The Research Of Energy Band Of Elastic Phononic Crystals

1.The effective speed of three-dimensional multiply-connected phononic crystalsIn previous studies,physicists focused on simply-connected phononic crystals,namely non-contacted scatters distributed in a solid or fluid background.This paper focuses on a new type of three-dimensional phononic crystals,i.e.,doubly-connected phononic crystals,in which the scatters and background medium cannot be distinguished strictly.A comparative study has been made on the acoustic band structure and the low-frequency effective velocities for a doubly-connected steel frame-type phononic crystal arranged by a simple cubic lattice in vacuum or water.Our study states that this new type of phononic crystal carries strong anisotropy.In particular,comparing with the conventional simply-connected phononic crystals,the double-connectivity enables the system with an additional effective longitudinal velocity.2.Weyl points in elastic wave phononic crystals and related topological surface statesRecently,topological physics in condensed matter physics are under more and more attention.Apart from topological insulators,physicists discovered topological semi-metallic phases.Weyl semi-metal is typical of topological semimetal.Actually,Weyl points or in other words Berry curvature pole in momentum space,can be achieved in a series of systems,such as photonic crystals and phononic crystals.But,as far as we know,Weyl points and related topological surface states in elastic systems have not been discussed.Woodpile phononic crystals arranged in hexagonal array...