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Immersive experimentation for realizing metamaterials, focusing functions and space-time transformations

English title Immersive experimentation for realizing metamaterials, focusing functions and space-time transformations
Applicant van Manen Dirk-Jan
Number 197182
Funding scheme Project funding
Research institution Institut für Geophysik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geophysics
Start/End 01.04.2021 - 31.03.2025
Approved amount 455'068.00
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Keywords (9)

Elastic; Scattering; Metamaterials; Inverse; Acoustic; Focusing; Waves; Boundary; Experimentation

Lay Summary (German)

Lead
In immersiven Wellenexperimenten wird ein akustisches oder elastisches physisches Experiment in eine numerische Umgebung eingebettet. Wellen können sich nahtlos von der physischen Domäne in die numerische Umgebung und umgekehrt ausbreiten. Die Interaktion zwischen beiden Domänen wird durch immersive Randbedingungen (IBC) gesteuert und erfolgt in Echtzeit unter Verwendung von Hunderten von Aktuatoren und Sensoren, welche über ein Hochleistungssteuersystem verbunden sind. IBCs können beliebige Randbedingungen und äußere Umgebungen projizieren. Sie werden zum Beispiel verwendet, um Wellenexperimente bei viel niedrigeren Frequenzen als bisher möglich durchzuführen. Wir schlagen vor, die Fähigkeit von IBCs zu nutzen um beliebige Randbedingungen an den Grenzen eines physischen Experiments zu erzeugen und so Metamaterialien zu realisieren und zu charakterisieren.
Lay summary
Metamaterialien sind Materialien mit technischen Eigenschaften, die in der Natur nicht zu finden sind. Die Forschung auf diesem Gebiet hat sich zuvor beispielsweise auf die Bestimmung der Subwellenlängenstruktur konzentriert um neuartiger Geräte wie akustische Unsichtbarkeitsumhänge, perfekte Linsen und perfekt absorbierender Oberflächen zu konstruieren. Die physikalische Realisierung bestimmter Arten von Metamaterialien, wie z. B. Paritätszeit-symmetrischen Materialien, bleibt jedoch eine Herausforderung und experimentelle Demonstrationen beschränken sich häufig auf 1D. Wir verwenden die Methoden und Einrichtungen, die für immersive Wellenexperimente entwickelt wurden, um allgemeine phononische und PT-symmetrische Metamaterialien in 3D zu realisieren. Wir schlagen auch vor, das niedrig-Latenz Hochleistungssteuersystem und die große Anzahl von Sensoren und Aktuatoren in einer geschlossenen Rückkopplungsschleife für Volumenwellensteuerung zu verwenden. Hierbei ist das primäre Ziel, mithilfe der Volumensteuerung nichtperiodische Zeitmaterialien durch sprunghafte Änderungen (in der Zeit) der effektiven Materialeigenschaften zu realisieren. 
Direct link to Lay Summary Last update: 17.02.2021

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Associated projects

Number Title Start Funding scheme
178342 Exhibition: Waves across the scales 01.04.2018 Agora

Abstract

In immersive wave experimentation, an acoustic or elastic physical experiment is immersed in a numerical environment such that waves propagate seamlessly from the physical domain into the numerical environment and vice-versa. The interaction between both domains is governed by an immersive boundary condition (IBC) and takes place in real-time, using hundreds of sources and sensors connected through a low-latency high-performance control system. IBCs can project arbitrary boundary conditions and exterior environments and are presently used to enable laboratory wave experimentation at much lower frequencies than was possible previously. We propose to use the ability of IBCs to impose arbitrary boundary conditions on a physical experimentation domain for the realization and characterisation of certain types of metamaterials. Metamaterials are materials with engineered properties that cannot be found in nature. Research in this field has previously focused on, e.g., determining sub-wavelength structure to produce effective material properties that can be characterized as having negative dynamic density and/or bulk modulus. This has led to the conception of such novel devices as acoustic cloaks, perfect lenses, and perfectly absorbing surfaces. However, the physical realization of certain types of metamaterials, such as parity-time (PT) symmetric materials, remains challenging and demonstrations are often limited to 1D. We use the methods and facilities developed for immersive wave experimentation, to implement general phononic and PT-symmetric metamaterials in 3D. We also propose to leverage the ability to control a large number of actuators in response to data from a large number of sensors, with low latency and in a closed feedback loop, for volumetric wave control. Our primary goal here is to use volumetric control to realize non-periodic time-materials, by being able to effect step-like changes in effective material properties. Wave scattering in such materials, at temporal discontinuities, is simpler than that at spatial discontinuities due to causality, which prevents reflection into the past. A recently proposed space-time cross-mapping method exploits this asymmetry to simplify the computation of scattered waves in space-varying environments. The method cross-maps space and time coordinates, allowing for the treatment of scattering at spatial discontinuities as scattering at temporal discontinuities. By identifying the wavefields obtained through the cross-mapping method as the so-called focusing functions appearing in data-driven geophysical imaging, a link between single-sided inverse scattering and wave propagation in time materials is established and then further explored. This makes it possible, for instance, to physically «compute» solution wavefields for the single-sided inverse scattering problem by conducting forward scattering experiments. Furthermore, as these space-time transformations reduce computational complexity, computationally cheaper methods can be developed and brought to bear on the single-sided inverse scattering problem. Finally, the use of focusing functions for full-waveform, single-sided imaging is investigated in this proposal. Since focusing functions are fully consistent with multiple scattering in the true medium, as well as form a complete dataset, the up- and downgoing parts of the focusing function can be jointly imaged using two-way methods without fear that the missing, transmitted part of the field negatively influences the imaging.The current proposal thus combines a mixture of experimental and theoretical work and leverages unique facilities to deliver a general framework for the characterisation and realization of phononic and PT-symmetric materials in 3D. It establishes new methods for computing focusing functions, as well as novel methods for imaging them. Finally, it links wave propagation in time-materials to single-sided inverse scattering, enabling physical computation of solution wavefields. All the proposed approaches are spatially and temporally broadband.
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