Seminar 15, Wednesday 28 October 2020, 14:00 (London Time)
Speaker : Michael I Weinstein (Dept of Applied Physics and Applied Mathematics, and Dept of Mathematics, Columbia University)
Title: Dynamics of waves in continuum honeycomb structures
Abstract: We overview results on the dynamics of waves (e.g. Schroedinger and Maxwell equations) in honeycomb structures and their deformations.
We study phenomena which arise from the presence of Dirac (conical) points in the bulk band structure.
These include the existence of robust edge (interface) states, which localize along certain sharp terminations, and along domain walls.
We then discuss recent work on the emergence of pseudo-magnetic fields in non-uniformly deformed honeycomb structures.
We apply these results to predict Landau-like energy levels in photonic crystals, and present numerical confirmation of the theory.
Biography: Michael I. Weinstein works on the mathematical modeling, analysis, and applications of wave phenomena across many areas of physical science. A recent focus has been on PDE (Partial Differential Equations) models which describe optical and quantum waves in novel media such as topological insulators and metamaterials. Such physical media have applications to technologies which could potentially revolutionize robust information transfer in computing and communication systems. Weinstein received a B.S. in Mathematics from Union College, summa cum laude, in 1977 and a Ph.D. in Mathematics from the Courant Institute at NYU in 1982. He is a Professor of Applied Mathematics in the Department of Applied Physics and Applied Mathematics and a Professor of Mathematics in the Department of Mathematics at Columbia University. Weinstein is a Fellow of the American Mathematical Society (AMS) and a Fellow of the Society for Industrial and Applied Mathematics (SIAM). In 2015, he received a Math + X Investigator Award from the Simons Foundation.
Seminar 16, Tuesday 03 November 2020, 14:00 (London Time)
Speaker : Massimo Ruzzene (University of Colorado Boulder, USA)
Title: Mechanics and dynamics of two-dimensional quasiperiodic composites
Abstract: Periodic configurations have dominated the design of phononic and elastic-acoustic metamaterial structures for the past decades. Unlike periodic crystals, quasicrystals lack translational symmetry but are unrestricted in rotational symmetry. This provides the opportunity to investigate novel classes of quasicrystal inspired elastic composites whose mechanical static and dynamic properties are largely unexplored. This presentation illustrates the performance of continuous elastic quasicrystals composites, here denoted as quasiperiodic (QP) composites, characterized by different rotational symmetry orders which is directly enforced through a design procedure in reciprocal space. Static mechanical properties are investigated as a function of symmetry order and filling fraction. Results indicate that higher order symmetries, such as 8-, 10- and 14-fold, lead to equivalent stiffness characteristics that interpolate those of the constituent materials while maintaining high levels of isotropy for all filling fractions. Thus, QP composites exhibit more uniform strain energy distributions when compared to periodic 4-fold and 6-fold symmetric configurations. Similarly, nearly-isotropic wave propagation is observed over a broader range of frequencies. The spectral dynamic properties are also investigated by enforcing rotational symmetry constraints in a wedge-type unit cell, which allows for the estimation of bandgaps, whose presence is confirmed in frequency response computations. Wave directionality and bandgaps are also estimated through parallel studies conducted on plate structures characterized by QP patterns of surface stubs. These experiments show clear bandgaps, illustrate how wave fronts reflect the rotational symmetry of the domains, and demonstrate that higher order geometries lead to isotropic propagation over a broader range of frequencies. The investigations presented herein open avenues for the general exploration of the properties of quasiperiodic media, with potentials for novel architectured material designs that expand the opportunities provided by periodic media.
Biography: Massimo Ruzzene is the Slade Professor of Mechanical Engineering and holds a joint appointment in the Smead Aerospace Engineering Sciences Department of CU Boulder. M. Ruzzene currently serves as the Associate Dean for Research of the College of Engineering and Applied Science. He joined CU in the summer of 2019, after serving as the Pratt and Whitney Professor in the Schools of Aerospace and Mechanical Engineering at Georgia Institute of Technology. M. Ruzzene received a PhD in Mechanical Engineering from the Politecnico di Torino (Italy) in 1999. He is author of 2 books, more than 180 journal papers and 250 conference papers. He has participated as a PI or co-PI in various research projects funded by the Air Force Office of Scientific Research (AFOSR), the Army Research Office (ARO), the Office of Naval Research (ONR), NASA, the US Army, US Navy, DARPA, the National Science Foundation (NSF), as well as companies such as Boeing, Eurocopter, Raytheon, Corning and TRW. Most of his current and past research work has focused on solid mechanics, structural dynamics and wave propagation with application to structural health monitoring, metamaterials, and vibration and noise control. M. Ruzzene is a Fellow of ASME and SES, an Associate Fellow of AIAA, and a member of AHS, and ASA. He served as Program Director for the Dynamics, Control and System Diagnostics Program of CMMI at the National Science Foundation between 2014 and 2016.
Seminar 17, Tuesday 10 November 2020, 14:00 (London Time)
Speaker: Philippe Lalanne (The Photonics, Numerical and Nanosciences Laboratory, CNRS, France)
Title: Metasurfaces for light shaping: a look into the past to better appreciate the present and future
Seminar 18, Tuesday 17 November 2020, 14:00 (London Time)
Speaker: Habib Ammari (ETH Zürich)
Title: Wave Interaction with Subwavelength Resonators
Abstract: In this lecture, the speaker reviews recent results on subwavelength resonances. His main focus is on developing a mathematical and computational framework for their analysis. By characterizing and exploiting subwavelength resonances in a variety of situations, he proposes a mathematical explanation for super-focusing of waves, double-negative metamaterials, Dirac singularities in honeycomb subwavelength structures, and topologically protected defect modes at the subwavelength scale. He also describes a new resonance approach for modelling the cochlea which predicts the existence of a travelling wave in the acoustic pressure in the cochlea fluid and offers a basis for the tonotopic map.
