arXiv subjects

Thierry Baasch

Publications and source records attributed to Thierry Baasch.

4 recordsLinked to original sources

arXiv2026

Acoustic radiation force on a liquid particle in a standing surface acoustic wave field

We develop a theory for the acoustic radiation force on a liquid particle in a 2D standing-wave field beyond the Rayleigh limit. The theory is valid for any frequency, includes the traveling-wave components due to the Rayleigh angle, and is thus applicable to a large class of surface acoustic wave applications. The analytical results are validated with respect to finite-element models. Using our analytical solution, we determine the parameter space for which Rayleigh-limit methods, such as the Gor'kov framework, remain applicable. This range is shown to depend on the particle properties, the Rayleigh angle, and even the particle position in the acoustic field. We propose a general form for the acoustophoretic contrast factor applicable to any wavelength of 1D standing-wave field, broadening the applicability of the classical Gor'kov framework. We show that the Rayleigh-angle effect can substantially weaken the acoustic radiation force, an effect that has been largely overlooked. We also confirm a frequency-dependent topological transition of the acoustic landscape that induces a switching of the field attractors and particle equilibrium points. These results advance the quantitative theory of acoustic forces, unveil previously unresolved dynamical features of acoustofluidic fields, and provide a theoretical foundation for SAW-based cell trapping, separation, and enrichment in acoustofluidics.

physics.flu-dyn↗

arXiv2025

The Feasibility of Acoustophoresis Multimodal Control

Actuating the acoustic resonance modes of a microfluidic device containing suspended particles (e.g., cells) allows for the manipulation of their individual positions. In this work, we investigate how the number of resonance modes $M$ chosen for actuation and the number of particles $P$ affect the probability of success $S$ of manipulation tasks, denoted Acoustophoretic Control Problems (ACPs). Using simulations, we show that the ratio of locally controllable volume to the state-space volume correlates strongly with $S$. This ratio can be efficiently computed from the pressure field geometry as it does not involve solving a control problem, thus opening possibilities for experimental and numerical device optimization routines. Further, we show numerically that in noise-free 1D systems $S \approx 1 - P/M$, and that in noisy 1D and 2D systems $S$ is accurately predicted by Wendel's Theorem. We also show that the relationship between $M$ and $P$ for a given $S$ is approximately linear, suggesting that as long as $P/M$ is constant, $S$ will remain unchanged. We validate this finding by successfully simulating the control of systems with up to $60$ particles with up to $600$ modes.

physics.app-ph↗

arXiv2025

Controllability Analysis of Multi-Modal Acoustic Particle Manipulation in One-Dimensional Standing Waves

Acoustic manipulation in microfluidic devices enables contactless handling of biological cells for Lab-on-Chip applications. This paper analyzes the controllability of multi-particle systems in a one-dimensional acoustic standing wave system using multi-modal actuation. By modeling the system as a nonlinear control system, we analyze its global and local controllability, quantifying these properties in terms of mode numbers. Our results show that sufficient modes enable dense reachability sets, while mode mixing with 10 modes grants a strict notion of controllability to 80\% of the state space in a two-particle system. These findings offer theoretical insights for designing acoustic manipulation algorithms, supporting efficient control in biomedical applications.

eess.SY↗

arXiv2024

Eckart streaming with nonlinear high-order harmonics: an example at gigahertz

Acoustic streaming shows great potential in applications such as bubble dynamics, cell aggregation, and nano-sized particle isolation in the biomedical and drug industries. As the acoustic shock distance decreases with the increase of incident frequency, the nonlinear propagation effect will play a role in acoustic streaming, e.g., Eckart (bulk) streaming at a few gigahertz (GHz). However, the theory of source terms of bulk streaming is still missing at this stage when high-order acoustic harmonics play a role. In this paper, we derive the source term including the contribution of higher-order harmonics. The streaming-induced hydrodynamic flow is assumed to be incompressible and no shock wave occurs during the nonlinear acoustic propagation as restricted by the traditional Goldberg number Γ< 1 or Γ\approx 1 which indicates the importance of nonlinearity relative to dissipation. The derived force terms allow evaluating bulk streaming with high-order harmonics at GHz and provide an exact expression compared to the existing empirical formulas. Numerical results show that the contribution of higher-order harmonics increases the streaming flow velocity by more than 20%. We show that the expression introduced by Nyborg should be avoided in numerical computations as it includes part of the acoustic radiation force that does not lead to acoustic streaming.

physics.flu-dyn↗