• 한국정밀공학회지
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• 제28권4호
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• pp.427-435
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• 2011

This paper deals with the measurement and analysis of the squeal noise according to the curvature of rail. The squeal noise is generated by the friction between the railway with curve and the wheel. The squeal noise is a big problem in Busan Metro Line 3. If the developing panel type ANC(Active Noise Control) system which is attached to the floor can reduce 5 dB in below 500 Hz, the sound pressure level of the whole band pass can be reduced about 4-4.8 dB in squeal noise above the curvature of R400. Curve squeal noise is the intense high frequency tonal that can occur when a railway vehicle transverses a curve. The frequency range is from around 500 to almost 20,000 Hz, with noise levels up to about 15 dB in curve.

• Journal of Power Electronics
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• 제16권3호
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• pp.849-860
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• 2016

The high-switching-frequency operation of power converters can achieve high power density through size reduction of passive components, such as capacitors, inductors, and transformers. However, a small-output capacitor that has small capacitance and low effective series resistance changes the small-signal model of the converter power stage. Such a capacitor can make the converter unstable by increasing the crossover frequency in the transfer function of the small-signal model. In this paper, the design and implementation of a high-frequency LLC resonant converter are presented to verify the power density enhancement achieved by decreasing the size of passive components. The effect of small output capacitance is analyzed for stability by using a proper small-signal model of the LLC resonant converter. Finally, proper design methods of a feedback compensator are proposed to obtain a sufficient phase margin in the Bode plot of the loop gain of the converter for stable operation at 500 kHz switching frequency. A theoretical approach using MATLAB, a simulation approach using PSIM, and experimental results are presented to show the validity of the proposed analysis and design methods with 100 and 500 kHz prototype converters.

• 전기전자학회논문지
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• 제20권3호
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• pp.318-321
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• 2016

IoT 산업이 빠르게 성장하면서 전원 관리 집적회로의 중요성이 부각되고 있다. 본 논문에서는 리플 Subtractor, 피드 포워드 커패시터, OTA를 이용한 LDO 구조를 제안한다. 이를 통해 10MHz가 넘는 고주파 영역에서도 -40dB 이상 높은 전원 전압 제거비(PSRR)를 얻었다. 설계된 Low-Dropout(LDO) 레귤레이터는 $0.18{\mu}m$ CMOS 공정에서 설계되었으며 시뮬레이션 결과 PSRR은 부하 전류 40mA, 500kHz에서 -73.4dB다. 최대 구동 가능 전류는 40mA이다.

• The Journal of Korean Physical Therapy
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• 제18권1호
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• pp.75-82
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• 2006

Purpose: This study conducted the following experiment to examine transdermal permeation effects or 500 KHz ultrasound with lidocaine HCl. Methods; First, to experiment skin permeation enhancement effects of 500 KHz ultrasound frequency, it produced apparatus and transducer of 500 KHz ultrasound and Franz diffusion cell for skim permenation experiment suitable to purposes of the experiment. Transdermal permeation experiment applied Lidocaine HCL gel to skin of hairless mouse depending on ultrasound frequency and duty cycle and analyzed permeation ratio with HPLC. Results: As a result of fixing lidocaine HCl gel at the same intensity with pulsed mode and continuous mode and comparing transdermal permeation ratio by frequency, transdermal permeation ratio was increased at 500 KHz ultrasound and remarkably increased at continuous ultrasound. It was found that 1 MHz and 500 KHz ultrasound in transdermal permeation experiment enhanced transdermal permeation of lidocaine HCl. In particular, transdermal permeation of 500 KHz using lidocaine HCl gel was highest. Conclusion: However, researches considering various frequencies, intensities and application hours in low frequency areas including 500 KHz ultrasound are needed to increase deep permeation or drugs.

• 한국정보통신학회논문지
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• 제4권5호
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• pp.1017-1025
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• 2000

인간의 청각시스템은 두 가지 요소 즉, ITD(Interaural Time Difference)와 IID(Interaural Intensity Difference)를 처리하여 음원의 위치와 추적을 하고 있다. 본 연구에서는 음원의 위치 검출을 위하여 ITD와 IID 뿐만 아니라 이전의 위치 정보를 이용하여 정확한 음원의 방향을 결정할 수 있는 TEPILD(Time Energy Previous Integration Location Detector) 모델을 제안하였다. TEPILD 모델에서 time function generator는 ITD, energy function generator는 IID를 처리할 수 있도록 하였다. 음원은 정현파(500Hz,1kHz, 2kHz, 3kHz), White noise, Pink noise, News, Music으로 하고 음원의 방향은 right, front right, front, front left, left로 하였다. 실험 결과 전체 평균 정확도가99.2로 좋은 결과를 얻을 수 있었으며, TEPILD가 음원 위치 검출기에 이용될 수 있음을 확인하였다.

