Alen Pavlic

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Pavlic

First Name

Alen

ORCID

0000-0002-3260-4090

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Publications 1 - 10 of 21

High sensitivity measurements of the Acoustic Contrast Factor of stiffness altered biological cells
Harshbarger, Cooper; Pavlic, Alen; Bernardoni, Davide; et al. (2022)
Acoustofluidics 2022: Abstract Book
On the streaming in a microfluidic Kundt's tube
Pavlic, Alen; Dual, Jürg (2021)
Journal of Fluid Mechanics
We derive an analytical solution for the acoustic streaming inside a rigid tube resulting from a pseudo-standing wave field, generated by two counterpropagating travelling waves. We solve the second-order axisymmetric problem that follows from the perturbation expansion of the governing equations. In the process, we impose no restriction on the diameter of the tube with respect to the thickness of the viscous boundary layer and acoustic wavelength. The derived solution is then used to study the evolution of streaming patterns inside the tube when geometrical and material parameters are varied. We show how the Schlichting streaming torus at the wall bounds the Rayleigh streaming near the axis of the tube. Decreasing the ratio (Xi) of the tube radius to the viscous boundary layer thickness gradually expands the Schlichting streaming, suppressing the Rayleigh streaming. Considering the average mass transport velocity, the Rayleigh streaming vanishes at the critical ratio Xi(M)(S) = 6.2 . The critical ratio is independent of fluid properties in the limit of large acoustic wavelength relative to the radius of the tube (Lambda). When decreases towards unity, large-scale Eckart-like streaming develops near the axis, superseding the Rayleigh streaming, while the Schlichting streaming remains at the wall. In addition, we demonstrate the relevance of the compressibility of the streaming flow and of the full inclusion of the spatial variation of the Reynolds stress that acts as the streaming source. The study is especially relevant for microfluidic systems, wherein the viscous boundary layer can reach significant thicknesses.
Acoustic Metal Particle Focusing in a Round Glass Capillary
Gerlt, Michael; Paeckel, Adrià; Pavlic, Alen; et al. (2021)
arXiv
Two-dimensional metal particle focusing is an essential task for various fabrication processes. While acoustofluidic devices can manipulate particles in two dimensions, the production of these devices often demands a cleanroom environment. Therefore, acoustically excited glass capillaries present a cheap alternative to labour-intensive cleanroom production. Here, we present 2D metal micro-particle focusing in a round glass capillary using bulk acoustic waves. Excitation of the piezoelectric transducer at specific frequencies leads to mode shapes in the round capillary, concentrating particles towards the capillary centre. We experimentally investigate the particle linewidth for different particle materials and concentrations. We demonstrate the focus of copper particles with 1 μm in diameter down to a line of width 60.8 ± 7.0 μm and height 45.2 ± 9.3 μm, corresponding to a local concentration of 4.5 % v/v, which is 90 times higher than the concentration of the initial solution. Through numerical analysis, we could obtain further insights into the particle manipulation mechanism inside the capillary and predict the particle trajectories. We found that a transition of the acoustic streaming pattern enables us to manipulate particles close to the critical particle radius. Finally, we used our method to eject copper particles through a tapered round capillary with an opening of 25 μm in diameter, which would not be possible without particle focusing. Our novel setup can be utilized for various applications, that otherwise might suffer from abrasion, clogging and limited resolution.
Interparticle attraction along the direction of the pressure gradient in an acoustic standing wave
Pavlic, Alen; Ermanni, Lorenzo; Dual, Jürg (2022)
Physical Review E
Scattering of an acoustic wave by particles gives rise to microstreaming, as well as to acoustic radiation and interaction forces on the particles. We numerically study these steady, nonlinear phenomena for a case of two elastic spheres in a standing wave. We show that if one or both spheres are smaller or comparable to the viscous boundary layer, the microstreaming close to the pressure node can lead to an interparticle attraction along the direction of the pressure gradient of the wave. Similar behavior is observed when, instead of size, density of one of the spheres is sufficiently larger relative to the other sphere. These findings could promote the acoustic manipulation of nanoparticles and bacteria.
