Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session D25: Mechanical Metamaterials IFocus
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Sponsoring Units: GSNP Chair: Johannes Overvelde, FOM Inst - Amsterdam Room: 402 |
Monday, March 2, 2020 2:30PM - 3:06PM |
D25.00001: Recent Progress on 3D Chiral Mechanical Metamaterials Invited Speaker: Martin Wegener We review our recent progress on three-dimensional (3D) microstructured chiral mechanical metamaterials. These architectures have been made by state-of-the-art 3D laser nanoprinting and lately also by rapid multi-focus multi-photon 3D laser nanoprinting. For the latter, the metamaterials contain more than one hundred thousand unit cells and more than three hundred billion voxels. |
Monday, March 2, 2020 3:06PM - 3:18PM |
D25.00002: 3D Acoustic Zero Index Metamaterial Changqing Xu, Guancong Ma, Yun Lai, Ying Wu In this talk, I will report our design of a three-dimensional (3D) acoustic double-zero-index medium (DZIM) made of a cubic lattice of metal rods. Despite of several realizations of 2D DZIM in the past, achieving such a medium in 3D has remained an elusive challenge. Here, we show how a four-fold degenerate point with conical dispersion can be induced at the Brillouin zone center, such that the material becomes a 3D DZIM with the effective mass density and compressibility simultaneously acquiring near zero values. To demonstrate the features of the DZIM, we have fabricated an acoustic waveguide filled with 3D DZIM to form a “periscope” with two 90° turns and observed nearly perfect tunneling of a normally incident planar wave through the waveguide. |
Monday, March 2, 2020 3:18PM - 3:30PM |
D25.00003: Micro-lattices for wide-band three-dimensional elastic wave attenuation Nikhil Gerard, Mourad Oudich, Yun Jing The past decade has witnessed the emergence of three-dimensional micro-lattices and state-of-the art manufacturing techniques that have enabled their realization. The ability to fabricate bulk materials that are precisely architected at the microscopic scale is exhilarating to various scientific communities. This has thus greatly revived the yearning for futuristic multifunctional materials. From the perspective of mechanical wave propagation, this implies complete control over micro-structure that can be designed for exotic wave-based applications. In this work, we put forth new design strategies to engineer micro-lattices for desirable elastic wave bandgaps and discuss their experimental realization. The band gaps can be attributed to local resonance and Bragg mechanisms and can be precisely tuned via both unit cell geometry and the intrinsic material employed for its fabrication. Alongside being thin, lightweight and/or displaying a negative Poisson’s ratio, our micro-lattices are equipped with the capability of attenuating elastic waves in all directions over a wide frequency range and can facilitate novel elastic wave functional materials. |
Monday, March 2, 2020 3:30PM - 3:42PM |
D25.00004: Elastic Weyl Points and Surface Arc States in Three-Dimensional Mechanical Metamaterials Xiaotian Shi, Rajesh Chaunsali, Feng Li, Jinkyu Yang We investigate a novel Weyl mechanical metamaterial inspired by the discovery of Weyl semimetal. We propose a three-dimensional mechanical structure in analog to the AA-stacked graphene with chiral intralayer coupling, which carries Weyl points of topological charge ±1. We numerically confirm the existence of the elastic Fermi arc and the associated gapless topologically protected surface states. The full-scale numerical simulation on the hollow 3D mechanical structure demonstrates that the surface elastic waves are robust and directional, which can pass a corner or defect without reflections. The findings from our work can contribute to the novel ways of manipulating elastic energy in 3D structures for potential applications in vibration isolation, advanced sensing, and energy harvesting. |
Monday, March 2, 2020 3:42PM - 3:54PM |
D25.00005: Demonstration of the Majorana-like bound state in an elastic bolted plate Chun-Wei Chen, Natalia Lera, Rajesh Chaunsali, Daniel Torrent, Jose Vicente Alvarez, Pablo San-Jose, Johan Christensen, Jinkyu Yang With the unveiling of the topological non-trivial phases, abundant demonstrations of the bulk-boundary correspondence in various domains of physics have been conducted in recent years. More recently, higher-order topological insulators are realized to reveal not only the boundary states but also the zero-dimensional corner states. In this work, another uniquely zero-dimensional non-propagating state, specifically a mechanical analog of the Majorana bound state, is shown numerically and experimentally in a mechanical system. We implement topological binding by creating a Kekulé distortion vortex on a two-dimensional thin plate with local resonators mounted in a honeycomb arrangement. It is renowned that Majorana bound states are protected by particle-hole (PH) symmetry. Similarly, to show our mechanical Majorana-like bound state is insensitive to certain type of disorder, we design a local perturbation to mimic the PH symmetry. We confirm that the Majorana-like bound state is indeed robust against the PH-symmetric perturbations and maintains pinned to Dirac frequency of the undistorted lattices. We anticipate that this finding will enrich the topological non-trivial phases in bosonic systems and broaden the applications of the energy localization or energy harvesting. |
