Computational material design for acoustic cloaking

Abstract

SUMMARYA topology optimization technique based on the topological derivative and the level set function is utilized to design/synthesize the microstructure of a pentamode material for an acoustic cloaking device. The technique provides a microstructure consisting of a honeycomb lattice composed of needle-like and joint members. The resulting metamaterial shows a highly anisotropic elastic response with effective properties displaying a ratio between bulk and shear moduli of almost three orders of magnitude. Furthermore, in accordance with previous works in the literature, it can be asserted that this kind of microstructure can be realistically fabricated. The adoption of a topology optimization technique as a tool for the inverse design of metamaterials with applications to acoustic cloaking problems is one contribution of this paper. However, the most important achievement refers to the analysis and discussion revealing the key role of the external shape of the prescribed domain where the optimization problem is posed. The efficiency of the designed microstructure is measured by comparing the scattering wave fields generated by acoustic plane waves impinging on bare and cloaked bodies.

Inverting the structure–property map of truss metamaterials by deep learning

“…This approach produces graded truss networks, whose effective anisotropic stiffness varies from point to point and can be tuned to match known stiffnesses at control points (e.g., anatomical sites in bone samples with measured stiffness). The spatial grading of UCs can be applied more generally to functionally graded structures, optimized, e.g., for the response to known loads (such as in multiscale topology optimization) ( 31 ) and, by locally tailoring wave motion by lattice topology, for wave guidance ( 6 ) and acoustic cloaking ( 65 ).…”

Acoustic Metamaterials in Aeronautics

“…Pentamode metafluids may be engineered with a lattice of carefully interconnected solid struts, creating a structure that exhibits a quasi-vanishing shear stiffness [69,70] (Figure 9). During the last decade, the scientific community produced a large number of papers on the topic, with numerical and theoretical papers and practical realizations of acoustic cloaking [71][72][73][74][75][76][77][78]. Alternative approaches exploiting coordinate transformations have been explored, like the so-called carpet cloaking [79][80][81][82][83][84][85][86][87], i.e., making an arbitrary-shaped surface act like a flat wall.…”

“…So far, however, practical realizations have been limited to static acoustics and, for the most part, intended for carpet cloaking of small objects [83,87] or based on large and/or massive devices [99,100]. Possibly the most interesting work has come from Mendez [78], who designed a feasible pentamode material for acoustic cloaking by topology optimization, starting from the desired metafluid acoustic characteristics, and numerically tested it.…”

Pentamode metamaterials with ultra-low-frequency single-mode band gap based on constituent materials

“…It has attracted wide attention for adjustable anisotropic modulus [3][4][5][6], vanishing shear modulus [3,7,8], interface impedance matching with water [9,10], and so on. These peculiar properties make pentamode metamaterials possess excellent ability of wave regulation, and they can be applied into the fields, such as acoustic/elastic cloaks [11][12][13][14][15], vibration and noise reduction [16,17], biomaterials [18] and seismic protection [19].…”