• Journal of Magnetics
• /
• v.2 no.1
• /
• pp.25-27
• /
• 1997

Ferrite tile absorber is of great concern for the application to anechoic chambers due to the growing demand of EMI or EMC measurements. This paper investigates the magnetic, dielectric and microwave absorbing properties of a Ni-An ferrite for the purpose. A design chart was constructed with the solutions of impedance-matching equation in the radio frequencies (30 MHz - 1 GHz). The material parameters for zero-reflection are predicted from the chart. The magnetic and dielectric properties of sintered Ni-Zn ferrite is found to be well suited for this requirements. A superior microwave absorbing properties (frequency band and absorber thickness) of the samples are demonstrated.

• Journal of the Korean institute of surface engineering
• /
• v.50 no.3
• /
• pp.212-218
• /
• 2017

$Mg_xNi_yZn_{1-x-y}Fe_2O_4$ ferrite powders were prepared by self-propagating high temperature synthesis followed by classifying with an ultrasonic wet-magnetic separation unit to get high pure nano-sized particles. The $Mg_xNi_yZn_{1-x-y}Fe_2O_4$ ferrites were well formed by using several powders like iron, nickel oxide, zinc oxide and magnesium oxide at 0.1 MPa of oxygen pressure. The ultrasonic wet-magnetic separation of pre-mechanical milled ferrite powders resulted in producing the powders with average size of 800 nm. The addition of a surfactant during the wet-magnetic separation process improved productivity more than twice. The coercive force, maximum magnetization and residual magnetization of the $Mg_xNi_yZn_{1-x-y}Fe_2O_4$ nano-powders with 800 nm size were 3651 A/m, $53.92Am^2/kg$ and $4.0Am^2/kg$, respectively.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2016.11a
• /
• pp.201.2-201.2
• /
• 2016

$Mg_xNi_yZn_{1-x-y}Fe_2O_4$ ferrite powders were prepared by self-propagating high temperature synthesis followed by classified by ultrasonic wet-magnetic separation method to get nano-sized particles with high purity. The $Mg_xNi_yZn_{1-x-y}Fe_2O_4$ ferrites were well formed by using several powders like iron, nickel oxide, zinc oxide and magnesium oxide at 0.1 MPa of oxygen pressure. The ultrasonic wet-magnetic separation of pre-mechanical milled ferrite powders produced the powders with average size of $3.7-0.8{\mu}m$. The addition of a surfactant during the separation process improved productivity more than twice. The coercive force, maximum magnetization and residual magnetization of the $Mg_xNi_yZn_{1-x-y}Fe_2O_4$ nano-powders with 810 nm size were 45.89 Oe, 53.92 emu/gOe, 0.4 emu/Oe, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.15 no.5
• /
• pp.406-411
• /
• 2002

Ni-Zn ferrite is required to have predominant and stable characteristics in the range of high frequency for the power line communication, so that microstructures and magnetic properties such as power loss and initial permeability in $Ni_{0.8}Zn_{0.2}Fe_2O_4$ were investigated in terms of variable $Bi_2O_3,CaO$ and $V_2O_5$ contents. $Bi_2O_3$ and $V_2O_5$ liquid phase created during sintering process promoted sintering and grain growth but much of the closed pore existed in the grains. The grain size of the specimens with $V_2O_5$ of over 0.5 wt% decreased as the result of "pinning effect"and the resonance frequency increased with CaO of 0.3we%. The high initial permeability of 81.52%, resonance frequency of 17.05 MHz and low power loss of 17,858 kW/$\textrm{m}^3$ were obtained from the samples with $Bi_2O_3$ of 0.5, CaO of 0.3, and $V_2O_5$ of 0.7 wt%.

• Proceedings of the Korean Magnestics Society Conference
• /
• 1995.10a
• /
• pp.72-73
• /
• 1995

• Journal of the Korean Magnetics Society
• /
• v.5 no.1
• /
• pp.15-20
• /
• 1995

We have prepared 20 kinds of Mn-Zn ferrites as content of CaO(0.1 mol%), NiO(0.0~0.60 mol%) and CoO(0.0~0.8 mol%) adding by the coprecipitation method and studied the magnetic properties as content of CaO, NiO and CoO adding. Initial permeability decrease as the content of NiO and CoO adding increases, while Curie tem~ perature increase as the content of NiO and CoO adding increases. $(H_{c})$, $(B_{s})$ and $(W_{h})$ increase as content of NiO adding increases.

