Additive manufacturing of locally resonant metamaterials

Abstract

For many engineering applications, vibrations and sound can cause a multitude of issues. Several methods for damping out these vibrations are utilised today such as insulation foam used in walls or heavy granite bases for machinery and optical equipment. More recently, the development of acoustic and elastic metamaterials has shown the possibility to manipulate propagating waves in ways that were not previously possible, such as wave attenuation at an exponential rate. Locally Resonant Metamaterials (LRMs) have been shown to attenuate waves with wavelengths two orders of magnitude greater than the lattice constant of the LRM, making them well suited for low frequency applications. They typically consist of a core, an elastic lining, and a matrix material. Much of the research into LRMs is modelling based, with fewer experimental results to correctly verify different designs. One reason for this is that the manufacture of LRMs can be difficult as they require multiple material properties, and design consistency, particularly as the LRM geometries become more complex. Additive manufacturing (aka 3D printing) promises the ability to make complex shapes reliably and repeatedly. Hence, 3D printing techniques could be used to make LRMs. In this project, a custom built 3D printer is developed, which utilises different deposition techniques to allow it to manufacture an LRM. This facilitates the fabrication of more varied designs of metamaterial, which would have been too impractical otherwise to manufacture. The printer is fully customisable in LabVIEW and utilises a unique `point-cloud' method to process part geometry. More recently, active applications of LRMs have been explored to achieve behaviours that passive metamaterials cannot. One subset of active metamaterials is the growing field of metamaterial energy harvesting. This is the principle that metamaterials can be used to convert vibrations and sound into another form of usable energy, such as electricity. Two concepts are introduced which use an LRM type design with a magnetic core. By the phenomenon of electromagnetic induction, as a propagating wave induces a periodic displacement on the core, a current is induced in adjacent wires which could potentially be stored for later use in an application.