  We have studied the plasmonic properties of aperiodic arrays of identical
nanoparticles (NPs) formed by two opposite and equal graded-chains (a chain
where interactions change gradually). We found that these arrays concentrate
the external electromagnetic fields even in the long wavelength limit. The
phenomenon was understood by identifying the system with an effective cavity
where plasmonics excitations are trapped between effective band edges,
resulting from the change of passband with NP's position. Dependence of
excitation concentration on several system's parameter was also assessed. This
includes, different gradings as well as NP's couplings, damping, and resonant
frequencies. In the spirit of the scaling laws in condensed matter physics, we
developed a theory that allows us to rationalize all these system's parameters
into universal curves. The theory is quite general and can also be used on many
other situations (different arrays for example). Additionally, we also provided
an analytical solution, in the tight-binding limit, for the plasmonic response
of homogeneous linear chains of NPs illuminated by a plane wave. Our results
can find applications on sensing, near field imaging, plasmon-enhanced
photodetectors, as well as to increase solar cell efficiency.
