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Active Vibration Control of a Simply Supported Plate with Piezoelectric Materials
Roh,Yong Rae 대한기계학회 1993 Korea - U. S. Vibration Engineering Seminar Vol.1 No.1
Undesirable vibration of a simply supported plate is controlled with piezoelectric sensors and actuators. Analytic solutions are obtained for amplitude response of the plate, reflecting the combined effect of external driving forces and piezoelectric control moments. Validity of the solution is verified through experiments for two types of external vibration exciters, i.e., a concentrated point exciter and a piezoelectric plate driver.
PZT-Induced Lamb Waves and Pattern Recognition for On-Line Health Monitoring of Jointed Steel Plates
Roh, Yong Rae,Kim, Don Young,Yang, Seung Han,Park, Seung Hee,Yun, Chung Bang Trans Tech Publications, Ltd. 2006 Key Engineering Materials Vol.321 No.-
<P>This paper presents a non-destructive evaluation (NDE) technique for detecting damages on a jointed steel plate on the basis of the time of flight and wavelet coefficient, obtained from wavelet transforms of Lamb wave signals. Probabilistic neural networks (PNNs) and support vector machines (SVMs) were applied for pattern classification. In this study, the applicability of the PNNs and SVMs was investigated for the damages in and out of the Lamb wave path. It has been found that the present methods are very efficient in detecting the damages simulated by the loose bolts on the jointed steel plate.</P>
Ultrasonic Transducers for Medical Volumetric Imaging
Roh, Yong-Rae The Acoustical Society of Korea 2010 韓國音響學會誌 Vol.29 No.e3
Three-dimensional ultrasound imaging is a new, exciting technology that allows physicians to use ultrasound to view pathology as a volume, thereby enhancing comprehension of patient anatomy. In this paper, a brief history of the 3-D ultrasound imaging is described in accordance with the development of transducer technology. Then, two representative types of 3-D imaging transducers are reviewed with description of the concept and operation principle of each type: mechanical transducer and matrix array transducer. The mechanical transducer is detailed into free-hand scanning and sequential scanning types. Advantages of each transducer over the other and the technical issues for further performance enhancement are also presented.
New Structure of SAW Resonator Filters on 64$^{\circ}$YX LiNbO3
Roh, Yong-Rae,Kim, Hak-Bong,Lee, Young-Jin,Koh, Kwang-Nak,Lee, Man-Hyung,Kim, Gang-Bo,Kim, Kwang-Hee The Acoustical Society of Korea 1996 韓國音響學會誌 Vol.15 No.e4
The double mode SAW resonator filters have the serious shortcoming that out-of-band rejection above the passband is quite poor. Hence a new structure of the double mode filter is designed with the COM (Coupling Of MOdes) theory with better out-of-band rejection characteristics while keeping all the beauties of the conventional type. The second goal of the design is to reduce the planar size of the structure so that mass productivity of low frequency devices can be improved. For those purposes, several IDT's and relfector gratings are added to or subtracted from the conventional structure so that the modification can lead to better overall performance as a filter. As results of the investigation, several new double mode SAW resonator filter structures are developed. A new structure shows 10dB more out-of-band rejection that the conventional type with 25% reduced device size. Good agreement is demonstrated between the analytical results and experimental results for an illustrative 325MHz four pole resonator filter on 64°YX LiNbO3.
Assessment of Soil Compaction Related to the Bulk Density with Land use Types on Arable Land
Hee-Rae Cho,Kang-Ho Jung,Yong-Seon Zhang,Kyung-Hwa Han,Ahn-Sung Roh,Kwang-Rae Cho,Soo-Jeong Lim,Seung-Chul Choi,Jin-il Lee,Yeo-Uk Yun,Byoung-Gu Ahn,Byeong-Ho Kim,Jun-Hong Park,Chan-Yong Kim,Sang-Jo Pa 한국토양비료학회 2013 한국토양비료학회지 Vol.46 No.5
Soil compaction is affected by soil texture, organic matter (OM), strength (ST) and soil moisture, which is difficult to understand the degree and effects of related factors. The purpose of the study is to assess the impact of them on the compaction with bulk density (BD). The analysis was conducted with data collected from national-wide monitoring sites including 105 upland soils, 246 orchard soils, and 408 paddy soils between 2009 and 2012. The distributions of soil physical properties were measured. The correlation and multi linear regression analysis were performed between soil physical properties using SAS. The regression equation of BD(y) includes ST, gravitational water contents (GWC), and OM as variables commonly, having additional factors, clay content and sand content in paddy soil and upland soil for only subsoil (p<0.001). Our results show that the BD could be explained about 40~50% by various physical properties. The regression was mainly determined by ST in orchard and upland soil and by the GWC in paddy soil. To mitigate soil compaction, it is important to maintain the proper level of OM in upland soil and to consider the moisture condition with soil texture in paddy soil when making work plan. Furthermore, it would be recommended the management criteria classified by soil texture for the paddy soils.