Browsing by Subject "Electronics and Industrial Physics"

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  • Bäckroos, Sami (Helsingin yliopisto, 2021)
    High pressure inside e.g. blood vessels or other biological cavities is a major risk factor for many preventable diseases. Most of the measuring methods require physical contact or other kinds of projected forces. Both variants can be unpleasant for the patient and additionally physical contact might warrant for either continuous disinfecting or single-use probes, depending on the measurement method and the target body part. We have been experimenting with handheld non-contacting pressure measuring devices based on acoustic waves. These excite mechanical waves, whose velocity varies with pressure, on the surface of a biological cavity. The tried excitation methods are nearly unnoticeable for the patient, allowing for more pleasant and waste free measurements. Using the data from the latest clinical trial, a new analysis algorithm was devised to improve the accuracy of the pressure estimates. Instead of the time-of-flight (TOF) of the main mechanical wave (MMW), the new algorithm estimates the pressure using the MMW and a previously unseen feature, improving the R^2 from 0.60 to 0.72.
  • Hyvönen, Jere (Helsingin yliopisto, 2021)
    High-intensity and -amplitude focused ultrasound has been used to induce cavitation for decades. Well known applications are medical (lithotripsy and histotripsy) and industrial ones (particle cleaning, erosion, sonochemistry). These applications often use low frequencies (0.1-5 MHz), which limits the spatial precision of the actuation, and the chaotic nature of inertial cavitation is rarely monitored or compensated for, constituting a source of uncertainty. We demonstrate the use of high-frequency (12 MHz) high-intensity (ISPTA=90 W/cm2 ) focused-ultrasound- induced cavitation to locally remove solid material (pits with a diameter of 20 µm to 200 µm) for non- contact sampling. We demonstrate breaking cohesion (aluminium) and adhesion (thin film on a substrate, i.e. marker ink on microscope glass). The eroded surfaces were analyzed with a scanning acoustic microscope (SAM). We present the assembly and the characterization of a focused ultrasound transducer and show quantification of the effect of different sonication parameters (amplitude, cycle count, burst count, defocus) on the size and shape of the resulting erosion pits. The quantitative precision of this method is achieved by systematic calibration measurements, linking the resulting erosion to acoustic parameters to ensure repeatability (sufficient probability of cavitation), and inertial cavitation monitoring of the focal echoes. We discuss the usability of this method for localized non-contact sampling.
  • Tommiska, Oskari (Helsingin yliopisto, 2021)
    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.
  • Malinen, Henri (Helsingin yliopisto, 2021)
    Dendrite prevention can be achieved by manipulating the local chemical concentration gradient by ultrasound. An ultrasonic field, which generates acoustic streaming, can manipulate the ionic flux at the electrode surface by altering the local ion concentration gradient at said surface according to the streaming pattern. The pattern is determined by the ultrasonic field and the geometry of the sonication volume. The preventive action can be directed to an arbitrary point on the surface, or be swept across it to achieve a smoother electroplating. Dendritic growth is concentrated to areas of higher concentration gradient. This is because at the electrode surface both the electric and convective fluxes tend to zero. If the reduction of ions into their metallic form is fast enough, the metal layer growth rate is determined by the diffusive flux, which is determined by the ion concentration gradient and the diffusion constant of the ion in the electrolyte. In this study, tin was used as the transported ion instead of lithium for safety reasons. A custom-made battery mockup cell was constructed for the experiments. The anode was imaged with a usb microscope camera to determine the growth of the dendrites during the process. The electroplating current and piezo driving power were varied between 100 mA to 275 mA and 0 to 6.6 W, respectively. With piezo driving electrical power less than 10 W, it was possible to lower the maximum lengths of dendrites. Finite element method simulations were conducted to validate the hypothesis and experimental results. This ultrasonic method could be used to allow rechargeable, lightweight, high capacity lithium metal batteries. The piezos could be integrated into battery chargers.
  • Puranen, Tuomas (Helsingin yliopisto, 2020)
    Acoustic levitation permits non-contacting particle manipulation. The position and orientation of the levitated particle can be controlled by altering the acoustic field. Existing acoustic levitators have employed a single frequency which limits the types of acoustic traps that can be created. The use of multiple frequencies makes it possible to control the forces acting on a particle independently in all directions. I predict theoretically the forces acting on particles placed in the acoustic fields created with multiple coexisting frequencies. I present two traps which demonstrate the benefits of multifrequency acoustic levitation. To realize the traps, I constructed a 450-channel phased array acoustic levitator with individual frequency, phase, and amplitude control for each channel.