Monday, March 2, 2020 3:54PM - 4:06PM |
D25.00006: Tuning of 2D Phononic Band Structures via Buckling Instability Tejas Dethe, Siddhartha Sarkar, Matevz Marincic, Andrej Kosmrlj Dispersion relation of propagating elastic waves through phononic crystals, which are periodic elastic structures, can be represented with band diagrams akin to the electronic band structures and band structures in photonic crystals. Of special interest in these diagrams are band gaps, which correspond to frequencies of waves that cannot be transmitted through the bulk of the phononic crystals. The location of band gaps depends on the material properties and on the geometry and symmetries of phononic structures. The symmetries of compressed elastic structures can be drastically altered via the buckling instability, and we are exploring how that affects the phononic band structures. First, we systematically investigated band diagrams for uncompressed 2D phononic structures that belong to different crystallographic groups. We employed recently developed tools for electronic systems, to analyze which band crossings are topologically protected/prohibited. We use this information to analyze how band structures are affected by the buckling instability, which causes a phononic structure to move from one crystallographic group to another. Such tuning of band structures with external load could then be used to engineer tunable sound filters as well as mechanical sensors. |
Monday, March 2, 2020 4:06PM - 4:18PM |
D25.00007: Robust gapless edge states and unconventional topological band properties in a two-dimensional elastic Kekulé phononic lattice Ting-Wei Liu, Fabio Semperlotti The existence of back-scattering-immune edge states in topological metamaterials has opened a new path for mechanical waveguide design. Recently, a “Brillouin-zone-folding" strategy was proposed to easily realize non-trivial topological properties in two-dimensional phononic systems. However, due to the intrinsic characteristics of phonons, the resulting edge states are generally gapped, indicating coupling between counter-propagating edge states. We report on the design of an elastic phononic structure that embeds a Kekulé distortion pattern to create the analogue of a quantum spin Hall system which, with proper tuning, can achieve fully decoupled and gapless edge states. Using ab initio numerical calculations, we also discover unconventional characteristics of the phononic band structure including a six-lobe pseudospin texture and Berry curvature. We also find that the existence of edge-states does not depend exclusively on the topological invariants of the adjacent bulk lattices but also on the relative translation of the unit cell pattern, therefore it is possible to obtain edge states on an edge dislocation of one bulk lattice. |
Monday, March 2, 2020 4:18PM - 4:30PM |
D25.00008: Valley Anisotropy and Valley Topological States in Elastic Metamaterials Shuaifeng Li, Ingi Kim, Satoshi Iwamoto, Jianfeng Zang, Jinkyu Yang Valley, as a new degree of freedom, has emerged as an efficient way in manipulating waves in electronics, photonics and phononics. We present the valley anisotropy by introducing asymmetrical metamaterials made of hard spiral and soft materials. We study the phononic band structure and valley pseudospin in these spiral elastic metamaterials. By numerical calculations, we show the deviated Berry curvature and valley Chern number. The adjustment of the geometrical parameters in the spirals allows an extreme tunability of the Berry curvature and valley Chern number, resulting in the topological transition. We exploit the adjustment of the geometrical parameters to demonstrate the formation of valley topological states unprecedented in conventional topological platforms. Lastly, we present the topologically protected transport of elastic waves in our anisotropic topological elastic metamaterials. |
Monday, March 2, 2020 4:30PM - 4:42PM |
D25.00009: Topological boundary modes in nonlinear mechanical lattices Di Zhou, Zeb Rocklin Mechanical lattices have been shown to possess interface modes lying in bulk band gaps. These boundary modes are protected by bulk topological invariants in which the geometric (Berry) phase is quantized by certain symmetries, the celebrated bulk-boundary correspondence. This relationship has been proved rigorously for linear mechanical systems, which can be mapped onto quantum systems, yet recent has demonstrated that the boundary modes extend into the nonlinear regime. In the present work, we investigate the topological protection of nonlinear normal modes. In particular, we consider a one-dimensional diatomic chain with spatial inversion symmetry, whose linear limit has a well-characterized topological invariant. By continuing the linear modes into the nonlinear regime via a mix of numerical and analytic methods, we characterize how nonlinear topological boundary modes emerge, paving the way to topological modes of strongly and inherently nonlinear systems. |
