Seminar 20 -S3: Homogenization and topological optimization for wave propagation in periodic media
Speaker: Rémi Cornaggia (Mécanique et Ingéniérie des Solides et des Structures, Sorbonne Université — Institut d’Alembert, France)
Abstract: We are interested in waves in two-phase periodic materials, either occupying the whole 2D domain, or a thin interface between homogeneous media. The phase distribution in these media is to be optimized to obtain specific dispersive or transmission properties.
In these two cases, a first homogenization step is used to describe the effective wave propagation. The two-scale asymptotic homogenization procedure leads to an “enriched” dispersive wave equation in the first case, and effective transmission conditions across an equivalent interface in the second one. In both cases, the effective coefficients of the model are defined through elementary “cell” or “band” problems that we address with FFT-based solvers.
A topological optimization procedure is then presented. First, relevant propagation indicators are extracted from the effective models, and serve to define cost functionals to be minimized to achieve certain goals. The sensitivity of the functional to a localized phase change in the representative cell, also called topological derivative (TD), is computed and indicates optimal locations where to perform these phase changes. A TD-based level-set algorithm is finally used to optain optimal microstructures.
Applications of the method will finally be presented: maximizing the dispersion in given directions in the full space, or enhancing the transmitted wave in a specific direction.
Biography: I am now (from 2020) Maître de conférences (assistant professor) at Sorbonne Université, teaching in the UFR d’ingénierie (engineering department) and conducting my research in team MISES of Institut Jean le Rond d’Alembert. I am interested in the modelling and simulation of acoustic and elastic waves, and to the homogenization and optimization of architected materials and composites.
I have been working mainly on inverse scattering problems, vibrations of heterogeneous beams, and homogenisation and optimisation of periodic materials to enhance dispersive effects. My favourite mathematical tools are topological derivatives of various cost functionnals or quantities of interest, volumic integral equations to reformulate scattering problems, and the two-scale homogenisation method to address periodic media. For numerics, I mainly use finite elements, boundary elements, and FFT-based methods for numerical homogenisation.
Seminar 19 -S3: Cylinder- and Coated-cylinder-systems as Multifunctional Metamaterials: An Effective Medium Description
Speaker: Maria Kafesaki (Department of Materials Science and Technology, University of Crete, Greece)
Abstract: Cylinder- and coated-cylinder-based metamaterials constitute one of the most appealing metamaterial categories, especially in high frequencies, i.e. THz to optical. The effective medium descriptions though employed for the analysis of such metamaterials show serious limitations, especially in the case of high-index dielectric cylinders or cylinders made of resonant materials, such as phonon-polariton or exciton-polariton materials. In this talk we will present an effective medium approach suitable for the analysis and description of cylinder-based metamaterials, of either simple or coated/multicoated cylinders. The approach is based on the well-known to the Solid State Physics community Coherent Potential Approximation (CPA) method, combined with a Transfer Matrix scheme for the case of multi-coated cylinders. We will demonstrate here the power of this approach in the case of polaritonic cylinder systems and in systems of graphene-made nanotubes. In both cases a rich metamaterial behavior has been observed, including frequency regions of engineerable negative permittivity, negative permeability, and in some cases negative refractive index and hyperbolic response.
Biography: Maria Kafesaki is Associate Professor in the Dept. of Materials Science and Technology of the University of Crete and Adjunct Researcher at the Institute of Electronic Structure and Laser (IESL) of Foundation for Research and Technology Hellas (FORTH). She obtained her Ph.D. in 1997, at the Physics Department of the University of Crete, Greece, on elastic wave propagation in complex media. She has worked as post-doctoral researcher in the Consejo Superior de Investigaciones Cientificas in Madrid, Spain, and in IESL of FORTH (1997-2001). Her current research is on the area of electromagnetic wave propagation in periodic and random media, with emphasis on photonic crystals and metamaterials, where she has large theoretical and computational experience. She has more than 130 publications in refereed journals (with more than 8300 citations and h-index=46, according to Web of Science, October 2022), and more than 80 invited talks at international conferences/schools and Institutions. She has participated in many European projects as well as in the organization of many international conferences and schools. She is Fellow of the Optica.
Seminar 18 -S3: Some recent advances in electromagnetic, acoustic, and flexural wave scattering: CPAL and shape recognition
Speaker: Mohamed D. Farhat (King Abdullah University of Science and Technology (KAUST), Saudi Arabia)
Abstract: In the first part of this webinar, I will present our recent contributions in the coherent perfect-absorber and laser (CPAL) for electromagnetic, elastodynamic, and acoustic waves. This intriguing effect is enabled by parity-time (PT)-symmetry breaking condition and leads to extremely precise rf sensors. In addition, the lasing operation of CPAL device is first observed theoretically and validated numerically (3D COMSOL full elasticity simulations) in elastic thin-plates. We further propose to accomplish ultra-sensitivity and robustness to noise by demonstrating a CPAL-locked sensor to detect extremely small-scale pressure perturbations. The results show that the sensitivity and resolvability of the CPAL-locked sensor may go well beyond the traditional acoustic sensors.
