Browsing by Author "Fatikow, Sergej"

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  • Droplet Probe for Characterization of Advancing and Receding Contact Angles of Single Fibers
    (2023) Freitas Vieira, Arthur; Vuckovac, Maja; Schlapp-Hackl, Inge; Hummel, Michael; Zhou, Quan
     A4 Artikkeli konferenssijulkaisussa
    Characterizing the wetting properties of fibers is crucial for many research and industry applications, including textiles for water-oil separation and composite materials. Those fibers are often soft, typically tens of micrometers in diameter but millimeters in length, making manipulation and characterization difficult. Contact angles of single fibers are usually determined by droplet shape analysis or force-based Wilhelmy method. However, these methods are unable to accurately measure contact angles above 60∘ or ensure reliable control of the liquid-fiber interaction process, especially for soft fibers prone to bending. Consequently, reliable characterization of the advancing and receding contact angles of single fibers remains a challenge. Here we report a novel method for characterizing the advancing and receding contact angles of both soft and rigid single fibers using a millimeter-sized droplet probe affixed to a disk and a numerical model of the system. By analyzing side-view images, we extract key geometrical parameters of the disk-droplet-fiber system, which, when used in detailed simulations, allows estimating the contact angle of fibers ranging from 20∘ to 140∘ . We applied this method to characterize three distinct micro-fibers: a highly hydrophilic rigid borosilicate glass fiber, a mildly hydrophilic soft PET fiber, and a rigid hydrophobic tungsten wire coated with a commercial super-repellent coating.
  • Formation of nanospikes on AISI 420 martensitic stainless steel under gallium ion bombardment
    (2019-10-01) Cenev, Zoran; Bartenwerfer, Malte; Klauser, Waldemar; Jokinen, Ville; Fatikow, Sergej; Zhou, Quan
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The focused ion beam (FIB) has proven to be an extremely powerful tool for the nanometer-scale machining and patterning of nanostructures. In this work, we experimentally study the behavior of AISI 420 martensitic stainless steel when bombarded by Ga+ ions in a FIB system. The results show the formation of nanometer sized spiky structures. Utilizing the nanospiking effect, we fabricated a single-tip needle with a measured 15.15 nanometer curvature radius and a microneedle with a nanometer sized spiky surface. The nanospikes can be made straight or angled, depending on the incident angle between the sample and the beam. We also show that the nanospiking effect is present in ferritic AISI 430 stainless steel. The weak occurrence of the nanospiking effect in between nano-rough regions (nano-cliffs) was also witnessed for austenitic AISI 316 and martensitic AISI 431 stainless steel samples.
  • Learning to Shape Liquid Droplets on an Air-Ferrofluid Interface with Sequences of Actuation
    (2023-10-13) Patikiri Arachchige, Diluka; Zhou, Quan
     A4 Artikkeli konferenssijulkaisussa
    Shape morphing of liquid droplets is important for advances in both medical and industrial applications. However current manipulation techniques lack methods to control shapes other than elliptical-shaped droplets. Here we propose using Long Short-Term Memory (LSTM) based model to learn and predict the evolution of the shape of a non-magnetic liquid droplet at an air-ferrofluid interface deformed with programmed sequential actuation of electromagnets. The resulting droplet shapes can be convex or concave. We can also predict the actuation sequences for a given shape sequence with an accuracy of 79.1 %. The proposed method could also be applied to a variety of other liquid droplet shape-morphing systems which utilize arrays of electromagnetic or electric actuators.
  • Rapid mode-switching for acoustic manipulation
    (2019-07-01) Latifi, Kourosh; Kopitca, Artur; Zhou, Quan
     A4 Artikkeli konferenssijulkaisussa
    Acoustic manipulation techniques are becoming increasingly common with a range of applications in the biomedical research, microassembly, and lab-on-a-chip. Recently, a class of devices have attracted considerable attention which utilize dynamic and reconfigurable acoustic fields, known as dynamic-field acoustic devices. A common method of applying dynamic fields is to use mode-switching by rapidly altering the excitation frequency. Such methods generally rely on the switching being performed faster than the time constant associated with the particle motion. Nevertheless, it remains a grand challenge to eliminate or at least reduce the switching time to a minimal value. In this paper, we suggest employing a high-speed controller to minimize the switching time, enabling continuous particle manipulation in a dynamic-field acoustic device. As a proof-of-concept, we apply such idea to a classic acoustic manipulation device, a Chladni plate which consists of a centrally-actuated vibrating plate. By employing a closed-loop real-time controller, we show successful manipulation of particles on the plate on predefined trajectories. The high-speed switching methodology can also be applied to other dynamic-field acoustic methods, such as surface acoustic wave (SAW) devices, acoustic levitators, and in-fluid acoustic devices. This can result in faster and smoother particle manipulation in such devices.
  • Robotic Fiber Fabrication based on Solidification Force Control
    (2022) Bettahar, Houari; Valisalmi, Teemu; Linder, Markus; Zhou, Quan
     A4 Artikkeli konferenssijulkaisussa
    In this paper, we propose a robotic fiber fabrication method based on solidification force control to achieve highly repeatable mechanical properties of fibers. Dextran material is used as the specimen in the experiments. It has been chosen because of its similar rheological behavior to silk protein at high mass concentrations. However, the viscosity of dextran material is very low at its liquid phase, so force control during fabrication is challenging. Here, we propose a novel approach that controls the mechanical properties of fiber by controlling the solidification force. We employ impedance control with force tracking to control the solidification force to carry out the threading experiments and examine the benefits of the proposed approach. The repeatability of the mechanical properties of the fabricated fibers has been studied and compared using three scenarios a) fiber fabrication without solidification force control, abbreviated as FFNC, b) fiber fabrication with solidification force control after 60 seconds of solidification from the beginning of the solidification force detection abbreviated as FFWC, and c) fiber fabrication with solidification force control immediately after the detection of the solidification force, abbreviated as FFSC. The experimental results show that fibers fabricated using FFSC scenario have the highest repeatability based on the coefficient of variation of properties of the fabricated fibers, where the obtained coefficient of variation of the toughness, stiffness, elongation, and strength are 12.8%, 13.6%, 14.8%, 12.7% respectively. The experimental results also showed that fibers' mechanical properties toughness, stiffness, elongation, and strength have a negative correlation with the fabrication pulling velocity.
  • Simultaneous and Independent Micromanipulation of Two Identical Particles with Robotic Electromagnetic Needles
    (2022) Isitman, Ogulcan; Kandemir, Hakan; Alcan, Gokhan; Cenev, Zoran; Zhou, Quan
     A4 Artikkeli konferenssijulkaisussa
    Magnetic manipulation of particles at close vicinity is a challenging task. In this paper, we propose simultaneous and independent manipulation of two identical particles at close vicinity using two mobile robotic electromagnetic needles. We developed a neural network that can predict the magnetic flux density gradient for any given needle positions. Using the neural network, we developed a control algorithm to solve the optimal needle positions that generate the forces in the required directions while keeping a safe distance between the two needles and particles. We applied our method in five typical cases of simultaneous and independent microparticle manipulation, with the closest particle separation of 30 μm.