Theory of acoustic metamaterials and metamaterial beams: An overview

Abstract

This paper presents a theoretical examination of acoustic metamaterials and their application in vibration absorption. Acoustic metamaterials are concerned as analogy to electromagnetic metamaterials which are suitable for refraction and decline of electromagnetic waves at certain frequencies. Due to the analogy with these materials, the acoustic metamaterials is required to have negative effective (dynamic) mass to enable vibration elimination at the certain frequency. The concept of negative effective mass is explained based on the motion of an externally excited mass-in-mass system where the vibration elimination at the certain frequency is due to the mass-spring unit. Using these vibration absorber units, the acoustic metamaterial beams are made. Depending on the way how the units are attached to the beam, the structure may absorb waves in one-direction (for example, longitudinal waves) or waves in two directions (such as, for instance, transversal and longitudinal waves). Moreover, according to the frequency properties of the absorber units the acoustic metamaterial beams may give one, two or multi-frequency gaps. This work provides an overview of the mathematical models of acoustic metamaterial beams and also contains some suggestions for future work.