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

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