Previous Webinars:


Seminar 10 S2: Hierachical geomaterials and seismic metamaterials: tracks for implementation

Speaker: Stéphane Brûlé (Menard – Région Rhône-Alpes & Auvergne, France)

Q & A:

Abstract: The transposition of the principles of periodic media to materials as specific as terrestrial materials requires rigorous definition of the validity conditions. In particular, the elasticity condition, the full complexity of the attenuation in viscoelastic material, the pattern of the sedimentary basin, the strong antagonism between amplification and attenuation, the soil-structure interaction, etc.

Indeed the possibilities of diffraction phenomena have been revealed by experiments on a real scale. The lenses tested are explored as phononic crystals and metamaterials. By the effects observed, we point out the diffraction including Bragg reflection and double image of the source as a result of the negative refraction of a flat lens. However, a metamaterial is defined as an artificial composite material made from the assembly of resonators of smaller dimensions, whose wavelength at resonance is much greater than their physical dimension. These possibilities of local resonances are verified for Helmholtz resonators or very soft soils with rigid inclusions.

On a macroscopic scale, a metamaterial is likely to exhibit properties that are not found in nature, such as negative refractive index. In addition to these early interpretations, there is an analysis of the modification of the polarization of surface waves. This new reading of the data opens the discussion on other descriptions of phenomena such as the existence of local resonances of rigid elements placed in a soil, and no longer of empty cylinders, as well as on static or dynamic homogenization approaches, dynamic anisotropy, transformational optics, surface resonators, etc. The modification of the signal by the fact of a structured soil and surface resonators are the link with Civil Engineering and the soil-structure interaction practiced in Earthquake Engineering. Research subjects converge in seismology and on the effects of secondary sources generated by surface buildings. The coupling of buildings such as surface resonators with structured soils constitutes an opportunity for development in the trapping of mechanical energy. In the era of energy transition, any free source of energy is of interest.

S. Brûlé et al. (2014) Experiments on Seismic Metamaterials: Molding Surface Waves. Physical Review Letters, 112(13)

S. Brûlé et al. (2017) Flat lens effect on seismic waves propagation in the subsoil. Scientific Reports, 7(1)

S. Brûlé and S. Guenneau (2021) Past, present and future of seismic metamaterials: experiments on soil dynamics, cloaking, large scale analogue computer and space–time modulations. Comptes Rendus. Physique, 21(7-8)

B. Ungureanu et al. (2015) Auxetic-like metamaterials as novel earthquake protections. EPJ Applied Metamaterials, 2

Y. Achaoui et al. (2017) Clamped seismic metamaterials: ultra-low frequency stop bands. New Journal of Physics, 19(6)

T. Varma et al. (2021) The Influence of Clamping, Structure Geometry, and Material on Seismic Metamaterial Performance. Frontiers in Materials, 8

Biography: Stéphane Brûlé, contributor in the field of seismic metamaterials, is a researcher in seismic risk assesment, soil dynamics, soil-structure interaction and geotechnical engineering, holder of a master’s degree research from École Normale Supérieure de Paris and Pierre and Marie Curie University and an engineering diploma in geotechnics of Grenoble-Alpes University in the field of soil mechanics, ground improvement and deep foundations. Stéphane Brûlé is the Phd studend of Stefan Enoch, director of research at CNRS, and was the leading author of the foundation paper for the field of seismic metamaterials [Physical Review Letters 112, 133901, 2014]. He also led with Sébastien Guenneau and Stefan Enoch, and others, the first experiment on lensing of surface Rayleigh waves via negative refraction [Scientific Reports 7, 18066, 2017].
He is also teaching in Universities and Engineering Schools (ENS Lyon, Polytech Grenoble, EOST, ESITC Paris, École des Mines d’Alès, Polytech Clermont), is a member of the International Technical Committee 203 « Geotechnical Earthquake Engineering and Associated Problems », and is also an active boardmember of the French committee of soil mechanics (CFMS) and of the French earthquake engineering association (AFPS).

Google Scholar


Seminar 9 S2: Multiple scattering analysis of quasi-periodic clusters of scatterers

Speaker: Daniel Torrent Martí (Physics Department, Universitat Jaume I, Spain)

Q & A:

Abstract: We will apply multiple scattering theory to the analysis of resonant modes of finite clusters of scatterers for flexural waves. It will be shown that this method allows the calculation of the real and imaginary part of the eigenfrequencies of finite structures, so that we can determine not only the resonant frequency but also its quality factor. We will apply this method to the study of two-dimensional clusters forming moiré lattices and to the quasi periodic infinite line, showing that both types of structures present a large amount of resonances of high quality. It will be shown therefore that quasi-periodic clusters are a promising family of structures for the design of wave-localization devices, since these results are in principle applicable to any kind of classical wave.

