Baekil Nam

Broadband RF Noise Suppression by Magnetic Nanowire-Filled Composite Films

The characteristics of the electromagnetic noise suppression have evaluated using magnetic nanowire-filled composite film on a microstrip line in the broadband radio-frequency range from 0.5 to 20 GHz. The ferromagnetic resonance frequency and the relative complex permeability with the change of aspect ratio were calculated by Kittels and Landau-Lifshitz-Gilbert equations. The FMR frequency is gradually increased with the increment of aspect ratio (up to 50) of magnetic nanowire. When the magnetic nanowires were mixed with various aspect ratio in composite, the FMR frequency exhibited the broadband frequency regions with 10-28 GHz, 5-14 GHz, 2.5-7 GHz, and 1-2.7 GHz for the change of magnetizations (4piMs: 20, 10, 5, and 2 kG), respectively. Using the calculated FMR frequency profile, the power losses were obtained in broadband frequency region. The transmission power absorption of the composite film on microstrip line was simulated using a 3-D FEM HFSS simulation program. The microstrip line model was composed of Cu conductor line and grounded dielectric substrates, which was designed by IEC standard (IEC 62333-2). The conduction electromagnetic noise was suppressed by the various aspect ratios of the magnetic nanowire-filled composite films in broadband frequency region.

RF Power Absorption Enhancement of Magnetic Composites with Conductive Grid

To evaluate the electromagnetic power absorption in near field, the magnetic composites with the conductive grids were simulated using the typical permeability frequency profiles. The transmission power absorptions of the magnetic composites on microstrip line were extracted by the 3D FEM simulation program of HFSS. The magnitudes of power absorptions were greatly enhanced up to 98% and broadened the absorbing frequency band over 5 ㎓ by the insertion of a conductive grid in magnetic composite. The initial frequency of the power absorption can controlled by the change of the ferromagnetic resonance frequencies of the magnetic composite.

Synthesis and Characterizations of Surface-Coated Superparamagentic Magnetite Nanoparticles

The uncoated magnetite and the 2, 3-meso-dimercaptosuccinic acid (DMSA)-coated Fe₃O₄ nanoparticles were synthesized by a coprecipitation method, respectively. The DMSA surface modification on magnetite nanoparticles was observed by FT-IR. The average particle sizes of the uncoated magnetite and the DMSA coated magnetite were exhibited approximately 10.4 and 12.3 nm by TEM results. DMSA surface-coated Fe₃O₄ can introduce a dense and thin outer hydroxyl group (-OH) shell. In order to characterize the magnetic behaviors, the magnetization processes of the magnetic nanoparticles were measured with the temperature range of 5 K to 300 K. The mean blocking temperatures of the uncoated Fe₃O₄ and the DMSA surface-coated Fe₃O₄ exhibited about 172 ±28 K and 215 ±30 K, respectively. The value of magnetization of the DMSA-coated Fe₃O₄ nanoparticles was not so different with that of the uncoated Fe₃O₄.

Analysis of effective permeability behaviors of magnetic hollow fibers filled in composite

In order to predict the permeability behaviors of magnetic hollow fibers and their composites in the high frequency region, we proposed a simple hollow approximation method for hollow shaped magnetic particles using the modified demagnetizing factors of Sato’s and Aharoni’s cylindrical approximation methods. The obtained demagnetizing factors of the hollow magnetic particle by the proposed simple hollow approximation were not distinguished from those of the Beleggia’s complicated analytical results. The effective permeability of the magnetic hollow fiber filled in composite was evaluated using the effective medium theory and self-consistent iteration method using the simple hollow approximation. As the hollow ratio increased, the resonance frequency of the permeability shifted to a higher frequency region for the hollow fiber composite as well as for the single hollow fiber. The results of the calculated permeability using the proposed simple hollow approximation were in good agreement with Beleggia’s com...

Thermal conductivity prediction of magnetic composite sheet for near-field electromagnetic absorption

The magnetic composite sheets were designed by using core-shell structured magnetic fillers instead of uncoated magnetic fillers to resolve concurrently the electromagnetic interference and thermal radiation problems. To predict the thermal conductivity of composite sheet, we calculated the thermal conductivity of the uncoated magnetic fillers and core-shell structured fillers. And then, the thermal conductivity of the magnetic composites sheet filled with core-shell structured magnetic fillers was calculated and compared with that of the uncoated magnetic fillers filled in composite sheet. The magnetic core and shell material are employed the typical Fe-Al-Si flake (60 μm × 60 μm × 1 μm) and 250 nm-thick AlN with high thermal conductivity, respectively. The longitudinal thermal conductivity of the core-shell structured magnetic composite sheet (2.45 W/m·K) enhanced about 33.4% in comparison with that of uncoated magnetic fillers (1.83 W/m·K) for the 50 vol. % magnetic filler in polymer matrix.

Metallic Crack Detections by Planar Inductive Coil Sensor Under AC and DC Magnetic Fields

To detect the surface and the opposite side cracks on iron specimen under AC and DC magnetic fields, the planar inductive coil sensors were employed. When the induced signals were measured, the planar inductive coil sensor and the magnetic field source were lifted off about 2 mm from the top surface of the specimen. AC magnetic fields and DC magnetic fields were applied to the specimens by single straight Cu coil and NdFeB permanent magnet, respectively. The detected signals at crack positions were good coincidence with those of the simulation results.

Synthesis and Magnetic Properties of FeCo/Edge-Oxidized Graphene Nanocomposites

The graphene oxide composites with magnetic nanoparticles have attracted in energy storage, and electromagnetic shield and absorption (ESA) applications [1].

The effects of shape anisotropy of the magnetic particles in a composite on RF power absorption

The shape anisotropy of the magnetic particles in a composite film for EMI applications plays a key role in their performance. For a few types of the particles such as wires and hollow fibers, permeabilities of the particles and in-line attenuation of the composite were evaluated by simulations. With the change of the shape anisotropy by aspect ratio or hollow ratio, power absorption could be controlled in frequency. In experiments, Ni/FeCo magnetic hollow fibbers were fabricated by electroless plating and power loss of the composite filled with the fibbers was evaluated.

RF Power Absorption Enhancement by Optimization of the Conductive Grid in a Magnetic Composite

Electromagnetic noise suppression was studied by near-field power absorption of a magnetic composite film composed of magnetic fillers and metallic mesh grid in nonmagnetic matrix, which were simulated using a commercial finite-element electromagnetic solver. The geometrical characteristics of the grid on the power absorption were evaluated using the transmission line method with a microstrip line. For conductive grid spacing and the period of lines composing a grid, maximum power absorption was obtained when the width of microstrip signal line was comparable with the grid spacing. The vertical position of the grid in magnetic composite was suggested to be at the center or top position of the composite for higher power absorption. The power absorptions and bandwidth of frequency were enhanced using thin metallic grid on magnetic composite in comparison with that of thick metallic grid.