  Two-dimensional ternary locally resonant phononic crystals 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
letter. The band structures are calculated by using the finite element method.
It is found that a complete bandgap at a significantly low frequency 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.
Consistent results are obtained from the numerical results and the analysis of
the spring-mass model.
