FEM-simulations of Tailored 3D Pressure Fields for US-assisted Oleogel Crystallization

Due to their high content of unsaturated fatty acids and controllable mechanical properties, oleogels show promise as a replacement for traditional fats in food products. Controlling the oleogel formation with ultrasound makes it possible to tune the mechanical properties of oleogels, e.g., improving their structural stability and/or mouthfeel. We previously demonstrated tuning of mechanical properties of oleo gels by ultrasonic standing waves (USW) in a closed chamber. Our previous USW chamber only allowed 1D control of the pressure field. To properly tailor the oleogel properties, a more sophisticated chamber design and pressure field control technique is required. A new design for USW chamber and the frequency-domain time-reversal technique for field control were studied via simulations. We show that the proposed technique can create tailored USW fields inside a chamber filled with oil. Further, we show results of particle tracing simulations, and compare the idealized model with realistic phased arrays of transducers, to determine the requirements for the arrays to achieve a suitable resolution for shaping the field.Peer reviewe

High-power and time-reversed ultrasound based on FEM simulations and experiments

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BEM-FEM Simulation of Acoustic Levitation Dynamics with Phased Arrays

We present a simulation model that can be used to study the movement of an object in an acoustic levitator. The model uses the boundary element method (BEM) to compute the levitator's acoustic field, and the finite element method (FEM) to compute the movement of the levitating object. The model was built to act as a virtual tool for testing how objects move in acoustic pressure fields generated by phased array transducers (PATs). This was demonstrated by comparing object dynamics for different PAT optimization methods. We studied the stability of the levitation in fields created by two optimization methods. The fields were optimized to levitate an ellipsoid in the middle of our PAT geometry. By slightly displacing the levitating object from the intended levitation spot, we were able to show that the levitation became unstable and that the object would drop out from the trap. The results demonstrate that the model can be used to rapidly validate optimizers instead of having to run long experiments.Peer reviewe

Simulation of Forward Propagated Signals in Acoustic Time Reversal

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Removing frequency dependent aberrations in acoustic microscopy

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Controlling oleogel crystallization using ultrasonic standing waves

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Practical Scale Modification of Oleogels by Ultrasonic Standing Waves

Lipid-based materials, such as substitutes for saturated fats (oleogels) structurally modified with ultrasonic standing waves (USW), have been developed by our group. To enable their potential application in food products, pharmaceuticals, and cosmetics, practical and economical production methods are needed. Here, we report scale-up of our procedure of structurally modifying oleogels via the use of USW by a factor of 200 compared to our previous microfluidic chamber. To this end, we compared three different USW chamber prototypes through finite element simulations (FEM) and experimental work. Imaging of the internal structure of USW-treated oleogels was used as feedback for successful development of chambers, i.e., the formation of band-like structures was the guiding factor in chamber development. We then studied the bulk mechanical properties by a uniaxial compression test of the sonicated oleogels obtained with the most promising USW chamber, and sampled local mechanical properties using scanning acoustic microscopy. The results were interpreted using a hyperelastic foam model. The stability of the sonicated oleogels was compared to control samples using automated image analysis oil-release tests. This work enabled the effective mechanical-structural manipulation of oleogels in volumes of 10-100 mL, thus paving the way for USW treatments of large-scale lipid-based materials.Peer reviewe

FEM-based time-reversal technique for an ultrasonic cleaning application

Työssäni tutkin mahdollisuutta käyttää akustista ajankääntömenetelmää (time-reversal) teollisen ultraäänipuhdistimen puhdistustehon kohdentamiseen. Akustisella ajankääntömenetelmällä pystytään kohdistamaan painekenttä takaisin alkuperäiseen pisteeseen, tallentamalla ko. pisteestä lähetetyt painesignaalit akustisilla antureilla (etusuunta) ja lähettämällä ne takaisin ajassa käännettyinä (takasuunta). Tässä työssä tutkitun kohdentamismenetelmän perusteena toimii elementtimenetelmällä toteutettu simulaatiomalli, jossa sekä ultraäänipuhdistin, että puhdistettava järjestelmä oli mallinnettu tarkasti. Simulaatiomallin avulla voitiin puhdistettavasta alueesta valita mielivaltainen piste johon halutaan kohdentaa puhdistustehoa. Simuloidun etusuuntaisen ajon tuloksena tuotetut signaalit tuotiin ulos mallista ja takasuuntainen ajo suoritettiin kokeellisessa ympäristössä käyttäen simuloituja signaaleja. Työssä esitetään vertailu simuloidun ja kokeellisen ajankääntömenetelmään perustuvan kohdentamisen tuloksista ja osoitetaan, että simuloiduilla signaaleilla on mahdollista kohdentaa akustista tehoa ennalta valittuun mielivaltaiseen pisteeseen. Lisäksi työssä esitetään analyysi anturien määrän vaikutuksesta kohdentamiskykyyn, tarkastellaan ultraäänipuhdistimen avaruudellista kohdentamiskykyä sekä vahvistetaan simulaatioissa tehdyn lineaarisen oletuksen paikkansapitävyys

FEM-based time-reversal enhanced ultrasonic cleaning

Pipe fouling is a challenging problem in many industrial applications. Current cleaning techniques require halting the production during the cleaning phase and the existing methods are unable to do targeted cleaning, even though fouling is often localized to certain areas inside the pipeline. To address this issue, we use FEM-simulated, time-reversed signals to focus ultrasound power onto a pre-determined location: a fouled pipe residing inside a Plexiglas container. Ultrasound cleaning with similar acoustic power was compared to the time-reversal enhanced method in terms of cleaning efficiency. The cleaning efficiency was determined by measuring how much fouling, by mass, both protocols removed from the surface of a Plexiglas pipe, using similar input electric power and equal cleaning time. Our results indicate that the proposed time-reversal-based technique removes three times more fouling than the standard ultrasound cleaning without focusing. The study extends our previous paper on FEM-based time-reversal focusing [1].Peer reviewe