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SURFACE texture, MICROWAVES, ABSORPTION, IRON powder, ALLOY powders, and ALLOYS

Aiming at enhancing the shape anisotropy of a microwave absorber and elongating the travel distance of microwave along the absorber surface for better absorption, we fabricated the textured nanoflaky powders of Fe–B alloy through the two-step ball milling method followed by dealloying. The complex permittivity and permeability of as-dealloyed powders were characterized systematically. The results showed that the flaky powders of Fe–B with textured structure possess enhanced microwave absorption properties: an optimal reflection loss ($R_{L} = -45.8$ dB) at 9.2 GHz with a matching thickness of 2.4 mm. [ABSTRACT FROM AUTHOR]

TACTILE sensors, SURFACES (Technology), IRON alloys, EULER-Bernoulli beam theory, FARADAY'S law, TOUCH, and PREHENSION (Physiology)

The tactile perception of an object’s surface material plays an important role in many intelligent fields including object recognition, robotic grasp, and environment exploration. Enlightened by the human active tactile perception process that originates from scanning a finger on the surface, a novel finger-like tactile sensor for surface material recognition has been designed according to the transduction mechanism of cilia and Villari effect of the iron–gallium alloy. Based on the structural dynamic theory of Euler–Bernoulli beam, the linear constitutive equations of magetostrictive material and the Faraday law of electromagnetic induction, the output voltage model of the sensor under vibration induced from the fingertip-surface scanning has been established. Furthermore, a prototype of the sensor, on the macroscale, is fabricated. In order to verify the performance, the sensor is used to measure induced vibration signals with texture properties during sliding on the surface and classify five similar texture surfaces with small differences with a classification algorithm. The experimental results indicate that the proposed tactile sensor is effective and highly accurate for surface material classification. The sensor is characterized by high sensitivity and quick response. It has the potential of being miniaturized and integrated into the finger of a robotic hand to realize surface material recognition in real time. [ABSTRACT FROM AUTHOR]

ELECTRIC fields, NUMERICAL calculations, GEOMETRIC modeling, FINITE element method, DIRECT currents, and METALLIC surfaces

In the process of solving electric field of the large-scale complex finite-element models, the fine control of the mesh on the outer surface of metal entity models is often difficult. Therefore, considering the basic geometric structure of the equipment, an efficient finite-element modeling method based on multilayer external surround entities (MESE) is proposed. Taking a simple 2-D model as an example, the algorithm of MESE generation, the principle of region division and related operation flow are introduced. The correctness of the method is validated through the typical case of parallel cylindrical conductors model, and the number of MESE is discussed as well. The proposed method is applied to the surface electric field calculation of the ±1100 kV ultrahigh-voltage direct current converter station valve hall. The calculated maximum electric field strength is 14.2 kV/cm. Furthermore, compared with the submodel method, the accuracy and efficiency of the proposed method are verified. [ABSTRACT FROM AUTHOR]

ELECTRIC lines, HIGH-voltage direct current transmission, SURFACE charges, SPACE charge, SYSTEMS on a chip, and ELECTRIC fields

Charges resulting from corona on dc transmission lines will be driven by the electric field to the space and form the ion flow field. Some space charges will accumulate on the surface of the insulated buildings in the vicinity of high-voltage direct current transmission lines and may lead to human body shock. An improved iterative method is used to solve the ion flow field and accumulated charges according to the boundary condition that the normal component of electric field on the insulated building surface is zero. The accumulated charges are calculated by a 3-D method of characteristics based on the known ion flow field, which avoids large-scale numerical calculation. The calculation results are in a good agreement with the measured data of reduced-scale test under laboratory conditions. [ABSTRACT FROM AUTHOR]

SILICA, MICROWAVES, GEOMETRY, RADAR absorbers, and RADAR cross sections

Thin flexible microwave absorbers are highlighted as current research focus not only for lightweight but also for their easy applicability on the surface of complex geometries. In order to achieve it, we prepared iron microflakes of planar size in the range of 5–15 $\mu \text{m}$ with the thickness of 1–2 $\mu \text{m}$ , and thereafter, silica coating has been provided on surface of flakes by utilizing modified Stöbers method to improve the oxidation resistance. The silica coating on surface of iron microfalkes has been established through different techniques, namely, Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. Rubber-based composites are prepared at different Fe at SiO2 loading fractions [40–70 parts per hundred (PHR)] in nitrile butadiene rubber (NBR) and their electromagnetic properties are investigated. The 70 PHR Fe at SiO2/NBR composite showed more than 90% microwave absorption [reflection loss (RL) > 10 dB] over 10.5–16.5 GHz at absorber thickness of ~1.2 mm and also showed tunable RL of more than 10 dB with variation of thickness from 1 to 2.0 mm within 4–18 GHz. Furthermore, Fe at SiO2 microflakes exhibited better microwave-absorption performance in comparison to uncoated Fe microflakes in the rubber composite, which may be due to improved impedance matching. [ABSTRACT FROM AUTHOR]