In the second part, we propose a new approach for acoustic airborne waveguiding that relies on imposing spinning on a column of air, leading to high modified acoustic refractive indices for specific azimuthal modes, reminiscent of acoustic spinning fiber (ASF). The obtained effect is nonreciprocal and tunable via the spinning frequency. It may be seen as the counterpart of the “Zeeman effect”. The concept is shown in the realm of airborne acoustics, yet it can be extended to other wave types, e.g., optics or elastodynamics.
Last but not least, I will shortly discuss a generative deep learning approach for shape recognition of an arbitrary object from its acoustic scattering amplitudes. The model exploits adversarial learning and variational inference to predict the unique shape of the object. The nonunique solution space is overcome by the multiangle and multifrequency phaseless far-field patterns.
Biography: Dr. Mohamed Farhat received his Ph.D. in Optics and Electromagnetism from Aix-Marseille University where he obtained as well his Master degree in Theoretical Physics. His PhD dissertation was titled by “Metamaterials for Harmonic and Biharmonic Cloaking and Superlensing.” He has authored over 100 publications, including 1 edited book, 94 journal papers, 7 book chapters, and 5 international patents, as well as over 90 conference papers, with over 4700 citations (Google Scholar), as of January 2023. He has organized several special sessions at the Meta conferences, and is active reviewer for many international journals in Physics including Physical Review Letters and Nature Physics. He has co-edited the book “Transformation Wave Physics: Electromagnetics, Elastodynamics and Thermodynamics” at Pan Stanford Publishing. His research is in the fields of plasmonics and metamaterials with applications spanning optical and acoustical waves.
Seminar 17 -S3: Computing The Optical Response Of Molecular Materials: From Nano To Device Scales
Speaker: Ivan Fernandez-Corbaton (Karlsruhe Institute of Technology, Germany)
Abstract: Advances in nanoscience and material science are accelerating the rate at which we can create new materials. But, quite often, experiments are ahead of theory due to the challenging multiscale and multidisciplinary character of the experimental systems. In my talk, I will present a novel methodology which, starting from ab initio quantum mechanical molecular simulations, allows one to compute the electromagnetic response of macroscopic photonic devices containing molecular materials.
Biography: Ivan Fernandez-Corbaton has worked in the Karlsruhe Institute of Technology (Karlsruhe, Germany) since 2014. Ivan’s research is focused on light-matter interactions. His favourite tools for the study and engineering of light-matter interactions are symmetries, conservation laws, and Hilbert spaces. Ivan got his Ph.D. in theoretical physics from Macquarie University (Sydney, Australia) in 2014, his M.Sc. in mobile communications from the Eurecom Institute (Sophia Antipolis, France) in 1998, and his electrical engineering degree from the Polytechnic University of Catalonia (Barcelona) in 1998. Before going back to academia as a Ph.D. student in 2010, Ivan worked from 1998 to 2010 as a research engineer, mostly in the design of signal processing algorithms for cellphone chips.
Seminar 16 -S3: Photonic topological metamaterials built of sub-wavelength resonators
Speaker: Sergey Skipetrov (Laboratoire de Physique et Modélisation des Milieux Condensés – CNRS, France)
Abstract: Arranging many identical entities (atoms, dielectric spheres, etc.) having the same resonant frequency in a dense two-dimensional structure and breaking the time-reversal symmetry by an external magnetic field may result in a photonic metamaterial with nontrivial topological properties. When the structure is periodic, the resulting topological bandgaps are characterized by non-zero Chern numbers and host topologically protected edge modes. Disorder in positions of resonators introduce localized modes inside the bandgap and eventually closes the latter when made sufficiently strong. More interestingly, disorder can also induce topological properties in an otherwise topologically trivial structure – a phenomenon known as the topological Anderson insulator. The resonant nature of scattering, the vector character of light, and the strong near-field coupling between neighboring resonators are at the origin of differences in behavior of the considered photonic structure with respect to electronic systems.
S. Skipetrov and P. Wulles (2022) Topological transitions and Anderson localization of light in disordered atomic arrays. Physical Review A, 105(4)
S. Skipetrov and P. Wulles (2022) Photonic topological Anderson insulator in a two-dimensional atomic lattice. arXiv
Biography: Sergey Skipetrov is a senior researcher at the French CNRS and the director of the Laboratory of Physics and Modelling of Condensed Matter in Grenoble. He obtained his PhD in physics from Moscow State University in 1998 and was hired as a permanent CNRS researcher in 2001 after one year as a postdoc in Grenoble and two years as a research scientist in Moscow. Sergey’s scientific interests are in the field of theory of wave scattering in disordered media, including fundamental phenomena (mesoscopic fluctuations, Anderson localization, topological photonics, nonlinear & quantum optics in the presence of disorder) and applications (noninvasive imaging and sensing of turbid media, using disorder to enhance functionality of optical devices). His main scientific achievements are the prediction of instability of speckle patterns in disordered media with Kerr nonlinearity (2000), the theoretical interpretation of experiments demonstrating Anderson localization of ultrasound (2008), the discovery of the absence of Anderson localization for light in three-dimensional ensembles of point scatterers (2014). Sergey was awarded the CNRS bronze medal in 2006.
