Two-dimensional ternary locally resonant phononic crystals with a comblike coating

Two-dimensional ternary locally resonant phononic crystals can be used for vibration control and noise insulation in the low (even audible) frequency range. They traditionally consist of cylindrical scatterers with uniform coatings in their exterior. An alternative coating profile with a comblike profile is proposed and investigated in this paper. The band structures are calculated using the finite element method. We find that a complete bandgap can be induced at a significantly low frequency, the wavelength of which is more than 20 times the lattice constant. The mechanism for such a change is suggested using an equivalent spring–mass model and analyzing the eigenmodes at the bandgap edges. Numerical results and the results predicted by the spring–mass model are coherent. (paper)