Nonmonotonic Radiative Heat Transfer in the Transition from Far Field to Near Field
Guillemot, V., R. Messina, V. Krachmalnicoff, R. Carminati, P. Ben-Abdallah, W. Poirier, and Y. De Wilde
Physical Review Letters 134, no. 19 (2025)
Résumé: We present high precision measurements of the radiative heat transfer of a glass microsphere immersed in a thermal bath in vacuum facing three different planar substrates (SiO2, SiC, and Au), which exhibit very different optical behaviors in the infrared region. Using a thermoresistive probe on a cantilever, we show the nonmonotonic behavior of the radiative flux between the microsphere and its environment when the microsphere is brought closer to the substrate in the far-field to near-field transition regime. We demonstrate that this unexpected behavior is related to the singularities of dressed emission mechanisms in this three-body system sphere-substrate bath with respect to the separation distance.
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Sensitivity of Lamb waves in viscoelastic polymer plates to surface contamination
Spytek, J., D. A. Kiefer, R. K. Ing, C. Prada, J. Grando, and J. De Rosny
Ultrasonics 149, 107571 (2025)
Résumé: Detecting surface contamination on thin thermoformed polymer plates is a critical issue for various industrial applications. Lamb waves offer a promising solution, though their effectiveness is challenged by the strong attenuation and anisotropy of the polymer plates. This issue is addressed in the context of a calcium carbonate (CaCO3) layer deposited on a polypropylene (PP) plate. First, the viscoelastic properties of the PP material are determined using a genetic algorithm inversion of data measured with a scanning laser vibrometer. Second, using a bi-layer plate model, the elastic properties and thickness of the CaCO3 layer are estimated. Based on the model, the sensitivity analysis is performed, demonstrating considerable effectiveness of the A1 Lamb mode in detecting thin layers of CaCO3 compared to Lamb modes A0 and S0. Finally, a direct application of this work is illustrated through in-situ monitoring of CaCO3 contaminants using a straightforward inter-transducer measurement.
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Modeling conductive thermal transport in three-dimensional fibrous media with fiber-to-fiber contacts
Gaunand, C., Y. De Wilde, A. François, V. Grigorova-Moutiers, and K. Joulain
Physical Review Applied 23, no. 3 (2025)
Résumé: Understanding heat transfers in fibrous materials, particularly conduction, is a major challenge due to their heterogeneous and multiscale nature, and the unknown contribution of fiber-to-fiber contacts. In most previous modeling studies, the existence of thermal contact resistance is not considered, and the computational complexity limits the size of simulated samples, which often leads to imprecise or inaccurate predictions. The same problem arises when considering electrical conduction through fibrous materials. In this work, we describe a computationally efficient simulation approach based on a multinodal representation to analyze the steady-state heat conduction through the solid structure in numerically generated three-dimensional fibrous networks, including contact resistance. We show that the solid conductivity in these networks is governed by a master curve that depends on a single parameter: a characteristic ratio representing the interplay between the intrinsic fiber conductivity and contact resistance as well as the influence of other geometric parameters, which numerically validates previous theoretical studies. However, we observe a deviation to this established theory for poorly connected networks. We derive an expression for a correction factor, considering the influence of correlations between fiber temperatures, and we then find good agreement with our simulation data. Our results demonstrate that the solid conductivity can be fully predicted based on geometric quantities, regardless of the extent of network connectivity, thus generalizing previous studies on this topic. This work, contributing to improve our understanding of conductive heat transport in fibrous media, may prove useful in the development of accurate predictive models and optimization strategies for fibrous insulation materials.
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Nearfield control over magnetic light-matter interactions
Reynier, B., E. Charron, O. Markovic, B. Gallas, A. Ferrier, S. Bidault, and M. Mivelle
Light: Science and Applications 14, no. 1 (2025)
Résumé: Light-matter interactions are frequently perceived as predominantly influenced by the electric field, with the magnetic component of light often overlooked. Nonetheless, the magnetic field plays a pivotal role in various optical processes, including chiral light-matter interactions, photon-avalanching, and forbidden photochemistry, underscoring the significance of manipulating magnetic processes in optical phenomena. Here, we explore the ability to control the magnetic light and matter interactions at the nanoscale. In particular, we demonstrate experimentally, using a plasmonic nanostructure, the transfer of energy from the magnetic nearfield to a nanoparticle, thanks to the subwavelength magnetic confinement allowed by our nano-antenna. This control is made possible by the particular design of our plasmonic nanostructure, which has been optimized to spatially decouple the electric and magnetic components of localized plasmonic fields. Furthermore, by studying the spontaneous emission from the Lanthanide-ions doped nanoparticle, we observe that the measured field distributions are not spatially correlated with the experimentally estimated electric and magnetic local densities of states of this antenna, in contradiction with what would be expected from reciprocity. We demonstrate that this counter-intuitive observation is, in fact, the result of the different optical paths followed by the excitation and emission of the ions, which forbids a direct application of the reciprocity theorem.
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