Seminar 15 -S3: Scattering light through temporal structure
Speaker: Emanuele Galiffi (Advanced Science Research Center Graduate Center – City University of New York, U.S.A)
Abstract: A sufficiently fast temporal drive can induce a host of peculiar temporal scattering phenomena, such as the temporal analogues of spatial reflection and diffraction, but obeying different causal relations. In this talk I will present a number of theoretical advances and new ideas in this direction, as well as two series of recent experiments that are pioneering the growing field of temporal electromagnetic control.
Firstly, I will demonstrate the first realization of electromagnetic time-diffraction, the temporal analogue of Young’s famous double-slit experiment, performed in Indium Tin Oxide at near-optical frequencies, and discuss its implications for the microscopic study of non-equilibrium dynamics in transparent conducting oxides, as well as its potential applications for temporal light modulation and for the direct measurement of the temporal coherence of optical pulses.
In the second part of the talk I will demonstrate the first observation of electromagnetic time-reflection, performed in a microwave waveguide, explaining why this phenomenon can be practically observed despite the recent claims of its unfeasibility, and I will show how this platform can be leveraged to achieve temporal coherent wave control, whereby a broadband pulse can be “instantaneously” erased or “sculpted” by means of an additional idler pulse, tailored to annihilate the first entirely or in part upon time-reflection.
Biography: I graduated from Imperial College in Physics in 2016, spending the year 2014-2015 at the University of Heidelberg as an exchange student, where I worked with Prof. Sandro Wimberger on my Master’s thesis on quantum reflection. I then worked initially on graphene and transformation optics, and later on space-time metamaterials as part of my PhD at Imperial College with Prof. Sir John Pendry within the Centre for Doctoral Training in Theory and Simulation of Materials, defending my PhD degree in 2020, after which I was awarded an EPSRC Doctoral Prize Fellowship which allowed me to work on chiral space-time media and to establish an ongoing experimental collaboration with the group of Prof. Riccardo Sapienza. In 2021 I was awarded a Junior Fellowship of the Simons Society of Fellows to work for three years on wave scattering and mode-tailoring in time-varying media with the group of Prof. Andrea Alu’, where I am currently hosted. When not trying to dream up new things to do with waves I enjoy probing my neighbours’ patience by playing my beloved guitar and singing, can’t get enough of waves!
Seminar 14 -S3: Twisted metamaterials for phononic waves
Speaker: Simon Yves (Advanced Science Research Center, City University of New York, USA)
Abstract: For the last two decades, metamaterials and metasurfaces have been extensively studied in order to induce extreme anisotropic behaviors such has hyperbolic propagation of waves. Such peculiar systems allow highly precise and tunable manipulation of the field in two or three dimensions. At the same time, moiré super-lattices and the rapidly expanding domain of twistronics in solid-state physics have provided new phase transitions phenomena such as flat band superconductivity for example. Inspired by these exciting new ideas, we implement macroscopic wave twistronics analogues to harness these new features in the context of enhanced wave manipulation. In particular, in this talk we present the cases of phononic hyperbolic metamaterials and metasurfaces and how they behave in presence of the symmetry breaking induced by a twist in the system. These results introduce some new opportunities provided by macroscopic wave twistronics with metamaterials, both from a fundamental and practical point of view.
- Postdoctoral Fellow at Photonics Initiative of CUNY Advanced Science Research Center (Andrea Alù lab, http://www.alulab.org/)
–> Metamaterials and metasurfaces in acoustics and elastodynamics
- PhD from Institut Langevin at ESPCI Paris, under the supervision of Geoffroy Lerosey, Fabrice Lemoult and Mathias Fink (https://www.institut-langevin.espci.fr/home)
–> Metamaterials for negative refraction and topological waves in acoustics and microwaves
- Master of Science : The International Centre for Fundamental Physics at Ecole Normale Supérieure Ulm (ICFP-ENS)
–> Condensed matter physics major
- Engineer at Ecole Supérieure de Physique et de Chimie de la Ville de Paris (ESPCI Paris)
–> Physics major
Seminar 13 -S3: A landscape method to unveil high-frequency localized modes in random acoustic metamaterials
Speaker: Régis Cottereau (Laboratoire de Mécanique et d’Acoustique, CNRS, Marseille, France)
Abstract: Mechanical media with randomly fluctuating parameters are fundamentally different from periodic (or homogeneous) media in that, above a certain threshold (and depending on dimensionality), eigenmodes are localized. While that feature may be extremely useful in practice, for any application involving vibration isolation, numerical methods currently lack for the prediction of these localized eigenmodes at a reasonable cost. Recently, the so-called localization landscape method was proposed  to predict such localized modes in quantum systems (Schrödinger equation). It allows to predict the locus of all the lowest localized eigenmodes by solving one single (cheap) elliptic problem. Although very elegant, this method is not useful for classical (acoustic) equations because the lower eigenmodes for this equation are de-localized and essentially hide the higher modes, which are of interest. The talk will discuss and compare the operators corresponding to the quantum and classical equations and describe a technique to use the localization landscape method with the acoustic operator.
