Beyond Order: Random, Aperiodic, and Hyperuniform Photonic Materials: introduction to the special issue Negro, L. D. A. L., C. A. O. Hui, M. Filoche, S. A. Schulz, S. Vignolini, and D. S. Wiersma Optical Materials Express 14, no. 5, 1293-1294 (2024)
Résumé: The editors introduce the feature issue on “Beyond Order: Random, Aperiodic, and Hyperuniform Photonic Materials,” which includes nine articles.
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Topology optimization for microwave control with reconfigurable intelligent metasurfaces in complex media Karamanos, T. D., M. Fink, and F. Lemoult Physical Review Applied 21, no. 4 (2024)
Résumé: Reconfigurable intelligent metasurfaces have been proposed as an efficient solution for improving wireless telecommunication systems in multiple-scattering or reverberating media. Concurrently, topology optimization has been successfully used as an inverse-design technique in many fields, and particularly in electromagnetics. In this work, we apply a gradient-based topology optimization for tuning the binary elements of a metasurface for a focusing goal in a complex environment. First, the metasurface unit cells are approximated as point sources and, then, the optimization problem is formulated. Afterwards, the proposed method is applied to find the optimal parameter sets for three distinct environments of increasing complexity, and the resulting focus for each case is demonstrated via numerical simulations. The combination of a reverberating cavity and a metasurface inside the latter is very powerful since everything can be solved analytically for focusing outside the cavity.
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Asymmetrical wakes over anisotropic bathymetries Euvé, L.-P., A. Maurel, P. Petitjeans, and V. Pagneux Journal of Fluid Mechanics 984 (2024)
Résumé: The study investigates the impact of a vertically layered bathymetry, consisting of submerged vertical plates, on a ship wake through theoretical analysis and experimental realization. For subwavelength distances between the plates, the analysis relies on a homogenized model that provides an effective, anisotropic, dispersion relation for the propagation of water waves. Our findings reveal that a highly asymmetric wake can be achieved, with the degree of asymmetry contingent upon the ship propagation direction in relation to the plate orientation. This anisotropy is characterized with respect to water depth and to ship length using the dimensionless depth and hull Froude numbers. Laboratory experiments align closely with theoretical predictions, confirming that the asymmetry of the wake can indeed be managed through manipulation of bathymetric conditions.
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Airborne ultrasound for the contactless mapping of surface thoracic vibrations during human vocalizations: A pilot study Wintzenrieth, F., M. Couade, F. Lehanneur, P. Laveneziana, M. C. Niérat, N. Verger, M. Fink, T. Similowski, and R. K. Ing AIP Advances 14, no. 3 (2024)
Résumé: Physical examination of the thorax is key to the clinical diagnosis of respiratory diseases. Among other examination techniques, palpation evaluates the transmission of high-frequency vibrations produced by vocalizations (tactile fremitus), which helps the physicians to identify abnormalities within the respiratory system. We propose the use of an airborne ultrasound surface motion camera (AUSMC) to quantitatively map the vibrations induced by subject vocalization. This approach could make the examination of vocal fremitus quantifiable, reproducible, and archivable. Massive data collection of vocal fremitus could allow using artificial intelligence algorithms to isolate vibration patterns that could help disease identification. Until now, in contrast, the interpretation of vocal fremitus has been subject to the physician’s experience and remains subjective. In the present work, we demonstrate the capabilities of the AUSMC to measure vocal fremitus thoracic vibration maps on 77 healthy volunteers. We have observed a spatial dependence of vibration maps on vocalization frequency. We observed that the left lung generates fewer surface vibrations than the right one, which was expected according to their respective dimensions. We also discuss the implications of our findings.
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Multiple scattering theory in one dimensional space and time dependent disorder: average field [Invited] Selvestrel, A., J. Rocha, R. Carminati, and R. Pierrat Optical Materials Express 14, no. 3, 801-815 (2024)
Résumé: We theoretically study the propagation of light in one-dimensional space- and time-dependent disorder. The disorder is described by a fluctuating permittivity ε(x, t) exhibiting short-range correlations in space and time, without cross correlation between them. Depending on the illumination conditions, we show that the intensity of the average field decays exponentially in space or in time, with characteristic length or time defining the scattering mean-free path ℓs and the scattering mean-free time τs. In the weak scattering regime, we provide explicit expressions for ℓs and τs, that are checked against rigorous numerical simulations.
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A simplified PPG based approach for automated recognition of five distinct emotional states Paul, A., A. Chakraborty, D. Sadhukhan, S. Pal, and M. Mitra Multimedia Tools and Applications 83, no. 10, 30697-30718 (2024)
Résumé: Emotion is a complicated state of mind, which normally reflects human perceptions and attitudes. Proper recognition of emotional states and its quality plays crucial role for the detection of critical diseases and subsequent treatment procedures. Generally, multi-lead, complicated Electroencephalogram (EEG) based analysis predominate the characterization of emotion detection. Nowadays, user-friendly, rich-cardiac-information and wearable characteristics of the photoplethysmogram (PPG) signal are also being used to identify the emotional states. However, a majority of the reported emotion detection techniques mostly uses PPG signal in multimodality approach. In this paper, a simple methodology is proposed to identify multiple emotional states via the analysis of the PPG signal alone. Normally, emotion induced alteration in the heart rate causes variation in the blood ejection rate and a subsequent deviation in the balance of the systolic and the diastolic phases. Consequently, a specific time-domain characteristic is identified to quantify such imbalance and its variability is then used as a feature to discriminate between the five most prominent emotional states via a threshold-based classification technique. The algorithm presents superior performance while evaluated on the PPG data collected from the standard DEAP dataset with an average detection accuracy of 97.78%. Compared to existing literatures, the superior results establish the effectiveness of the proposed algorithm for the detection of multiple emotional states using PPG signal only. Moreover, the use of a single PPG feature and the application of a simple threshold-based classification technique also justify its promises for implementation in real-life, healthcare applications.
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