Enhanced and reduced transmission of acoustic waves with bubble meta-screens

We present a class of sonic meta-screens for manipulating air-borne acoustic waves at ultrasonic or audible frequencies. Our screens consist of periodic arrangements of air bubbles in water or possibly embedded in a soft elastic matrix. They can be used for soundproofing, but also for exalting transmission at an air/water interface or even to achieve enhanced absorption

How to use disorder for guiding a broadband acoustic wave ?

International audienceIn 1989, the concept of transverse localization was introduced as a new form of localization of light in the sense of Anderson [H. De Raedt et al. Phys. Rev. Lett., vol. 62, no. 1, pp. 47-50, 1989.]. Recently T. Schwartz et al. [Nature, vol. 446, p. 52, 2007] reported the first experimental demonstration of this prediction. To do so, they studied the propagation of light in 2 dimensional disordered photonic lattices, and proved that light was indeed exponentially localized in the transverse plane. Here, we present an equivalent scheme to guide MHz-ultrasonic broadband waves. We explore propagation of MHz-ultrasound in a medium which is either ordered or disordered in the two transverse dimensions (x,y) but invariant in the propagation direction (z). Our samples are made of parallel arrangements of cylindrical scatterers (0.8mm in diameter) embedded in a soft elastic matrix. In the disordered case, the probe beam is laterally confined with an exponential transverse intensity profile, which gives the first demonstration of the transverse localization of acoustic waves. Moreover we prove that the typical dispersion experienced by the pulsed waves in the ordered sample is almost cancelled in the Anderson localized one, hence resulting in a spatio- temporally guided wave

Time-reversal imaging of seismic sources and application to the great Sumatra earthquake

International audienceThe increasing power of computers and numerical methods (like spectral element methods) allows continuously improving modelization of the propagation of seismic waves in heterogeneous media and the development of new applications in particular time reversal in the three-dimensional Earth. The concept of time-reversal (hereafter referred to as TR) was previously successfully applied for acoustic waves in many fields like medical imaging, underwater acoustics and non destructive testing. We present here the first application at the global scale of TR with associated reverse movies of seismic waves propagation by sending back long period time-reversed seismograms. We show that seismic wave energy is refocused at the right location and the right time of the earthquake. When TR is applied to the Sumatra-Andaman earthquake (26 Dec. 2004), the migration of the rupture from the south towards the north is retrieved. Therefore, TR is potentially interesting for constraining the spatio-temporal history of complex earthquakes