1. M. Filoche and S. Mayboroda (2012) Universal mechanism for Anderson and weak localization. Proceedings of the National Academy of Sciences, 109(37)
2. D. Colas et al. (2022) Crossover between quantum and classical waves and high-frequency localization landscapes. Physical Review B, 106(18)
Biography: After engineering studies in France and Spain, Régis Cottereau obtained his PhD in numerical mechanics from Ecole Centrale Paris (France) in 2007 and performed post-doctoral research at BarcelonaTech. He was recruited as a CNRS research professor in 2008, and worked for 10 years at Laboratoire de Mécanique des Sols, Structures et Matériaux, in the south of Paris. In 2012-2013, he did a sabbatical in the High Performance Computing team at Universidade Federal do Rio de Janeiro (Brazil), and finally moved, in 2018, to Laboratoire de Mécanique et Acoustique, in Marseille. Régis works in the general field of wave propagation in heterogeneous media, with a particular focus on random media. His tools are both numerics and analysis, in particular asymptotic analysis and homogenization. Applications of interest include railway-induced vibrations and seismic engineering.
Seminar 12 -S3: Ultra-sensitive Plasmonic Biosensors based on Two-Dimensional NanoMaterials
Speaker: Shuwen Zeng (CNRS, L2n-UTT, France)
Abstract: Surface plasmon resonance sensors are commonly used an effective tool for real-time monitoring biomolecular interactions. The sensing mechanism is based on the evanescent field perturbation at the metallic sensing substrate induced by the binding of chemical and biological molecules. Molecular binding interactions could be measured from the signal of reflected light, under the condition that the surface plasmon resonance is excited by the incident light. In this talk, I will present the use of hybrid 2D nanomaterials-based metasurface nanostructure as an enhanced sensing substrate. The thickness of the plasmonic sensing substrate is tuned in an atomic scale and optimized to improve the sensing capability. Here, both a sharp phase signal change and phase-related Goos-Hänchen signal shift were achieved due to the strong resonance at the surface of the sensing film. The enhanced plasmonic sensitivities of 2D nanostructures were systematically investigated. It is worth noting that the tunability of atomic layer led to the sensing substrate optimized with a narrow scale < 1 nm. Through a precise engineering of the metasurface substrates, 3 orders of magnitude improvement of the sensitivity were demonstrated compared to the one with pure gold sensing substrate. This hybrid 2D nanomaterial-based metasurfaces would provide a good opportunity for developing portable theranostic devices in clinical applications.
Biography: Dr. Shuwen ZENG is currently a tenured CNRS academic researcher (Chargée de Recherche CNRS) at French National Centre for Scientific Research (CNRS), France. She has been awarded EU Marie Skłodowska-Curie Individual Fellow in 2018 with Photonics department at XLIM Research Institute, CNRS. She also worked as a research fellow at CNRS-International-NTU-THALES Research Alliance (CINTRA)/UMI 3288, Singapore from 2014 to 2018. Before that, she received the Ph.D. degree from the School of Electrical and Electronic Engineering at Nanyang Technological University, Singapore. Her main research interests focus on engineering optical micro-/nanostructures-based ultrasensitive chemical and biological sensors. Dr. Zeng is a member of the IEEE Photonics Society (IPS) and the Optical Society of America (OSA). She also currently serves as the main chair of Pacific Rim Conference on Lasers and Electro-Optics (CLEO Pacific Rim) and the IEEE Optoelectronics Global Conference (OGC) Technical Program Committees. She is also the associate editor of Sensors Journal and Journal of Frontiers of Nanophotonics in Biomedical Engineering. Dr. Zeng has published more than 60 peer-reviewed papers (Chemical Reviews, Chemical Society Reviews, Advanced Materials, Small, etc.) and contributed over 25 conference talks (CLEO, SPIE, ICMAT, etc.).
Seminar 11 -S3: Topological Metasurfaces
Speaker: Patrice Genevet (Université Côte d’Azur, Centre de Recherche sur l’Hétéro-Epitaxie et ses Applications (CRHEA), CNRS, Valbonne, France)
Abstract: Research on topological photonics has considerably grown, transferring condensed matter concepts of topological insulators with the discovery of the integer Quantum-Hall effect into the realm of photonics. Today, nanophotonics, which is related to light manipulation with subwavelength objects, offers new opportunities to address light properties. New degrees of freedom in the design of optical components are attained by considering the response of topological nanostructures. So far, optical metasurfaces, made of subwavelength arrangements of nanostructures, have relied on resonant phase scattering occurring in Mie resonators or ultrathin pillars. Full wavefront control requires finding sets of nanostructures that can provide 2π optical phase retardation on the incoming beam. Ultimately, and despite all the efforts in understanding the physical mechanisms leading to optimal designs, including powerful optimization methods, metasurface designs often require witless numerical parameter searches. Relying on symmetry-breaking arguments and topological properties of the associated non-Hermitian matrices representing the metasurfaces, we provide new guidelines for achieving 2π phase coverage in transmission and reflection. This framework allows us to unravel the physical principles underlying Huygens metasurfaces, showing that it exploits degeneracies of transmission- or reflection-matrices Zeros, so-called exceptional points, corresponding to transmissionless and reflectionless states. Overall, symmetry-breaking leading to a displacement of a Zero-Pole pair with its branch cut crossing the real axis, provides a very intuitive design approach for achieving full resonant phase scattering. Encircling EPs and/or zeros in the nanostructure parameter space to provide full 2π-phase are considered, entrusting metasurfaces and flat optics with additional light modulation schemes. Our results explain the importance of topological defects and how they can be manipulated for achieving realistic and insightful metasurface designs.