Monday, March 2, 2020 4:42PM - 4:54PM |
D25.00010: Programmable higher-order Euler buckling modes in hierarchical beams Maria-Gabriella Tarantino, Kostas Danas We present a numerical-aided experimental study on the buckling of hierarchical beams comprising multiple self-similar modules. Each module consists of multiple elemental beams and is arranged in series to form the hierarchical beam. We show, through a combination of experiments and computations, that these beams exhibit stable and realizable higher-order buckling modes. By contrast to the canonical Euler buckling problem, such modes emerge naturally in the proposed self-similar beams since they correspond to almost identical critical loads. By harnessing the imperfection sensitivity of the hierarchical structures, we 3D-print weakly imperfect polymer samples with a small geometric imperfection corresponding to the desired eigenmode. The ability to trigger higher-order buckling modes is found to depend on two main geometrical parameters which lead to scale coupling. Those are the slenderness of the macroscopic hierarchical beam and the slenderness of the lower-scale elemental beam. With increasing slenderness of the hierarchical beam, we observe a significant softening in the overall stress-strain response and patterns exhibiting curvature localization in the post-bifurcation regime. |
Monday, March 2, 2020 4:54PM - 5:06PM |
D25.00011: Programmable metastructures featuring adaptable stiffness based on local bistability Janav P. Udani, Andres F. Arrieta We present a novel class of programmable structures displaying large stiffness adaptability from local changes of shape. We connect a series of locally bistable semi-spherical shells (domes) within structural element geometries to create highly programmable properties. We demonstrate the property programmability by manufacturing and testing the dome patterned metasheets and beam-like metastructures, the properties of which are adapted by changing the local state of individual domes. We present bending and in-plane stiffness curves characterizing the global response as a function of the local unit cell states. Our results reveal extreme adaptability of properties ranging from high stiffness to high compliance as a result of the local changes of stable states. The properties of the metastructures depend on the local bistable state adopted by the domes and the global connectivity of the metastructures, thus departing from constraints imposed by specific constitute material choice for obtaining adaptability. We demonstrate the applicability of these metastructures in compliant/soft robotics particularly to enable stiffening without compromising on shape reconfiguration, all while using a simplified single input control to shift between stable states. |
Monday, March 2, 2020 5:06PM - 5:18PM |
D25.00012: Navigating the landscape of nonlinear mechanical metamaterials for advanced programmability Eder Medina, Patrick Farrell, Katia Bertoldi, Christopher Rycroft We consider a flexible mechanical metamaterial comprising an elastomeric matrix with an embedded square array of circular holes. First, we use the deflated continuation technique of bifurcation analysis to explore its complex energy landscape, characterized by multiple bifurcations from which stable and unstable branches emanate. We then investigate how this landscape can be exploited for real-time programmability. We find that the response of the system can be constantly reprogrammed by locally manipulating it to move it from one stable branch to another and that small targeted imperfections can be harnessed to enhance such programmability. |
Monday, March 2, 2020 5:18PM - 5:30PM |
D25.00013: Space-time phononic crystals with anomalous topological edge states Yuanchen Deng, Mourad Oudich, Molei Tao, Yun Jing We introduce a one-dimensional topological phononic phase system with a dynamic modulation of its intrinsic properties that keep the topological feature of the system unchanged, while it leads to a multiplication of the edges-state into the continuum at the subwavelength regime. We use this feature to access the functionality of exciting the edge-state in the Bragg regime using harmonic deep subwavelength acoustic wave where the wavelength is about 55 times the whole topological system's length. This remarkable property introduces a promising alternative to achieve wave manipulation at the deep-subwavelength scale. |
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