Seminar 13-S2, Tuesday 25 January 2022, 14:00 (London Time)

Speaker: Marc Dubois (Mutliwave Imaging SAS, France)

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Title: MRI metamaterial

Abstract: Magnetic resonance imaging (MRI) relies on a precise control of spin magnetic moments in the body tissues. To achieve such control, one needs to induce a uniform radiofrequency (RF) magnetic field flux (B1+) across the imaged volume. In 7T MRI scanners, the proton (1H) Larmor frequency reaches 300 MHz. Due to the high relative permittivity of human tissues, the associated RF wavelength can shrink down to 11 cm, which is comparable to the dimensions of some human organs. Consequently, spatially varying phase and amplitude of the RF fields generate signal inhomogeneities across the image. For head imaging, signal losses become strongly visible in the temporal lobes and cerebellum regions of the brain.
Different approaches have been implemented to improve B1+ field uniformity of transmit coils such as passive and active RF shimming. Active RF shimming is based on coils with multiple independently controllable transmit elements or channels. These additional degrees of freedom can be exploited to mitigate B1+ inhomogeneities. But, it raises challenges in terms of workflow and patient safety (specific absorption rate). In contrast, passive RF shimming relies on the insertion of passive structures between the subject and the coil. Devices based on high-permittivity dielectric materials and/or metamaterials have seen strong developement in the past years. Induced currents (displacement or conduction currents) generate a secondary RF field that corrects the initial B1+ field. This talk will review some of the achievements and remaining challenges of RF passive shimming in high field MRI applications.

Biography: Marc joined Multiwave Imaging from the French National Research Agency laboratory Institut Fresnel in 2020. Prior to assuming the role of CEO, he led research and development activities for Multiwave Imaging with a focus on developing MRI devices that would drastically improve standards of care in hospitals and clinics around the world.
Marc completed his PhD at Institut Langevin in Paris at Université Paris Diderot-Paris VII and was later trained in world leading laboratories on wave control and metamaterials including at University of California, Berkeley where he spent 2 years as a post-doctoral researcher.
Upon his return to France, he first joined the renowned French National Research Agency laboratory Institut Fresnel where he combined his knowledge of metamaterials with his deep interest in magnetic resonance imaging. With funding from consecutive European projects of excellence in MRI, he joined the Center of Magnetic Resonance in Biology and Medicine (CRMBM) where he honed his skills in MRI across all magnetic field strengths.

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Seminar 14-S2, Tuesday 01 February 2022, 14:00 (London Time)

Speaker: Alice Vanel (ETH Zurich, Switzerland)

Title: TBA

Abstract:

Biography: tba

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Seminar 15-S2, Tuesday 08 February 2022, 14:00 (London Time)

Speaker: Guoliang Huang (Structured Materials and Dynamics Laboratory, Mizzou Engineering, USA)

Title: TBA

Abstract:

Biography: tba

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Seminar 16-S2, Tuesday 15 February 2022, 14:00 (London Time)

Speaker: Jean-François Semblat (ENSTA Paris | Institut Polytechnique de Paris & IMSIA | Institute of Mechanical Sciences and Industrial Applications, France)

Title: Wave-structures interaction due to earthquakes: from the local to the global scale

Abstract:

Biography: tba

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Seminar 17-S2, Tuesday 22 February 2022, 14:00 (London Time)

Speaker: Mário Silveirinha (Instituto Superior Técnico, University of Lisbon, Portugal)

Title: TBA

Abstract:

Biography: tba

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Seminar 18-S2, Tuesday 01 March 2022, 14:00 (London Time)

Speaker: Simon Horsley (Department of Physics and Astronomy, University of Exeter, UK)

Title: TBA

Abstract:

Biography: tba

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Seminar 20-S2, Tuesday 15 March 2022, 14:00 (London Time)

Speaker: Martin van Hecke (Università degli Studi di Cagliari, Italy)

Title: Metamaterials that Compute

Abstract: Collections of two-state hysteretic elements called hysterons describe the intricate pathways, hysteresis loops and memory effects observed in crumpled sheets and amorphous media. Such hysterons also naturally arise in many mechanical metamaterials and are then associated with buckling and snapping. Here we bridge these two fields, and explore, in experiments on corrugated sheets, on metamaterials, and in models, the pathways that these systems exhibit. In particular, we show that
interactions between hysterons make these systems process information, and show examples of elementary mechanical computations such as counting.

Refs: M.van Hecke, PRE 104, 054608 (2021)
H. Bense and M van Hecke, PNAS 118 e2111436118 (2021)

See also: www.universiteitleiden.nl/a-computer-made-of-floppy-rubber 

Biography: Martin van Hecke is a group leader at AMOLF, Amsterdam, and a professor of physics at Leiden University. Since 2011, his research has focussed on mechanical metamaterials, from patterned elastic media to origami. In particular he has developed new design techniques to make complex metamaterials that straddle the boundary between material and machine, and that form complex patterns or can self-fold when compressed. He is a fellow of the APS and was awarded an ERC-advanced grant in 2021. He is now exploring if and how complex materials – from metamaterials to crumpled sheets – can store and process information.

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Seminar 22-S2, Tuesday 29 March 2022, 14:00 (London Time)

Speaker: Michalis Vassiliou (Department of Civil, Environmental and Geomatic Engineering (DBAUG), ETH Zürich)

Title: TBA

Abstract:

Biography: tba

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Seminar 23-S2, Tuesday 05 April 2022, 14:00 (London Time)

Speaker: Rémi Carminati (Institut Langevin, ESPCI Paris, PSL University, France)

Title: TBA

Abstract:

Biography: tba

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Seminar 24-S2, Tuesday 12 April 2022, 14:00 (London Time)

Speaker: Carsten Rockstuhl (Karlsruhe Institute of Technology, Institute of Theoretical Solid State Physics, Germany)

Title: A T-matrix approach to describe them all: materials, metamaterials, and metasurfaces

Abstract: A T-matrix, also called transition matrix, expresses how an object converts an incident into a scattered field. The object can be classical, like a traditional scatterer for which the T-matrix can be obtained from Maxwell’s equations, or a molecule, which prompts a quantum-chemical treatment to capture its T-matrix. When combined with a renormalization of the T-matrix upon periodically arranging the object, many properties can be analytically expressed. Examples of such properties aee effective material parameters or expressions of how a metasurface diffracts light. Both can be used to design optical materials inversely. In this contribution, I describe the latest developments along these lines and emphasize the combined consideration of ordinary molecular materials and materials.

Biography: Carsten Rockstuhl received a Ph.D. degree from the University of Neuchâtel, Switzerland, in 2004. After a PostDoc period at AIST in Tsukuba, Japan, he has been since 2005 with the Friedrich Schiller University Jena, Germany. In 2013, he was appointed full professor at the Karlsruhe Institute of Technology, Karlsruhe, Germany. He is heading groups at the Institute of Theoretical Solid State Physics and the Institute of Nanotechnology. His research interests cover many aspects in the context of theoretical and computational nano-optics. He works on nanostructured photonic materials, plasmonics, scattering theory, integrated photonics, quantum optics, and nonlinear photonics.

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Seminar 27-S2, Tuesday 03 May 2022, 14:00 (London Time)

Speaker: Chengzhi Shi (George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta)

Title: TBA

Abstract:

Biography: tba

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