Role of nanophotonics in the birth of seismic megastructures (1904.05323v1)

Abstract: The discovery of photonic crystals thirty years ago, in conjunction with research advances in plasmonics and metamaterials, has inspired the concept of decameter scale metasurfaces, coined seismic metamaterials, for an enhanced control of surface (Love and Rayleigh) and bulk (shear and pressure) elastodynamic waves. The powerful mathematical tools of coordinate transforms, effective medium and Floquet-Bloch theories, which have revolutionized nanophotonics, can be translated in the language of civil engineering and geophysics. Experiments on seismic metamaterials made of buried elements in the soil demonstrate that the fore mentioned tools make possible a novel description of complex phenomena of soil-structure interaction during a seismic disturbance. But the concepts are already moving to more futuristic concepts and the same notions developed for structured soils are now used to examine the effects of buildings viewed as above surface resonators in megastructures such as metacities. But this perspective of the future should not make us forget the heritage of the ancient peoples. Indeed, we finally point out the striking similarity between an invisibility cloak design and the architecture of some ancient megastructures as antique Gallo-Roman theaters and amphitheatres.

• The paper demonstrates how nanophotonic principles are applied to design seismic metamaterials that effectively manage wave propagation.
• It employs analytical methods and numerical simulations to validate engineered seismic structures that reduce energy impact via mechanisms like negative refraction.
• The study proposes practical urban implementations, suggesting seismic megastructures can protect cities by redirecting and mitigating damaging wave effects.

The Role of Nanophotonics in Seismic Megastructures

The paper "Role of Nanophotonics in the Birth of Seismic Megastructures" by Stéphane Brûlé, Stefan Enoch, and Sébastien Guenneau examines the intersection of nanophotonic principles with seismic wave control, introducing the concept of seismic metamaterials applied to civil engineering and geophysics. This research leverages mathematical frameworks from photonics—coordinate transforms, effective medium theory, and Floquet-Bloch formalism—to address the interaction of seismic waves with structured geological and architectural entities.

Key Concepts and Theoretical Underpinnings

The authors propose seismic megastructures as an analogue to photonic crystals, using the analogy to explore seismic wave interactions with engineered environments. These megastructures, encompassing both subterranean and above-ground components, are engineered to influence seismic wave propagation using principles akin to those found in electromagnetic metamaterials. The paper identifies three primary seismic metamaterial types:

1. Seismic Soil-Metamaterials (SSM): Structured by cylindrical voids or rigid inclusions, SSMs utilize Bragg scattering and effective negative refraction, akin to photonic crystals.
2. Buried Mass-Resonators (BMR): Similar to tuned mass dampers, these resonate under seismic excitation, modifying ground motion.
3. Above-Surface Resonators (ASR): Tall buildings and other structures that interact with seismic signals as resonators, echoing the behavior of acoustic metamaterials.

Empirical Evidence and Numerical Simulations

Empirical validation is provided by large-scale experiments and simulations using configurations like cylindrical holes that resemble concepts from plasmonics and photonic lenses. These experiments, particularly in France, have demonstrated reduced seismic energy impact via structured media, indicative of negative refraction and lensing at seismic scales.

Numerical simulations through commercial software like COMSOL MULTIPHYSICS showcase the wave detouring effects of engineered seismic structures, akin to electromagnetic cloaks. For instance, anisotropically designed seismic cloaks redirect shear waves, minimizing their impact on specific structures while highlighting the resilience against compressional components.

Implications and Future Directions

The theoretical and practical implications of this work are substantial, suggesting methodologies for constructing 'metacities' wherein urban architecture is strategically designed to manage seismic disturbances. The parallels drawn with architectural designs such as medieval Bologna's towers suggest historical inadvertent insights into wave management, further motivating the integration of ancient architectural concepts into modern seismic design.

The paper posits that seismic metamaterials present a cutting-edge frontier for civil engineering, positing cities as dynamic systems where wave behavior can be predictively managed. Emergent phenomena from this research encourage the development of new materials and configurations, transforming urban planning with a scientific rigor previously limited to theoretical physics and nanotechnology.

Conclusion

While the research does not sensationalize its claims, it stands on bold theoretical and empirical foundations, hypothesizing novel urban mitigation approaches. Future work could see the realization of ubiquitous seismic cloaking technologies and elastic waves manipulation, encompassing broad-ranging applications from urban safety to architectural preservation. Research exploring the integration of metamaterials in building design might eventually culminate in a transformative approach to handling geophysical hazards, reshaping how cities are planned and resilient structures are conceived.