Recent progress in programmable acoustic metamaterials and their principles: A review

Programmable acoustic metamaterials allow to manipulate sound waves at desirable frequency ranges intelligently, which makes it a viable and practical alternative to many noise cancellation applications. These kinds of metamaterials are amenable to intelligent programming and find place in a variety of real-life applications such as acoustic cloaking, noise cancellation, stealth applications, noise focusing, etc., simply with intelligent programming of the microstructure and the control of micro-movement of the various control boundaries instead of rebuilding new structures every time. Metamaterials are artificially designed materials that possess unique, unusual physical and mechanical properties, making them good lightweight candidates for various noise-shielding applications. However, many papers have been published on studying passive kinds of metamaterial structures whose material properties are fixed in space and time once designed and fabricated. This article is about a different class of metamaterials which are programmable and changeable through various control boundaries forming the structures for the applications pertaining to acoustic isolation (vibro-acoustics) and acoustic mitigation. The incorporation of shape memory polymers or smart polymers into the metamaterial structures enables fine and coarse tuning of these structures to the incoming noise frequency spectrum on a real-time basis. This article reviews some recent trends in progress made with smart materials and programmable metamaterials, their various programming techniques, the fundamental concept involved, various design strategies of such materials and their emergent applications in various fields of technology. The current fabrication challenges and future outlook in this promising field are also discussed.