• Journal of Magnetics
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• 제21권1호
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• pp.57-60
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• 2016

Non Destructive Testing (NDT) methods that are capable of detecting the wall thinning and defects through insulation and cladding sheets are necessary. In this study we developed a Pulsed Eddy Current (PEC) system to detect wall thinning of ferro magnetic steel pipes covered with 95 mm thick fiber glass thermal insulator and shielded with aluminum plate of thickness 0.4 mm. In order to confirm the thickness change due to wall thinning, two different sensors, a hall sensor and a search coil sensor were used as a detecting element. In both the cases, the experimental data indicates a considerable change in the detected pulse corresponding to the change in sample thickness. The thickness of the tube was made to change such as 2.5 mm, 5 mm and 8 mm from the inner surface to simulate wall thinning. Fast Fourier Transform (FFT) was calculated using window approach and the results were summarized which shows a clear identification of thickness change in the test specimen by comparing the magnitude spectra.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 제4회 영호남학술대회 논문집
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• pp.47-51
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• 2002

ECT(eddy currentign testing) is very effective technique to detect a flaw within a conductor. Co-based amorphous wire was used as a sensor head. The wire has almost 0 magneto-striction and high permeability. An uniform magnetic field was applied to 1mm thick copper plate and $25{\mu}m$ thick aluminum sheet conductor using spiral typed coil The size of the coil has $40mm{\times}40mm$ outer width and $8mm{\times}8mm$ inner width. The copper plate and aluminum sheet has 0.5mm and 0.1mm wide gap, respectively. The frequency range of applied field was 100kHz-600kHz. The induced voltage difference of 2.5mV was obtained in the maximum voltage and minimum one measured across the gap of the 1mm thick conductor. In the case of aluminum sheet, 0.4mV was obtained. From this results, the effectiveness of Co-based amorphous wire was confirmed in the ECT technique.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.497-502
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• 2005

In mobile phones of multimedia era, microspeakers of high quality sound are essential parts to generate human voice in speaker phone and MP3 song player. In this paper, two types of microspeakers, outer permanent magnet (PM) and combined PM type, are analyzed using electromagnetic, mechanical, acoustical and their coupling analysis. For performance comparison, voice coil diameter is chosen as a design parameter to change excitation position and magnet volume for both types. For combined PM type, sound pressure level (SPL) is improved due to increased PM volume compared to outer PM type. Also, with the decreased voice coil diameter for combined PM type, the 1st resonant mode of the diaphragm is more efficiently excited due to concentrative excitation, resulting in lower and broader frequency range. Therefore, it can be said that the combined PM type microspeakers are more advantageous for high performance microspeaker which are essential for multimedia era.

• 전기학회논문지
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• 제58권3호
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• pp.578-585
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• 2009

In this paper, we present the design of an electromagnetic scanning mirror with torsional springs. The scanning mirror consisting of torsional springs and electromagnetic coils was designed for the applications of laser animation systems. We analyzed and optimized three types of torsional springs, namely, straight beam springs (SBS), classic serpentine springs (CSS), and rotated serpentine springs (RSS). The torsional springs were analyzed in terms of electrical resistance, fabrication error tolerance, and resonance mode separation of each type using analytical formula or numerical analysis. The RSS has advantages over the others as follows: 1) A low resistance of conductors, 2) wide resonance mode separation, 3) strong fabrication error tolerance, 4) a small footprint. The double-layer coils were chosen instead of single-layer coils with respect to electromagnetic forces. It resulted in lower power consumption. The geometry of the scanning mirror was optimized by calculations; RSS turn was 12 and the width of double-layer coil was $100{\mu}m$, respectively. When the static rotational angle is 5 degrees, the power consumption of the mirror plate was calculated to be 9.35 mW since the resistance of the coil part and a current is $122{\Omega}$ and 8.75 mA, respectively. The power consumption of full device including the mirror plate and torsional springs was calculated to be 9.63 mW.

