement metamaterial concepts for
mass-efficient sound barriers. The acoustical behavior of the material system
was studied through a representative two-dimensional model consisting of a
segmented plate with a contact interface. Multiple harmonic peaks were observed
in response to a purely single frequency excitation, and the strength of the
response was found to depend on the degree of non-linearity introduced. The
lower and closer an excitation frequency was to the characteristic resonance
frequencies of the base system, the stronger was the predicted higher harmonic
response. The broadband sound transmission loss of these systems has also been
calculated and the low frequency sound transmission loss was found to increase
as the level of the broadband incident sound field increased. The present
findings support the feasibility of designing material systems that transfer
energy from lower frequency bands, where a sound barrier is less efficient, to
higher bands where energy is more readily dissipated.