Biography: Patrice Genevet obtained his PhD at University of Nice Sophia Antipolis in France on localized spatial solitons in semiconductor lasers and amplifiers. After his PhD, he did five years of postdoctorate fellowship (2009-2014) in the Capasso group (SEAS, Harvard University) in collaboration with Prof. Scully (Texas A&M University). In 2014, he obtained the position of senior research scientist at A*STAR, Singapore. In 2015, He joined CNRS as ‘Chargé de Recherche de Première classe’. He is the recipient of several awards, including the Highly Cited Researcher by the Web of Science every year since 2018, the ERC starting Grant 2015 on Functional flat optical components and applications, the ERC Proof of Concept 2019, the Aimé-Cotton Price 2017 from the French Optical Society, and the Fabry-de Gramont price from the French optical Society. He serves as an associate editor for Optics Letters and Science Advances. P. Genevet research activities concern the development of optical metasurfaces for sensing, imaging, and LiDAR applications. He owns 6 patents, more than 100 publications and a H factor of 48 (Google Scholar).
Seminar 10 -S3: Topology optimization of electromagnetic metamaterials
Speaker: Benjamin Vial (Imperial College London, UK)
Abstract: In recent years, technological advances in nanofabrication have opened new application in the field of photonics. To engineer and develop novel functionalities, rigorous and efficient numerical methods are required. In parallel, tremendous advances in algorithmic differentiation, in part pushed by the intensive development of machine learning and artificial intelligence, have made possible large scale optimization of devices with a few extra modifications of the underlying code. In this presentation I will outline the concepts behind auto-differentiation and give details about topology optimization algorithms. I will present various examples of application in Electromagnetism and metamaterials, such as cloaking and illusion devices. Finally, I will detail the development of three different software libraries for the resolution of Maxwells equations: a Finite Element code with high level interface for problems commonly encountered in photonics, an implementation of the Fourier Modal Method for multilayered bi-periodic metasurfaces and a Plane Wave Expansion Method for the calculation of band diagrams in two dimensional photonic crystals. All of them are endowed with automatic differentiation capabilities and typical inverse design examples will be presented.
Biography: I received the Master’s degree in Engineering from Centrale Marseille (Marseille, France) and the Master’s degree in Physics from Aix Marseille University (Marseille, France) in 2009. I then joined Fresnel Institute, CNRS (Marseille, France) where I pursued a PhD in collaboration with the company Silios Technologies (Peynier, France). This joint project dealt with the theoretical, numerical and experimental study of electromagnetic metamaterials using a modal approach and their application to infrared multispectral filtering. I received my PhD for this work from Centrale Marseille in April 2013. I then joined the Antennas and Electromagnetics research group at Queen Mary, University of London (London, UK) in July 2014, as part of the QUEST project. My work focused on topology optimization techniques for the design of invisibility cloaks and novel metamaterial based devices with specific electromagnetic properties. Since August 2022, I am a Research Assistant in Imperial College London, working in the Department of Mathematics, where I am working on mechanical metamaterials for energy harvesting.
My research is mainly focused on wave physics including metamaterials, Transformation Optics, homogenization techniques, resonant phenomena, light-matter interaction, scattering, diffraction, modal analysis, and topology optimization, for applications in Photonics and Mechanics.
Seminar 9 -S3: Holographic metasurfaces for the new generation of biomedical ultrasound applications
Speaker: Noé Jiménez (Instituto de Instrumentación para Imagen Molecular – i3M, CSIC – Spanish Research Council)
Q & A:
Abstract: Optical holograms can modulate light wavefronts to generate visible images. In the same way, acoustic images can also be synthesized by holograms, shaping the areas where mechanical waves present a high amplitude, and areas where the media is at rest. In this work, we present the recent advances of acoustic holograms and structured media to engineer the acoustic wavefront to focus ultrasound beams for biomedical applications. We show how we can engineer ultrasonic wavefronts by using acoustic metasurfaces. This results in complex holographic lenses, or acoustic holograms, that can shape therapeutical acoustic images for the non-invasive treatment of neurological disorders, to produce cavitation patterns for localized drug delivery, and uniform thermal patterns of arbitrary shape for targeted hyperthermia. In this way, acoustic holograms emerge as a disruptive and low-cost approach for biomedical ultrasound applications in neurology, including blood-brain barrier opening for localized drug-delivery or neuromodulation using low-cost systems. In addition, increasing the temperature using low-cost and MRI-compatible holographic transducers might be of great interest for many biomedical applications, such as ultrasound hyperthermia, physiotherapy, or high intensity focused ultrasound, where the control of specific thermal patterns is needed.
