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SUMMARY:Coherent elastic waves in multiple scattering media: influence of 
 resonances and positional correlations of scatterers - Tony Valier-Brasier
  (Sorbonne Université)
DTSTART:20230427T150000Z
DTEND:20230427T160000Z
UID:TALK199261@talks.cam.ac.uk
DESCRIPTION:The propagation of elastic waves in heterogeneous media is a f
 undamental research topic that concerns composite materials\, porous mater
 ials\, colloids and emulsions\, with the aim of characterising these mater
 ials or optimising their performance. This subject has benefited from rene
 wed interest with the development in the 2000s of metamaterials and in par
 ticular locally resonant metamaterials. These materials consist of a fluid
  or solid matrix containing an ordered or random distribution of scatterer
 s\, whose resonances alter wave propagation. In some cases\, the macroscop
 ic mechanical properties of these materials are modified in non-ordinary w
 ays\, opening the way to wave control or damping. Other strategies have be
 en implemented to control or guide waves\, such as phononic crystals or to
 pological metamaterials. Recently\, the control of spatial correlations in
  random scatterer distributions has emerged as a new approach\, and in par
 ticular the use of hyperuniform distributions has proven to be particularl
 y relevant.\nIn this context\, the objective of the presented work is to s
 tudy the influence of positional correlations between scatterers and stron
 g sub-wavelength resonances on the propagation of coherent elastic waves. 
 To achieve this\, the work is based on the systematic comparison of result
 s from statistical models\, numerical simulations and experiments. The num
 erical results are obtained using the MuScat calculation code\, developed 
 in the laboratory. This code is based on the resolution of the multiple sc
 attering equations as well as on the development of the incident and scatt
 ered fields on the cylindrical or spherical harmonics. It allows the treat
 ment of various wave interaction problems with many scatterers\, without a
 ny restriction on the distribution of the particles\, nor on their polydis
 persity in size or elasticity.\nThe MuScat code is used to study the influ
 ence of positional correlations between scatterers on coherent waves. Two 
 types of correlation are investigated: short-range correlations\, which ar
 e based simply on an exclusion distance between each pair of scatterers\, 
 and long-range correlations\, which apply to the whole distribution. One t
 ype of material that exhibits these long-range correlations is hyperunifor
 m media\, which are characterised by the cancellation of density fluctuati
 ons as the volume of the medium tends towards infinity. Numerical simulati
 ons highlight the elastic wave transparency regime of hyperuniform media\,
  as well as the existence of complete stop bands. Short-range correlations
 \, which are much simpler to implement\, lead to similar results.\nIn a se
 cond step\, we investigate the propagation of coherent elastic waves in a 
 distribution of dense beads embedded in a softer solid matrix. This partic
 le-matrix pair exhibits two sub-wavelength dipolar resonances: a translati
 onal resonance that affects both longitudinal and transverse waves and a r
 otational resonance that affects only transverse waves. Longitudinal coher
 ent waves are then strongly influenced by the translational resonance and 
 the study of statistical models shows that wave conversions are particular
 ly important. Transverse coherent waves are influenced by translational an
 d rotational dipole resonances\, and increasing concentration leads to the
  simultaneous propagation of two coherent waves. The influence of spatial 
 correlations\, especially short-range correlations\, finally allows to opt
 imise these non-ordinary effects.
LOCATION:Seminar Room 2\, Newton Institute
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