• Journal of Magnetics
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• v.21 no.1
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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.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.242-242
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• 2013

현재 크라이오펌프의 주요 관심기술은 생산성 향상을 위한 급속 재생기술의 확보와 극저온 냉동기의 효율 향상 기술 및 저진동 기술의 확보이다. 크라이오펌프는 크게 냉동기 모듈과 펌프모듈로 구성되고, 냉동기 모듈은 주로 G-M 극저온 냉동기, Stirling 극저온 냉동기 또는 맥동관 극저온 냉동기 등을 사용하는데, 이것은 주로 압축기, 왕복기, 재생기, 구동장치 등으로 펌프모듈은 cryoarray와 펌프 body로 구성된다. 최근에 구조가 간단하고 장수명 및 저진동의 장점을 가진 맥동관 극저온 냉동기의 효율이 급속히 증가함에 따라 초전도, 액화 등의 분야에서 기존의 G-M 극저온 냉동기를 대체하는 추세이다. 본 연구에서는 지식경제부 제조기반산업원 천기술사업 "급속재생형 저진동 크라이오펌프 개발" 사업을 통해 급속 재생, 저진동, 고신뢰성 확보를 위해 기존의 G-M 극저온 냉동기를 맥동관 극저온 냉동기로 대체 적용 개발 및 국산화를 도모하고자 한다. 또한 상용화에 따른 공정 개발을 소개하고자 한다.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.405-407
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• 2005

As the screen size of LCD increases, EEFL(External Electrode Fluorescent Lamp) has been suggested to be applicable as backlight source for LCD . Since the electrodes of EEFL are outside of the tube, EEFL enhances the lifetime compared with CCFL(Cold Cathode Fluorescent Lamp), and a single inverter can drive multiple EEFL tubes of which luminance is uniform Therefore, a compact design can be realized and the cost of EEFL application would be much lower than that of CCFL. Moreover, EEFL inverter has higher efficiency per unit power than CCFL inverter. In this paper, a complementary full-bridge PWM(Pulse Width Modulation) inverter was designed for 32-inch LCD TV backlight which has 20 EEFL tubes and adapted two different driving methods to the EEFL inverter. The validity of this study is confirmed from the experimental results.

• Proceedings of the KIEE Conference
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• 1998.07a
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• pp.82-84
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• 1998

The normal zone propagation velocity and minimum quench energy (MQE) of cable-in-conduit conductors (CICC) has been investigated at the different background magnetic fields and supercritical helium pressures. The sample CICC of 2 m in length was fabricated with triplet NbTi/Cu strands inserting into a round stainless-steel tube. The heat pulse disturbance with duration time about 400 ms was acted on the center region of the CICC to quench the strands. The normal zone propagation velocity increased with operating current of the CICC. The measured velocity with respect to operation current could be fitted with numerical results.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.186-191
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• 2008

In this study, a room temperature AMRR (Active magnetic regenerative refrigerator) was fabricated, and experimentally investigated. Gadolinium (Gd) was selected as a magnetic refrigerant with Curie temperature of 293 K. Permanent magnet was utilized to magnetize and demagnetize the AMR. To produce large magnetic field above 1 T in the magnetic refrigeration space, a special arrangement of permanent magnets, so called Halbach array, is employed. Sixteen segments of the permanent magnets magnetized different direction, constitute a hollow cylindrical shaped permanent magnet. The AMR is reciprocated along the bore of the magnet array and produces cooling power. Helium is selected as the working fluid and a helium compressor is utilized to supply helium flow to the regenerator. The fabricated AMRR has different structure and compared to a convectional AMRR since it has an additional volume after the regenerator. Therefore, the cooling ability is generated not only by magnetocaloric effect of magnetic refrigerant but also by the pulse tube effect. It is verified that the cooling ability of AMR is increased due to the magnetocalric effect by the fact that the temperature span becomes $16^{\circ}C$ while the temperature span is only $8^{\circ}C$ when the magnetic field is not applied to the regenerator.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.11
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• pp.868-875
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• 2014

The requirement of acoustic material which is used in underwater environment more increases. The material is used to reduce acoustic signature and radiate noise for underwater vehicle. Underwater acoustic material was made by viscoelastic material such as rubber and polyurethane etc. The mechanical and acoustic characteristics of these material change with hydrostatic pressure. In order to improve an acoustic performance according to hydrostatic pressure, several kinds of scatterers were added to viscoelastic material. In this paper, acoustic modelling and analysis techniques of underwater acoustic material with hydrostatic pressure were introduced and proposed. The specimens for pulse tube test were made and echo reductions were calculated and measured with hydrostatic pressure. Also the characteristics of echo reduction of the specimens with hydrostatic pressure were obtained and discussed.