Biography: Noé Jiménez, Ph.D. in Acoustics from the Universitat Politècnica de València, (Spain) in 2015. Noé Jiménez is currently “Ramón y Cajal” Fellow (tenured) at Spanish Research Council. In 2015 he joined the CNRS (UMR6613, France) for a post-doctoral position to research on acoustic metamaterials and in 2017 he joined the Institute of Instrumentation for Molecular Imaging as a “Juan de la Cierva” post-doctoral fellow to research on ultrasonic metamaterials for biomedical applications. He has been visiting researcher at Columbia University (NY, USA) and at the University of Salford (Manchester, UK). He was awarded by the Spanish Royal Society of Physics in 2019 for his scientific contribution to transcranial ultrasound propagation using acoustic holograms. He is the author of 5 patents in the field of biomedical applications of ultrasound, published 44 JCR papers, edited 2 complete books, and 7 book chapters, and participated in more than 200 conferences. He teaches at the Applied Physics department of the Universitat Politècnica de València. His research interests concern from fundamental research in mechanical waves in complex and artificially structured media such as metamaterials, to its application for innovative biomedical ultrasound techniques.
Seminar 8 -S3: Denoising of radar images by AI.
Speaker: Ronald Aznavourian (Institut Fresnel, Marseille, France)
Abstract: A lot of applications are possible with AI: classification, to sort a lot of images in many different categories, denoising, to improve the quality of a signal or an image, and “generative”, to create a fake image which seems to be very real. Here, I propose to use an autoencoder to denoise radar images. In order to achieve this, I first propose to create an adequate dataset of 60,000 images to train the autoencoder.
Biography: Ronald’s background is mainly in computer science. He graduated from an engineering school in networks, systems and multimedia and worked on morphing applied to numerical simulations during his engineering thesis. He is now a PhD student, in the third year of his thesis, in the field of image processing, under the supervision of Julien Marot, at the Institut Fresnel. He uses AI, and more particularly neural networks to denoise images, as well as bio-inspired single-objective optimization methods, such as the Grey Wolf Optimizer (GWO), or multi-objective optimization methods based on Genetic Algorithms, such as the Non-dominated Sorted Genetic Algorithm-II (NSGA-II) to optimize neural networks or even invisibility cloaks.
Seminar 7 -S3: First lecture on micropolar chiral elasticity
Speaker: Yi Chen (Karlsruher Institut für Technologie, Germany)
Abstract: In this lecture, I will introduce some basics of micropolar continuum elastic theory and its applications to the continuum modeling of chiral elastic metamaterials. Due to mirror symmetry breaking, chiral elastic metamaterials can exhibit interesting properties impossible within achiral ones, such as static push-to-twisting coupling and dynamic chiral phonons or acoustical activity. With the examples, one can see micropolar continuum theory can correctly describe the above behavior as well as related size effects. In traditional chiral metamaterials, mostly with cubic symmetry, chiral phonons and acoustical activity are allowed only along several phonon propagation directions. Chiral elastic metamaterials that support isotropic chiral phonons are preferred in practical applications. Here, chiral elastic metamaterials with isotropic properties are designed based on quasicrystalline lattice and periodic cubic lattice. Both designs are verified numerically by phonon band structure calculations.
Biography: Yi Chen received his B.S. and Ph.D. degrees in Solid Mechanics from Beijing Institute of Technology in 2012 and 2018, respectively. He then worked as a Postdoctoral Fellow in Beijing Institute of Technology. Since September 2019, he joined in Prof. Martin Wegener’s group at Institute of Applied Physics, Karlsruhe Institute of Technology (KIT), Germany, as a Humboldt Postdoctoral Researcher.
His current research includes acoustic/elastic metamaterials, topological materials, micropolar elasticity theory, metamaterials with nonlocal interactions. He has over 20 papers published in mechanics/physics/material journals, including Nature Communications, Science Advances, Physical Review Letters, Journal of The Mechanics and Physics of Solids, etc.
Seminar 6 -3: Bending waves in quasiperiodic beams and plates
Speaker: Bart Van Damme (Empa – Materials Science and Technology, Swiss)
Q & A:
Abstract: Flexural waves in slender structures, beams or plates, take an important place in engineering applications since they are easily excited and play a dominant role for noise generation. The reduction of flexural motion is an old problem, be it for building materials, automotive applications, or precision instruments. The vast majority of metamaterial studies in the vibroacoustic domain is aiming at vibration reduction of one- and two-dimensional structures. Their models are very often based on the periodicity assumption, giving physical insights with minimal calculation power. However, nature shows us that materials without translational symmetry in their structure can give rise to exotic wave scattering behaviour, very similar to Bragg scattering but with different rotational symmetries leading to 5- and 10-fold diffraction patterns. At the same time, Penrose showed mathematically that planes can be filled with combinations of a limited number of polyhedra in a fully aperiodic way. Despite the absence of any translational periodicity, these structures are uniquely defined and have recognizable local rotational symmetries. They are therefore called quasicrystals. We present two examples of bending waves in quasicrystalline structures, both numerical and experimental. The first case shows unexpected low-frequency band gaps in beams with two periodic arrays of slits. The scattering of bending waves due to the aperiodic changes in bending stiffness results in interaction between the two periodic Bragg band gaps. The second example shows the formation of band gaps and localized modes in a quasicrystal plate dressed with scatterers in a Penrose pattern. Band gaps occur at lower frequencies than in a periodic array of scatterers with the same density, but is therefore less efficient. In both cases the structures showcase areas with low and high vibrational amplitudes, a fact that might be exploited to lead high energy concentrations away from critical points.