Biography: Daniel Torrent studied physics at the University of Valencia and obtained his PhD in the Electronics Engineering Department of the Polytechnic University of Valencia, on July 25th 2008. During his career he has contributed to the development of both theoretical and experimental tools to understand the propagation of acoustic, elastic and electromagnetic waves in complex media. After four years of research stays in the University of Lille (France) and the Univeristy of Bordeaux – CNRS (France), he has been awarded by the “Ramón y Cajal” Fellowship, and currently is working as a researcher at the “Univeritat Jaume I” in Castellón de la Plana (Spain).

Google Scholar


Seminar 8 S2: Mathematical analysis of subwavelength metamaterials: sensors, biomimicry and topological edge modes

Speaker: Bryn Davies (Department of Mathematics, Imperial College London, UK)

Q & A:

Abstract: The aim of our work is to conduct rigorous analyses of subwavelength scattering problems and use these results to establish the mathematical foundations for the design of high-contrast metamaterials. We will present results that characterise a system’s resonance in terms of the eigenstates of the generalized capacitance matrix. We will use this theory to explore applications including the design of cochlea-inspired metamaterials, enhanced sensors based on exceptional points and tuneable topological wave guides. The talk will discuss results developed in collaboration with Habib Ammari, Erik Orvehed Hiltunen and Sanghyeon Yu, who are all former colleagues from Bryn’s time at ETH Zurich.

Biography: Dr Bryn Davies is a Research Associate in the Department of Mathematics at Imperial College London. His research concerns the analysis of wave propagation in complex media. He has used integral methods and asymptotic techniques to study problems from the fields of topological insulators, subwavelength waveguides, enhanced sensing and bio-inspired metamaterials.

Google Scholar


Seminar 7 S2: Acoustic and elastic wave propagation in microstructured media with interfaces: homogenization, simulation and optimization

Speaker: Marie Touboul (Department of Mathematics, University of Manchester, UK)

Q & A:

Abstract: The design of media at a microstructured scale allows to control wave propagation in a fine way and to obtain exotic effects at the macroscopic scale. Thanks to homogenization methods, the microstructure can be advantageously replaced, at the macro scale, by a homogeneous effective medium. Then, it raises the question of optimization tools in order to design the microstructure that allows to achieve a desired macroscopic effect. In this context, the consideration of interfaces (microstructured interfaces, imperfect interfaces) can lead to modifications in the homogenization methods, the numerical methods, or the optimization methods classically used. Two different cases of interfaces will be presented (PhD work, supervised by Cédric Bellis and Bruno Lombard):
(i) Homogenization and optimization are first carried out for microstructured interfaces. The homogenization of a highly contrasted, and therefore resonant, microstructured interface is studied in the time-domain and leads to resonant jump conditions on an effective interface (coll: Kim Pham, Agnès Maurel, Jean-Jacques Marigo). The introduction of auxiliary variables allows to get a local evolution problem in time which is then solved numerically to perform time-domain simulations for the effective resonant meta-interface. Finally, the sensitivity of the effective non-resonant model to the geometry of the microstructure is determined using topological derivatives (coll: Rémi Cornaggia) in order to develop a topological optimization of the microstructure.

(ii) Homogenization of solids with imperfect interfaces of the spring-mass type is then performed (coll: Raphaël Assier). The wavefields are approximated at low-frequency for possibly nonlinear cracks. An approximation of both the wavefields and the dispersion relation is also obtained at higher frequencies for a 1D array of linear cracks.

Biography: Marie Touboul has just received her PhD from the University of Aix-Marseille (supervisors: Cédric Bellis and Bruno Lombard at the Laboratory of Mechanics and Acoustics). She is currently working as a postdoctoral researcher with Professor William Parnell in the Mathematics of Waves and Materials research group (Department of Mathematics, University of Manchester). Her work lies at the interface of applied mathematics, waves, and mechanics of solids.

Google Scholar


Seminar 6 S2Bringing metamaterials to creative industries and hospitals

Speaker: Gianluca Memoli (School of Engineering and Informatics, University of Sussex)

Q & A:

Abstract: According to different recent market research reports, acoustic metamaterials are quickly going up the TRL scale, moving to applications. In this talk, I will therefore present two examples of applications: one relative to sound delivery and one to noise management, both for audible frequencies in air.
First, I will describe how combinations of metasurfaces can be used to achieve sound delivery with wavelength precision at variable distances, for creative applications. I will touch on the possibility of applying the thin-lens equation and on the verification of COMSOL simulations using human volunteers.
Secondly, I will discuss how my team came to design meta-material based movable panels to COVID wards. I will touch on the criticality of noise in hospitals, on the specific combination of unit cells that we used and on the challenges to test the performance of our panels using standard techniques, both in the laboratory and in-situ.