  • Helander, Petteri (Helsingin yliopisto, 2020)
    Omnidirectional microscopy (OM) is an emerging technology capable of enhancing the threedimensional (3D) microscopy widely applied in life sciences. In OM, precise position and orientation control are required for the sample. However, the current OM technology relies on destructive, mechanical methods to hold the samples, such as embedding samples in gel or attaching them to a needle to permit orientation control. A non-contacting alternative is the levitation of the sample. But, until now, the levitation methods have lacked orientation control. I enable omnidirectional access to the sample by introducing a method for acoustic levitation that provides precise orientation control. Such control around three axes of rotation permits imaging of the sample from any direction with a fixed camera and subsequent 3D shape reconstruction. The control of non-spherical particles is achieved using an asymmetric acoustic field created with a phase-controlled transducer array. The technology allows 3D imaging of delicate samples and their study in a time-lapse manner. I foresee that the described method is not only limited to microscopy and optical imaging, but is also compatible with automated sample handling, light-sheet microscopy, wall-less chemistry, and noncontacting tomography. I demonstrate the method by performing a surface reconstruction of three test samples and a biological sample. In addition, a simulation study and the levitation of test samples were used to characterize the levitation technique's performance. Both the shape reconstruction and orientation recovery were done by a computer vision based approach where the different images are stitched together. The results show the rotation stability and the wide angle range of the method.
  • Lassila, Petri (Helsingin yliopisto, 2021)
    Lipid-based solid-fat substitutes (such as oleogels) structurally modified using ultrasonic standing waves (USW), have recently been shown to potentially increase oleogel storage-stability. To enable their potential application in food products, pharmaceuticals, and cosmetics, practical and economical production methods are needed compared to previous work, where USW treated oleogel production was limited to 50-500 µL. The purpose of this work is to improve upon the previous procedure of producing structurally modified oleogels via the use of USW by developing a scaled up and convenient approach. To this aim, three different USW chamber prototypes were designed and developed, with common features in mind to: (i) increase process volumes to 10-100 mL, (ii) make the sample extractable from the treatment chamber, (iii) avoid contact between the sample and the ultrasonic transducer. Imaging of the internal structure of USW treated oleogels was used as the determining factor of successful chamber design. The best design was subsequently used to produce USW treated oleogels, of which the bulk mechanical properties were studied using uniaxial compression tests, along with local mechanical properties, investigated using scanning acoustic microscopy. Results elucidated the mechanical behaviour of oleogels as foam-like. Finally, the stability of treated oleogels was compared to control samples using an automated image analysis oil release test. This work enables the effective mechanical-structural manipulation of oleogels in volumes of 10-100 mL, paving the way to possible large-scale lipid-based materials USW treatments.
  • Kekkonen, Tuukka (Helsingin yliopisto, 2021)
    The sub-λ/2 focusing, also known as super resolution, is widely studied in optics, but only few practical realizations are done in acoustics. In this contribution, I show a novel way to produce sub- λ/2 focusing in the acoustic realm. I used an oil-filled cylinder immersed in liquid to focus an incident plane wave into a line focus. Three different immersion liquids were tested: water, olive oil, and pure ethanol. In addition to the practical experiment, we conducted a series of finite element simulations, by courtesy of Joni Mäkinen, to compare to the experimental results.
  • Mustonen, Joonas (Helsingin yliopisto, 2021)
    Pipe fouling is a challenging problem in many industrial applications. Established cleaning techniques require that the production is aborted during the cleaning phase. These techniques are unable to focus cleaning power, even though fouling often is localized to certain areas inside the pipeline. This study introduces an effective method to clean fouling inside complex structures. We use finite-element modelling (FEM) -based time-reversed signals to focus ultrasound power onto a predetermined pipe residing inside a Plexiglas container. We compare the cleaning effect obtained by this method with the cleaning obtained with standard ultrasound cleaning when using the same input electric power and cleaning time. Our results indicate that the proposed time-reversal based technique removes more fouling compared to when using the standard technique. Moreover, we demonstrate ability to relocate the focus including changing the target from one pipe to another one inside the container.
  • Järvinen, Miikka (Helsingin yliopisto, 2020)
    Two different bio transfer standards (BTS), composed of fatty acid bilayers, NanoRuler and NanoStar were developed. NanoRuler consists of a nanometer scale staircase with eight steps that are 5 nm tall each and NanoStar is designed to have topological structure with sharp edge and three height planes 5 nm elevated with respect to each other. With NanoRuler nanometer vertical calibration from 5 nm to 40 nm is possible and NanoStar allows the evaluation of the instrument transfer function (ITF). Due to the soft nature of the standards, the topographical stability was researched. Thus, an investigation of the topographical stability of three NanoRulers and one NanoStar across 24 months was done by measuring the surface topography with a custom-built Scanning White Light Interferometer (SWLI). The BTS were measured over 100 times during the experiments and were stored in laboratory conditions. The step heights of the structures were calculated with a histogram method and the surface roughness of the samples was evaluated using the Sq parameter. The step height analysis method was compared to the standard method (ISO 5436-1) where applicable and no notable differences were found. In both roughness and step height data no linear or non-linear trends were found, and the step heights compared well with the literature values. For NanoRuler the step heights were 4.9 nm, 10.1 nm, 15.1 nm, 20.1 nm, 25 nm, 30.1 nm, 35.1 nm and 40.2 nm and the respective stabilities were 0.3 nm, 0.3 nm, 0.6 nm, 0.9 nm, 1.3 nm, 1.6 nm, 2.1 nm, and 2.5 nm. For NanoStar the step heights were -5.1 nm and 5.2 nm with stabilities 0.3 nm and 0.4 nm respectively. The NanoRuler had a surface roughness stability of 0.02 nm whereas NanoStar had a roughness stability of 0.01 nm. After 24 months both BTS types preserved their topographical structure and no issues with surface topographical stability were observed.