• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.400-400
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• 2010

우리는 기본 진공 $10^{-11}\;Torr$의 UHV surface magneto-optical Kerr effect (SMOKE) 시스템을 quarter-wave plate를 사용하였던 기존의 방식에서 PEM (photo elastic modulator)를 사용하는 방식으로 장비의 기능을 향상시켰다. 기존 quarter-wave plate를 사용하는 방식의 경우 Kerr signal을 구하기 위해 편광자와 검광자를 수직으로 두어 광량을 0으로 만들어야 한다. 그러나 금속의 경우 대부분 가시광선 영역에서 큰 반사율 때문에 측정되는 광량이 편광자와 검광자를 거치면서 넓은 각도 범위에서 최소값을 갖기 때문에 정확한 영점을 잡는 데 한계가 있다. 이러한 단점을 해결하기 위하여 우리는 PEM을 이용한 위상변조방식을 사용하였다. 위상변조 방식은 Kerr signal과 관계된 양을 PEM을 이용하여 50 kH ($1{\omega}$)와 100 kH ($2{\omega}$)의 진동 주파수에 공조시키고 이를 Lock-in-amplifier를 사용하여 탐지하기 때문에 좋은 sensitivity를 얻을 수 있을 뿐 아니라 Kerr ellipticity와 Kerr rotation을 동시에 측정할 수 있다. 자화에 필요한 전자석은 순철로 된 코어를 제작하여 챔버에 부착하였고 10 A에서 최대 7 kOe의 고자장을 얻을 수 있어 포화자화가 큰 물질에 대해서도 필요한 자성영역까지 측정이 가능하게 하였다. 또 저온 측정을 위해 SMOKE 샘플 홀더를 개조하여 액체 질소를 이용하여 100 K 근방의 영역에서 온도를 제어할 수 있도록 저온 장치를 구성하였다. 여기에서 샘플 근처에 위차한 e-beam heater가 장착된 고온 부분과 액체 질소 냉각, 온도감지를 위한 센서, cartridge heater가 장착된 저온 부분을 sapphire plate로 분리하여 저온용 cartridge heater의 파손을 최소화하였다. 이러한 SMOKE 시스템을 구성한 후에 우리는 Fe/Cr(001)시스템의 자성특성에 대해 연구하였다. Fe/Cr 시스템은 Fe/Cr/Fe의 exchange coupling이나 bulk Cr의 복잡한 자성 특성 때문에 주목을 받아왔다. 이 연구에서 우리는 저온 및 상온에서 Cr(001) 단결정 위에 증착된 Fe 박막의 자성 특성을 보고한다.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.1
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• pp.20-25
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• 2008

Acoustic holography exhibits the spatial distribution of sound pressure in time or frequency domain. The obtained picture often contains far more than what we need in practice. For example. when we need to know only the locations and overall propagation pattern of sound sources. a method to show only what we need has to be introduced. One way of obtaining the necessary information is to use envelope in space. The spatial envelope is a spatially slowly-varying amplitude of acoustic waves which contains the information of sources' location. A spatial modulation method has been theoretically developed to get a spatial envelope. By applying the spatial envelope. not only the necessary information is obtained but also computation time is reduced during the process of holography. The spatial envelope is verified as an effective visualization scheme in time domain by being applied to complicated sound fields.

• Journal of Advanced Navigation Technology
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• v.8 no.2
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• pp.105-111
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• 2004

This paper describes the design of navigation system for an unmanned target drone which is operated by Korean army as for anti-air gun shooting training. Current target drone is operated by pilot control of on-board servo motor via remote control system. Automatic flight control system for the target drone greatly reduces work load of ground pilot and can increase application area of the drone. Most UAVs being operated nowdays use high-priced sensors as AHRS and IMU to measure the attitude, but those are costly. This paper introduces the development of low-cost automatic flight control system with low-cost sensors. The integrated automatic flight control system has been developed by integrating combining power module, switching module, monitoring module and RC receiver as an one module. The performance of navigation for low cost unmanned aerial vehicle, unmanned target drone as our test bed in this paper is verified by both Hardware in the loop simulation(HILS) to test performance of GPS as GPS output frequency high and results of flight test.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.7 no.5
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• pp.97-105
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• 2008

The micro capacitors are passive elements necessary to electronic circuits and wireless portable PAN(personal area network) and Mobile Communications device modules in the baseband circuits in combination with another passive and active devices. As capacitance is proportionally increased with dielectric constant and electrode areas, in addition, inversely decreased the thickness of the dielectric material, thus thin film capacitors are generally seen as a preferable means to achieve high performance and thin film capacitors are used in a variety of functional circuit devices. In this paper, propose dielectric material as AIN(Aluminium nitride) to make micro thin film capacitor, and this capacitor has the MIM(metal-insulator-metal) structure. AIN thin films are widespread applied because they had more excellent properties such as chemical stability, high thermal conductivity, electrical isolation and so on. In addition, AIN films show low frequency response for baseband signal ranges, I-V and C-V electrical characterization of a thin film micro capacitor. The above experimental test and estimated results demonstrate that the thin film capacitor has sufficient and efficient functional performance to be the baseband range frequency of general electronics circuit and passive device applications.