• Proceedings of the KIEE Conference
• /
• 2000.07c
• /
• pp.1652-1654
• /
• 2000

고상반응법을 이용하여 $Ni_{0.6-x}Cu_{x}Zn_{0.4}Fe_{2}O_4$(x=0, 0.1, 0.2, 0.3) ferrite 분말을 제조하고 1200$^{\circ}C$에서 열처리하여 Cu 첨가에 따른 입자변화와 전자파흡수 특성과의 관계를 조사하였다. Ni를 Cu로 0.1 mol 치환했을 때 까지는 포화자화 및 전자파흡수능이 치환하지 않았을 때와 거의 비슷하였으나, 그 이상 첨 가시는 직선적으로 감소하였다.

• Journal of the Korean Ceramic Society
• /
• v.29 no.3
• /
• pp.177-182
• /
• 1992

The effect of heat-treatment temperature on the microwave absorbing properties was investigated in Ni0.8Zn0.2Fe2O4 specimens. The composite specimens were prepared by modling and curing the mixture of prereacted ferrite powder and silicone rubber. The measurement of complex permeability and permittivity was made by the reflection/transmission method. The most sensitive material constants with heat-treatment temperature is the imaginary (loss) component of permeability. The higher the heat-treatment temperature, the greater the magnetic loss. The composite specimens with high magnetic loss exhibited superior microwave absorbing properties. The quantitative estimation of microwave absorbing properties were made by plotting the observed material constants on the calculated solution map of impedance-matching.

• Proceedings of the KIEE Conference
• /
• 1994.07b
• /
• pp.1478-1480
• /
• 1994

In this paper, the microwave absorption properties of two layered absorber were evaluated. The two layer absorber were composed of Ni-Zn ferrite/rubber absorber and Ferroxplana/rubber absorber. The most absorption properties condition were obtained when the transforming layer and absorbing layer were Ferroxplana/robber absorber and Ni -Zn ferrite/rubber absorber. respectivity. The optimal thickness of the transforming and the absorbing layer were 4(mm) and 1(mm), respective1y.

• Proceedings of the Korean Institute of Resources Recycling Conference
• /
• 2004.12a
• /
• pp.3-11
• /
• 2004

The power loss analysis was carried out for Ni-Cu-Zn ferrite samples with different content of NiO and ZnO. The power loss, Pcv decreases monotonically wi increasing temperature and attains to a certain value at around $100\~120$ degrees Celsius. The frequency dependence of Pcv can be explained by $Pcv\~f^n$', and n is independent of the frequency, f up to 1MHz. The Pcv decreases with an increase in ZnO/NiO. The Pcv was separated to hysteresis loss, Ph and residual loss, (Pcv-Ph). The temperature characteristics and compositional dependence of Pcv can be attributed to the Ph, while (Pcv-Ph) is not affected by both temperature and ZnO/NiO. By analyzing temperature and composition dependence of Ph and initial permeability, ${\mu}^i$ following equations could be formularized. $${\mu}_i{\mu}o=I_x\;^2/(K_1+bs_ol_s)\;\;\;\;(1)$$ $Wh=13.5(I_s\;^2/{\mu}_i{\mu}_o)\;\;\;\;(2)$$ Were ${\mu}_o$ is permeability of vacuum, $I_s$ saturation magnetization, $K_1$ anisotropy constant, $S_o$ internal heterogeneous stress, $I_s$, magnetostriction constant, b unknown constant. Wh hysteresis loss per one cycle of excitation (Ph: Wh*f). Steinmetz constant of Ni-Cu-Zn ferrites, $m=1.64\~2.2$ is smaller than the one of Mn-Zn ferrites, which suggests the difference of loss mechanism between these materials.