Subwavelength bandgap phononic crystals with mixed resonant modes

A new kind of subwavelength bandgap phononic crystals with water host is proposed. Scatterers of these phononic crystals are Helmholtz resonators decorated by bubbles. The subwavelength ratio can reach 0.005; the relative bandwidth can reach 1.38, which is far larger than those (0.25) of existing subwavelength bandgap phononic crystals with water host. The formation mechanism of these subwavelength band gaps is achieved, i.e., bubbles cause a significant reduction of the elasticity coefficient of springs in the ‘mass-spring’ model. Two broadening mechanisms of subwavelength band gaps are obtained: one is the interaction between scatterers is relatively large, the other is there are several different resonant modes in a band gap. The latter was not mentioned in the previous literature. These conclusions are important to design new types of subwavelength hydroacoustic devices.