• Journal of international Conference on Electrical Machines and Systems
• /
• v.1 no.3
• /
• pp.330-335
• /
• 2012

Brushless doubly-fed machine (BDFM) doesn't use brush and slip ring, and has advantages such as high system reliability, small capacity of its frequency converter, low system cost, adjustable power factor and speed, etc. At the same time, it has good applicable potentials on the variable frequency motors and the variable speed constant frequency generators. However, due to the complicacy and particularity of BDFM in the structure and operating mechanism, the effect of magnetic field modulation directly influences the operating efficiency of BDFM. To study the effect of different cage rotor structures on the magnetic field modulation of BDFM, the rotor magnetomotive force (MMF) of BDFM with cage rotor is studied by the analytical method. The components and features of rotor harmonic MMFs are discussed. At the same time, the method to weaken the higher harmonics is analyzed by the theoretic formulae. Furthermore, the magnetic field modulation mechanism is expounded on in detail and the relationship between the magnetic field modulation effect and the operating efficiency of BDFM is established. And then, a new method for estimating the magnetic field modulation effect is proposed. At last, the magnetic field modulation effects of four BDFM prototypes with different cage rotor structures are compared by the MMF analysis and the efficiency data of electromagnetic design. The results verify the effectiveness of the new method for estimating the magnetic field modulation effect of BDFM with cage rotor.

• Proceedings of the Korean Magnestics Society Conference
• /
• 2009.12a
• /
• pp.217-219
• /
• 2009

A GMI magnetic field sensor working based on time-coded principle has been investigated and designed. The laboratory model has been constructed and tested carefully, demonstrating the sensitivity of $3\;{\mu}s/{\mu}T$ in the field range of ${\pm}100\;{\mu}T$. An amorphous thin wire, $100\;{\mu}m$ in diameter ${\times}50\;mm$ in length, was chosen to be sensing element which was fit into a small field modulation coil of 60 mm in length. The sensor is working based on a time-coded principle that, with the magnetic field modulation was chosen in range of hundreds of Hz, the change in time interval of two adjacent GMI peaks relating to external DC magnetic field is proportional to the intensity of the external field to be measured. This mechanism has made a great improvement to the linearity of the sensor.

• Journal of Magnetics
• /
• v.15 no.4
• /
• pp.221-224
• /
• 2010

A laboratory sensor model was designed, constructed, and tested based on a newly proposed working principle of magnetic field detection. The principle of sensing employed a time-coded method in correlation with exploiting the advantageous features of the GMI effect. The sensor demonstrated a sensitivity of $10\;{\mu}s/{\mu}T$ in the field range of ${\pm}100\;{\mu}T$. The sensing element in the form of an amorphous thin wire, $100\;{\mu}m$ in diameter ${\times}50\;mm$ long, was fit into a small field modulation coil of 60 mm length. At a magnetic field modulation in the range of hundreds of Hz, the change in time interval of two adjacent GMI voltage peaks was linearly related to the external magnetic field to be measured. This mechanism improved the sensor linearity of the GMI sensor to better than 0.2% in the measuring range of ${\pm}100\;{\mu}T$.

• Journal of Magnetics
• /
• v.14 no.3
• /
• pp.129-131
• /
• 2009

A time-coded giant magnetoimpedance (GMI) magnetic field sensor was investigated and designed. The successfully constructed and tested laboratory model demonstrated a sensitivity of 5 ${\mu}s/{\mu}T$ in the field range of $\pm200{\mu}T$. The sensing element in the form of an amorphous thin wire, 100 mm in diameter $\times50$ mm long, was fit into a small field modulation coil of 60 mm length. At a magnetic field modulation in the range of hundreds of Hz, the change in time interval of two adjacent GMI voltage peaks was linearly related to the external magnetic field to be measured. This mechanism improved the sensor linearity to better than 0.3% in the measuring range of $\pm200{\mu}T$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1995.05a
• /
• pp.90-95
• /
• 1995

This paper describes the highly-sensitive Si magnetic sensor using the amplitude modulation in order to real ice the integrated magnetic sensor which to sensor a weak magnetic field. Generally, the most important two parameters in Hall IC which degrade the ability of magnetic detection are the variation of offset according to the variation of temperature and the noise of amplifiers. In this paper, we use a Hall element and compensator to reduce the offset and the nouse of amplifiers by Using amplititude modulation method.

