• 한국항행학회논문지
• /
• 제28권4호
• /
• pp.428-435
• /
• 2024

본 논문에서는 다중 입출력 주파수 변조 연속파 (MIMO FMCW; multiple input multiple output frequency modulation continuous wave) 레이다 기반 HAR (human activity recognition) 시스템의 설계 및 구현 결과를 제시하였다. 다중 입력 다중 출력 레이다 센서를 통한 포인트 클라우드 데이터를 활용하여 HAR 시스템을 구현하면 사생활 보호와 함께, 안전성 및 정확성 측면에서 장점이 있다. 본 논문에서는, MIMO FMCW 레이다 센서로부터의 포인트클라우드 데이터 기반 HAR을 위해 PointPillars와 DS-CNN (depthwise separable convolutional neural network)을 기반으로 최적 경량 네트워크를 개발하였다. 경량화된 네트워크를 통해 고해상도 포인트 클라우드 데이터를 처리하여 높은 인식 정확도와 함께 효율성을 달성하였다. 결과적으로, 98.27%의 정확도와 11.27M Macs (multiply-accumulates) 연산 복잡도로 구현 가능함을 확인하였다. 또한, 개발한 모델을 라즈베리파이(Raspberry-Pi) 시스템에 구현하여 최대 8 fps의 속도로 포인트 클라우드 데이터 처리가 가능함을 확인하였다.

• Journal of Mechanical Science and Technology
• /
• 제17권9호
• /
• pp.1388-1396
• /
• 2003

The hydrodynamic instability of the three-dimensional boundary layer on a rotating disk introduces a periodic modulation of the mean flow in the form of stationary cross flow vortices. The instability labeled Type II by Faller occurs first at lower Reynolds number than that of well known Type I instability. Detailed numerical values of the amplification rates, neutral curves and other characteristics of the two instabilities have been calculated over a wide range of parameters. Presented are the neutral stability results concerning the two instability modes by solving the appropriate linear stability equations reformulated not only by considering whole convective terms but also by correcting some errors in the previous stability equations. The present stability results agree with the previously known ones within reasonable limit. Consequently, the flow is found to be always stable for a disturbance whose dimensionless wave number is greater than 0.75. Some spatial amplification contours have been computed for the stationary disturbance wave, whose azimuth angle $\varepsilon$= 11.29$^{\circ}$ to 15$^{\circ}$ and for the moving disturbance wave, whose azimuth angle $\varepsilon$ = 12.5$^{\circ}$ to 15$^{\circ}$. Also, some temporal amplification contours have been computed for the stationary disturbance wave, whose azimuth angle $\varepsilon$= 11.29$^{\circ}$ to 15$^{\circ}$ and for the moving disturbance wave, whose azimuth angle $\varepsilon$= 12$^{\circ}$ to 15$^{\circ}$. The flow instability was observed by using a white titanium tetrachloride gas over rotating disk system. When the numerical results are compared to the present experimental data, the numerical results agree quantitatively, indicating the existence of the selective frequency mechanism.

• Smart Structures and Systems
• /
• 제15권1호
• /
• pp.135-150
• /
• 2015

Large concrete structures are prone to cracks and damages over time from human usage, weathers, and other environmental attacks such as flood, earthquakes, and hurricanes. The health of the concrete structures should be monitored regularly to ensure safety. A reliable method of real time communications can facilitate more frequent structural health monitoring (SHM) updates from hard to reach positions, enabling crack detections of embedded concrete structures as they occur to avoid catastrophic failures. By implementing an unconventional mode of communication that utilizes guided stress waves traveling along the concrete structure itself, we may be able to free structural health monitoring from costly (re-)installation of communication wires. In stress-wave communications, piezoelectric transducers can act as actuators and sensors to send and receive modulated signals carrying concrete status information. The new generation of lead zirconate titanate (PZT) based smart aggregates cause multipath propagation in the homogeneous concrete channel, which presents both an opportunity and a challenge for multiple sensors communication. We propose a time reversal based pulse position modulation (TR-PPM) communication for stress wave communication within the concrete structure to combat multipath channel dispersion. Experimental results demonstrate successful transmission and recovery of TR-PPM using stress waves. Compared with PPM, we can achieve higher data rate and longer link distance via TR-PPM. Furthermore, TR-PPM remains effective under low signal-to-noise (SNR) ratio. This work also lays the foundation for implementing multiple-input multiple-output (MIMO) stress wave communication networks in concrete channels.

• 한국전자파학회논문지
• /
• 제30권4호
• /
• pp.307-313
• /
• 2019

Ka-대역 밀리미터파 복합모드 탐색기에 적용할 수 있는 진행파관 증폭기(traveling wave tube amplifier: TWTA)는 고전압생성부(high voltage power supply: HVPS), 변조부(grid modulator), 제어부(command & control), 고조파부(RF assembly)로 구성되는 고출력 펄스형 송신기이다. 펄스 반복 주파수(pulse repetition frequency: PRF)와 전원공급기 스위칭 주파수가 동기/가변되어 -17.9 kV 고전압을 생성하는 고전압 전원 공급기와 RF 펄스 변조를 위한 고속 그리드 스위칭 변조기를 설계하였다. 체적이 3.18 L로 소형화로 제작된 TWTA는 그리드 on/off 신호의 상승/하강시간이 최대 18.5 ns 이하 고속펄스 스위칭 특성을 가지고, 첨두전력은 564.9 W 이상으로 고출력 성능을 보였다. 또한 PRF와 PRF/2 범위 내에서 -68.4 dBc 이하의 우수한 불요파 성능을 확인하였다.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
• /
• 제5B권2호
• /
• pp.181-188
• /
• 2005