• 조명전기설비학회논문지
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• 제22권8호
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• pp.109-115
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• 2008

현재 우리나라의 접지시스템의 설계기준은 낮은 주파수에서 측정된 저항값을 기반으로 한다. 고주파 성분을 포함하는 뇌서지가 접지시스템에 인가되면, 접지임피던스는 정상상태의 저항과 매우 다르게 된다. 이 논문은 접지시스템의 고주파 성능에 대한 물의 저항률의 영향을 파악하기 위하여 대지를 모의하는 수조를 이용하여 물의 저항률에 따른 어드미턴스의 주파수 의존성을 기술하였다. 500[${\Omega}{\cdot}m$] 이상의 높은 물의 저항률에서 용량성 효과에 의해 주파수가 증가함에 따라 어드미턴스와 컨덕턴스가 증가하는 것으로 나타났다. 반면에, 500[${\Omega}{\cdot}m$] 미만의 낮은 저항률에서는 유도성 효과에 의해 주파수가 증가함에 따라 어드미턴스와 컨덕턴스가 감소하는 것으로 나타났다. 또한 200[kHz]에서 5[MHz]에 이르는 주파수 범위에서 전류와 전압의 위상차가 증가하는 것으로 나타났다. 결론적으로, 접지시스템의 주파수 의존성은 대지의 저항률과 밀접한 관계가 있으며, 주파수와 대지저항률이 접지시스템의 성능에 미치는 영향에 대한 고려가 필요하다.

• International Journal of Computer Science & Network Security
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• 제23권9호
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• pp.8-16
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• 2023

In Japan, high-speed ground transportation service using linear motors at speeds of 500 km/h is scheduled to begin in 2027. To accommodate 5G services in trains, a subcarrier spacing frequency of 30 kHz will be used instead of the typical 15 kHz subcarrier spacing to mitigate Doppler effects in such high-speed transport. Furthermore, to increase the cell size of the 5G mobile system, multiple base station antennas will transmit identical downlink (DL) signals to form an expanded cell size along the train rails. In this situation, the forward and backward antenna signals are Doppler-shifted in opposite directions, respectively, so the receiver in the train may suffer from estimating the exact Channel Transfer Function (CTF) for demodulation. In a previously published paper, we proposed a channel estimator based on Delay and Doppler Profiler (DDP) in a 5G SISO (Single Input Single Output) environment and successfully implemented it in a signal processing simulation system. In this paper, we extend it to 2×2 MIMO (Multiple Input Multiple Output) with spatial multiplexing environment and confirm that the delay and DDP based channel estimator is also effective in 2×2 MIMO environment. Its simulation performance is compared with that of a conventional time-domain linear interpolation estimator. The simulation results show that in a 2×2 MIMO environment, the conventional channel estimator can barely achieve QPSK modulation at speeds below 100 km/h and has poor CNR performance versus SISO. The performance degradation of CNR against DDP SISO is only 6dB to 7dB. And even under severe channel conditions such as 500km/h and 8-path inverse Doppler shift environment, the error rate can be reduced by combining the error with LDPC to reduce the error rate and improve the performance in 2×2 MIMO. QPSK modulation scheme in 2×2 MIMO can be used under severe channel conditions such as 500 km/h and 8-path inverse Doppler shift environment.

• Journal of Astronomy and Space Sciences
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• 제34권4호
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• pp.251-256
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• 2017

The electric coupling between the lithosphere and the ionosphere is examined. The electric field is considered as a timevarying irregular vertical Coulomb field presumably produced on the Earth's surface before an earthquake within its epicentral zone by some micro-processes in the lithosphere. It is shown that the Fourier component of this electric field with a frequency of 500 Hz and a horizontal scale-size of 100 km produces in the nighttime ionosphere of high and middle latitudes a transverse electric field with a magnitude of ~20 mV/m if the peak value of the amplitude of this Fourier component is just 30 V/m. The time-varying vertical Coulomb field with a frequency of 500 Hz penetrates from the ground into the ionosphere by a factor of ${\sim}7{\times}10^5$ more efficient than a time independent vertical electrostatic field of the same scale size. The transverse electric field with amplitude of 20 mV/m will cause perturbations in the nighttime F region electron density through heating the F region plasma resulting in a reduction of the downward plasma flux from the protonosphere and an excitation of acoustic gravity waves.

• 전자공학회논문지S
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• 제35S권10호
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• pp.186-192
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• 1998

이 논문은 고속전철, 지하철과 같은 철도차량의 추진제어시스템에 적용될 수 있는 고능률 저주파 스위칭 PWM 기법에 관한 것이다. 500Hz이하의 낮은 스위칭 주파수로써 6스텝까지의 과변조제어를 연속적으로 수행할 뿐만 아니라 고주파 함유율을 저하 시키기 위한 PWM 방법으로 동기 기법을 공가벡터변조에 적용하였으며 DSP를 사용하여 구현하였다. 제안된 기법의 우수성과 효용성은 디지털 시뮬레이션과 실용량 모델의 실험을 통해 보인다. 실험은 전동차 추진제어장치인 1.65MVA IGBT VVVF인버터와 160톤의 전동차를 등가화한 관성부하를 통해 수행되었다.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2007년도 7th International Meeting on Information Display 제7권1호
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• pp.605-608
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• 2007

The discharge characteristics of the face-to-face sustain electrode structure employing auxiliary address pulse are investigated under a sustain driving frequency of 20 kHz and various auxiliary address pulse widths (500 ns, $1{\mu}s$, $2\;{\mu}s$) in the 6-in. test panel (42-in. Full HD grade) with a pressure of 450 Torr and a 4 % Xe-content. The luminance and the luminous efficiency at the auxiliary address pulse width of 500 ns are improved more than these of $1\;{\mu}s$ and $2\;{\mu}s$. At the auxiliary address pulse width of 500 ns, the luminous efficiency shows about 0.96 lm/W at the auxiliary pulse of 90 V and the sustain voltage of 260 V.