• Current Applied Physics
• /
• v.18 no.11
• /
• pp.1212-1217
• /
• 2018

The electric field-induced modifications of magnetic anisotropy in CoFeB/MgO systems are studied using X-ray resonant magnetic scattering and magneto-optical Kerr effect. Voltage dependent changes of the magnetic anisotropy of -12.7 fJ/Vm and -8.32 fJ/Vm are observed for Ta/CoFeB/MgO and Hf/CoFeB/MgO systems, respectively. This implies that the interfacial perpendicular magnetic anisotropy is reduced (enhanced) when electron density is increased (decreased). X-ray resonant magnetic scattering measurements reveal that the small in-plane magnetic component of the remanent state of CoFeB/MgO systems with weak magnetic anisotropy changes depending on the applied voltage leading to modification of the magnetic anisotropy at the CoFeB/MgO interface.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2015.08a
• /
• pp.139.2-139.2
• /
• 2015

In this study, We applied the magnetic field that has CW frequency and AM frequency to heating magnetic nano powder. For this experiment, We set up the devices flat-type magnetic field generator with CW frequency and AM frequency. We supplied the current to encircling coil by adjusting the power of generating of magnetic field device for AC voltage through Slidacs and using way of LC resonance circuit and SMPS(Switching Mode Power Supply). Above the encircling coil, We covered the circular flat insulator like glass. And we located the well plate containing the magnetic nano powder liquor above the circular flat insulator and exposed the magnetic field to this well plate. Using the flat-type magnetic field generator with CW and AM frequency and the magnetic field measurement sensor(Magnetic pick up coil or Hall sensor), We measured the strength of the magnetic field of circular flat insulator's surface in each position. The temperature of the magnetic nano powder in the well plate was quantitatively measured by the magnetic field strength through the Fluoroptic thermometer.

• Journal of the Korean Magnetic Resonance Society
• /
• v.3 no.2
• /
• pp.71-83
• /
• 1999

The dynamics of the dipolar demagnetizing field is investigated by numerical simulation. The effects of radiation damping, molecular diffusion, and relaxation processes on the dipolar demagnetizing field are examined in terms of the modulation pattern of the z-magnetization and the signal intensity variation. Simulations for multi-components suggest applications for sensitivity enhancement in favorable conditions.

• Progress in Medical Physics
• /
• v.18 no.4
• /
• pp.221-225
• /
• 2007

Monte Carlo calculations were performed to demonstrate the dose modulation with dynamic magnetic fields in phantom. The goal of this study is to obtain the uniform dose distributions at a depth region as a target on the central axis of photon beam under moving transverse magnetic field. We have calculated the depth dose curves for two cases of moving magnetic field along a depth line, constant speed and optimal speed. We introduced step-by-step shift and time factor of the position of the electromagnet as an approximations of continuous moving. The optimal time factors as a function of magnetic field position were calculated by least square methods using depth dose data for static magnetic field. We have verified that the flat depth dose is produced by varying the speed of magnetic field as a function of position as a results of Monte Carlo calculations. For 3 T magnetic field, the dose enhancement was 10.1% in comparison to without magnetic field at the center of the target.

• Journal of Magnetics
• /
• v.17 no.1
• /
• pp.42-45
• /
• 2012

We have developed an alternating magnetic field stimulation system consisting of a switched-mode power supply and a digital control circuit which modulates a duty ratio to maintain a magnetic field intensity of a few mT even while the frequency increases up to 4 kHz with a controllable coil temperature below $30^{\circ}C$ in air. This duty ratio modulation and water circulation are advantageous for cell culture under ac-magnetic field stimulation by preventing the incubator from exceeding a cell-viable temperature of $37^{\circ}C$. Although the temperature of the coil when subjected to a sinusoidal voltage rapidly increased, that of our system modulated by the duty factor did not change. This is a potentially valuable method to investigate the effects of intermediate frequency magnetic field stimulation on biological entities such as cells, tissues and organs.