Laser ultrasonic investigation of chromium coating impact on elastic guided waves in zirconium tubes
Diboune, H., D. A. Kiefer, F. Lyonnet, P. Barberis, F. Bruno, S. Mezil, and C. Prada
Journal of the Acoustical Society of America 159, no. 1, 398-407 (2026)
Résumé: The impact of a chromium (Cr) coating on the elastic guided waves propagating in zirconium alloy (called M5 Framatome and referred to as M5 hereafter) nuclear cladding tubes is studied both theoretically and experimentally. Longitudinal modes are measured on different 9.5 mm-diameter tubes by a non-contact laser ultrasonic technique. These modes are calculated using the M5 elastic constants determined from x-ray diffraction measurements. Since Cr has a much higher shear wave velocity than the M5 alloy, the dispersion of observed guided modes is significantly modified by the coating. In the mid-frequency range, characterized by shear wavelengths on the order of the tube thickness, the second longitudinal mode appears to be particularly sensitive to the coating. In a higher frequency range, it is observed that modes are well measured in a frequency-wavenumber domain corresponding to the leaky surface wave of a Cr coated infinite M5 substrate. A simple but effective model predicts the observability of each mode, in good qualitative agreement with experimental observations.
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Homogenization of resonant bubble screens: Influence of bubble shape and lattice arrangement
Pham, K., and A. Maurel
Journal of the Acoustical Society of America 159, no. 1, 357-372 (2026)
Résumé: A time-domain effective model for acoustic wave propagation through a two-dimensional periodic array of gas bubbles embedded in a liquid is presented. The model is expressed as transmission conditions: pressure remains continuous, whereas the normal velocity exhibits a jump induced by the internal pressure of the bubbles. This internal pressure follows a damped mass–spring equation, with damping arising solely from radiative coupling to the surrounding liquid, which makes the resonance frequency and quality factor of the array emerge unambiguously. Aside from the bubble density in the lattice, these quantities are fully governed by two independent geometric parameters: a dimensionless capacitance, depending solely on bubble shape, and a lattice coefficient, depending solely on lattice geometry. For plane wave scattering, comparisons with direct numerical simulations demonstrate that the model accurately reproduces the resonant behavior of bubble screens across a range of configurations, including spherical, spheroidal, and cylindrical bubbles, as well as square and rectangular lattices. This generalizes the classical model of Leroy et al. [Eur. Phys. J. E 29(1), 123–130 (2009)] for spherical bubbles in square lattices. Notably, the model reveals—and simulations confirm—that the resonance frequency shift relative to an isolated bubble, usually positive (blue shift), can become negative (red shift) in rectangular lattices with aspect ratios exceeding seven.
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Single-shot hyperspectral wavefront imaging
Blochet, B., N. Lebas, P. Berto, D. Papadopoulos, and M. Guillon
Nature Communications 17, no. 1 (2026)
Résumé: Single-shot hyperspectral wavefront sensing is essential for applications like spatio-spectral coupling metrology in high-power laser or fast material dispersion imaging. Under broadband illumination, traditional wavefront sensors assume an achromatic wavefront, which makes them unsuitable. We introduce a hyperspectral wavefront sensing scheme based on the Hartmann wavefront sensing principles, employing a multicore fiber as a Hartmann mask to overcome these limitations. Our system leverages the angular memory effect and limited spectral correlation width of the multicore fiber, encoding wavefront gradients into displacements and the spectral information into uncorrelated speckle patterns. This method retains the simplicity, compactness, and single-shot capability of conventional wavefront sensors, with only a slight increase in computational complexity. It also allows a tunable trade-off between spatial and spectral resolution. We demonstrate its efficacy for recording the hyperspectral wavefront cube from single-pulse acquisitions at the Apollon multi-petawatt laser facility, and for performing multispectral microscopic imaging of dispersive phase objects.
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Seismic wave interaction with buried cavity networks: Analytical modeling and resonance effects
Maurel, A., S. Brulé, S. Guenneau, and K. Pham
Wave Motion 141, 103666 (2026)
Résumé: We study the scattering of elastic waves by a periodic array of cavities buried in an elastic half-space. This configuration is relevant in seismology, where shallow voids can locally amplify ground motion. Building on homogenized interface models developed for infinite media, we extend the approach to account for the presence of a stress-free surface. The resulting model yields an analytical solution to the 2D elastodynamic problem for incident longitudinal L and transverse T waves. A semi-analytical multimodal solution is used for validation. The analysis reveals the conditions under which resonances occur in the soil layer between the cavity tops and the surface, with particular emphasis on the low-frequency resonance that dominates in seismic contexts. The model identifies the key parameters governing resonance and provides insights into the transition from infinite to finite cavity arrays. It offers a simplified yet accurate framework for assessing site-specific seismic amplification.
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