Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session L36: Focus Session: Reconfiguring and Actuating Soft Matter I: Metamaterials |
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Sponsoring Units: GSOFT Chair: Vincenzo Vitelli, Leiden University Room: 211 |
Wednesday, March 4, 2015 8:00AM - 8:12AM |
L36.00001: Buckling in a topological metamaterial Anne Meeussen, Jayson Paulose, Vincenzo Vitelli Controlling the nonlinear response of mechanical metamaterials paves the way toward designing materials with adaptive and tunable mechanical properties. Buckling, a change in load-bearing state from axial compression to off-axis deformation, is a ubiquitous nonlinear instability that is often exploited to change the local or global mechanical response in metamaterials composed of slender elements. We create localized buckling regions in cellular metamaterials by engineering states of self-stress, regions where the response is dominated by stretching or compression of the constituent beams rather than bending at the stiff hinges connecting them. Unique to our approach is the use of topological states of self-stress, which originate in a topological invariant that characterizes the vibrational spectrum of the repeating unit cell. Unlike typical states of self-stress which result from additional geometric constraints induced by excess beams in a region, these topological states do not change the number of beams at each hinge. We demonstrate the phenomenon through numerical calculations of the linear response of the proposed metamaterial, and through experiments probing the nonlinear regime including localized buckling at specific regions. [Preview Abstract] |
Wednesday, March 4, 2015 8:12AM - 8:24AM |
L36.00002: Holey Sheet! A Programmable Mechanical Metamaterial Bastiaan Florijn, Corentin Coulais, Martin van Hecke We probe the mechanics of BiHolar metamaterials, 2D elastic media with a square lattice of circular holes of two different sizes. Biaxial loading of these BiHolar structures leads to a wealth of mechanical responses, including mechanically switchable hysteresis and memory effects. We show that we can program the mechanical response with the loading force and the hole size ratios.\footnote{Bastiaan Florijn, Corentin Coulais, and Martin van Hecke, Phy. Rev. Lett. \textbf{113}, 175503 (2014)} [Preview Abstract] |
Wednesday, March 4, 2015 8:24AM - 8:36AM |
L36.00003: Tunable acoustic metamaterials Sahab Babaee, Nicolas Viard, Nicholas Fang, Katia Bertoldi We report a new class of active and switchable acoustic metamaterials composed of three-dimensional stretchable chiral helices arranged on a two-dimensional square lattice. We investigate the propagation of sounds through the proposed structure both numerically and experimentally and find that the deformation of the helices can be exploited as a novel and effective approach to control the propagation of acoustic waves. The proposed concept expands the ability of existing acoustic metamaterials since we demonstrate that the deformation can be exploited to turn on or off the band gap, opening avenues for the design of adaptive noise-cancelling devices. [Preview Abstract] |
Wednesday, March 4, 2015 8:36AM - 8:48AM |
L36.00004: Origins of topological bulk modes in isostatic lattices D. Zeb Rocklin, Bryan Chen, Martin Falk, Tom Lubensky, Vincenzo Vitelli Mechanical lattices under periodic boundary conditions with coordination $z =2 d$, where $d$ is the spatial dimensionality, and with a gapped phonon spectrum at all wavenumbers not equal to zero are isostatic. When cut, these lattices with $N$ sites in two dimensions necessarily have of order $N^{1/2}$ zero modes on their boundaries. Recently, Kane and Lubensky showed that these systems can be described by a super-symmetric Hamiltonian analogous to that of the Su-Schrieffer model for polyacetylene and they identified a topological invariant, the \emph{topological polarization}, that determines on which edges zero modes lie in finite systems. We show that a family of two-dimensional four-site-per-unit-cell isostatic lattices possess topologically protected \emph{bulk} zero modes. These ``Weyl modes'' are novel, tunable low-energy mechanisms of the mechanical lattice. They are the analogs of the zero-energy electronic modes of topological semimetals. We discuss how adjusting the lattice parameters induces Weyl modes and alters their wavevectors (generally incommensurate with the lattice) and how they can transport zero modes from one edge to an opposite one as surface wavenumber varies. An accompanying talk discusses the novel dynamical properties of the system. [Preview Abstract] |
Wednesday, March 4, 2015 8:48AM - 9:00AM |
