Broadening band gaps of Bragg scattering phononic crystal with graded supercell configuration

A new phononic crystal with graded supercell configuration is proposed to broaden the Bragg scattering band gaps. The proposed phononic crystal is made up of a periodic arrangement of supercells, and the supercells are composed of unit cells with graded structural parameters. The mechanical model of the graded phononic crystals is established based on transfer matrix method to investigate in-plane elastic waves propagating and band structures of the periodic system. Numerical results show that the graded structural design can merge adjacent multiple band gaps into an extremely broad one. Modal analysis shows that the mechanism of band gap broadening is that the graded supercell configuration breaks some symmetries of the phononic crystal, resulting in the opening of Dirac cone and creation of new band gaps. The effects of the main structural parameters related to graded supercell design on band gap broadening are studied by simulation and verified by experiment. The present study is beneficial to the design of new functional materials with broadband vibration isolation performance.