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In this paper, we use shape memory alloy springs, electromagnets, ordinary springs and two metal beams to construct a double-layer phononic crystal beam. The electromagnets can be controlled to be in contact or separated by means of temperature and electric current. Firstly, we use transfer matrix method to derive the theorical solutions of the bandgap properties, and compare them with finite element results. Then, we focus on the influences of different parameters on bandgap properties to see how they can be effectively regulated. Finally, we take account of the symmetry of the structure and excitations for simplification and get two basic solutions, based on which the bandgap characteristics for an arbitrary excitation are obtained via superposition. It is shown that temperature and electric current can change the bandgap characteristics effectively, and while both the lattice constant and SMA spring stiffness have a global and huge influence, the ordinary spring stiffness and magnetic force all exhibit a local and detailed modification to the bandgaps. When the metastructured beam is perfectly symmetric but subjected to an antisymmetric excitation, we can obtain an extremely low and wide bandgap. The structure designed here is expected to play a role in actively controlled low-frequency noise reduction.

A double-layer metastructured beam with contact-separation switchability