L36.00005: Dynamics in an isostatic mechanical lattice with topological zero-energy bulk modes at finite wavevector Bryan Gin-ge Chen, David Zeb Rocklin, Martin Falk, Tom Lubensky, Vincenzo Vitelli Weakly connected mechanical systems near the isostatic threshold are marginally stable and exhibit large deformations in response to tiny perturbations, meaning that they enter the nonlinear regime immediately. Kane and Lubensky have defined a new topological invariant of isostatic mechanical lattices which leads within linear elasticity to zero energy modes localized at boundaries akin to the edge modes studied in topological quantum matter. This invariant is defined only if the phonon spectrum is gapped away from the acoustic modes at zero momentum, and indeed some lattices admit zero energy bulk modes at nonzero momentum, known as Weyl modes. We present the results of theory and simulations on the dynamics and energy transport in a family of lattices where the wavelengths of these Weyl modes can be tuned via a continuous parameter. Our findings include (1) the Weyl modes provide a route to inducing large deformations in the bulk of a mechanical system via boundary activation (2) the deformation corresponding to the Weyl modes propagates via a nonlinear shock and (3) we elucidate the connection between Weyl modes and the unit-cell shape changing mechanisms that are generic to isostatic lattices. [Preview Abstract] |
Wednesday, March 4, 2015 9:00AM - 9:12AM |
L36.00006: Reversible Shape Memory Optical Gratings Qiaoxi Li, Cary Tippets, Yulan Fu, Eugene Donev, Sara Turner, Valerie Ashby, Rene Lopez, Sergei Sheiko Recent advancements in the understanding of the mechanisms that control shape memory in semi-crystalline polymers, has led to the development of protocols that allow for reversibility in complex shape transformations. The shifting between two programmable shapes is reversible without applying any external force. This is made possible by thermodynamically driven relaxation of extended polymer chains on heating is then inverted by kinetically preferred pathways of polymer crystallization on cooling. Reversible shapeshifting was applied to modulation of photonic gratings to create hands-free reversibly tunable optical elements. We have fabricated a sub-micron ratio optical square grating that presents reversible magnitude changes of its diffraction intensity (up to about 38{\%} modulation) when subject to changes in temperature. This result is attributed to programmable changes in the grating height due to reversible shape memory and is repeatable over multiple cycles. Besides, roughness-induced variations in scattering signal observed upon heating-cooling cycles may offer another way to monitor kinetics of polymer melting and crystallization. Grants: NSF DMR-1407645, [Preview Abstract] |
Wednesday, March 4, 2015 9:12AM - 9:24AM |
L36.00007: Real-time tunable microparticle diffraction based on magnetics M. Prikockis, A. Chen, R. Sooryakumar Photonic crystals and diffraction gratings are key components in color displays, bio/chemical sensors and security coded documentation, among others. Most magnetically responsive photonic crystals rely on electrostatic repulsion and magnetic attraction between constituent particles to tune the inter-particle spacing and thus, their resulting optical signatures. We present a 2D tunable diffraction device based on an all magnetic confinement and manipulation scheme previously developed for fluid borne magnetic dipoles (Scientific Reports 3, 3124 (2013)). The confinement platform consists of thin-film permalloy shapes patterned on a silicon surface and a precessing magnetic field.~ By adjusting the orientation of the field, inter-particle dipolar and trap confinement forces are tuned, thereby enabling the confined magnetic beads to repel or attract one another. A bench top epi-illumination microscope delivers a narrow incident light cone that is diffracted and subsequently imaged. We investigate the white light diffraction from beads in various overall confining potentials, as a function of the orientation of the magnetic field. The presence of the confining potential and field-tunable inter-particle spacing gives rise to a wide range of tunable diffraction patterns. [Preview Abstract] |
Wednesday, March 4, 2015 9:24AM - 9:36AM |
L36.00008: Soft color-composites for optical switching and dimming Francisco Lopez Jimenez, Priyank Upadhyaya, Johannes Liljenhjerte, Kumar Shanmugam, Pedro Reis We present a novel class of soft and actuable color-composites, whose optical transmittance can be switched and tuned by mechanical deformation, on demand. Our samples are fabricated with a spatially heterogeneous arrangement of regions of optically clear and dyed silicone-based rubbers, which can either be distributed in periodic arrays or randomly. Our devices can discretely transition from clear to opaque or exhibit a continuous variation of their transmittance depending on: the geometry of the substructure, the material properties of the components and the mode of loading. We evaluate the optical response of our color-composite structures through precision experiments and investigate the underlying mechanics through finite element modeling, which we use to systematically further explore the design space. [Preview Abstract] |
Wednesday, March 4, 2015 9:36AM - 9:48AM |
