• Journal of Magnetics
• /
• 제18권2호
• /
• pp.173-177
• /
• 2013

Cantilever-detected high-frequency electron spin resonance (ESR) is a powerful method of sub-terahertz and terahertz ESR spectroscopy for a tiny magnetic sample at low temperature. In this technique, a small magnetization change associated with ESR transition is detected as deflection of a sample-mounted cantilever. So far, we have succeeded in ESR detection at 370 GHz using a commercial piezoresistive microcantilever. The spin sensitivity was estimated to ${\sim}10^{12}$ spins/gauss. In order to further increase the sensitivity, we adopt a fiber-optic-based detection system using a Fabry-Perot interferometer in place of piezoresistive system. Fabry-Perot cavity is formed between an optical-fiber end and microcantilever surface, and a change in the interference signal, corresponding to the cantilever deflection, is sensitively detected. This system is suitable for low-temperature and high-magnetic-field experiments because of its compact setup and less heat dissipation. In this study, performance of Fabry-Perot interferometer is evaluated, and its application to cantilever-detected ESR measurement is described.

• Nuclear Engineering and Technology
• /
• 제53권12호
• /
• pp.4033-4041
• /
• 2021

To better understand the permeability of uranium sandstone, improve the leaching rate of uranium, and explore the change law of pore structure characteristics and blocking mechanism during leaching, we systematically analyzed the microstructure of acid-leaching uranium sandstone. We investigated the variable rules of pore structure characteristics based on nuclear magnetic resonance (NMR). The results showed the following: (1) The uranium concentration change followed the exponential law during uranium deposits acid leaching. After 24 h, the uranium leaching rate reached 50%. The uranium leaching slowed gradually over the next 4 days. (2) Combined with the regularity of porosity variation, Stages I and II included chemical plugging controlled by surface reaction. Stage I was the major completion phase of uranium displacement with saturation precipitation of calcium sulfate. Stage II mainly precipitated iron (III) oxide-hydroxide and aluminum hydroxide. Stage III involved physical clogging controlled by diffusion. (3) In the three stages of leaching, the permeability of the leaching solution changed with the pore structure, which first decreased, then increased, and then decreased.

• 소성∙가공
• /
• 제22권2호
• /
• pp.74-79
• /
• 2013

The ultra-precision polishing method using MR fluid has come into the spotlight for polishing metals and optical materials. The MR fluid jet polishing process can be controlled using a change of viscosity by an imposed magnetic field. The MR fluid used for polishing process is a mixture of CI particles, DI water, $Na_2CO_3$ and glycerin. The efficiency of polishing depends on parameters such as polishing time, magnetic field, stand-off distance, pressure, etc. In this paper, the MR fluid jet polishing was used to polish nickel and brass mold materials, which is used to fabricate backlight units for 3-D optical devices in mobile display industries. In MR jet polishing, ferromagnetic materials like nickel can decrease the polishing efficiency by interaction with the cohesiveness of the MR fluid more than non-ferromagnetic materials like copper. A series of tests with different polishing times showed that the surface roughness of brass (Ra=1.84 nm) was lower than that of nickel (Ra=2.31 nm) after polishing for 20 minutes.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
• /
• 제49권6호
• /
• pp.411-420
• /
• 2000

The energy storage systems are being widely researched for the high quality of the electric power. The FES(flywheel energy system) is especially, on the center of the research because it does not make any pollution and its life is long. The FES converts the electrical energy into the mechanical kinetic energy of the flywheel and reconverts the mechanical energy into the electrical energy. In order to store as much energy as possible, the flywheel is supposed to be rotated with very high speed. The motor/generator of the FES should be high efficient at high speed, and generate constant torque with respect to the rotation. In this paper, a motor/generator employing a Halbach array of permanent magnets is designed and constructed to meet the requirements, and its characteristics are examined. The magnetic field is analysed by using the magnetic surface charge method. The armature winding is designed for the harmonic components to be minimized by using the FFT. The sinusoidal current for the motor driving are generated by the hysteresis current controller. A sample superconducting flywheel energy storage system is constructed with a duralumin flywheel which has a maximum rotating speed of 40,000[rpm] and a stored energy of 240[Wh] and its validity is examined through the experiment.

• 한국해양공학회지
• /
• 제20권2호
• /
• pp.59-65
• /
• 2006

Steel, as a reinforcing mechanism in concrete, provides the tensile strength that is lacking in concrete, alone, and the high alkaline environment (pH 12.5) in concrete offers satisfactory protection against most corrosion of the steel. However, the corrosion of reinforcing steel in concrete can occur by chloride attack or carbonation, and it can cause a loss of integrity a section and concrete failure through cracking and spalling. In this study, a transient electro magnetic method (TEM) of a nondestructive technique is adapted to study the measuring method of steel corrosion in mortar. The sensor was made of an enameled wire, with a diameter of 0.25mm and anacril. He sensor configuration used was a coincident loop type. The secondary electro motive force (2nd EMF) was measured with SIROTEMIII, which equipped the accelerator. The accelerator allowsthe transmitter to turn off approximately $10\sim15$ times faster than normal. The high-resolution time series, used for very shallow or a high resistivity investigation was selected. After steels were corroded by the salt spray, during 4, 8, 15 and 25 days, they were embedded in mortar. The content results acquired in this study are as follows. The variation of the secondary electro motive force (2nd EMF) was shown by the change of steel surface with different corrosion time steel. It was confirmed that measurement of steel corrosion in mortar by a transient electro-magnetic method (TEM) can be possible.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2008년도 춘계학술대회논문집
• /
• pp.479-482
• /
• 2008

