Study of defect mode characteristics in acoustic metamaterials

Abstract

The development of novel material architectures incorporating unconventional geometric designs (e.g., microstructural instabilities, multi-length scale geometries), or adaptive constituent elements (e.g., piezo electrics) has created a powerful tool to design metamaterials for efficient dispersion manipulation and precise control of acoustic waves. Various aspects of the acoustic dispersion (e.g., wave speed, damping ratio, band gap position and widths) have been investigated with a primary focus on wave characteristics in the acoustic pass bands, promoting their utility in applications, e.g., wave guiding, energy harvesting. However, recent studies on topological waves, truncation and bandgap resonances have highlighted potential benefits of leveraging acoustic waves in the bandgap, e.g., signal propagation, passive flow control. Motivated by this, we explore the dispersion behavior of finite mass-spring-damper acoustic metamaterial models with material defects. The eigen analysis reveals a (defect) resonance in the acoustic band gap, producing a highly localized defect mode. The dependence of this resonance frequency, the degree of localization and phase response of the eigenmode, on the defect parameters are explored. Subsequently, the potential utility of these defect modes in flow control applications is also explored and presented.