• Geomechanics and Engineering
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• 제18권6호
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• pp.605-614
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• 2019

The present paper seeks to investigate propagation and reflection of waves at free surfaces of homogeneous, anisotropic and rotating micropolar fibre-reinforced medium with voids. It has been observed that, in particular when P-wave is incident on the free surface, there exist four coupled reflected plane waves traveling in the medium; quasi-longitudinal displacement (qLD) wave, quasi-transverse displacement (qTD) wave, quasi-transverse microrotational wave and a wave due to voids. Normal mode Analysis usually called harmonic solution method is adopted in concomitant with Snell's laws and appropriate boundary conditions in determination of solution to the micropolar fibre reinforced modelled problem. Amplitude ratios which correspond to reflected waves in vertical and horizontal components are presented analytically. Also, the Reflection Coefficients are presented using numerical simulated results in graphical form for a particular chosen material by the help of Mathematica software. We observed that the micropolar fibre-reinforced, voids and rotational parameters have various degrees of effects to the modulation, propagation and reflection of waves in the medium. The study would have impact to micropolar fibre-reinforecd rotational-acoustic machination fields and future works about behavior of seismic waves.

• 전기전자학회논문지
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• 제3권1호
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• pp.1-10
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• 1999

In this paper, the design for the shaped offset cassegrain antenna system combined with corrugated feed horn is presented. First, spherical-mode wave theory is applied to the corrugated conical horn and its radiation patterns are investigated. Using the radiation patterns, design data of the corrugated conical horn are obtained by efficiency investigation of horn antenna. When the investigation is completed, the flare angle and length of the corrugated conical horn is determined. Next, the main and sub-reflector is designed using Snellis law and the conservation principle of energy. Then the uniform direction and energy density of the traveling wave at the aperture of the main-reflector is obtained. The maximum size of the main-reflector is determined by investigation of the illumination and spillover efficiency. Finally, the curvature of the main-reflector is modified to satisfy the condition of the uniform phase. From the calculated efficiencies, the designed site of the main-reflector and sub-reflector, system gain of the shaped offset cassegrain antenna has been obtained 40.5dB in Ka-band frequency. It has better characteristics than the result of SABOR with 39dB gain.

• 한국소음진동공학회논문집
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• 제11권4호
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• pp.65-70
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• 2001

An investigation into asymmetric vibrations of a clamped circular place under a harmonic excitation is made. We examine a primary resonance. in which the frequency of excitation is near the natural frequency of an asymmetric mode of the plate. We found not only a response haying the form of standing wave but also one having the form of traveling wave, which was not observed by Sridhar, Mook and ${Nayfeh}^{(1)}$

• 한국위성정보통신학회논문지
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• 제2권2호
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• pp.10-15
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• 2007

위성방송수신 및 위성 양방향 인터넷, VSAT 등의 위성통신서비스를 차량 이동 시에도 이용할 수 있기 위해서는 차량에 탑재하기 용이하도록 소형이며 높이가 낮은 안테나 구조가 요구된다. 또한 중위도 지역에서 평면 안테나 상태로 45도 빔틸트 특성을 갖고, Ku 밴드의 위성통신용으로 충분한 고이득을 얻기 위해, 빔폭이 좁고 사이드로브가 적으며 저손실 구조의 배열안테나 개발이 필요하다. 본 논문에서는 이러한 성능을 만족시키기 위해, 진행파형 누설파 모드를 기초로 한 수직 편파로 동작하는 도파관 종방향 슬롯 배열안테나를 제안하였다. 16개 누설파 소자의 배열안테나 이득은 30 dBi 이었으며, 빔폭은 4.9도, 사이드로브 레벨은 -20 dB 이하, 중심주파수에서 빔틸트 각도는 45도를 얻었다. 급전선로는 도파관의 병렬급전 방식으로 설계하여 광대역, 저손실 특성을 얻을 수 있었다.