• 전기학회논문지P
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• 제62권1호
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• pp.6-11
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• 2013

In this paper, the temperature characteristics of mold transformer for the distribution power system have been analyzed by using computational fluid dynamics(CFD). The model has been modeled by coil, cores, insulating materials and frames about 3MVA grade mold transformer and analyzed the temperature distribution of the structure with a heat fluid. The fluid, which is incompressible ideal gas, is analyzed as a turbulent flow phenomenon on the assumption that it is natural cooling of transformer cooling system. Through this study, by examining the temperature distribution and hot-spot of the structure field of the mold transformer, cooling design and temperature distribution information, which are demanded for designing are estimated.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집 Vol.3 No.2
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• pp.964-967
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• 2002

The effectiveness of silicon nitride SiNx surface passivation is investigated and quantified. This study adopted single-layer antireflection (SLAR) coating of SiNx for efficiency improvement of solar cell. The silicon nitride films were deposited by means of plasma enhanced chemical vapor deposition (PECVD) in planar coil reactor. The process gases used were pure ammonia and a mixture of silane and helium. The thickness and the refractive index on the films were measured by ellipsometry and chemical bonds were determined by using an FT-IR equipment. This films obtained were analyzed in term of hydrogen content, refractive index for gas flow ratio $(NH_3/SiH_4)$, and efficiency of solar cell. The polycrystalline silicon solar cells passivated by silicon nitride shows efficiency above 12.8%.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.120-123
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• 1999

We designed and constructed a non-destructive evaluation system using an HTS DC SQUID electronic gradiometer. Our DC SQUID electronic gradiometer is composed of two DC SQUID magnetometers. The system included a non-magnetic stainless steel cryostat and a set of coaxial exciting coils, which were used to induce an eddy current in the test material. We also have calculated the eddy current density produced by an exciting coil in any direction of the testing object. We could compute the eddy current density distribution in 3D. The SQUIDs were computer controlled and the output data from the electronic gradiometer was obtained by using a Labview software.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.224-229
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• 2008

With the wide use of mobile phones, a paging signal by a sound transducer acts as an environmental noise on many occasions, thus necessitating an alternative paging signal by a vibration motor. Conventional vibration motors employ three-phase windings with mechanical brushes for commutation. In this paper, a new one-phase brushless and sensorless vibration motor is introduced utilizing digital signal processor chips in cell-phones. For electromagnetic field analysis, two-dimensional modeling can be implemented to determine the back electromotive force using axisymmetric boundary conditions. Geometric design parameters, such as coil pitch and magnet pitch. are considered for performance optimization. Through the experiments, it is shown that the proposed design has the equivalent performance with reduced number of parts, thus enhancing manufacturing productivity and reducing manufacturing cost.

• 전기전자학회논문지
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• 제8권2호
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• pp.195-206
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• 2004

RFID 시스템에서 리더와 트랜스폰더 사이에 원활한 데이터 전송이 이루어지기 위해서는 리더 안테나와 트랜스폰더 안테나 사이에 공진 주파수 정합이 필요하다. 공진 주파수에 부정합이 발생하면, 트랜스폰더 안테나 코일에 유도되는 전압이 감소하게 되며, 따라서 트랜스폰더의 내부 전원 전압이 감소하게 된다. 또한, 리더 안테나 코일에 zero modulation의 확률이 증가하게 되어 궁극적으로 인식 거리의 감소를 가져오게 된다. 본 논문에서는 이러한 공진 주파수의 부정합이 초래하는 현상에 대해 이론적으로 분석을 하고, 수식적으로 모델링하였다. 또한, 공진주파수 부정합을 보상하기 위한 방법에 대해 언급하였다. 리더와 트랜스폰더 사이의 데이터 전송에 관해 본 논문에서 유도된 수식 및 분석된 이론들은 다양한 응용 분야를 위한 RFID 시스템의 신속한 개발에 큰 도움이 될 수 있을 것으로 기대된다.

• 비파괴검사학회지
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• 제23권4호
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• pp.356-363
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• 2003

플랜트, 산업용 설비로서 사용되어지고 있는 강관의 결함 검출을 위한 와전류검사장비를 개발하였다. 강관은 내부 불균일 한 전자기적 특성을 포함하고 있는 자성체로서 와전류검사의 응답신호를 왜곡시키므로 이러한 전자기적 특성의 균일화를 위해 자기포화가 요구된다. 자기포화가 없을 경우 결함신호는 잡음신호와 구별되지 않았으나 약 0.62A의 전류가 코일에 가해졌을 때 자기포화되어 결함을 검출 할 수 있었다 자기포화형 탐촉자는 헬름홀츠 코일을 적용하여 제작하였고 내부 대역 통과필터를 이용하여 직류자기장으로 야기되는 잡음신호를 최소화하였다. 개발된 장비를 이용한 현장실험 결과 1m/sec의 이송속도에서 관통홀$({\phi}=2.0mm)$ 결함을 정확히 검출 할 수 있었다.