Evidence of metamaterial physics at the geophysics scale: the METAFORET experiment

Abstract

The METAFORET experiment was designed to demonstrate that complex wave physics phenomena classically observed at the meso- and micro-scales in acoustics and in optics also apply at the geophysics scale. In particular, the experiment shows that a dense forest of trees can behave as a locally resonant metamaterial for seismic surface waves. The dense arrangement of trees anchored into the ground creates anomalous dispersion curves for surface waves, which highlight a large frequency band-gap around one resonant frequency of the trees, at ∼45 Hz. This demonstration is carried out through the deployment of a dense seismic array of ∼1000 autonomous geophones providing seismic recordings under vibrating source excitation at the transition between an open field and a forest. Additional geophysical equipment was deployed (e.g. ground-penetrating radar, velocimeters on trees) to provide essential complementary measurements. Insights and interpretations on the observed seismic wavefield, including the attenuation length, the intensity ratio between the field and the forest and the surface wave polarization, are validated with 2D numerical simulations of trees over a layered halfspace.

Past, present and future of seismic metamaterials: experiments on soil dynamics, cloaking, large scale analogue computer and space–time modulations

“…We further note the theoretical and experimental observation of subwavelength stop bands for MHz Rayleigh waves propagating within an array of nickel pillars grown on a lithium niobate substrate [36]. In our opinion, these two seminal works that predate the area of seismic metamaterials have touched upon the essence of the wave physics at work in large scale mechanical metamaterials: control of surface seismic waves in the Bragg [1,35,37,38] and subwavelength [2,21,36,[39][40][41] regimes. In all fairness, seismologists and earthquake engineers had already noted 40 years ago the effect of soil roughness on the propagation of seismic waves [42].…”

Hypothesis Tests on Rayleigh Wave Radiation Pattern Shapes: A Theoretical Assessment for Source Screening (Independent Review: LANL Source Physics LCP) [Slides]

“…While this theoretical analysis did not use not waveform data, our results do suggest that radiation pattern shapes provide screening power as a physically-interpretable, sourcetype discriminant in some idealized cases. Such cases include controlled, laboratory experiments with engineered structures, or natural, horizontally stratified structures that are leveraged in seismic studies elsewhere (Biagi et al, 1990;Hudson et al, 2020;Knox et al, 2016;Lott et al, 2020;Lu et al, 2007;Toksöz et al, 1971). If future application of our tests with locally recorded data prove successful, we will begin testing it on regional, low frequency data.…”

Active Cloaking and Illusion of Electric Potentials in Electrostatics

“…eyes, antennas, airborne or satellite detectors/sensors). Over the last two decades, theoretical and experimental studies on cloaking have been conducted in several research fields such as electromagnetism 1,2,3 , acoustics 4,5,6 , thermodynamics 7,8,9,10 , solid mechanics 11 , elastic 12,13,14,15 , and seismic wave propagation 16,17,18,19 .…”