Person: Babaee, Sahab
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Babaee
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Sahab
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Babaee, Sahab
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Publication Non-Linear Mechanics of Three-Dimensional Architected Materials; Design of Soft and Functional Systems and Structures(2016-09-07) Babaee, Sahab; Bertoldi, Katia; Vlassak, Joost; Clarke, DavidIn the search for materials with new properties, there have been significant advances in recent years aimed at the construction of architected materials whose behavior is governed by structure, rather than composition. Through careful design of the material's architecture, new mechanical properties have been demonstrated, including negative Poisson's ratio, high stiffness to weight ratio and mechanical cloaking. However, most of the proposed architected materials (also known as mechanical metamaterials) have a unique structure that cannot be recon figured after fabrication, making them suitable only for a specific task. This thesis focuses on the design of architected materials that take advantage of the applied large deformation to enhance their functionality. Mechanical instabilities, which have been traditionally viewed as a failure mode with research focusing on how to avoid them, are exploited to achieve novel and tunable functionalities. In particular I demonstrate the design of mechanical metamaterials with tunable negative Poisson ratio, adaptive phononic band gaps, acoustic switches, and reconfigurable origami-inspired waveguides. Remarkably, due to large deformation capability and full reversibility of soft materials, the responses of the proposed designs are reversible, repeatable, and scale independent. The results presented here pave the way for the design of a new class of soft, active, adaptive, programmable and tunable structures and systems with unprecedented performance and improved functionalitiesPublication Elastic metamaterials for tuning circular polarization of electromagnetic waves(Nature Publishing Group, 2016) Zárate, Yair; Babaee, Sahab; Kang, Sung H.; Neshev, Dragomir N.; Shadrivov, Ilya V.; Bertoldi, Katia; Powell, David A.Electromagnetic resonators are integrated with advanced elastic material to develop a new type of tunable metamaterial. An electromagnetic-elastic metamaterial able to switch on and off its electromagnetic chiral response is experimentally demonstrated. Such tunability is attained by harnessing the unique buckling properties of auxetic elastic materials (buckliballs) with embedded electromagnetic resonators. In these structures, simple uniaxial compression results in a complex but controlled pattern of deformation, resulting in a shift of its electromagnetic resonance, and in the structure transforming to a chiral state. The concept can be extended to the tuning of three-dimensional materials constructed from the meta-molecules, since all the components twist and deform into the same chiral configuration when compressed.Publication Reconfigurable origami-inspired acoustic waveguides(American Association for the Advancement of Science (AAAS), 2016) Babaee, Sahab; Overvelde, Johannes; Chen, Elizabeth; Tournat, V.; Bertoldi, KatiaWe combine numerical simulations and experiments to design a new class of reconfigurable waveguides based on three-dimensional origami-inspired metamaterials. Our strategy builds on the fact that the rigid plates and hinges forming these structures define networks of tubes that can be easily reconfigured. As such, they provide an ideal platform to actively control and redirect the propagation of sound. We design reconfigurable systems that, depending on the externally applied deformation, can act as networks of waveguides oriented along one, two, or three preferential directions. Moreover, we demonstrate that the capability of the structure to guide and radiate acoustic energy along predefined directions can be easily switched on and off, as the networks of tubes are reversibly formed and disrupted. The proposed designs expand the ability of existing acoustic metamaterials and exploit complex waveguiding to enhance control over propagation and radiation of acoustic energy, opening avenues for the design of a new class of tunable acoustic functional systems.Publication Honeycomb phononic crystals with self-similar hierarchy(American Physical Society (APS), 2015) Mousanezhad, Davood; Babaee, Sahab; Ghosh, Ranajay; Mahdi, Elsadig; Bertoldi, Katia; Vaziri, AshkanWe highlight the effect of structural hierarchy and deformation on band structure and wave-propagation behavior of two-dimensional phononic crystals. Our results show that the topological hierarchical architecture and instability-induced pattern transformations of the structure under compression can be effectively used to tune the band gaps and directionality of phononic crystals. The work provides insights into the role of structural organization and hierarchy in regulating the dynamic behavior of phononic crystals, and opportunities for developing tunable phononic devices.Publication Hierarchical honeycomb auxetic metamaterials(Nature Publishing Group, 2015) Mousanezhad, Davood; Babaee, Sahab; Ebrahimi, Hamid; Ghosh, Ranajay; Hamouda, Abdelmagid Salem; Bertoldi, Katia; Vaziri, AshkanMost conventional materials expand in transverse directions when they are compressed uniaxially resulting in the familiar positive Poisson’s ratio. Here we develop a new class of two dimensional (2D) metamaterials with negative Poisson’s ratio that contract in transverse directions under uniaxial compressive loads leading to auxeticity. This is achieved through mechanical instabilities (i.e., buckling) introduced by structural hierarchy and retained over a wide range of applied compression. This unusual behavior is demonstrated experimentally and analyzed computationally. The work provides new insights into the role of structural organization and hierarchy in designing 2D auxetic metamaterials, and new opportunities for developing energy absorbing materials, tunable membrane filters, and acoustic dampeners.Publication Wave propagation in cross-linked random fiber networks(AIP Publishing, 2015) Babaee, Sahab; Shahsavari, A. S.; Wang, Pai; Picu, R. C.; Bertoldi, KatiaWe numerically investigate the propagation of small-amplitude elastic waves in random fiber networks. Our analysis reveals that the dynamic response of the system is not only controlled by its overall elasticity, but also by the local microstructure. In fact, we find that the longest fibersegment plays a key role in dynamics when the network is excited with waves of short wavelength. In this case, the Bloch modes are highly non-affine as the longest segments oscillate close to their resonances. Based on this observation, we predict the low frequency dispersion curves of random fiber networks.