Serge Mensah

Topological imaging in bounded elastic media

HighlightsTEM is modified for the analysis of scattered acoustic signals in bounded media.The approach relies on a combination of Dirichlet and Neumann boundary conditions.Ultrasonic fields are analyzed through the Green’s function.The method is applied for slit imaging from experimental data. Abstract Detecting, imaging and sizing defects in a bounded elastic medium is still a difficult task, especially when access is complex. Adjoint methods simplify the task as they take advantage of prior information such as the geometry and material properties. However, they still reveal a number of important limitations. Artifacts observed on the conventional topological energy image result from wave interactions with the boundaries of the inspected medium. The paper describes a method for addressing these artifacts, which involves forward and adjoint fields specified in terms of the boundary conditions. Modified topological energies are then defined according to the type of analyzed flaw (open slit or inclusion). Comparison of the numerical results with the experimental data confirms the relevance of the approach.

Tunable microbubble generator using electrolysis and ultrasound

This letter reports on a method for producing on demand calibrated bubbles in a non-chemically controlled solution using localized micro-electrolysis and ultrasound. Implementing a feedback loop in the process leads to a point source of stable mono-dispersed microbubbles. This approach overcomes the inertial constraints encountered in microfluidics with the possibility to produce from a single to an array of calibrated bubbles. Moreover, this method avoids the use of additional surfactant that may modify the composition of the host fluid. It impacts across a broad range of scientific domains from bioengineering, sensing to environment.

Weld inspection by focused adjoint method

HighlightsDetection/characterization of defects in SMA weld using virtual in‐depth sources.Noise reduction in topological imaging is analytically and numerically demonstrated.Improved detection probability and enhanced topological image quality are obtained. ABSTRACT This paper reports a methodology for the non‐destructive ultrasonic evaluation of welds, based on probing, residue back‐focusing and topological energy calculation using an enhanced (focused) adjoint method. The proposed method combines the advantages of time reversal to compensate for the cumulative distorsions experienced by a wave propagating in a heterogeneous medium, and topological imaging to highlight the defect location. The synergistic effect of this combined approach makes it possible to detect anomalies in the most efficient way. The method paves the way towards a matched‐insonification imaging of anomalies in anisotropic media.

Taking advantage of acoustic inhomogeneities in photoacoustic measurements

Abstract. This paper proposes a method for improving the localization and the quantification of the optical parameters in photoacoustic (PA) tomography of biological tissues that are intrinsically heterogeneous in both optical and acoustic properties. It is based on the exploitation of both the PA signal, generated by the heterogeneous optical structures, and the secondary acoustic echoes due to the interaction between a primary PA wave generated near the tissue surface and the heterogeneous acoustic structures. These secondary echoes can also be collected through proper measurements of the PA signals. The experimental procedure is presented along with the method to filter the signal and the reconstruction algorithm that includes the account of the acoustic information.