In order to more closely examine the vacuum arc phenomena, it is necessary to predict the magnetohydrodynamic (MHD) characteristics by the multidisciplinary numerical modeling, which is coupled with the electromagnetic and hydrodynamic fields, simultaneously. In this study, the thermal-fluid characteristics of high current vacuum arcs were calculated by a commercial multiphysics package, ANSYS, in order to obtain Joule heat, Lorentz force and the interactions with flow variables. We assumed the diffused-mode arc within an AMF vacuum interrupter. It was found with four different currents that the temperature distributions on the anode surface are diffused uniformly without concentration in 7kA for both types (cup and coil-type). But the arc plasma transition and an increase of thermal flux density for increasing the applied current have caused the change of temperature distributions on the anode surface. We should need further studies on the two-way coupling method and radiation model for arc plasmas in order to accomplish the advanced analysis method for multiphysics.

• Journal of Magnetics
• /
• 제21권1호
• /
• pp.1-5
• /
• 2016

We investigated the half-metallicity and magnetism at the (001) and (110) surfaces of CsSe in cesium chloride and zinc-blende structures by using the all-electron full-potential linearized augmented plane wave method within the generalized gradient approximation. From the calculated local density of states, we found that all the surfaces preserve the half-metallicity of the bulk structures. The surfaces with a greater polarity have stronger ferromagnetic properties when terminated with Se atoms; the non-polar surfaces do not change their electronic or magnetic properties considerably as compared with the bulk structures.

• 한국자기학회지
• /
• 제14권2호
• /
• pp.59-64
• /
• 2004

나노 결정립 구조를 갖는 Fe-Al-O 연자성 산화막을 이온빔 에칭법으로 에칭하면서 연자기적 특성의 변화를 조사하였다. 두께가 감소할수록 보자력과 각형비가 증가하고 AFM 으로 조사한 표면굴곡도 증가하는 것으로 보아 결정립의 크기가 증가하는 것으로 판단된다. 이러한 현상은 비정질을 열처리한 나노결정립 연자성 재료와 다르게 성막하는 과정의 온도 상승에 의한 결정성장이 원인으로 판단된다. 따라서 우수한 연자성 박막을 제조하기 위해서는 두께 및 성막시간 등 최적 제조조건을 찾아야 한다. 마그네트론 스퍼터링법으로 제조된 Fe-Al-O 산화막의 경우 900 nm 이상에서 보자력이 1 Oe 이하인 연자성 박막을 얻을 수 있었다.

• 한국화재소방학회:학술대회논문집
• /
• 한국화재소방학회 2008년도 추계학술논문발표회 논문집
• /
• pp.428-433
• /
• 2008

The strength capacity properties of concrete are much influenced by water content which has a significant effect on concrete spalling, especially, in high temperature areas. Therefore, the properties of the material's shall be closely examined first by measuring the water content in each material in order to analyze Concrete Fire Characteristics, and a reliable measuring method shall be presented in order to derive the following influence. The method used to measure the water content within concrete is mainly divided into 4 types; ASTM method, Nuclear Magnetic method, Ultrasonic measurement method, Radio Wave method, etc. It is essential to use a reliable measuring method for each experiment. In this experiment, we measured the water content and humidity of concrete by two methods; Relative/Absolute humidity method using VISALA HM44 measuring equipment which is easily measurable compared with other methods regardless of the shape of the experimental model, and a water content measuring experiment using ASTM C 566. If the aggregates are under the condition that their surface is dry but in saturation, there is no change of water content according to concrete curing methods. However if the aggregates are absolutely dry, the water content is significantly changed according to concrete curing methods.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2000년도 추계학술대회 논문집
• /
• pp.951-954
• /
• 2000

This paper presents a new cutting method, i.e. diamond cutting, aided by electrolysis, in order to cut ferrous materials with diamond tools. Diamond cutting is widely applied in manufacturing ultraprecision parts such as magnetic disk, polygon mirror, spherical/non-spherical mirror and copier drum, etc. because of the diamond tool edge sharpness. In general, however, diamond cutting cannot be applied to cutting steels, because diamond tools wear excessively in cutting iron based materials like steel due to their high chemical interaction with iron in high temperature. In order to suppress the diffusion of carbon from the diamond tool and to reduce increase of cutting force due to size effect, we attempt to change chemically the compositions of iron based materials using electrolysis in a limited part which will be soon cut. Through experiments under several micro-machining and electrolysis conditions, cutting using electrolysis, compared to conventional cutting, was found to result in a great decrease of the cutting force, a better surface and much less wear tool.