arXiv subjects

Ofer Manor

Publications and source records attributed to Ofer Manor.

9 recordsLinked to original sources

arXiv2026

Turning Porous Functional Materials into Directional Transport Platforms with Unidirectional Surface Acoustic Waves

Porous media underpin absorption, filtration, separation, and high-area interfacial transport in chemical and diagnostic systems, yet sustained directional flow through them remains difficult because tortuous pore networks and strong acoustic losses promote bypassing, weak flow, and counterflow. Here, we show that floating-electrode unidirectional transducers (FEUDTs) convert porous materials into actively pumped transport platforms by generating predominantly unidirectional surface acoustic waves (SAWs) that couple more effectively than conventional interdigital transducers across wet multilayer interfaces. By varying pore size, permeability, sample thickness, and fluid viscosity, we find that transport is strongly enhanced when the SAW wavelength is comparable to the characteristic pore dimension, providing a practical design rule for acoustically activated porous media. Under these conditions, FEUDTs drive directional flow velocities up to 0.6 mm s$^{-1}$ at sub-watt input power, about 600 times faster than diffusion alone. FEUDTs also sustain pumping in prewetted porous media, where capillary contributions are removed, yielding velocities that exceed capillary-driven flow under matched conditions while remaining far above thermally induced transport. A reduced theoretical framework captures the main experimental trends and identifies transducer architecture, pore geometry, and actuation strength as the key parameters governing long-range, tunable transport in porous functional materials.

cond-mat.soft↗

arXiv2026

Using surface acoustic waves to drive thin film flow over an obstacle

We study a new paradigm for ultrasonic driven object coating by using a model system where MHz-level surface acoustic waves (SAWs) drive the spreading of a silicone oil film atop topographical obstacles. We use experiments to show that nanometer-amplitude SAWs, propagating in the substrate of a piezoelectric actuator, propel macroscopic oil films to climb and traverse solid obstacles placed on the actuator. The oil dynamics reveal rich coupling between ultrasonic forcing, capillarity, and gravity; the balance of which determines coating success. We formulate a simplified two-dimensional theoretical model that incorporates obstacle geometry directly in the oil thin-film evolution equation, introducing a new representation of acoustic streaming in the presence of substrate height variations. Despite the simplifications inherent in the modeling, simulations show qualitative agreement with the experiments, providing evidence that the model captures the key physics.

physics.flu-dyn↗

arXiv2025

Monte-Carlo based model for the extraction of oil from oil-water mixtures using wetting and surface acoustic waves

This work presents a Monte Carlo (MC) based microscopic model for simulating the extraction of oil from oil-in-water emulsions under the influence of surface acoustic waves (SAWs). The proposed model is a two-dimensional Ising-lattice gas model that employs Kawasaki dynamics to mimic the interactions between oil, water, and air, as well as external forces such as gravity and acoustic stress. By incorporating both acoustic streaming and acoustic radiation pressure, the model captures key experimental observations, including selective oil extraction and droplet motion under SAW excitation. The results highlight the critical role of acoustic radiation pressure in enabling oil film formation and detachment, governed by the balance between capillary and acoustic stresses. The study provides qualitative agreement with experimental findings and offers insights into the essential mechanisms driving acoustowetting-induced phase separation, demonstrating the utility of discrete modeling for complex fluid dynamics problems.

physics.flu-dyn↗

arXiv2025

Using wetting and ultrasonic waves to extract oil from oil/water mixtures

Oil and water placed atop of a solid surface respond differently to a MHz-level surface acoustic wave (SAW) propagating in the solid due to their different surface wetting properties. We observe that, under SAW excitation, oil films, whether non-organic silicon oil or organic sunflower oil, are extracted continuously from sessile drops, comprising emulsions of the oil in question in a solution of water and surfactants. The mechanism responsible for the extraction of oil from the mixtures is the acoustowetting phenomenon: the low surface tension oil phase leaves the mixture in the form of 'fingers' that, away from the drop, spread opposite the path of the SAW. The high surface tension water phase remains at rest. Increasing either the SAW intensity or the oil content in the mixture enhances the rate at which oil leaves the emulsion. We further observe acoustic-capillary flow instabilities at the free surface of the oil film and the formation of spatial gradients in the emulsion oil-concentrations in the presence of SAW. Our study suggests the potential for using SAW for heterogeneous removal of oil from oil-in-water mixtures to complement current phase separation methods.

physics.flu-dyn↗

arXiv2023

Acoustic Resonance Effects and Cavitation in SAW Aerosol Generation

The interaction of surface acoustic waves (SAWs) with liquids enables the production of aerosols with adjustable droplet sizes in the micrometer range expelled from a very compact source. Understanding the nonlinear acousto-hydrodynamics of SAWs with a regulated micro-scale liquid film is essential for acousto-microfluidics platforms, particularly aerosol generators. In this study, we demonstrate the presence of micro-cavitation in an MHz-frequency SAW aerosol generation platform, which is touted as a leap in aerosol technology with versatile application fields including biomolecule inhalation therapy, micro-chromatography and spectroscopy, olfactory displays, and material deposition. Using analysis methods with high temporal and spatial resolution, we demonstrate that SAWs stabilize spatially arranged liquid micro-domes atop the generator's surface. Our experiments show that these liquid domes become acoustic resonators with highly fluctuating pressure amplitudes that can even nucleate cavitation bubbles, as supported by analytical modeling. The observed fragmentation of liquid domes indicates the participation of three droplet generation mechanisms, including cavitation and capillary-wave instabilities. During aerosol generation, the cavitation bubbles contribute to the ejection of droplets from the liquid domes and also explain observed microstructural damage patterns on the chip surface eventually caused by cavitation-based erosion.