Biography: Habib Ammari is a Professor of Applied Mathematics at ETH Zürich. Before moving to ETH, he was a Director of Research at the Department of Mathematics and Applications at Ecole Normale Supérieure in Paris. He received a Bachelor’s degree in 1992, a Master’s degree in 1993, and a Ph.D. in applied mathematics in 1995, all from the Ecole Polytechnique, France. Following this, he received a Habilitation degree in Mathematics from the University of Pierre & Marie Curie in Paris three years later. Habib Ammari is a world leading expert in wave propagation phenomena in complex media, mathematical modelling in photonics and phononics, and mathematical biomedical imaging. He has published more than two hundred research papers, eight high profile research-oriented books and edited eight books on contemporary issues in applied mathematics. He has advised thirty four PhD students and twenty three postdoctoral researchers. Habib Ammari was awarded with several international prizes.
Seminar 19, Tuesday 24 November 2020, 14:00 (London Time)
Speaker: Vincent Pagneux (Laboratoire d’Acoustique de l’Université du Maine, CNRS, France)
Seminar 20, Tuesday 01 December 2020, 14:00 (London Time)
Speaker: Oliver B. Wright (Division of Applied Physics, Faculty of Engineering, Hokkaido University, Sapporo, Japan)
Title: Acoustic Metamaterial Wizardry
Abstract: Acoustic metamaterials are non-naturally occurring structures consisting of arrays of sub-wavelength resonators designed to manipulate the propagation of sound, exhibiting effective negative density or modulus [1,2]. Counterintuitive metamaterial properties such as acoustic negative refraction, superlensing and cloaking have been demonstrated.
Another example is extraordinary acoustic transmission, i.e. the passage of more acoustic energy than expected through a small sub-acoustic-wavelength aperture acting as an acoustic meta-atom. This has been be demonstrated in a variety of systems, having first been shown in optics. I will first present our experimental work in this field using kHz airborne acoustics , in which case we find giant transmission, with enhancements up to ~60, by use of an aperture closed with a membrane. I will then show how gigantic transmission enhancement, by more than a factor of 500, can be achieved in solid acoustics [4,5].
Closely related to extraordinary acoustic transmission is the phenomenon of enhanced transmission between acoustically mismatched media. I will review experimental work on the enormously enhanced passage of acoustic waves from water to air based on the use of a kHz acoustic metasurface .
Finally, I will present recent kHz experiments on acoustic metabeams  and metarods  with perfect bandgaps that prevent all vibrations from passing along them at certain frequencies. The era of metawands that do not vibrate is upon us.
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 S. H. Lee and O. B. Wright, Phys. Rev. B 93, 024302 (2016).
 J. J. Park, K. J. B. Lee, O. B. Wright, M. K. Jung and S. H. Lee, Phys. Rev. Lett. 110, 244302 (2013).
 S. Mezil, K. Chonan, P. H. Otsuka, M. Tomoda, O. Matsuda, S. H. Lee and O. B. Wright, Sci. Rep. 6, 33380 (2016).
 T. Devaux, H. Tozawa, P. H. Otsuka, S. Mezil, M. Tomoda, O. Matsuda, E. Bok, S. H. Lee and O. B. Wright, Sci. Adv. 6, 8507 (2020).
 E. Bok, J. J. Park, H. Choi, C. K. Han, O. B. Wright and S. H. Lee, Phys. Rev. Lett. 120, 044302 (2018).
 K. Fujita, M. Tomoda, O. B. Wright and O. Matsuda, Appl. Phys. Lett. 115, 081905 (2019).
 A. Ogasawara, K. Fujita, M. Tomoda, O. Matsuda,, O. B. Wright, Appl. Phys. Lett. 116, 241904 (2020).
Biography: Oliver B. Wright received his B.A. in physics at University College, Oxford and his Ph.D. in low-temperature solid-state physics at the Cavendish Laboratory, Cambridge. In 1982 he continued this research at CRTBT, C.N.R.S. in Grenoble, France. In 1984 he joined Schlumberger to work on optical sensors in Montrouge, Paris. In 1986 he moved to Nippon Steel Corporation, working as a Senior Researcher at their Electronics Research Laboratories, Sagamihara, Japan, mainly in the field of non-destructive characterization of materials using laser acoustic techniques and electromagnetic acoustic transducers. In 1994 he worked on related topics at C.N.R. Istituto di Acustica in Rome and in 1995 at C.N.R.S. in Besançon, France. Since 1996 he has been working as a professor in the Faculty of Engineering at Hokkaido University in Sapporo, Japan, specializing in particular on laser picosecond ultrasonics, surface acoustic wave imaging and acoustic metamaterials. In 2013 he founded the company Plum Science that makes novel waveguide-based desk lights and stand lights, on sale in many countries.
Seminar 21, Tuesday 08 December 2020, 14:00 (London Time)
Speaker: Jean-Jacques Greffet (Université Paris-Saclay, France)
Title: Tailoring thermal emission with metasurfaces