Biography: Bart has a masters degree in physical engineering. He got his PhD in physics in 2011, investigating nonlinear elastic waves for nondestructive testing. He is currently a member of the Laboratory for Acoustics/Noise Control at Empa, the Swiss Federal Laboratories for Materials Science and Technology. He investigates dynamic properties and elastic wave propagation in complex materials and structures. Examples are engineered wood materials for musical instruments or lightweight construction, new materials to abate railway noise, or the design and practical implementation of metamaterials with optimized isolating and absorbing properties. He teaches Engineering Acoustics at ETH Zurich and is currently co-supervising several master and PhD students.
Seminar 5 -S3: Willis couplings in one-dimensional and quasi-one-dimensional acoustic systems
Speaker: Jean-Philippe Groby (CNRS, LAUM – Laboratoire d’Acoustique de l’Université du Mans, France)
Q & A:
Abstract: Since the seminal work of Willis in the 80’s, the eponymous materials have received an increasing attention, because of their analogy with bi-isotropic/anisotropic electromagnetic metamaterials. The Willis coupling parameters couple the potential and kinetic energy in the acoustic conservation relations, therefore enhancing the ability to control waves in metamaterials compared to other materials that do not exhibit such coupling. In this talk, I will present a general method to derive the closed form expressions of the effective properties, including the Willis coupling, of asymmetric and nonreciprocal one dimensional acoustic systems. This method relies on the Pade’s approximation of the matrix exponential, the latter being nothing but the transfer matrix that may relate the state vectors at both sides of a unit cell. The effective properties of various one-dimensional asymmetric resonant systems are first derived, numerically and experimentally validated, and analyzed. The nonlocal feature of the Willis coupling is then investigated in a simple fluid laminate system. The asymmetric and nonreciprocal Willis couplings are finally analytically derived and discussed in a system constituted of a periodic arrangement of thermoacoustic amplifiers.
Biography: Jean-Philippe Groby is CNRS research director at the Acoustics Laboratory of Le Mans University. He holds an Engineering degree from École Centrale de Marseille (École Supérieur d’Ingénieurs de Marseille), a M.Sc. in Acoustics, and a Ph.D. in Mechanical Engineering (2005) from the University of the Mediterranean Aix-Marseille II. He has been a post-doctoral fellow in KULeuven, École Polytechnique (CMAP, UMR CNRS 7641), Supélec (L2S, UMR CNRS 8506), and IEMN (UMR CNRS 8520). His research focuses on acoustic waves in complex and structured media, as well as in metamaterials. He has been actively involved in the professional life of the acoustic community in Europe, notably serving as a chair of the COST Action DENORMS CA 15125. He is currently chair of the EAA Technical Committee on Acoustic Materials.
Seminar 4 -S3: Latent symmetries: An introduction
Speaker: Malte Röntgen (Universität Hamburg, Germany)
Q & A:
Abstract: In this talk, I will give an introduction to the emerging topic of latent symmetries. A latent symmetry is in general not apparent from a geometric inspection of the system. Instead, it becomes visible after a suitable dimensional reduction: The so-called isospectral reduction, which is akin to an effective Hamiltonian. As I will show in this talk, latent symmetries can lead to very interesting phenomena, including the induction of local symmetries on the system’s eigenstates or even degeneracies in the eigenvalue spectrum. Their study thus allows to gain knowledge about the system’s structure that remains hidden from a direct observation. The concept is exemplified through several wave-physical examples.
M. Röntgen et al. (2021) Latent Symmetry Induced Degeneracies. Physical Review Letters, 126(18)
M. Röntgen et al. (2022) Hidden symmetries in acoustic wave systems. arXiv
C. Morfonios et al. (2021) Cospectrality preserving graph modifications and eigenvector properties via walk equivalence of vertices. Linear Algebra and its Applications, 624
C. Morfonios et al. (2021) Flat bands by latent symmetry. Physical Review B, 104(3)
M. Röntgen et al. (2021) On symmetries of a matrix and its isospectral reduction. arXiv
Biography: Malte Röntgen studied Physics in Kiel and Hamburg. He did his PhD at the Centre for Optical Quantum Technologies in Hamburg, where he currently works as a Post-Doc.
Seminar 3 -S3: Time-modulated composites: some recent results on field-pattern materials
Speaker: Ornella Mattei (Department of Mathematics, San Francisco State University, USA)
Q & A:
Abstract: Field patterns are a new type of wave propagating in one-dimensional linear media with moduli that vary both in space and time [1, 2, 3]. Specifically, the geometry of these space-time materials is commensurate with the slope of the characteristic lines so that a disturbance does not generate a complicate cascade of subsequent disturbances, but rather concentrates on a periodic space-time pattern, that we call field pattern. Field patterns present spectacularly novel features. One of the most interesting ones is the appearance of a wave generated from an instantaneous source, whose amplitude, unlike a conventional wake, does not tend to zero away from the wave front. Furthermore, when the parameters of the material are suitably chosen, so that the condition of PT-symmetry is unbroken, the wavefront propagates maintaining the same amplitude. This is particularly remarkable if one observes that, due to the instantaneous time modulation, energy is not conserved but it increases exponentially in time.