L36.00009: Effects of graphene on electro-optic switching and spontaneous polarization of a ferroelectric liquid crystal Rajratan Basu A small quantity of graphene flakes was doped in a ferroelectric liquid crystal (FLC), and the field-induced ferroelectric electro-optic switching was found to be significantly faster in the FLC$+$graphene hybrid than that of the pure FLC. Further studies revealed that the suspended graphene flakes enhanced the FLC's spontaneous polarization by improving smectic-$C$ ordering resulting from the pi-pi electron stacking, and reduced rotation viscosity by trapping some of the free ions of the FLC media. These effects coherently impacted the FLC-switching phenomenon, enabling the FLC molecules to switch faster on reversing an external electric field. [Preview Abstract] |
Wednesday, March 4, 2015 9:48AM - 10:00AM |
L36.00010: Effects of graphene on electro-optic response and ion-transport in a nematic liquid crystal Daniel Kinnamon, Alfred Garvey, Rajratan Basu A small quantity of graphene flakes was doped in a nematic liquid crystal (LC), and the nematic electro-optic switching was found to be significantly faster in the LC$+$graphene hybrid than that of the pure LC. Additional studies revealed that the presence of graphene reduced the free ion concentration in the nematic media by ion-trapping process. The reduction of mobile ions in the LC was found to have subsequent impacts on the LC's conductivity and rotational viscosity, allowing the nematic director to respond faster on switching the electric field on and off. [Preview Abstract] |
Wednesday, March 4, 2015 10:00AM - 10:12AM |
L36.00011: Sound and Noisy Light: Optical Control of Phonons in Photo-switchable Structures Sophia Sklan, Jeffrey Grossman We present a novel means of controlling phonons via optical tuning. Taking as a model an array of photoresponsive materials (photoswitches) embedded in a matrix, we numerically analyze the vibrational response of an array of bistable harmonic oscillators with stochastic spring constants. Changing the intensity of light incident on the lattice directly controls the composition of the lattice and therefore the speed of sound. Furthermore, modulation of the phonon bandstructure at high frequencies results in a strong confinement of phonons. The applications of this regime for phonon wave-guides, vibrational energy storage, and phononic transistors is examined. [Preview Abstract] |
Wednesday, March 4, 2015 10:12AM - 10:24AM |
L36.00012: Meta-Atom Interactions and Coherent Response in rf SQUID Metamaterials Melissa Trepanier, Daimeng Zhang, Oleg Mukhanov, Philipp Jung, Susanne Butz, V.P. Koshelets, Alexey Ustinov, Steven Anlage An rf SQUID (radio frequency superconducting quantum interference device) metamaterial can be modeled as an array of coupled nonlinear oscillators with resonant frequencies that are extremely tunable with temperature, dc magnetic field, and rf current. The metamaterial is driven by an external rf field and its response to that field defines its metamaterial characteristics. In the presence of disorder (nonuniform applied dc magnetic flux for instance) the SQUIDs may or may not oscillate coherently in response to the external rf field. Since we are interested in metamaterial applications, a strong coherent response is desirable. The coherence is affected by a variety of factors including flux uniformity, array size, degree of coupling, strength of the driving field, and uniformity in SQUID parameters. In this talk we will present experimental and simulation results exploring the effect of these parameters on coherence. [Preview Abstract] |
Wednesday, March 4, 2015 10:24AM - 10:36AM |
L36.00013: ABSTRACT WITHDRAWN |
Wednesday, March 4, 2015 10:36AM - 10:48AM |
L36.00014: Combinatorial 3D Mechanical Metamaterials Corentin Coulais, Eial Teomy, Koen de Reus, Yair Shokef, Martin van Hecke We present a class of elastic structures which exhibit 3D-folding motion. Our structures consist of cubic lattices of anisotropic unit cells that can be tiled in a complex combinatorial fashion. We design and 3d-print this complex ordered mechanism, in which we combine elastic hinges and defects to tailor the mechanics of the material. Finally, we use this large design space to encode smart functionalities such as surface patterning and multistability. [Preview Abstract] |
Wednesday, March 4, 2015 10:48AM - 11:00AM |
L36.00015: Mechanical topological matter Lisa Nash, Dustin Kleckner, Vincenzo Vitelli, Ari M. Turner, William T.M. Irvine Topologically protected states can arise in electronic systems with broken time-reversal symmetry. We present a classical mechanical model for a solid in which broken time-reversal symmetry gives rise to topologically protected edge-modes, analogous to the edge modes in the quantum Hall effect. We will discuss numerical and experimental observations of these chiral edge-modes, their topological characterization, robustness and broader phenomenology. [Preview Abstract] |
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