  The results of numerical modelling of sonic crystals with resonant array
elements are reported. The investigated resonant elements include plain slotted
cylinders as well as various their combinations, in particular, Russian doll or
Matryoshka configurations. The acoustic band structure and transmission
characteristics of such systems have been computed with the use of finite
element methods. The general concept of a locally resonant sonic crystal is
proposed, which utilises acoustic resonances to form additional band gaps that
are decoupled from Bragg gaps. An existence of a separate attenuation mechanism
associated with the resonant elements, which increases performance in the lower
frequency regime has been identified. The results show a formation of broad
band gaps positioned significantly below the first Bragg frequency. For low
frequency broadband attenuation a most optimal configuration is the Matryoshka
sonic crystal, where each scattering unit is composed of multiple concentric
slotted cylinders. This system forms numerous gaps in the lower frequency
regime, below Bragg bands, whilst maintaining a reduced crystal size viable for
noise barrier technology. The finding opens new perspectives for construction
of sound barriers in the low frequency range usually inaccessible by
traditional means including conventional sonic crystals.
