A review of methods of achieving the optimal band gap in two-dimensional phononic crystal structures

Phononic crystals are advanced structures which are created by repetition of inclusions in an elastically different host material. The distinguishing feature of these materials is the existence of a band gap. complete band gap is a frequency range that the phononic crystal prevents the propagation of elastic or acoustic waves in all directions whose frequency is in that range. Due to the feature of band gap, phononic crystals are suitable for managing the propagation of elastic waves. In this research, two-dimensional phononic crystal structures have been investigated. In order to reach the optimal band gap, many works have been done on the phononic crystal structures. In this article, the above efforts have been investigated including rotation of non-circular inclusions, adding an inclusion to the primary unit cell, changing the type of lattice and the shape of the inclusion, hybrid phononic crystal, nested phononic crystal, heterostructure phononic crystal, hierarchical phononic crystal and the use of Smart materials.