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Role of Nanophotonics in the Birth of Seismic Megastructures Stéphane Brule, Stefan Enoch, Sebastien Guenneau

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Role of Nanophotonics in the Birth of Seismic Megastructures Stéphane Brule, Stefan Enoch, Sebastien Guenneau Role of nanophotonics in the birth of seismic megastructures Stéphane Brule, Stefan Enoch, Sebastien Guenneau To cite this version: Stéphane Brule, Stefan Enoch, Sebastien Guenneau. Role of nanophotonics in the birth of seismic megastructures. Nanophotonics, Walter de Gruyter, 2019, 8 (10), pp.1591-1605. 10.1515/nanoph- 2019-0106. hal-02399050 HAL Id: hal-02399050 https://hal.archives-ouvertes.fr/hal-02399050 Submitted on 8 Dec 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Distributed under a Creative Commons Attribution| 4.0 International License Nanophotonics 2019; 8(10): 1591–1605 Review article Stéphane Brûlé, Stefan Enoch and Sébastien Guenneau* Role of nanophotonics in the birth of seismic megastructures https://doi.org/10.1515/nanoph-2019-0106 Received April 8, 2019; revised July 6, 2019; accepted July 6, 2019 1 Introduction: birth of a new era for metamaterials Abstract: The discovery of photonic crystals 30 years ago in conjunction with research advances in plasmonics and One may wonder what is the link between seismic megas- metamaterials, has inspired the concept of decameter tructures and nanophotonics, where photonics merge scale metasurfaces, coined seismic metamaterials for an with nanoscience and nanotechnology, and where spatial enhanced control of surface (Love and Rayleigh) and bulk confinement considerably modifies light propagation and (shear and pressure) elastodynamic waves. These power- light-matter interaction [1]. ful mathematical tools of coordinate transforms, effective Seismic megastructures interact with decametric to medium and Floquet-Bloch theories which have revolu- hectometric wavelengths, while nano-optics usually refer tionized nanophotonics, can be translated in the language to situations involving ultraviolet, visible, and near-infra- of civil engineering and geophysics. Experiments on seis- red light i.e. free-space wavelengths ranging from 300 to mic metamaterials made of buried elements in the soil 1200 nm. demonstrate that the fore mentioned tools make a pos- As a transposition of the definition of nanophotonics, sible novel description of complex phenomena of soil- we would like to postulate that “seismic megastructures structure interaction during a seismic disturbance. But involve the science and engineering of mechanical wave- the concepts are already moving to more futuristic con- matter interactions that take place on wavelength and cepts and the same notions developed for structured soils subwavelength scales where artificial structured matter are now used to examine the effects of buildings viewed controls the interactions”. Two large scale experiments as above surface resonators in megastructures such as carried out in France in 2012 [2, 3] demonstrate that it is metacities. But this perspective of future should not make possible to start the analysis of structured soils with the us forget the heritage of the ancient peoples. Indeed, we specific tools of condensed matter, in particular photonic finally point out the striking similarity between an invis- crystals (PCs) and metamaterials. ible cloak design and the architecture of some ancient In the first large scale experiment, which took place megastructures as the antique Gallo-Roman theaters and near the French city of Grenoble in August 2012, an array amphitheatres. of boreholes were drilled in a sedimentary soil where the Keywords: metasurfaces; seismic metamaterials; cloak- Rayleigh wave velocity was first estimated to be 78 m/s, ing; lensing; earthquake protection; seismic ambient thanks to a preliminary seismic test that pointed the wave noise. time arrival at various offsets from a rotating source at 50 Hz (a vibrating probe set on a crane). The experimen- tal mesh was made of three discontinuous lines of ten boreholes 0.32 m in diameter. The length of columns was about 5 m and the mesh spacing was 1.73 m. Numerical simulations performed with finite elements predicted a *Corresponding author: Sébastien Guenneau, Aix Marseille Univ, stop-band centered around 50 Hz for elastic surface waves CNRS, Centrale Marseille, Institut Fresnel, 52 Avenue Escadrille propagating in such a large scale phononic crystal. It Normandie Niemen, 13013 Marseille, France, was experimentally confirmed that there was 5 times less e-mail: [email