Refraction behavior investigation and focusing control of phononic crystals under external magnetic fields.

• Ferromagnetic shape memory alloys, as a new type smart material, used in phononic crystals firstly. • This article is the first time to control negative refraction and focusing by using magnetic field. • It provides a novel strategy for the tunable PCs with negative refraction and focusing behaviors. The refraction and focusing behaviors of two-dimensional phononic crystals (PCs) tuned by external magnetic fields are investigated systematically. The PCs are constructed by inserting ferromagnetic shape memory alloys (FSMAs) between tungsten cylinders and water matrix. Under the magnetic field, material parameters of FSMAs will vary, which furthermore changes the frequency spectrum and equi-frequency surfaces of acoustic waves in sonic crystals. It is revealed that the refraction angle can be tuned from a positive value to a negative one when the PC slab suffers from continuous magnetic fields. Moreover, the focusing behavior can be achieved and controlled artificially by applying a proper magnetic field. These interesting phenomena of the tunable sonic crystals with FSMAs can provide us guidance for the design and application of novel acoustic devices, as well as the active control of acoustic waves. [ABSTRACT FROM AUTHOR]