• Journal of the Korean Society for Heat Treatment
• /
• v.4 no.4
• /
• pp.44-52
• /
• 1991

The effect of deformation temperature and manganes contents on the tensile properties of duplex stainless steels with the structure of both ferrite and austenite were investigate. For this investigation, Fe-19% Cr-5% Ni-4~8% Mn alloys were prepared. The result obtained from this experiment are summerized as follows. With decreasing deformation temperature, tensile strengths of duplex stainless steel increased. Elongation showd to be increased and then decreased after representing the highest value at specific temperature. Tensile properties of duplex stainless steel were controlled by TRIP behavior in this experimental range of austenite contents. Tensile strengths decreased with increasing Mn contents. With increasing Mn contents, elongation decreased in the high temperature region, but increased in the low temperature region. The peak temperature representing the maximum elongation were changed to low temperature and the width of peak appeared to be broaden with increasing Mn contents.

• Journal of the Korean Ceramic Society
• /
• v.28 no.6
• /
• pp.483-487
• /
• 1991

Ferrite electromagnetic wave absorber whose attenuation ability are mainly relied on their magnetic loss, has been used in relatively narrow wave frequency ranges. In this study, we tried to produce a wide-range electromagnetic wave absorber by laminating sintered ferrite (Mn0.07Ni0.28Zn0.65Fe2O4) and dielectrics (Cordierite). We also investigated effects of dielectric constant and thickness on the attenuation behavior of the absorber. Applicable band width, in which the attenuation is greater than 20 dB can be widened from 100∼700 MHz of ferrite alone to 100∼900MHz by employing the laminated structure. Thickness of dielectrics to achieve wide-range application decreased as the dielectric constant increased.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.19 no.2
• /
• pp.200-206
• /
• 2006

An electric power efficiency of electrodeless fluorescent lamp depens on a big relative property of gas, gas pressure, lamp formation, ingredients of magnetic substance and shape and action frequency etc. in lamp. We used magnetic substance that opens self-examination material of electrodeless fluorescent lamp antenna. We used Mn-Zn type as the Ferrite. We have examined resistance, impedance and Q-factor's frequency characteristic by ferrite. Coil turns were changed from 13 to 15 turns to recognize brightness change of lamp by winding number. Optical equipment (LS-100) was used to measure brightness. We could know Q-factor's difference according to material is important part of antenna design. When an electrodeless fluorescent lamp was made using T company's PE22, it showed the highest brightness. As number of winding is increased the brightness increased, and starting characteristic became good.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
• /
• 2001.11a
• /
• pp.315-318
• /
• 2001

We are proposing a new mobile phone antenna, which has a specially manufactured Mn-Zn cylindrical ferrite bead inside of the helical coil of the antenna. The extended antenna radiation patters and the spatial peak SAR averaged over 1 gram simulated tissue with and without the ferrite bead insertion were measured at 824 MHz. The results show that the ferrite bead resulted in SAR reduction about 20 %, and reflection coefficient increase about 7 % for the extended antenna. The applicability of this scheme to the antenna mass production is quite feasible.

• Journal of electromagnetic engineering and science
• /
• v.6 no.1
• /
• pp.71-75
• /
• 2006

In this study, EM wave absorbers based on Au coated conductive sheets were prepared, and their reflection and transmission coefficients were investigated. An Au coated conductive sheet showed the transmission loss higher than 40 dB in $1{\sim}18$ GHz. Ba ferrite EM wave absorbers with an Au coated conductive sheet showed enhanced EM wave absorption and shield to compare with Ba ferrite EM wave absorbers without conductive sheets. Proposed EM wave absorbers with conductive sheets are useful to protect EM machines from EM interference by strayfields.

• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.31A no.6
• /
• pp.143-148
• /
• 1994

In order to study the effect of D.C resistivity of sample on electromagnetic loss of ferrite at microwave frequency, samples were prepared for having differences in resistivity of an order of two. Microwave permeability($\mu$), permitivity($\varepsilon$) and effective linewidth(${\Delta}H_{eff}$), and ferromagnetic resonance linewidth(${\Delta}$H) were characterized. Tan${\delta}{\mu}$, tan${\delta}{\varepsilon}$ and ${\Delta}H_{eff}$ were decreased with increasing the resistivity and (${\Delta}$H) was increased with increasing Fe concentration, which was due to an increase of anisotropy magnetic field (=Ha).