In this paper, a DC smoothing filterless soft switching pulse modulated high frequency AC power conversion circuit connected to utility. frequency AC power source is proposed for consumer induction heating hot water producer, steamer and super heated steamer. The operating principle of DC link filterless utility frequency AC-high frequency AC (HF AC) power conversion circuit defined as high frequency cycloinverter is described, which can operate under a principle of ZVS/AVT and power regulation based on alternate asymmetrical PWM in synchronization with the utility frequency single phase AC positive or negative half wave voltage. The dual mode modulation control scheme based on high frequency PWM and commercial frequency AC voltage PDM for the proposed high frequency cycloinverter are discussed to enlarge its soft switching commutation operating range for wide HF AC power regulation. This high frequency cycloinverter is developed for high frequency IH Dual Packs Heater (DPH) type boiler used in consumer and industrial fluid pipeline systems. Based on the experiment and simulation results, this high frequency cycloinverter is proved to be suitable for the consumer use IH-DPH boiler and hot water producers. The cycloinverter power regulation and power conversion efficiency characteristics are evaluated and discussed.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2003년도 ICCAS
• /
• pp.2274-2277
• /
• 2003

A cylindrical permanent magnet inside the four-phase permanent magnet (PM) stepping motor is employed as the rotor. The stator has four teeth around, which its coils are wound. The mode of excitation can be classified into 3 modes: single-phase excitation, two-phase excitation and ministep excitation. The ministep drive is a method to subdivide one step into several small steps by means of electronics. The paper presents the programmable ministep technique drive. This technique decodes the results obtained from the counter to locate the data in Read Only Memory (ROM). The Sinusoidal Pulse Width Modulation (SPWM) is transformed to binary file and saved to the ROM. The experiment is performed with the four-phase PM stepping motor and drives from a two-phase programmable sinusoidal ministep signal, instead of square wave. The results show that the performances of the proposed programmable ministep technique drive have high efficiency, smooth step motion, and high speed response. Moreover, the resolution of sinusoidal ministep signal can be controlled by the input frequency (f command).

• 전자공학회논문지D
• /
• 제36D권6호
• /
• pp.87-96
• /
• 1999

협대역 마이크로파 아날로그 광전송을 위한, 이중 변조구조를 이용한 새로운 전광 전계흡수 광변조기의 선형화 방법이 제안되었으며, 이론적으로 고찰되었다. 주-변조기와 소자 길이, 흡수층의 밴드갭 파장 그리고 DC 바이어스 전압을 달리하는 부-변조기의 주-변조기와의 이중 변조구조를 적용하여, 주-변조기의 3차 비선형 왜곡 성분인 CTB(composite triple beat distortion)를 최소화하는 동작점이 작은 바이어스전압으로 이동함과 더불어 ~30dB의 CYB의 억제효과를 얻을 수 있었다. CTB의 억제에 따라 협대역 채널 대역에서의 ~20dB 동작영역의 향상을 이룰 수 있었다.

• 한국광학회지
• /
• 제8권5호
• /
• pp.410-414
• /
• 1997

Laser projection display(LPD)는 레이저를 이용한 full color의 대형화면을 구현하는 system이다. $TeO_2$와 $LiNbO_3$ 단결정을 음향광학 매질과 transducer로 사용하여 이 system에 쓰이는 영상 신호 처리용 음향광학변조기(Acousto Optic Modulator : AOM)를 제작하고 그 특성을 평가하였다. AOM은 transducer에서 발생된 초음파가 가장 효과적으로 음향광학 매질에 전달되도록 simulation한 후 제작하였으며 제작된 AOM은 특성평가와 더불어 설계값에 맞게 제작되었는가를 회절효율 측정을 통해 검증하였다. LPD System에 실장된 AOM의 회절효율은 85%이며 rise time은 41.5 ns이다.

• 유공압시스템학회논문집
• /
• 제2권2호
• /
• pp.8-13
• /
• 2005

This paper investigates a fast, accurate and inexpensive hydraulic motor speed control system using high speed on-off solenoid valves. In order to retain the advantages of the two position valve and obtain better performance, the valves are operated by pulse width modulation(PWM) control. PWM signal is generated from a LabWIEW program in microcomputer in order to set up various duty ratio and frequency of carrier wave in PWM signal with varying system parameters. As the results of experiments, the speed control of a hydraulic motor was successfully implemented using on-off solenoid valves. In order to attenuate the pressure ripple and speed variation due to discontinuously controlled flow through the on-off valves, a resonator hose fabricated for automobile power steering system was connected between the valve and a hydraulic motor. From experimental results obtained in the hydraulic motor system with a resonator hose, it was ascertained that the resonator hose showed excellent performances in reducing pressure ripple and motor speed variation.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2008년도 춘계학술대회 논문집
• /
• pp.10-11
• /
• 2008

We developed the equipment palpating cell proliferation using a high brightness LED. This equipment was fabricated using a micro-controller and a high brightness LED, and designed to enable us to control light irradiation time, intensity, frequency and so on. Especially, to control the light irradiation frequency, FPGA was used, and to control the change of output value, TLC5941 was used. Control stage is divided into 30 levels by program. Consequently, the current value could be controlled by the change of level in Continue Wave(CW) and Pulse Width Modulation(PWM), and the output of a high brightness LED could be controlled stage by stage. And then, each experiment was performed to irradiation group and non-irradiation group for bone marrow cells. MIT assay method was chosen to verify the cell increase of two groups and the effect of irradiation on cell proliferation was examined by measuring 590nm transmittance of ELISA reader. As a result, the cell increase of bone marrow cells was verified in irradiation group as compared to non-irradiation group.