Biography: Gianluca Memoli is a Senior Lecturer at the University of Sussex and the acting CEO of Metasonixx Ltd. A physicist and an engineer, he fell in love with metamaterials in 2016, when he arrived at Sussex from the National Physical Laboratory and used metasurfaces to levitate objects without transducer arrays. A passionate science communicator and a proud father of two, he holds a UKRI fellowship whose aim is to bring metamaterials to creative industries. He co-chairs (with Tim Starkey) the Special Interest Group on Acoustic Metamaterials shared between the UK Acoustic Network and the UK Metamaterials Network.

Google Scholar


Seminar 5 S2Towards scalable Photonic Neural Networks with (3+1)D integrated optics

Speaker: Daniel Brunner (Institut FEMTO-ST, Université Bourgogne Franche-Comté CNRS UMR 6174, Besançon, France)

Q & A:

Abstract: Integrated photonic architectures have the potential to revolutionize neural network computing. However, conventional 2D lithography strongly limits the size of integrated photonic neural networks due to fundamental scaling laws. We want to overcome this problem by integrating neural networks using 3D printed photonic waveguides. For that we demonstrate complex 3D multimode waveguide networks based on polymer waveguides surrounded by air. Furthermore, we recently developed a (3+1)D direct laser writing technique where we dynamically and locally control the writing power in order to realize single mode step or graded index waveguides.

Biography: Daniel Brunner is a CNRS researcher with the FEMTO-ST, France. His interests include novel computing using quantum or nonlinear substrates with a focuses on photonic neural networks. He was received several University and the IOP’s 2010 Roys prize and the IOP Journal Of Physics:Photonics emerging leader 2021 prize. He edited one Book and two special issues, has presented his results 45+ times upon invitation and has published 50+ scientific articles.

Home – Prof. Daniel Brunner

Google Scholar


Seminar 4 S2Self-collimation, Veselago lens, Dirac cones and embedded states in continuum in acoustics without phononic crystals and metamaterials

Speaker: Alexei Maznev (Department of Chemistry, Massachusetts Institute of Technology, USA)

Q & A:

Self-collimation a.k.a. phonon focusing of surface acoustic waves on Ge (111)

Abstract: The concepts of photonic crystals and metamaterials initially appeared in optics and electromagnetism, and were subsequently extended to acoustic waves. However, a number of phenomena thought to be specific to these “artificial” media have been observed in solid state acoustics with conventional materials – in some cases well before the advent of metamaterials and photonic/phononic crystals. In this talk, which will cover both historical and recent research, we will discuss several such phenomena: (i) “self-collimation” of bulk and surface acoustic waves in natural crystals; (ii) negative group velocity, Veselago lens and Dirac cones exhibited by guided acoustic waves in plates; (iii) robust embedded states in continuum on natural crystal surfaces and in simple layered structures.

Biography: Alex Maznev received Diploma in physics from the Moscow Institute of Physics and Technology and PhD from the General Physics Institute of the Russian Academy of Sciences (thesis on laser-generated SAWs including the first experimental observation of surface phonon focusing). He held postdoctoral positions at the Freie Universität Berlin, as an Alexander von Humboldt Fellow, and at MIT, where he developed an optical heterodyning scheme for laser-induced transient grating experiment currently used in many labs. Subsequently, he worked as an industrial researcher (mainly at Philips Electronics North America) developing metrology systems for semiconductor industry using optical and optoacoustic techniques, before returning to MIT as a staff scientist.  His current interests involve a broad range of topics pertaining to wave propagation phenomena, primarily in acoustics and related fields such as phonon-mediated heat transport on micro/nanoscale.  He is collaborating with many groups around the world and has held visiting positions at Université du Maine in France, Hokkaido University in Japan, University of Witwatersrand in South Africa, and Universität Heidelberg in Germany.

Home – Prof. Alexei Maznev

Google Scholar


Seminar 3 S2: Manipulating water waves using bathymetric plate arrays

Speaker: Richard Porter (School of Mathematics, University of Bristol, UK)

Q & A:

Abstract: This talk will describe how closely-spaced arrays of vertical plates protruding from the bed of an incompressible fluid can be used to produce interesting effects on water waves propagating on the surface of the fluid. We will consider how both fully depth dependent and depth-averaged (shallow water) models are formulated and how they compare and illustrate their use in a number of different settings. For instance, we can generate examples of bathymetric devices which represent all-frequency all-angle refractive devices which allow negative refraction and for which the phase velocity is directed towards the source. Other examples include the use of bathymetric plate arrays to perfectly transmit energy through bends in waveguides and, when formed into a cylinder, act as a bathymetric lens.

