• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.3
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• pp.96-101
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• 2015

Induction machine requires a rotating magnetic field for energy conversion. The current to generate a rotating magnetic field is the magnetization current. This magnetization current corresponds to the reactive power. Reactive power is higher than active power at start-up of induction motor. As the rotation speed is increased, their magnitudes are reversed each other. The active power is higher than the reactive power at near the synchronous speed. This paper is dealing with the analysis result for the changes of the magnetizing current and reactive power when the induction machine is operating as a motor or generator near synchronous speed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.5
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• pp.985-988
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• 2017

Magnetic induction (MI) based communication is one of the near-field communication techniques, which makes use of induced magnetic fields. In order to develop the MI based underwater communication networks, we evaluate and compare the loss performance between direct-MI and MI-waveguide in underwater environment.

• Journal of Magnetics
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• v.18 no.2
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• pp.105-110
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• 2013

The design model and key parameters of the material design for the control of induced magnetic flux at the near-field and efficient power transfer in a modified wireless power transfer (WPT) system with a large air gap of wireless electric vehicles were investigated through analytical simulations for magnetic vector and time-domain transient analysis. Higher saturation magnetic core with low core loss induced a stronger vertical magnetic field by the W-type primary coil in the WPT system with a gap of 20 cm at 20 kHz, which is shown from the vector potentials of the magnetic induction. The transient analysis shows that the higher magnetic fluxes through the pick-up cores lead to a linear increment of the alternating voltage with a sinusoidal waveform in the non-contact energy transfer system.

• Korean Journal of Audiology
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• v.18 no.3
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• pp.105-111
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• 2014

Assistive listening devices (ALDs) refer to various types of amplification equipment designed to improve the communication of individuals with hard of hearing to enhance the accessibility to speech signal when individual hearing instruments are not sufficient. There are many types of ALDs to overcome a triangle of speech to noise ratio (SNR) problems, noise, distance, and reverberation. ALDs vary in their internal electronic mechanisms ranging from simple hard-wire microphone-amplifier units to more sophisticated broadcasting systems. They usually use microphones to capture an audio source and broadcast it wirelessly over a frequency modulation (FM), infra-red, induction loop, or other transmission techniques. The seven types of ALDs are introduced including hardwire devices, FM sound system, infra-red sound system, induction loop system, telephone listening devices, television, and alert/alarm system. Further development of digital wireless technology in hearing instruments will make possible direct communication with ALDs without any accessories in the near future. There are two technology solutions for digital wireless hearing instruments improving SNR and convenience. One is near-field magnetic induction combined with Bluetooth radio frequency (RF) transmission or proprietary RF transmission and the other is proprietary RF transmission alone. Recently launched digital wireless hearing aid applying this new technology can communicate from the hearing instrument to personal computer, phones, Wi-Fi, alert systems, and ALDs via iPhone, iPad, and iPod. However, it comes with its own iOS application offering a range of features but there is no option for Android users as of this moment.

• Proceedings of the KIEE Conference
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• 2002.04a
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• pp.21-24
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• 2002

In this paper, induced voltages of the secondary conductors of a linear induction motor(LIM) with cage-type secondary are measured and analyzed when the LIM is fed by PWM inverter. The attenuation constant of the induced voltage of the secondary conductors near entry and exit zones of the the travelling magnetic field are determined from the experiment results.

• Progress in Superconductivity and Cryogenics
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• v.12 no.4
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• pp.13-16
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• 2010

The Lorentz force distribution of a high $T_c$ superconducting tape with increasing transport currents in magnetic field ($H_a$) was visualized. The external magnetic field was applied normally to the coated conductor tape surface after zero-field cooling, and the transport current ($I_a$) was increased stepwise from 0 to 90 % of the values of the critical current ($I_c$ ($H_a$)) at applied filed, Ha. The field distribution (H(x)) near the sample surface across the tape width (2w) was measured using the scanning Hall probe method. Applying an inversion to the measured field distribution, we obtained the underlying current distribution (J(x)), from which the magnetic induction, B(x) was calculated with Biot-Savart law. Then Lorentz force per unit length was calculated using F(x)=J(x)${\times}$B(x), which appears to be very inhomogeneous along the tape width due to the complicated distributions of J(x) and B(x).

• Journal of the Korean Magnetics Society
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• v.7 no.4
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• pp.180-185
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• 1997

Variations of core loss and coercivity with heat treatment condition have been studied in amorphous ribbon core specimens. All measurements were performed at 10 kHz with a maximum induction of 0.1 T. With increasing annealing time, both core loss and coercivity of core specimens decreased first, reaching minimum values, and increased thereafter. Specimen heat treated in an air showed better soft magnetic properties than those treated in Ar atmosphere. The specimens annealed under magnetic field higher than 6 Oe in radial direction showed reduced core loss and coercivity. The field annealing effects were increased with increasing cooling rate near Curie temperature of the material. The specimen annealed under an applied field in perpendicular direction of the core showed increased coercivity and decreased permeability.

• Journal of Korean Society of societal Security
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• v.1 no.4
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• pp.73-81
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• 2008

Electromagnetic induction surveys are one of the useful methods to detect the location and buried depth of underground utilities by measuring horizontal and vertical magnetic fields. It can effectively detects single buried utility with the accuracy of within 20 cm. However when another utility is buried near to target one, the accuracy of utility location considerably decreases due to the distortion of magnetic fields caused from adjacent utility. This study shows the ways to verify the location and buried depth of target utility when magnetic fields does not show symmetric distribution due to adjacent another utility. Using Bluetooth wireless communication tools, we developed the way to records measured magnetic fields to handheld PDA. We investigated the criteria for minimum distance of two adjacent utilities to separate the individual responses through field model test.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.11
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• pp.1453-1463
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• 1999

An electromagnetic flowmeter, based on a magnetic induction principle; provides an obstructionless flowmeter that essentially averages the velocity distribution over the pipe cross-sectional area. To predict the installation effects, the flowmeter installed near $90^{\circ}$ elbow is simulated by using a commercial code FLUENT(ver. 4.48) for the laminar flow field and a code developed through this study for magnetic field. The installation effects of the flowmeter are estimated by varying a number of the dependent parameters such as the radius of the elbow(Rc=1D, 1.5D, 2D, 3D), the location, Reynolds number and the direction of electrodes plane(${\varphi}$). It was found that all these factors affect the performance of the electromagnetic flowmeter significantly. The longer installation distance from the elbow is not always optimal to minimize the error, and also there exists an optimal location to install the EMF for a minimum error. Especially the flow signal with the electrodes plane direction of ${\varphi}=45^{\circ}$ is shown to yield smallest measurement error regardless of the Reynolds number and the curvature of elbow.

• Journal of the Korean Magnetics Society
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• v.23 no.2
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• pp.68-76
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• 2013

Currently, wireless power transmission technology based on magnetic induction was employed in battery charger for smart phone application. The system consists of wireless power transmitter in base station and receiver in smart phone. Size and thickness of receiver was strictly limited in the newest smart phone. In order to achieve high efficiency of a tiny small wireless power receiver module, sub-millimeter thick electromagnetic wave shielding sheet having high permeability and Q was essential component. It was found that magnetic field from transmitter to receiver can be intensified by sufficient shielding cause to minimize leakage magnetic flux by those magnetic properties. This leads to high efficiency of wireless power transmission and protects crucial integrated circuit of main board from electromagnetic noise. The important soft magnetic materials were introduced and summarized for the current small-power wireless power charger and NFC application and mid-power home appliance and high-power automotive application in the near future.