Ústav fyzikálního inženýrství

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Enhanced magnetic field concentration using windmill-like ferromagnets
(AIP Publishing, 2024-02-01) Bort-Soldevila, Natanael; Cunill-Subiranas, Jaume; Barrera, Aleix; Del-Valle, Nuria; Silhanek, Alejandro V.; Uhlíř, Vojtěch; Bending, Simon; Palau, Anna; Navau, Carles
Magnetic sensors are used in many technologies and industries, such as medicine, telecommunications, robotics, the Internet of Things, etc. The sensitivity of these magnetic sensors is a key aspect, as it determines their precision. In this article, we investigate how a thin windmill-like ferromagnetic system can hugely concentrate a magnetic field at its core. A magnetic sensor combined with such a device enhances its sensitivity by a large factor. We describe the different effects that provide this enhancement: the thickness of the device and its unique windmill-like geometry. An expression for the magnetic field in its core is introduced and verified using finite-element calculations. The results show that a high magnetic field concentration is achieved for a low thickness-diameter ratio of the device. Proof-of-concept experiments further demonstrate the significant concentration of the magnetic field when the thickness-diameter ratio is low, reaching levels up to 150 times stronger than the applied field. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Simulation of optomechanical interaction of levitated nanoparticle with photonic crystal micro cavity
(Optica Publishing Group, 2024-02-13) Maňka, Tadeáš; Šiler, Martin; Liška, Vojtěch; Zemánek, Pavel; Šerý, Mojmír; Brzobohatý, Oto
We propose and analyze theoretically a promising design of an optical trap for vacuum levitation of nanoparticles based on a one-dimensional (1D) silicon photonic crystal cavity (PhC). The considered cavity has a quadratically modulated width of the silicon wave guiding structure, leading to a calculated cavity quality factor of 8 x 105. An effective mode volume of approximately 0.16 mu m3 having the optical field strongly confined outside the silicon structure enables optical confinement on nanoparticle in all three dimensions. The optical forces and particle -cavity optomechanical coupling are comprehensively analyzed for two sizes of silica nanoparticles (100 nm and 150 nm in diameter) and various mode detunings. The value of trapping stiffnesses in the microcavity is predicted to be 5 order of magnitudes higher than that reached for optimized optical tweezers, moreover the linear single photon coupling rate can reach MHz level which is 6 order magnitude larger than previously reported values for common bulk cavities. The theoretical results support optimistic prospects towards a compact chip for optical levitation in vacuum and cooling of translational mechanical degrees of motion for the silica nanoparticle of a diameter of 100 nm.
Zero-field spin wave turns
(AIP Publishing, 2024-03-11) Klíma, Jan; Wojewoda, Ondřej; Roučka, Václav; Molnár, Tomáš; Holobrádek, Jakub; Urbánek, Michal
Spin-wave computing, a potential successor to CMOS-based technologies, relies on the efficient manipulation of spin waves for information processing. While basic logic devices such as magnon transistors, gates, and adders have been experimentally demonstrated, the challenge for complex magnonic circuits lies in steering spin waves through sharp turns. In this study, we demonstrate with micromagnetic simulations and Brillouin light scattering microscopy experiments, that dipolar spin waves can propagate through 90 degrees turns without distortion. The key lies in carefully designed in-plane magnetization landscapes, addressing challenges posed by anisotropic dispersion. The experimental realization of the required magnetization landscape is enabled by spatial manipulation of the uniaxial anisotropy using corrugated magnonic waveguides. The findings presented in this work should be considered in any magnonic circuit design dealing with anisotropic dispersion and spin wave turns.
Innovative approach for quantitative determination of ingested microplastics by Daphnia magna: use of differential scanning calorimetry and thermogravimetry
(Springer Nature, 2024-04-08) Procházková, Petra; Kalčíková, Gabriela; Maršálková, Eliška; Zlámalová Gargošová, Helena; Kučerík, Jiří
Due to the serious environmental impacts of plastic pollution, some conventional plastics have been replaced with biodegradable alternatives. However, these biodegradable options can also fragment and form microplastics, which can be ingested by and harm various biota. The standard methods for quantifying ingested microplastics involve digestion of the gut or the whole organism using acidic, alkaline, or oxidative processes. However, these aggressive methods may destroy biodegradable microplastics, leading to erroneous results. Therefore, in this study, we employed thermal analysis methods, specifically differential scanning calorimetry (DSC) and thermogravimetry (TG), to quantify the ingestion of poly-3-hydroxybutyrate (P3HB), a biodegradable microplastic, by the freshwater crustacean, Daphnia magna. During chronic experiments, we analysed organisms exposed to P3HB with sizes smaller than 125 and 63 m, at concentrations ranging from 1.56–25 mg L1. DSC identified an endothermic peak associated with the melting of semicrystalline P3HB, and its enthalpies were utilised to compute the number/mass of P3HB ingested by D. magna. Notably, shifts in melting points suggested that higher concentrations induced particle agglomeration, and these agglomerates could not penetrate deeply into the organism. The TG approach involved subtracting the mass loss between 200 and 400 °C in D. magna specimens exposed to P3HB suspensions from controls without P3HB exposure. Both methods provided comparable data, revealing that, depending on particle size, individual D. magna ingested up to 10% of their body mass. Our findings indicate that both methods effectively detect P3HB (and potentially other plastic fragments), with DSC demonstrating better sensitivity. While the suggested approach did not enable us to calculate the level of determination or quantification, we were able to demonstrate that DSC can detect P3HB in only one specimen of D. magna exposed to the lowest suspension concentration. This indicates that D. magna exposed to the 63 m fraction ingested approximately 3 g of P3HB, whereas those exposed to the 125 m P3HB ingested around 4 g of P3HB. The introduced methods expand the possibilities for detecting ingested microplastics and probably also nanoplastics, in zooplankton and possibly also other species.
Next-generation photocatalytic system: Ga2O3-modified Ga Nanoislands on graphene for H2 production
(Elsevier, 2024-05-24) Bartošík, Miroslav; Edelmannová, Miroslava Filip; Mach, Jindřich; Kočí, Kamila
Study investigates Ga2O3/Ga on Graphene/SiO2/Si, prepared via temperature-controlled growth of Ga, for photocatalytic hydrogen generation, marking the first exploration of this system for such purpose. Thin surface ultra-wide band gap Ga2O3 layer effectively photoemits electron-hole pairs under UVC and the metallic Ga cores enhance electric field separating charge carriers by formation of localized surface plasmon (LSP) resonances. These effects increase hydrogen yields. Computational analysis of LSP-induced electric field enhancement quantitatively supports proposed fundamental mechanism underlying sample's photoactivity. The most active photocatalyst (Ga-M) with medium-size Ga particles (radius 14 nm) exhibited ten thousand times higher activity per gram than commercial TiO2.

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