  Energy absorbers and energy-harvesting devices have been under the scope of
scientists and engineers for decades to fulfill specific technological needs,
mainly concerned with sound and vibration absorbers, and efficient mechanical
energy converters. In this paper, as a proof of concept, we build a
mass-in-mass device to study the response of a linear absorber immersed in one
of the spheres composing a linear array of equal elastic spheres. Spheres
barely touch one another and can thus sustain nonlinear solitary wave
propagation only. The linear intruder absorbs a given amount of energy
depending on the frequency content of the incident solitary wave. A numerical
simulation is developed to account for the experimental finding. The validation
of the numerical model allows for the theoretical study of the energy absorbed
by any number of intruders, and to demonstrate that the former increases
exponentially with the latter, indicating that only ten of the intruders is
enough to absorb the system energy. A detailed study of the transmitted energy
from an external source into the chain reveals that, due to nonlinearity, the
array of spheres is able to convert almost any mechanical shock to a well
defined solitary or trains of solitary waves, whose frequency content is nearly
independent on the excitation amplitude. This property leads to the design of a
device, which is optimized to absorb energy over a broad frequency range.