In this talk, we will explain how stable modes that do not blow up in time, even though the associated energy does, can be generated by suitably designing the spatial geometry of the composite, which must be related to the periodicity of the time modulation as well as the material properties. We will start from the classical results for the one-dimensional case, obtained in [1, 2, 3] in collaboration with Graeme W. Milton. Then, we will extend such design concepts to the two dimensional case and show the most recent results obtained in collaboration with Vincenzo Gulizzi.
Biography: Ornella Mattei has been an Assistant Professor in the Department of Mathematics at San Francisco State University since 2019. She received her PhD in Methods and Mathematical Models for Engineering from the University of Brescia, Italy, in 2016, under the guidance of Angelo Carini (University of Brescia) and Graeme W. Milton (University of Utah). Before moving to San Francisco, she was a Postdoctoral Researcher in the Department of Mathematics at the University of Utah. She has broad interests in the Mathematics of Materials Science, with special emphasis on composites and electromagnetics.
Seminar 2 -S3: Metamaterials for Medical Ultrasound
Speaker: Chengzhi Shi (GWW School of Mechanical Engineering, Georgia Institute of Technology, Atlanta)
Q & A:
Abstract: The development of acoustic metamaterials and the resulted manipulation of ultrasound wave propagation have led to many important technologies that can potentially be applied in medical diagnostics and therapy such as transcranial ultrasound, enhanced cavitation effect for histotripsy and thrombolysis, and noninvasive kidney stone management. In this talk, we will focus on two metamaterial applications in medical imaging and therapy: transcranial imaging enabled by non-Hermitian complementary acoustic metamaterial (NHCMM) and fast sonothrombolysis through vortex ultrasound induced shear stress. High-resolution transcranial imaging using noninvasive high-frequency ultrasound is challenging due to the impedance mismatch between skull and soft tissues and the intrinsic loss because of the porous skull. The development of active NHCMM can compensate the transmission loss resulting from both effects simultaneously that enhances transcranial transmission for high-resolution imaging. For the treatment of blood clots, sonothrombolysis has been demonstrated to be effective. However, the treatment usually last for more than 15 hours when treating large clot, which is undesirable for the patient and surgeon and can sometimes before life threatening for severe cases of cerebral venous sinus thrombosis (CVST). The active metasurface generated vortex ultrasound induces contactless shear stress in the blood clot that drastically enhances fibrinolysis in blood clots that remarkably reduce the required treatment time with low risk of hemorrhage, especially in treating large, completely occluded, acute clots. Such capability makes the vortex ultrasound based endovascular sonothrombolysis a life-saving tool for severe cerebral venous sinus thrombosis, which has an increasing trend among young patients due to the COVID-19 pandemic.
Biography: Dr. Chengzhi Shi is an Assistant Professor in the George W. Woodruff School of Mechanical Engineering at Georgia Institute of Technology. He is also a program faculty of Bioengineering, Parker H. Petit Institute for Bionengineering and Bioscience, and Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech. Before joining Georgia Tech, Dr. Shi earned his Ph.D. degree from the University of California, Berkeley in 2018 and his M.S. and B.S. degrees from Shanghai Jiao Tong University in 2013 and 2010. His research interests include physical acoustics, wave propagation, metamaterials, ultrasound imaging, and therapeutic ultrasound. He has published many highly cited papers in prestigious journals including Science, PNAS, and Nature Communications. Dr. Shi has won prestigious awards including NSF CAREER and ONR YIP awards.
Seminar 1 -S3: Beyond the limitations of passive acoustic metamaterials using dispersion engineering and complex frequency excitations
Speaker: Andrea Alù (City University of New York)
Q & A:
Abstract: In this talk, we discuss our latest results on acoustic metamaterials, in which we theoretically introduce and experimentally demonstrate complex dispersion engineering of acoustic waves on elastic metamaterials, and excitation at complex frequencies to realize virtual absorption and virtual gain. Our results open new avenues for sound manipulation using metamaterials, going beyond conventional limits. We will discuss the basic principles behind the described phenomena and the implications for technologies.
Biography: Andrea Alù is a Distinguished Professor at the City University of New York (CUNY), the Einstein Professor of Physics at the CUNY Graduate Center, and the Founding Director of the Photonics Initiative at the CUNY Advanced Science Research Center. He received his Laurea (2001) and PhD (2007) from the University of Roma Tre, Italy, and, after a postdoc at the University of Pennsylvania, he joined the faculty of the University of Texas at Austin in 2009, where he was the Temple Foundation Endowed Professor until Jan. 2018. Dr. Alù is a Fellow of NAI, AAAS, IEEE, MRS, OSA, SPIE and APS, and has received several scientific awards, including the Blavatnik National Award in Physics and Engineering, Dan Maydan Prize in Nanoscience, the IEEE Kiyo Tomiyasu Award, the Vannevar Bush Faculty Fellowship from DoD, the ICO Prize in Optics, the NSF Alan T. Waterman award, the OSA Adolph Lomb Medal, and the URSI Issac Koga Gold Medal.