Waves, complexity and information (OCI)

Rod forest : a ultrasonic multiple scattering model

Leader

Alexandre AUBRY

Tel.: +33 (0)1 80 96 30 66

Co-leader

Sébastien POPOFF

Tel.: +33 (0)1 80 96 39 48

Permanent staff

Alexandre AUBRY

Tel.: +33 (0)1 80 96 30 66

Julien DE ROSNY

Tel.: +33 (0)1 80 96 30 52

Arnaud DERODE

Tel.: +33 (0)1 80 96 30 67

Mathias FINK

Tel.: +33 (0)1 80 96 30 69

Abdelwaheb OURIR

Tel.: +33 (0)1 80 96 30 39

Sébastien POPOFF

Tel.: +33 (0)1 80 96 39 48

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Non-contact assessment of Cardiac Velocity profiles using Ultrasound based Surface Motion Camera: A feasibility study Sadhukhan, D., E. Saloux, C. Dorme, M. Fink, R. K. Ing, and A. Hodzic IEEE Journal of Biomedical and Health Informatics, 1-10 (2025) Abstract: Tissue Doppler imaging (TDI) mode of echocardiography plays a crucial role in diagnosing several cardiac conditions by recording the myocardial contraction velocities. To mitigate the need of experts for performing echocardiography, several studies have proposed the use of Seismocardiogram as an easier alternative to measure the cardiac timings. However, exact correlation with tissue Doppler measured cardiac velocities has not been explored. Moreover, most of the applications only use single channel contact accelerometers on the chest, thus limiting their utility. In this work, we propose the use of a novel airborne ultrasound based surface motion camera (SMC) for non-contact multichannel recording of cardiac induced surface velocities from the chest. Validation study was conducted on 30 healthy subjects with simultaneous recordings of single channel ECG along with the chest surface velocities followed by clinical Echocardiography. The SMC recorded surface velocity waveforms show correlation similarity of over 0.6 with Tissue Doppler velocity waves extracted from the echocardiographic images. Discrete time warping based distance analysis was also performed to quantify their morphological similarity. Quantitative parameters including the peak systolic velocity and amplitude ratio extracted from the chest recordings show a linear correlation (R<sup>2</sup> greater than 0.8) with that of the TDI values. Additionally, multichannel recording allows visualization of the velocity profiles on the chest and efficiently captures the spatial variations for left ventricular and septal sites. Hence, this new modality shows the potential to be a vital diagnostic technique for non-contact and robust monitoring of the cardio-mechanical functions.
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) Abstract: 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.
Output control of dissipative nonlinear multimode amplifiers using spacetime symmetry mapping Chen, C. W., K. Wisal, M. Fink, A. D. Stone, and H. Cao Nature Physics (2025) Abstract: In many linear and nonlinear systems, time-reversal symmetry makes it possible to control the output waves by appropriately shaping the input waves. However, time-reversal symmetry is broken in systems with energy dissipation, necessitating a different approach for relating the input and output fields. We theoretically consider a saturated multimode fibre amplifier in which light generates a heat flow and suffers thermo-optical nonlinearity, thus breaking time-reversal symmetry. We identify a spacetime symmetry that maps the target output back to an input field. This spacetime symmetry mapping applies phase conjugation, gain and absorption substitution but not time reversal, and it holds in a steady state and for slowly varying inputs. Our approach enables coherent wavefront control of nonlinear dissipative systems.
Temporal chirp, temporal lensing, and temporal routing via space-time interfaces Pacheco-Peña, V., M. Fink, and N. Engheta Physical Review B 111, no. 10 (2025) Abstract: A time interface (a rapid change of the constitutive parameters of a material in time), applied within an unbounded medium where a wave travels, can enable frequency conversion and is considered the temporal analog of a spatial interface between two materials. Here, we study light-matter interactions in four dimensions, 4D (space, x,y,z, and time, t), by exploring the implications of applying time interfaces, not to the entire space where a wave travels, but to certain regions of space in order to create spatial interfaces in time. Different configurations such as induced perpendicular, parallel, and oblique spatial interfaces via a temporal interface are discussed. It is shown how such four-dimensional combination of temporal and spatial interfaces can enable interesting features such as the 4D generalized Snell's law and temporal chirp, temporal lensing, and temporal routing of electromagnetic waves. Such exotic possibilities may provide new ways to manipulate light-matter interactions via a combination of temporal and spatial interfaces.

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Presentation of the thematics

The technological and scientific advances of the past fifteen years, to which the Langevin Institute has made pioneering contributions, have significantly expanded our ability to control optical, electromagnetic, and acoustic fields with unprecedented spatiotemporal precision. Thanks to these developments, it is now possible to explore and exploit an impressive number of degrees of freedom, thus opening up innovative prospects for numerous applications.

On one hand, telecommunications particularly benefit from these advances, enabling faster, more reliable, and more secure transmissions. On the other hand, imaging in complex media has greatly benefited from these progresses through a comprehensive matrix approach, fully leveraging all available information to significantly improve the quality and precision of the images obtained.

In parallel with these applied works, more fundamental studies are being conducted, notably on gravity waves, which are particularly suitable for exploring time-dependent media. These fundamental research efforts are essential to deepen our understanding of complex phenomena and to open new research pathways.

Thus, the manipulation of information in complex environments is becoming more sophisticated and efficient, facilitating developments in various sectors such as medicine, earth sciences, engineering, and many others.

In summary, the contributions of the Langevin Institute play a crucial role in transforming these scientific discoveries into practical and innovative solutions, thereby redefining the boundaries of what is possible.

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Waves, complexity and information (OCI)

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