Streaming in a Kundt's tube of an arbitrary diameter
Pavlic, Alen; Dual, Jürg (2020)
Cell mechanics in an ultrasonic standing wave
Pavlic, Alen; Dual, Jürg (2022)
Biophysical Journal
Dependence of the acoustic radiation force and microstreaming on the material and shape of a particle in an ultrasonic standing wave
Pavlic, Alen; Nagpure, Pushkin; Ermanni, Lorenzo; et al. (2022)
22nd International Symposium on Nonlinear Acoustics (ISNA 2022). Programme
Efficient modeling of sharp-edge acoustofluidics
Pavlic, Alen; Roth, Lukas; Harshbarger, Cooper Lars; et al. (2023)
Frontiers in Physics
Sharp-edge structures exposed to acoustic fields are known to produce a strong non-linear response, mainly in the form of acoustic streaming and acoustic radiation force. The two phenomena are useful for various processes at the microscale, such as fluid mixing, pumping, or trapping of microparticles and biological cells. Numerical simulations are essential in order to improve the performance of sharp-edge-based devices. However, simulation of sharp-edge structures in the scope of whole acoustofluidic devices is challenging due to the thin viscous boundary layer that needs to be resolved. Existing efficient modeling techniques that substitute the need for discretization of the thin viscous boundary layer through analytically derived limiting velocity fail due to large curvatures of sharp edges. Here, we combine the Fully Viscous modeling approach that accurately resolves the viscous boundary layer near sharp edges with an existing efficient modeling method in the rest of a device. We validate our Hybrid method on several 2D configurations, revealing its potential to significantly reduce the required degrees of freedom compared to using the Fully Viscous approach for the whole system, while retaining the relevant physics. Furthermore, we demonstrate the ability of the presented modeling approach to model high-frequency 3D acoustofluidic devices featuring sharp edges, which will hopefully facilitate a new generation of sharp-edge-based acoustofluidic devices.
Microstreaming and acoustic interaction forces between two particles in a standing wave within a viscous fluid
Pavlic, Alen; Ermanni, Lorenzo; Dual, Jürg (2021)
Acoustofluidic 2021: Abstract Book
Sharp-edge-based acoustofluidic chip capable of programmable pumping, mixing, cell focusing and trapping
Pavlic, Alen; Harshbarger, Cooper; Rosenthaler, Luca; et al. (2023)
Physics of Fluids
Precise manipulation of fluids and objects on the microscale is seldom a simple task, but, nevertheless, crucial for many applications in life sciences and chemical engineering. We present a microfluidic chip fabricated in silicon–glass, featuring one or several pairs of acoustically excited sharp edges at side channels that drive a pumping flow throughout the chip and produce a strong mixing flow in their vicinity. The chip is simultaneously capable of focusing cells and microparticles that are suspended in the flow. The multifunctional micropump provides a continuous flow across a wide range of excitation frequencies (80 kHz–2 MHz), with flow rates ranging from nl min−1 to μl min−1, depending on the excitation parameters. In the low-voltage regime, the flow rate depends quadratically on the voltage applied to the piezoelectric transducer, making the pump programmable. The behavior in the system is elucidated with finite element method simulations, which are in good agreement with experimentally observed behavior. The acoustic radiation force arising due to a fluidic channel resonance is responsible for the focusing of cells and microparticles, while the streaming produced by the pair of sharp edges generates the pumping and the mixing flow. If cell focusing is detrimental for a certain application, it can also be avoided by exciting the system away from the resonance frequency of the fluidic channel. The device, with its unique bundle of functionalities, displays great potential for various biochemical applications.

Publications 1 - 10 of 21

Alen Pavlic

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