153 / 2021-03-31 15:43:24

Customized inverse design of broadband acoustic metamaterials

Acoustic metamaterials, Broadband, Topology optimization, Customized, Wave motion

Acoustic metamaterials (AMMs), novel artificial micro-structural materials with acoustic/elastic wave properties which cannot be found or realized in natural materials, making it possible to completely and freely manipulate wave propagation. To achieve the practical metamaterials and metadevices, this report performs the systematic inverse design of double-negative acoustic metamaterials, metasurfaces, topological insulators and pentamode metamaterials based on the bottom-up topology optimization to realize customized broadband functionalities. Under the simultaneous increasing or non-increasing mechanisms, we develop a unified topology optimization framework of double-negative AMMs involving different acoustic microstructure symmetries, minimal structural feature sizes and dispersion extents of effective parameters. Meanwhile, we demonstrate the essences of double negativity derived from the novel artificial multipolar LC (inductor-capacitor circuit) and Mie resonances which can be induced by controlling mechanisms in optimization. We experimentally show the desired broadband subwavelengh imaging by using the 3D-printed optimized space-coiling metamaterial. We aslo systematically designed the acoustic Dirac cones with customized double, triple and quadruple degeneracies at different wavelength scales. Using the proposed methodology, novel square-symmetric, chiral and orthogonal-symmetric sonic crystals (SCs) are constructed in a square lattice with tailored Dirac cones. As illustrative examples, zero-index acoustic cloaking and Talbot effect near the Dirac points of the optimized SCs are demonstrated numerically. Moreover, a novel acoustic pseudo-spin topological insulator is obtained, which entails a robust zigzag wave propagation and broadband, unidirectional, and topologically protected transport with a record-breaking relative bandwidth of 30.51%. In addition, we designed most pentamode metamaterials possessing broadband single-mode range of exclusive longitudinal waves; some even feature record-breaking relative single-mode bandwidths exceeding 150%. Upon shielding lights on the beneficial topological features of the broadband PMs, we extract the main topological features to form simplified PM configurations, i.e., multiple symmetric solid blocks with slender rods, which can induce the multiform multiple-order rotational vibrations or the integration of the low-order rotational vibrations and anisotropic local resonances for the broadband single-mode nature. At a higher design level, we establish a dedicated inverse-design strategy, under the function-macrostructure-microstructure paradigm, to conceive a novel broadband subwavelength underwater pentamode shielding device, which enables the conversion of propagating acoustic wave to the evanescent surface wave mode within the frequency range [1000 Hz, 4000 Hz]. Inverse design and wave manipulation of broadband AMs, topological insulators and PMs in this report can effectively guide the precision design ofacoustic and elastic waves in the artificial periodic materials, and provide the key structural fundamentals for designing novel acoustic wave devices and equipments.