protected]. https://orcid.org/0000- elastic energy behind the seismic metamaterial after the 0002-5924-622X Stéphane Brûlé and Stefan Enoch: Aix Marseille Univ, CNRS, boreholes had been carried out, in comparison with what Centrale Marseille, Institut Fresnel, 52 Avenue Escadrille Normandie was measured in the absence of boreholes. This confirmed Niemen, 13013 Marseille, France an analogy could be drawn with photonic band gaps in Open Access. © 2019 Sébastien Guenneau et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 Public License. Unauthenticated Download Date | 12/8/19 8:07 PM 1592 S. Brûlé et al.: Role of nanophotonics in the birth of seismic megastructures optics. Moreover, the measured elastic energy was 2.3 Ricker wavelet (or “Mexican hat wavelet”). The signal was times larger at the rotating source when it was in presence characterized by a mean frequency value at 8.15 Hz (λP-wave of the array of boreholes, which is also analogous to the ~ 74 m) with a range of frequencies going from 3 to 20 Hz local density of states obtained for a source placed near (30 < λP-wave < 200 m). At 5 m from the impact, the peak a mirror in optics (or a PC). These results suggested the ground acceleration was around 0.9 g (where g = 9.81 m.s−2 strong potential of the large-scale periodic structure for is the gravity of Earth) which was significant, but necessary the control of spontaneous emissions of seismic waves in to compensate for the strong attenuation versus distance a way similar to what has been achieved for light in PCs in earth materials. Importantly, the void grid spacing (7 m) 40 years ago [4, 5], and we shall go back to this historical was lower than the smallest wavelength measured, and connection in the next section. thus we could unambiguously refer to this structured soil Although we coined this large scale phononic crystal as a “seismic metamaterial”. as “seismic metamaterial”, the observed physical phe- To capture the ground motion’s field, we set 30 three- nomena were mostly interpreted in light of Bragg scatter- component velocimeters (vx, vy, vz) with a corner frequency ing phenomena, and thus we must admit the terminology of 4.5 Hz (−3 dB at 4.5 Hz) electronically corrected to 1 Hz. used was not fully legitimate at this stage. The sensors were used simultaneously with a common In the second large scale experiment, which took place time base and were densely set in a quarter of the inves- near the French city of Lyon in September 2012, the large tigation area (refer Supplementary Figure 1 in [3]). The scale phononic crystal was made of five rows of self-stable pounder was consecutively dropped at five different boreholes 2 m in diameter with a center-to-center spacing places (see [3] for more information), and 7–12 times at of 7 m, see Figure 1A and B. The depth of the boreholes each source location. Sensors remained fixed during the was 5 m. The measurement of the velocity of the pressure whole test and the complete field of velocity (80 m × 80 m) wave in the soil was given by a preliminary seismic test, was obtained by means of the source symmetry and the pointing once again the first wave arrival at various offsets symmetry of the array of boreholes with respect to a plane from the source. We measured the velocity around 600 m/s. passing through the x-axis. The artificial source this time consisted of the fall of the 17 We checked that most of the energy of the source was ton steel pounder from a height of about 12 m to gener- converted into energetic surface waves. In time-domain, ate clear transient vibration pulses. The typical waveform we discovered two main phenomena, illustrated in of the source in time-domain looked like a second order Figure 1C–E. The first one was a significant wave reflection A B 1 S C A Source Land streamer 0.8–1.0 B 0.6–0.8 0.4–0.6 0.2–0.4 0.0–0.2 –40 –40 –40 –35 –35 –35 CD–30 –30 E –30 –25 –25 –25 –20 –20 –20 –15 –15 –15 –10 –10 –10 –5 –5 –5 0 0 0 5 5 5 10 10 10 15 15 15 20 20 20 25 25 25 30 30 30 35 35 35 40 40 40 –40–35 –30–25 –20–15 –10 –5 0 5 10 15 20 25 30 35 40 –40–35 –30–25 –20–15 –10 –5 0 5 10 15 20 25 30 35 40 –40–35 –30–25 –20–15 –10 –5 0 5 10 15 20 25 30 35 40 Figure 1: Experiment on a flat seismic lens: (A) Photo (courtesy of S. Brûlé) of the array of boreholes, (B), (C–E) Chronology of the x–y spatial distribution of normalized v2(t) from (C) 1.900 s to (D) 2.124 s to (E) 2.345 s. Unauthenticated Download Date | 12/8/19 8:07 PM S. Brûlé et al.: Role of nanophotonics in the birth of seismic megastructures 1593 at the contact with the long-side of the grid up to 2.1 s.
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