NANOWIRES, NANOMEDICINE, MAGNETIC materials, OXIDES, and SERUM albumin

The objective of targeting technologies in the field of nanomedicine is to specifically focus therapies on diseased cells in order to deliver the treatment to these cells without harming healthy ones. The use of magnetic materials in such biomedical applications offers many advantages. They can be functionalized with an agent that enhances the biocompatibility and the targeting while, at the same time, they can be controlled and monitored remotely. Iron nanowires (Fe NWs), which usually have a native oxide shell, are specifically attractive, since they are highly biocompatible, strongly magnetic, and can be coated with different biological agents. Shape anisotropy makes these NWs permanently magnetic and, therefore, can be exploited for multifaceted remote manipulations, rendering them versatile nano-robots. As such, they have been used before in combination with a magnetic field to induce cancer cell death. In order to minimize the side effects of this method, this paper aims to enhance the targeting ability of these NWs toward particular cells. Specifically, leukemic cells are targeted by functionalizing Fe NWs with anti-CD44 antibodies, a cell surface marker, which is overexpressed in leukemic cells compared to healthy blood cells. Fe NWs were electrochemically fabricated with an average diameter of 35 nm and a length around $3~\mu \text{m}$. They were coated with bovine serum albumin to facilitate their conjugation covalently with an anti-CD44 antibody by using 3-(3-dimethyl-aminopropyl) carbodiimide and of N-hydroxysuccinimide. In order to confirm the presence of anti-CD44 antibodies on the surface of the NWs, immunostaining and Fourier transform infrared spectroscopy were used. In addition, cytotoxicity effects of bare Fe NWs and coated and functionalized NWs were studied by using cell proliferation assays. These studies illustrated that the NWs have a high level of biocompatibility. [ABSTRACT FROM AUTHOR]

AMORPHOUS alloys, METAL powders, ACIDS, SOLUTION (Chemistry), METALLIC surfaces, and INSULATING materials

By introducing the SiC/GaN power devices, the high-frequency switching dc–dc converters are expected to have higher efficiency and lightweight. This paper focuses on the Fe-based amorphous alloy powder (Fe–Si–B–Cr–C based) used in the metal composite bulk magnetic core for high-frequency power inductor and transformer. In terms of eddy-current loss at MHz band or beyond, iron-based metal composites are required to have fine magnetic particles with surface insulation layer. In this paper, the finest amorphous powder with a median diameter of 2.57 $\mu \text{m}$ made by water atomization process was used. In order to fabricate the amorphous powder with surface insulation layer, a surface-modification scheme through the two-step acid solution processing using phosphoric acid and hydrochloric acid was introduced. As a result, the surface-modification scheme enabled to make a single-phase silica thin layer on the surface of the amorphous powder, and the silica thin layer was considered to be derivable from the silicon element in the amorphous (Fe–Si–B–Cr–C based) powder. [ABSTRACT FROM AUTHOR]

NANOFABRICATION, MAGNETIC cores, IRON alloys, AMORPHOUS alloys, METAL powders, and PARTICLE size distribution

The authors proposed the iron-based metal composite bulk magnetic core for high efficient and lightweight MHz switching DC–DC converter using SiC/GaN power devices. Although the iron-based metal composite bulk magnetic core exhibited a lower core loss than that of Ni-Zn ferrite in MHz frequency band, its relative permeability was low around 10. In this paper, in order to increase the permeability of such composite magnetic core with low core loss, we investigated an effect of mixing amorphous alloy powder having different particle size distributions. This method estimated increasing volume fraction of amorphous alloy powder and decreasing the demagnetization field of the composite magnetic core. From the experimental results, the composite magnetic core with an optimal mixing ratio of 2.4 $\mu \text{m}$ and 12.8 $\mu \text{m}$ median diameter Fe-based amorphous alloy (Fe-AMO) powders exhibited a relative permeability of 20.5 which was 2.4 times higher than that of composite magnetic core using 2.4 $\mu \text{m}$ median diameter Fe-AMO powders. And its core loss was 555 kW/m3 at 1 MHz in frequency and under 20 mT in maximum flux density. [ABSTRACT FROM AUTHOR]

MICROSTRUCTURE, PARTICLE size distribution, MAGNETIC recorders & recording, MIXTURES, and HIGH temperature metallurgy