• Nuclear Engineering and Technology
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• 제33권4호
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• pp.409-422
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• 2001

The dynamic character of a system of the governing differential equations for the one- dimensional two-fluid model, where the momentum flux parameters are employed to consider the velocity and void fraction distribution in a flow channel, is investigated. In response to a perturbation in the form of a＇traveling wave, a linear stability analysis is peformed for the governing differential equations. The expression for the growth factor as a function of wave number and various flow parameters is analytically derived. It provides the necessary and sufficient conditions for the stability of the one-dimensional two-fluid model in terms of momentum flux parameters. It is demonstrated that the one-dimensional two-fluid model employing the physical momentum flux parameters for the whole range of dispersed flow regime, which are determined from the simplified velocity and void fraction profiles constructed from the available experimental data and $C_{o}$ correlation, is stable to the linear perturbations in all wave-lengths. As the basic form of the governing differential equations for the conventional one-dimensional two-fluid model is mathematically ill posed, it is suggested that the velocity and void distributions should be properly accounted for in the one-dimensional two-fluid model by use of momentum flux parameters.s.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 Techno-Fair 및 추계학술대회 논문집 전기물성,응용부문
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• pp.175-176
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• 2008

An ultrasonic motor of high torque with a new configuration for application in automobiles is proposed. The newly designed stator is two sided vibrator consisting of a toothed metal disk with a piezoelectric ceramic ring bonded on both faces of the disk which generates a flexural traveling wave along the circumference of disk. In this configuration, the displacement on the surface of stator may not be confined. It also produces a large vibrating force and amplitude because the vibrator is sandwiched by two piezoelectric plates. It is possible to increase the torque by improving the vibration characteristics. To compute the vibration mode of the motor of diameter 48 mm, the finite element method was used. A 6th mode was chosen as the operation mode with a resonance frequency of about 64.4 kHz. According to this design and measured its performance, a prototype was fabricated. The performance measurement of the prototype motor showed that its stall torque was about 1.8 Nm and efficiency was 37 % at 60 % of the maximum torque.

• 한국정보전자통신기술학회논문지
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• 제2권2호
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• pp.69-77
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• 2009

위성방송수신 및 위성 양방향 인터넷, VSAT 등의 위성통신서비스를 차량 이동시에도 이용할 수 있기 위해서는 차량에 탑재하기 용이하도록 소형이며 높이가 낮은 안테나 구조가 요구된다. 또한 중위도 지역에서 평면 안테나 상태로 45도 빔틸트 특성을 갖고, Ka 밴드의 위성통신용으로 충분한 고이득을 얻기 위해, 빔폭이 좁고 사이드로브가 적으며 저손실 구조의 배열안테나 개발이 필요하다. 본 논문에서는 이러한 성능을 만족시키기 위해, 진행파형 누설파 모드를 기초로 한 도파관 종방향 슬롯 배열안테나를 제안하였으며, 특히 슬롯 배열들 각각의 폭을 조절하여 복사 전력을 제어함으로써 복사 패턴의 사이드로브 레벨을 저감시켰다. 32개 누설파 소자의 배열안테나 이득은 34 dBi 였으며, 빔폭은 3.6도, 사이드로브 레벨은 -25 dB 이하로 기존의 경우보다 약 8 dB 의 저감 개선효과를 얻었다. 중심주파수 20.0 GHz에서 빔틸트 각도는 43도를 얻었다. 급전선로는 도파관의 코퍼레이트 급전방식으로 설계하여 광대역, 저손실 특성을 얻을 수 있었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.1275_1276
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• 2009

Micropump is very useful component in micro/nano fluidics and bioMEMS applications. Using the flexural vibration mode of PZT bar, a piezopump is successfully made. The PZT bar is polarized with thickness direction. The proposed structure for the piezo-pump consists of an input and an output port, piezoelectric ceramic actuator, actuator support, diaphragm. The traveling flexural wave along the bar is obtained by dividing two standing waves which are temporally and spatially phase shifted by 90 degrees from each other. Fluid is drawn into a forming chamber, eventually the forming chamber closes trapping the fluid therein.

• 한국광학회지
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• 제13권6호
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• pp.473-478
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• 2002

원형으로 굽은 평판 광도파로를 직선 광도파로로 등각사상화 시켰다. 단조 증가하는 굴절률 분포를 갖는 바깥쪽 클래드영역의 누설모드를 표현하기 위해 진행파형 수정된 Airy함수가 처음으로 소개되었다. 모의 전산을 통해 유도된 방법에 의한 굽음손실 및 field해 분포를 계산하고, WKB에 의한 결과와 비교하였다. 모의 전산결과 기존의 WKB 방법에 비해 회기점에서 수렴하는 해를 구할 수 있었으며, 더 정확한 굽음 손실을 계산할 수 있었다.

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