• Korean Journal of Remote Sensing
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• v.18 no.6
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• pp.359-367
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• 2002

In this paper, a new embedded wavelet packet image coder algorithm is proposed for an effective image coder using correlation between partitioned coefficients. This new algorithm presents parent-child relationship for reducing image reconstruction error using relations between individual frequency sub-bands. By parent-child relationship, every coefficient is partitioned and encoded for the zerotree data structure. It is shown that the proposed wavelet packet image coder algorithm achieves low bit rates and rate-distortion. It also demonstrates higher PSNR under the same bit rate and an improvement in image compression time. The perfect rate control is compared with the conventional method. These results show that the encoding and decoding processes of the proposed coder are simpler and more accurate than the conventional ones for texture images that include many mid and high-frequency elements such as aerial and satellite photograph images. The experimental results imply the possibility that the proposed method can be applied to real-time vision system, on-line image processing and image fusion which require smaller file size and better resolution.

• Korean Journal of Optics and Photonics
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• v.32 no.2
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• pp.62-67
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• 2021

We have experimentally demonstrated sum-frequency generation (SFG) in a periodically poled lithium niobate (PPLN) crystal, using a mode-locked picosecond-pulsed fiber laser and a continuous-wave (CW) diode laser with a narrow linewidth. The mode-locked fiber laser had a center wavelength of 1560.7 nm and a spectral width of 1.1 nm, and the CW diode laser had a center wavelength of 1551.0 nm and a spectral width of 6 MHz. To effectively realize SFG, both of the spatial modes of the two lasers were made to overlap in the PPLN crystal by using a single-mode optical fiber. The pulse-mode SFG with pulsed- and CW-mode lasers was successfully observed in the spectral and time domains. These results are expected to be applicable in various ways, such as optical frequency measurement and high-resolution laser spectroscopy studies using optical frequency combs.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.2
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• pp.51-58
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• 2019

The LTE system decided to build an integrated disaster safety communication network in order to cope with disasters quickly after the April 16, 2014 disaster, and 333 agencies in 8 areas will build a unified disaster safety communication network. It plans to integrate LTE-R, a railway integrated wireless network, and LTE-M, a land-based communication network, in the 700MHz band. LTE-R, a wireless integrated network, and the Ministry of Land, Transport and Maritime Affairs, are currently using VHF and TRS, which are voice communication-oriented communication systems, in order to cope with demand for high-speed railway service, With this possible LTE-R, it is possible to provide advanced services such as radio-based train control and improve railway safety. The company plans to invest KRW 1.1 trillion in new routes to be launched in 2018 and the existing route to be improved in the future, and to build up all routes of general and high-speed railways to LTE-R by 2027.

• The Journal of Korean Institute of Information Technology
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• v.16 no.11
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• pp.61-68
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• 2018

This paper describes design of a 10.525 GHz self oscillating mixer semiconductor IC chip combining voltage controlled oscillator and frequency mixer using silicon CMOS technology for Doppler radar applications. The p-core type VCO included in the self oscillating mixer minimizes the noise contained in the transmitted signal. This noise minimization increases the sensing distance and acts in a direction favorable to the reaching distance and the sensitivity of the motion detection sensor. Simulation results for phase noise show that a VCO designed as a P-core has a noise characteristic of -106.008 dBc / Hz at 1 MHz offset and -140.735 dBc / Hz at 25 MHz offset compared to a VCO designed with N-core and NP-core showed excellent noise characteristics. If a self-oscillating mixer is implemented using a p-core designed VCO in this study, a motion sensor with excellent range and reach sensitivity will be produced.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.12 no.1
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• pp.1-6
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• 2019

An extremely small size multi-loop phase-locked loop(PLL) keeping phase noise performances has been proposed. It has been designed to have the loop filter made of small single capacitor with multiple Frequency Voltage Converters (FVCs) because the main goal is to make the size of the proposed PLL extremely small. Multiple FVCs which are connected to voltage controlled oscillator(VCO) make multiple negative feedback loops in PLL. Those multiple negative feedback loops enable the PLL with the loop filter made of an extremely small size single capacitor operate stably. It has been designed with a 1.8V $0.18{\mu}m$ CMOS process. The simulation results show that the proposed PLL has the 1.6ps jitter and $10{\mu}s$ locking time.

• Phonetics and Speech Sciences
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• v.12 no.4
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• pp.73-80
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• 2020

In this study, a method for measuring the jitter component in continuous speech is presented. In the conventional jitter measurement method, pitch variabilities are commonly measured from the sustained vowels. In the case of continuous speech, such as a spoken sentence, distortion occurs with the existing measurement method owing to the influence of prosody information according to the sentence. Therefore, we propose a method to reduce the pitch fluctuations of prosody information in continuous speech. To remove this pitch fluctuation component, a curve representing the fluctuation is obtained via polynomial interpolation for the pitch track in the analysis interval, and the shift is removed according to the curve. Subsequently, the variability of the pitch frequency is obtained by a method of measuring jitter from the trajectory of the pitch from which the shift is removed. To measure the effects of the proposed method, parameter values before and after the operations are compared using samples from the Kay Pentax MEEI database. The statistical analysis of the experimental results showed that jitter components from the continuous speech can be measured effectively by proposed method and the values are comparable to the parameters of sustained vowel from the same speaker.