Grain size and size distribution reduction in L10 FePt granular thin film is becoming critical to increase the areal storage density and realize the full potential of heat-assisted magnetic recording media. FePt and amorphous carbon or mixture with other segregants are often deposited at elevated temperature in order to promote the L10 ordering in FePt. Due to the materials system and high temperature involved in the fabrication process, the bimodal distribution of the grains is often observed with a significant amount of small grains with diameter <3 nm. The bimodal distribution of the grains could potentially lead to a significant microstructure nonuniformity and thus grain-to-grain properties variation, such as Curie temperature (Tc), texture, ordering, and magnetic properties. In this paper, we performed a detailed analysis on microstructure evolution of FePt-C thin film during the growth process on different initial layer conditions to understand the origin of bimodal grain size distribution in the FePt-C media. Experimental modeling study of depositing FePt on continuous carbon layer at elevated temperature was conducted to understand the nucleation and growth process. [ABSTRACT FROM AUTHOR]

BRAGG gratings, WAVELENGTHS, SURFACE plasmon resonance, DISTRIBUTION (Probability theory), and SIMULATION methods & models

In this paper, we propose a design process for a plasmonic grating structure to induce the resonance at a target wavelength. In a specific condition, surface gratings may induce the surface plasmon propagation due to the diffraction and the resonance wavelength of the surface plasmon propagation is dependent on the grating shape. The grating configuration was designed by the topology optimization scheme based on the reaction-diffusion equation. To shift the resonance wavelength to the target wavelength, this paper maps the frequency response function to a probability distribution function (PDF). The mean value from the PDF becomes a part of the objective function and the design objective is set to minimize the distance between the present resonance wavelength and the target wavelength while keeping the energy intensity. The process of simulation and optimization was performed using the commercial package COMSOL combined with MATLAB programming. [ABSTRACT FROM AUTHOR]

STRUCTURAL optimization, OPTICAL fiber cladding, CALIBRATION, ELECTROMAGNETIC fields, and LASER beams

A methodology of optimizing the process of combined laser cladding with induction preheating is proposed and verified. The resultant shape of the deposited layer consisting of a series of parallel tracks should be as uniform as possible and resistant with respect to cracks of any origin. The main aim is to develop a technique (based on a simple experiment) of calibrating geometrically more complex 3-D arrangements. The task consists of a solution of a strongly nonlinear coupled electromagnetic-thermal problem (forward part) and multi-parametric optimization (backward part). The solution of the forward part uses a specific $h$ -adaptive technique developed by authors that allows working with continuously varying geometry of the system due to added powder material. [ABSTRACT FROM AUTHOR]

NUMERICAL analysis, ELECTROMECHANICAL devices, BOUNDARY element methods, PARAMETER estimation, ELECTRIC fields, and PROBABILITY theory

This paper presents the numerical analysis and experiments on the electromechanical behavior of conducting wired-shape particles. We investigate the effects of particle ending profiles and orientation on the initial motion. The boundary element method is used to analyze the electric field, forces, and torques on the particles. The calculated liftoff electric field is smaller than the estimated value based on a model of infinitely long cylinder, and slightly decreases for a particle with a sharp end when the sharp tip is separated from the electrode. The measured liftoff electric field agrees with the tendency obtained from the numerical analysis. Particles mostly began the motion at either end. When the sharp tip was separated from the electrode, the initial motion almost exclusively took place at the sharp end. On the other hand, the probability was slightly higher for the motion at the rounded end when the sharp tip was close to the electrode. The numerical calculation clarifies that the electrostatic and gravitational torques contribute to such liftoff behavior. [ABSTRACT FROM AUTHOR]

POLYETHERS, LUBRICATION & lubricants, MAGNETIC recording media, DIAMOND-like carbon, MAGNETIC disks, and ADSORPTION

This paper examines the adsorption properties of the perfluoropolyether (PFPE) lubricant SNH2 with an ionic end-group (i.e., amine salt with a diphenylether moiety) for magnetic disk surfaces in heat-assisted magnetic recording (HAMR) drives. For comparison, the well-known lubricant Z-tetraol was used as a reference material. Initially, strong interactions between the ionic end-groups of SNH2 and an applied electric field in the lubricant solution were established. The surface free energy and bonding ratio were also compared before and after ultraviolet (UV) light exposure to diamond-like carbon (DLC) disk surfaces onto, which the lubricants were coated, with their photoelectron currents measured during UV exposure. In addition, the structural characteristics of the SNH2 lubricant on the DLC surface were analyzed using a time-of-flight secondary mass spectroscopy. Furthermore, the thermal stabilities of the lubricant films were compared following laser heating. Overall, SNH2 showed higher adsorption to the DLC surface than Z-tetraol and interacted more strongly with the electric field in the lubricant solution. Furthermore, although SNH2 without UV exposure showed a large polar surface energy, this energy decreased considerably after UV exposure. This decrease is attributed to interactions between photoelectrons emitted from the DLC surface and the ionic bonds of the SNH2 molecules; the cationic segments of the SNH2 ionic bonds dissociate, whereas the anionic main-chains chemisorb on the DLC surface at the electron holes generated from the ejected photoelectrons. SNH2 after the UV exposure showed high thermal stability because of its strong bonding to the DLC surface. Overall, these results demonstrate that a PFPE lubricant with ionic end-groups may be an effective lubricant for HAMR applications. [ABSTRACT FROM AUTHOR]