• Proceedings of the KIEE Conference
• /
• 1998.07g
• /
• pp.2553-2555
• /
• 1998

A single crystal Mn-Zn ferrite was directly etched by focused $Ar^+$ laser beam in $CCl_2F_2$ gas atmosphere. AES has been performed for locally investigating the surface composition of an etched layer. MnCl, ZnCl being created after the substrate and $CCl_2F_2$ chemically reacting was remained in the vicinity of laser irradiation area because of their low vapor pressure. Various patterns using computer were formed on the substrate. The etched grooves and patterned shapes were observed by SEM measurement.

• Journal of the Korean Ceramic Society
• /
• v.29 no.8
• /
• pp.639-645
• /
• 1992

Effects of additives on electromagnetic properties of a Ni-Cu-Zn ferrite for a noise filter in high frequency regions were studied. Both resistivity and permeability were increased with the amount of Mn2O3 up to 1wt%, then decreased with further addition. Addition of Co2O3 decreased the permeability of the ferrite and shifted the resonance frequency to a higher frequency region, which was thought due to the stabilization of domain walls. Therefore it was possible to improve both the permeability and the loss and to control the cut-off frequency by the concurrent addition of Mn2O3 and Co2O3.

• Journal of the Korean Society for Heat Treatment
• /
• v.18 no.1
• /
• pp.3-11
• /
• 2005

Using various thermo-mechanical schedules characterized by varying reheating temperature, deformation temperature and strain, the austenite recrystallization and ferrite refinement of a Nb bearing low carbon steel(0.15C-0.25Si-1.11Mn-0.04Nb) were investigated. For single pass heavy deformations at $800^{\circ}C$, the 40% deformed austenite was not recrystallized while the 80% deformed one was fully recrystallized. Ferrite grains formed in the 80% deformed specimen was not very small compared with those in the 40% deformed specimen, which implied the recrystallized austenite was not more beneficial to ferrite refinement than the non-recrystallized one. In case of deformation in low temperature austenite region, a multi-pass deformation made finer ferrites than a single-pass deformation, as the total reduction was the same, due to more ferrite nucleation sites in the non-recrystallization of austenite for multi-pass deformation. When specimen was deformed at $775^{\circ}C$ that was $10^{\circ}C$ higher than $Ar_3$, the ferrite of about $1{\mu}m$ was formed through deformation induced ferrite transformation(DIFT), and the amount of ferrite was increased with increasing reduction. Dislocation density was very high and no carbides were observed in DIFT ferrites, presumably due to supersaturated carbon solution. By deformation in two phase(50% austenite+50% ferrite) region the very refined ferrite grains of less than $1{\mu}m$ were formed certainly by recovery and recrystallization of deformed ferrites and, a large portion of ferrites were divided by subgrain boundaries with misorientation angles smaller than 10 degrees.

• Journal of the Korean Ceramic Society
• /
• v.16 no.3
• /
• pp.142-154
• /
• 1979

The effects of microstructures and some additives $(CoO and Al_2O_3$) on the magnetic properties such as initial permeability, $\mu$-T curve, coercive force, and magnetic induction of MnZn ferrites have been studied. The powder was prepared by Hot Petroleum Drying Method. The basic composition of MnZn ferrites was 25.5mole % MnO, 22.0 mole% ZnO, 52.5 mole% $Fe_2O_3$. CoO in a concentration range from 0.05 to 0.5 mole% and $Al_2O_3$ from 2.5 to 7.5 mole% were added. Sintered density increased up to 97.5% of theoretical density. Permeability increased as average grain size increased, and that coercive force decreased as average grian size increased. Magnetic induction increased as sintered density increased. The variation of initial permeability with temperature in a temperature range from 0$^{\circ}$ to $60^{\circ}C$ was lowered (a flatter $\mu-T$ curve) as sintering temperature decreased. The compensation temperature To ofmagnetocrystalline anisotropy constant K1 and initial permeability varied with the species and amount of additives. When 0.05 mole% CoO was added to the basic composition, initial permeability at $15^{\circ}C$ increased from 5200 to 5900. The variation ofinitial permeability with temperature in a temperature range from 0^{\circ}to $60^{\circ}C$ was smaller (a flatter $\mu$-T curve) than that of the basic composition of Mn Zn ferrites. When 2.5 mole% $Al_2O_3$ was added, initial permeability at $15^{\circ}C$ decreased from 5200 to 3000. But the variation of initial permeability with temperature in a temperature range from 0$^{\circ}$to $60^{\circ}C$ was smaller (a flat ter $\mu-T$ curve) than when 0.05 mole% CoO was added. Experimental results showed that the conditions necessary for the occurrence of a very high permeability and a flat $\mu$-T curve were controversial even in a temperature range from $0^{\circ}$to $60^{\circ}C$.