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

Defect localization by an extended laser source on a hemisphere

The primary goal of this study is to localize a defect (cavity) in a curved geometry. Curved topologies exhibit multiple resonances and the presence of hotspots for acoustic waves. Launching acoustic waves along a specific direction e.g. by means of an extended laser source reduces the complexity of the scattering problem. We performed experiments to demonstrate the use of a laser line source and verified the experimental results in FEM simulations. In both cases, we could locate and determine the size of a pit in a steel hemisphere which allowed us to visualize the defect on a 3D model of the sample. Such an approach could benefit patients by enabling contactless inspection of acetabular cups.Peer reviewe

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

Removing frequency dependent aberrations in acoustic microscopy

Peer reviewe

Scaling-up the Ultrasound-Enhanced Electrospinning Device

Ultrasound-enhanced electrospinning (USES) is an electrospinning method that utilizes focused ultrasound to produce nanofibers. The focused ultrasound creates an acoustic fountain on a polymer solution surface. With a high-voltage electric field, electrospinning is initiated from the fountain. Until now USES has been limited by its production rate due to the use of a single ultrasound transducer. Here we present a multi-transducer USES device, with a similar footprint as our old device. Increase in throughput was studied using three of the transducers. Simultaneous, stable spinning, with three transducers was not achieved, however we double the amount of produced fiber with two transducers. Compared to the previous USES device, the results indicate that USES can potentially be scaled up.Peer reviewe

The Role of Acoustic Streaming in Ultrasound-Enhanced Electrospinning - a FEM Simulation Study

We present a finite element method (FEM)-based simulation model for acoustic streaming and fountain formation. Streaming field predicted by the model shows agreement with experiments in a validation study. After validation, the model is used to predict the acoustic streaming field in our ultrasound-enhanced electrospinning device. The predicted field gives velocity magnitudes in the micrometers per second range. While this appears slow, such a rate is hypothesized to be significant for the process. Finally, surface force driven acoustic streaming is observed by the simulations.Peer reviewe

Ultrasonic Fouling Detector Powered by Machine Learning

Guided waves can be used to monitor structural health in industrial pipelines, and e.g. allow detection of accumulated precipitation on the surface of pipe. Propagation of guided waves in a tubular structure carrying possible fouling can be separated from a clean structure due to variation in wave propagation properties at the fouled area. In addition, multiple propagation paths around the tubular structure allow locating the fouled areas. In this study, we obtained dispersion curves of a tubular structure loaded with a local fouling layer of different thickness by using numerical simulations. We combined the dispersion curve information with simulated and measured times-of-arrival of guided wave propagation to second order helicoidal paths and used a Gaussian Process machine learning approach to estimate location of fouling on a steel pipe.Peer reviewe

Quantifying the Role of Transport by Acoustic Streaming in MHz Focused-Ultrasound-Based Surface Sampling

We have developed an ultrasound-based surface sampling method permitting surface studies for liquid immersed samples. The method employs high-intensity focused ultrasound, which can remove material from predetermined areas and induce acoustic streaming that causes the immersion liquid to flow. In this study, we studied several conditions of acoustic streaming, which can affect particle transport away from the sampled surface. First, we explored suitable acoustic streaming conditions by finite element modelling. Next, we measured the induced streaming fields by particle image velocimetry. This study comprised cases, when a high-intensity focused ultrasound beam encountered a solid surface at different transducer-surface distances. A change in direction of streaming occurred when a focusing transducer was moved from −2λ defocus to -4λ defocus (towards the surface). Thus, we found suitable conditions for an upwards directing acoustic streaming field. This kind of defocus condition can be coupled to the surface sampling process allowing efficient particle transport for subsequent chemical analysis.Peer reviewe