physics.flu-dyn↗

arXiv2023

Active coating of a water drop by an oil film using a MHz-frequency surface acoustic wave

We employ a millimeter-scale piezoelectric acoustic actuator, which generates MHz-frequency surface acoustic waves (SAWs) in a solid substrate, to actively coat a drop of water by a macroscopic film of silicon oil as a paradigm for a small scale and low power coating system. We build upon previous studies on SAW induced dynamic wetting of a solid substrate, also known as the acoustowetting phenomena, to actively drive a model low surface-energy liquid -- silicon oil -- coat a model liquid object -- a sessile drop of water. The oil film spreads along the path of the propagating SAW and comes in contact with the drop, which is placed in its path. The intensity of the SAW determines the rate and the extent to which a macroscopically thick film of oil will climb over the drop to partially or fully cover its surface. The dynamic wetting of the drop by the oil film is governed by a balance between acoustic, capillary, and gravitational contributions. Introducing a water drop as an object to be coated indicates the opportunity to coat liquid phase objects by employing SAWs and demonstrates that oil films which are actuated by SAWs may traverse curved objects and liquid surfaces.

cond-mat.soft↗

arXiv2020

Bifurcation study for a surface-acoustic-wave driven meniscus

A thin-film model for a meniscus driven by Rayleigh surface acoustic waves (SAW) is analysed, a problem closely related to the classical Landau-Levich or dragged-film problem where a plate is withdrawn at constant speed from a bath. We consider a mesoscopic hydrodynamic model for a partially wetting liquid, were wettability is incorporated via a Derjaguin (or disjoining) pressure and combine SAW driving with the elements known from the dragged-film problem. For a one-dimensional substrate, i.e., neglecting transverse perturbations, we employ numerical path continuation to investigate in detail how the various occurring steady and time-periodic states depend on relevant control parameters like the Weber number and SAW strength. The bifurcation structure related to qualitative transitions caused by the SAW is analysed with particular attention on the {appearance and interplay of Hopf bifurcations where branches of time-periodic states emerge. The latter correspond to the regular shedding of liquid ridges from the meniscus. The obtained information is relevant to the entire class of dragged-film problems.

nlin.PS↗

arXiv2018

Connecting monotonic and oscillatory motions of the meniscus of a volatile polymer solution to the transport of polymer coils and deposit morphology

We study the connection between the polymer deposition patterns to appear following the evaporation of a solution of poly-methyl-methacrylate (PMMA) in toluene, the transport of the polymer coils in the solution, and the motion of the meniscus of the solution. Different deposition patterns are observed when varying the molecular mass and initial concentration of the solute and temperature and are systematically presented in the form of morphological phase diagrams. The modi of deposition and meniscus motion are correlated. They vary with the ratio between the evaporation-driven convective flux and diffusive flux of the polymer coils in the solution. In the case of a diffusion-dominated solute transport, the solution monotonically dewets the solid substrate by evaporation, supporting continuous contact line motion and continuous polymer deposition. However, a convection-dominated transport results in an oscillatory ratcheting dewetting-wetting motion of the contact line with more pronounced dewetting phases. The deposition process is then periodic and produces a stripe pattern. The oscillatory motion of the meniscus differs from the well documented stick-slip motion of the meniscus, observed as well, and is attributed to the opposing influences of evaporation and Marangoni stresses, which alternately dominate the deposition process.

cond-mat.soft↗

arXiv2016

A partially wetting film of water and surfactant under the influence of a propagating MHz surface acoustic wave

We use both theory and experiment to study the response of {\it partially wetting} films of water and surfactant solutions to a propagating MHz vibration in the solid substrate in the form of a Rayleigh surface acoustic wave (SAW). The SAW invokes a drift of mass in the liquid film, which is associated with the Schlichting boundary layer flow (also known as the Schlichting streaming). We study thin films that are governed by a balance between the drift and capillary stress alone. We demonstrate weak capillary contributions, such as for silicon oil films, support dynamic wetting and lead to the spreading of the liquid over the solid substrate along the path of the SAW. Strong capillary contributions, such as for water films, support however a concurrent dynamic wetting and dewetting along the path of the SAW, such that the film displace along the solid substrate. In addition, such films may support the formation of a capillary train-wave that propagate along the the same path. We further note the mechanism for film dynamics we discuss here is different to the more familiar Eckart streaming mechanism, which is associated with a film thickness that is greater than the wavelength of the sound leakage off the SAW and usually observed to support the motion of drops. The thickness of the films we discuss here is small in respect to the wavelength of the sound leakage, rendering contributions from the Eckart streaming, acoustic radiation pressure, and the attenuation of the SAW small.

physics.flu-dyn↗