• Design & Manufacturing
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• v.15 no.3
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• pp.26-31
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• 2021

In this study, laser-induced periodic surface structure (LIPSS) was fabricated on Ni, Si, and GaAs samples using a flat-top beam with a uniform energy distribution that was fabricated using a Gaussian femtosecond laser with a mechanical slit and tube lens. Unlike the Gaussian beam, the flat-top beam has a uniform beam profile, therefore the center and the periphery of the fabricated LIPSS have similar line periodicity. In addition, LIPSS was obtained not only in metals but also in metalloids and metals and metalloid compounds by using the narrow pulse width characteristic of a femtosecond laser.

• The Journal of the Acoustical Society of Korea
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• v.28 no.8
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• pp.806-814
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• 2009

This paper reviews a study about sound reflection control using an active sound absorber. An active sound absorber includes sound transmitting and receiving piezocomposite sensor layers molded by water tight epoxy, and connected with a feedback controller. The multi-layer sensors and the controller consists a closed feedback loop, whose intrinsic characteristics shows excellent impedance matching performance within specified frequency band, and consequently, minimizes reflection waves. Multilayer sound transmission model is derived based on one dimensional model, and its performance is verified with experiment using a pulse tube setup.

• Journal of Veterinary Clinics
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• v.33 no.4
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• pp.237-242
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• 2016

A 1.86 kg, 3-year-old, female, Maltese was presented to the Veterinary Medical Teaching Hospital of Seoul National University after being hit by a car. The patient was diagnosed with urinary bladder rupture, diaphragmatic hernia and fracture of ilium, tibia and fibula. Repair surgery was performed after stabilizing treatment. During the surgery, hypoxia was identified and it worsened after positive pressure ventilation (partial pressure of oxygen in arterial blood ($PaO_2$): 52 mmHg, pulse oximetry ($SpO_2$): 87%, arterial hemoglobin oxygen saturation ($SpO_2$): 85.8%). In addition to hypoxia, blood pressure decreased to 30 mmHg. Positive pressure ventilation was discontinued because hypoxia and hypotension were aggravated. After suturing the diaphragm, air was withdrawn to form negative pressure within the thorax. However, negative pressure was not attained despite continuous withdrawal of air. A thoracostomy tube was placed because tension pneumothorax was strongly suspected. The patient recovered through close monitoring with the tube for 3 days. Due to limitation of evaluation of the lung, predicting occurrence of tension pneumothorax is difficult in patient of diaphragmatic hernia. Therefore, it is recommended that indicators of tension pneumothorax should be closely monitored during diagnosis and repair procedures of diaphragmatic hernia.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.295-300
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• 2001

A variety of high voltage DC power supplies employing the high frequency inverter are difficult to achieve soft switching considering a quick response and no overshoot response under the wide load variation ranges which are used in medical-use x-ray high voltage generator from 20kV to 150kV in the output voltage and from 0.5mA to 1250mA, respectively. The authors develops soft switching high voltage DC power supply designed for x-ray power generator applications, which uses series resonant inverter circuit topology with a multistage voltage multiplier instead of a conventional high voltage diode rectifier connected to the second-side of a high-voltage transformer with a large turn ratio. A constant on-time dual mode frequency control scheme operating under a principle of zero-current soft switching commutation is described. Introducing the multistage voltage multiplier, the secondary transformer turn-numbers and stray capacitance of high-voltage transformer is effective to be greatly reduced. It is proved that the proposed high-voltage converter topology with dual mode frequency modulation mode control scheme is able to be the transient response and steady-state performance in high-voltage x-ray tube load. The effectiveness of this high voltage converter is evaluated and discussed on the basis of simulation analysis and observed data in experiment.