Biography: Richard Porter has worked at the University of Bristol for over 25 years, first as a Research Assistant before becoming a lecturer in Applied Mathematics. His research interests mainly focus on the interaction of water waves with marine structures and developing mathematical tools for approximating solutions to the boundary-value problems that arise. The principle topics of interest include trapped and near-trapped waves, the design and modelling of ocean wave energy converters, the influence of floating ice and cracks in ice sheets on wave propagation and, more recently, metamaterials and their application in water wave settings.
He has published six papers with his father, been known to cycle to overseas conferences, and appeared in a BBC documentary which he has never watched.

Google Scholar


Seminar 2 S2: Valley-Hall topological acoustics

Speaker: Zhiwang Zhang (School of Physics, Nanjing University, China)

Q & A:

Abstract: The discrete valley degree of freedom, i.e., quantum states of energy extrema in momentum space, is attracting growing attention because of its potential as a new type of information carrier like spins in spintronics. Transferring the valley concept to classical wave systems through valley-like frequency dispersions, has been made possible using engineered artificial lattices such as photonic and sonic crystals. 

In this webinar, we will start with a brief introduction on valley-projected topological acoustics and then discuss our recent works in this topic, which include the experimental realizations of the topological acoustic delay line[1], the directional acoustic antenna[2] and the valley-projected edge states based on the subwavelength soda cans[3]. Lastly, in this context, we also consider non-Hermiticity combining sonic crystals with gain[4]. Here, we take advantage of electro-thermoacoustic coupling from biased carbon nanotube films used as lattice coatings. We construct a topological whispering gallery made out of such coated lattice and show how the mode chirality can be broken and a topological “saser”, the analogous topological “laser” in acoustics, can be realized.

[1] Zhang, Z. et al. Phys. Rev. Appl. 9, 034032 (2018).

[2] Zhang, Z. et al. Adv. Mater. 30, 1803229 (2018).

[3] Zhang, Z. et al. Research 2019, 5385763 (2019).

[4] Hu, B. et al. Nature597, 655 (2021).

Biography: Zhiwang Zhang is currently a postdoctoral researcher in Department of Physics, Nanjing University under the support of the China National Postdoctoral Program for Innovative Talents. He received his Laurea (2015) and PhD (2020) from Nanjing University, China, and visited Universidad Carlos III de Madrid, Spain, as a joint training PhD student (2018-2019). He majors in acoustics and focus on physical acoustics and acoustic metamaterials. His current researches mainly concern the topological protected states in 2D/3D acoustic systems and achieving the functional device based on the topological acoustics.

Google Scholar


Seminar 1 S2Odd robotic matter

Speaker: Corentin Coulais (Van der Waals-Zeeman Instituut, Faculty of Science, University of Amsterdam, Netherland)

Q & A:

Abstract: Controlling how waves propagate, attenuate and amplify in simple, scalable geometric structures is a daunting challenge for science and technology. In this talk, I will discuss how odd media—media in which energy conservation and chiral symmetries are simultaneously broken—can be used to steer mechanical waves in unprecedented ways. Combining experiments on mechanical lattices of distributed robots with wave physics and continuum mechanics, I will discuss the emergence of unidirectionally amplified waves, of topological waves and of one-way solitons in odd media. I will further show how these odd waves can be used to induce locomotion and unusual responses to impacts and hence pave the way towards a novel generation of materials with animate properties.

Biography: Corentin Coulais is Associate Professor at the University of Physics of the University of Amsterdam. Coulais’ Machine Materials group investigates designer soft materials, with a particular emphasis on how mechanical metamaterials can programmed to achieve advanced mechanical tasks. Coulais explores the structure-property relationship in metamaterials with highly nonlinear degrees of freedom, by combining additive manufacturing, precision-desktop experiments, numerical methods and theory inspired from condensed matter. Recent highlights include shape-changing (2016), non-reciprocal topological (2017), self-folding (2018) and multifunctional (2021) metamaterials. He has recently pioneered robotic materials, which combine the notions of emergence and symmetries inherent to condensed matter with the capabilities of robotics. This has led to early experimental observations of non-Hermitian wave phenomena such as unidirectional amplification (2019) and non-Hermitian topology (2020). Coulais has received the NWO VENI (2015), ERC Starting (2019) and leads multiple collaborations with industry. More information on his research activities can be found at coulaislab.com

Google Scholar