Low-frequency Gibbs-type oscillation in finite solid-fluid sonic crystals and its application in sub-wavelength wave isolation for waterborne sound

Blocking underwater sound waves using sub-wavelength structures, i.e. with the unit size much smaller than the incident wavelength, is a known challenge and highly desirable in practical applications. In this work, we show that this can be easily achieved utilizing the Gibbs-type oscillation properties of finite solid-fluid sonic crystals (SFSCs). First, the influence of solid parameters and the period number of SFSC on the Gibbs-type oscillation within the first Bragg passband is comprehensively investigated. Based on this, isolations with periodic cells of sub-wavelength size are designed and numerically demonstrated through finite element simulations. The results show that the broadband underwater sound blocking effect does exist in a finite SFSC whose total thickness is only one quarter of the incident wavelength, while a very low transmittance of less 1% is achieved. Our work will provide a new approach to control low-frequency underwater sound waves using Bragg sonic crystals.