BISMUTH, SELENIDES, MAGNETIC properties, NICKEL, SURFACE preparation, and MAGNETIC fields

We have investigated magnetic properties of Ni film specimens deposited either on GaAs or on Bi2Se3 surfaces. The magnetization saturation field along the out-of-plane direction observed in the Hall data was weaker for the Ni/Bi2Se3 sample than for the Ni/GaAs sample. On the other hand, planar Hall resistance measurements showed the larger in-plane coercive field for Ni/Bi2Se3 than for Ni/GaAs. These changes of magnetic hardness observed along the out-of-plane and in-plane directions in the Ni/Bi2Se3 specimen are consistent with effects arising from spin–orbit interaction at the surface of the Bi2Se3 topological insulator. [ABSTRACT FROM AUTHOR]

AMORPHOUS alloys, EPOXY resins, MAGNETIC cores, SURFACE preparation, and DC-to-DC converters

To realize a compact, lightweight and high-efficiency megahertz (MHz) switching DC–DC converter using SiC/GaN power device, inductor/transformer core must have small core loss at such high frequency to maintain high efficiency of the converter. This paper focuses on Fe-based amorphous (Fe-AMO) alloy powder used in metal composite bulk magnetic core for MHz switching DC–DC converter, where fine Fe-AMO powder with a mean diameter of 2.56~ \mu \textm was used to suppress MHz band eddy current inside the Fe-AMO powder body. When applying Fe-AMO powder to the closely packed composite core together with epoxy resin, high electrical-resistivity layer must be formed on the Fe-AMO powder surface in order to suppress the overlapped eddy current between adjacent Fe-AMO powders. In this paper, about 10 nm-thick oxidized layer of the Fe-AMO powder surface was successfully formed by using annealing in dry air. This paper describes on the surface-oxidized Fe-AMO powder/epoxy-resin composite bulk core transformer and its application to GaN power device MHz switching LLC resonant DC–DC converter. By using the Fe-AMO composite core transformer, the fabricated 48 V-input/24 V-output LLC resonant converter exhibited 90% over efficiency in the output power range of 24 to 120 W, which was higher efficiency when using the Ni–Zn ferrite core transformer. [ABSTRACT FROM AUTHOR]

POROSITY, MAGNETS, ELECTRIC discharges, SINTERING, and MAGNETIC properties

Traditional techniques for consolidating melt spun RE–Fe–B powders tend to incur significant volumes of non-magnetic material, like porosity and the polymer binder. Several alternative consolidation techniques are being studied in an effort to reduce the non-magnetic component and improve the overall performance of such magnets. Rapid electric discharge sintering (REDS) offers one method of fully densifying melt spun RE–Fe–B flakes in a rapid and efficient way with minimal material wastage. This paper attempted to consolidate stoichiometric RE2Fe14B, RE-lean and RE-rich compositions with REDS, spark plasma sintering and conventional hot-tool techniques. The relative magnetic performance and physical condition of the samples are compared. The success of a consolidation technique depends on the melt spun RE–Fe–B chemistry, the relative density of the final compact, and the ability to avoid excessive grain growth in the magnet microstructure. [ABSTRACT FROM AUTHOR]

AMORPHOUS magnetic materials, MAGNETIC particles, MAGNETIC materials, MAGNETIC fluids, and MAGNETIC nanoparticles

Magnetoimpedance (MI) has been proposed as a sensible detection method for quantifying the concentration of magnetic microparticle and nanoparticle. The use of samples with severe surface roughness, induced by acid treatments, seems to enhance the detection power. Here, we clarify the role of surface modification in the detection of magnetic particles and ferrofluids. Experimentally, lithography is used to produce a regular pattern of pits in an amorphous ribbon. The influence of the patterning on the MI of the sample, in the presence of magnetic nanoparticles, is analyzed. Contrary to what has been published previously, the patterning seems to worsen the particle detection capability. To clarify the situation, a thorough study is performed with numerical simulations using a finite-element analysis resembling the experimental conditions in a 2-D geometry. The presence of magnetic particles is simulated as a continuum medium with a given permeability, which is a realistic assumption for the case for ferrofluids. The conclusion is that the effect of the magnetic particles on MI depends strongly on the characteristics of the patterning and on the concentration of particles. The simulation results not only qualitatively explain ours experimental results, but also help interpreting previous reports and hints the optimal conditions for the surface patterning in order to maximize the sensibility of the sample to the presence of magnetic particles. [ABSTRACT FROM AUTHOR]