Soft elastomers: A playground for guided waves
Delory, A., F. Lemoult, M. Lanoy, A. Eddi, and C. Prada
The Journal of the Acoustical Society of America 151, no. 5, 3343-3358 (2022)
Résumé: Mechanical waves propagating in soft materials play an important role in physiology. They can be natural, such as the cochlear wave in the inner ear of mammalians, or controlled, such as in elastography in the context of medical imaging. In a recent study, Lanoy, Lemoult, Eddi, and Prada [Proc. Natl. Acad. Sci. U.S.A. 117(48), 30186-30190 (2020)] implemented an experimental tabletop platform that allows direct observation of in-plane guided waves in a soft strip. Here, a detailed description of the setup and signal processing steps is presented as well as the theoretical framework supporting them. One motivation is to propose a tutorial experiment for visualizing the propagation of guided elastic waves. Last, the versatility of the experimental platform is exploited to illustrate experimentally original features of wave physics, such as backward modes, stationary modes, and Dirac cones.
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Time-reversal of Sub-THz Pulses in Complex Media
Mokh, A., R. Khayatzadeh, A. Ourir, M. Kamoun, A. Tourin, M. Fink, and J. De Rosny
Progress In Electromagnetics Research B 95, 141-162 (2022)
Résumé: Abstract|For the last 20 years, the time-reversal (TR) process has been successfully applied to focus pulses in the microwave frequency range and in complex media. Here we examine the specic conditions to obtain the same results but in the sub-THz frequency range. Because of the stronger attenuation at this much higher frequency, it is more challenging to exploit the TR self-focusing property. The TR of pulses is studied in two kinds of complex media: metallic waveguide and leaky reverberating cavity. For each medium, we propose one or two models to assess the quality of the focusing. For the waveguide, we show that the angle of incidence is an important parameter. Based on these results, we perform TR experiments at 273 GHz with a bandwidth that can be as large as 2 GHz. TR experiments are successfullyrst conducted in a 1m long and 10mm diameter straight hollow cylinder and then in a 5m long and 12mm diameter curved waveguide. Finally, we present results obtained in a cavity of 72 cm3 that leaks through a copper grid. The best focusing is observed with the longer waveguide.
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Label-free, non-invasive, and repeatable cell viability bioassay using dynamic full-field optical coherence microscopy and supervised machine learning
Park, S., V. Veluvolu, W. S. Martin, T. Nguyen, J. Park, D. L. Sackett, C. Boccara, and A. Gandjbakhche
Biomedical Optics Express 13, no. 6, 3187-3194 (2022)
Résumé: We present a novel method that can assay cellular viability in real-time using supervised machine learning and intracellular dynamic activity data that is acquired in a labelfree, non-invasive, and non-destructive manner. Cell viability can be an indicator for cytology, treatment, and diagnosis of diseases. We applied four supervised machine learning models on the observed data and compared the results with a trypan blue assay. The cell death assay performance by the four supervised models had a balanced accuracy of 93.92 ±0.86%. Unlike staining techniques, where criteria for determining viability of cells is unclear, cell viability assessment using machine learning could be clearly quantified.
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Real-time 3D imaging with Fourier-domain algorithms and matrix arrays applied to non-destructive testing
Marmonier, M., S. Robert, J. Laurent, and C. Prada
Ultrasonics 124, 106708 (2022)
Résumé: Real-time 3D ultrasound imaging with matrix arrays remains a challenge in Non-Destructive Testing (NDT) due to the time-consuming reconstruction algorithms based on delay-and-sum operations. Other algorithms operating in the Fourier domain have lower algorithmic complexities and therefore higher frame rates at the cost of more storage space, which may limit the number of reconstruction points. In this paper, we present an implementation for real-time 3D imaging of the Total Focusing Method (TFM) and the Plane Wave Imaging (PWI), as well as of their Fourier-domain counterparts, referred to as k-TFM and k-PWI. For both types of acquisition, the Fourier-domain algorithms are used to increase frame rates, and they are compared to the time-domain TFM and PWI in terms of image quality, frame rates and memory requirements. In order to greatly reduce their memory requirements, a new implementation of k-TFM and k-PWI is proposed. The four imaging methods are then evaluated by imaging in real time a block of stainless steel containing a 3D network of spherical porosities produced by additive layer manufacturing using a powder bed laser fusion process.
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