• Journal of the Korean Ceramic Society
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• v.33 no.5
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• pp.495-506
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• 1996

Monodispersed colloidaly yttria(Y2O3) can be used in a variety of applications such as phosphors. IR transparent materials and fine ceramics. For preparing monodispersed yttria homogeneous precipitation has been regarded as a fovorable method that is monodispersed yttria can be obtained through calcining monodispersed colloidal compound of yttrium (eg:Y(OH)CO3.nH2O)which can be prepared by homogeneous precipitation with urea. It is however still required to find out the quantitative effects of important variables of precipitation such as concentration of yttrium and urea reaction temperature and initial pH of reactant even though homogeneous precipitation of Y3+ with urea has been studied extensively. Among the effects of these variables we investiga-ted 1) the effect of yttrium concentration on the shape and size of precipitate and the reation rate 2) range of yttrium concentration required to make monodispersed colloidal particles 3) the reason for limited concentra-tion range of yttrium and 4) the effect of ultrasonic radiation on the limited concentration.

• Proceedings of the KIEE Conference
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• 2005.10b
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• pp.286-288
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• 2005

If we are to realize the everyday benefits promised by pervasive computing and context-aware applications, we must first develop the infrastructure to provide contextual location and orientation information through pervasive computing elements. We have implement indoor positioning system to supply orientation information. We have used ultrasound in indoor positioning system for distance and orientation measurements, then propose a set of methods to calculate orientation from an array of well placed ultrasonic sensors operating in the indoor positioning system. We have design and implement a indoor positioning system using a combination of hardware and software and demonstrate end-to-end functionality of the system.

• IEMEK Journal of Embedded Systems and Applications
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• v.7 no.3
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• pp.143-150
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• 2012

In this paper, we introduce an intelligent quadruped walking robot that can perform stable walking and a couple of intelligent behaviors. The developed robot has two sets of ultrasonic sensors and six sets of infrared sensors and can perform obstacle avoidance by detecting obstacles and estimating the distances and directions of those obstacles. The robot also has a stereo camera and can paly soccer by detecting a ball and estimating the 3 dimensional coordinates of the ball. In performing those intelligent behaviors, the robot needs to have the capability of generating its walking patterns, solving the inverse kinematics problem, and interfacing several sensors in realtime. Therefore we designed a hierarchical controller that consists of a main controller and an auxiliary controller. The main controller is a 32-bit DSP that can perform fast floating-point opertaion and the auxiliary one is a 8-bit micro-controller. We showed that the developed quadruped walking robot successfully perform those intelligent behaviors through experiments.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.12 no.6
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• pp.14-21
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• 2003

With the increased use of lasers in industrial welding applications, techniques for monitoring and controlling these processes become increasingly important. It is very important that we understand the dynamic behaviors of the laser induced Plume in welding, because the laser induced plume has considerable effects on welding efficiency and the quality of materials. As the plume fluctuation was associated with keyhole instability, unstable vapor plume indicated the process was unstable and would result in poor welds. An Infrared Thermal-vision Camera can be utilized compensate for incurracies encountered in real-time monitoring during laser welding. We have results that instabilities of plume are closely related with hot cracking and defect of laser welding.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.1
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• pp.59-63
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• 2008

Time reversal (TR) of nondispersive body waves has been used in many applications including ultrasonic NDE. However, the study of the TR method for Lamb waves on thin structures is not well established. In this paper, the full reconstruction of the input signal is investigated for dispersive Lamb waves by introducing a time reversal operator based on the Mindlin plate theory. A broadband and a narrowband input waveform are employed to reconstruct the $A_0$ mode of Lamb wave propagations. Due to the frequency dependence of the TR process of Lamb waves, different frequency components of the broadband excitation are scaled differently during the time reversal process and the original input signal cannot be fully restored. This is the primary reason for using a narrowband excitation to enhance the flaw detectability.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.4
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• pp.371-382
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• 2001

The recognition of such natural wave guides as plates, rods, hollow cylinders, multi-layer structures or simply an interface between two materials combined with an increased understanding of the physics and wave mechanics of guided wave propagation has led to a significant increase in the number of guided wave inspection applications being developed each year. Of primary attention Is the ability to inspect partially hidden structures, hard to access areas, and teated or insulated structures. An introduction to some physical consideration of guided waves followed by some sample problem descriptions in pipe, ice detection, fouling detection in the foods industry, aircraft, tar coated structures and acoustic microscopy is presented in this paper. A sample problem in Boundary Element Modeling is also presented to illustrate the move in guided wave analysis beyond detection and location analysis to quantification.

• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.717-719
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• 1988

The continued interest in diagnostic applications of ultrasound has led to a need for more detailed knowledge of the ultrasonic properties of biological tissues. In this paper, temperature dependence of ultrasound velocity and attenuation is considered through a fundamental experiment. Acryl and Pig Liver are used as specimen. Data is collected over the temperature range of 20-50 C. As a result, we know that ultrasound velocity and attenuation coefficient are uniformly changed in proportion as specimen's temperature.

• The Journal of the Acoustical Society of Korea
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• v.6 no.1
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• pp.29-38
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• 1987

In clinical applications of hyperthermia, temperatures can be measured at only a few locations, whereas accurate temperature profiles need to be known for efficient therapy. For doing this, bio-heat transfer equation was modified into 1 dimensional 2 boundary value problem for simplicity and the efficiency of time, and solved by Galerkin's method. The results were then applied to annular array transducer for both the calculation of its axial temperature distribution and the estimation of temperature profiles from a few measured temperature data.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.869-872
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• 2000

The aim of present work was to fabricate the piezoelectric composite materials of low megahertz applications such as non-destructive testing of materials. Among all the various composites, those with PZT rods embedded in Spurrs epoxy with regular periodicity (1-3 connectivity) was fabricated by dice and fill method. The fabricated size of the PZT cell were 0.18X0.18, 0.28X0.28mm$^2$, respectively. And the volume ratio of the PZT cell were 52, 64%, respectively. The resonant frequency and anti-resonant frequency of the composites were 3.5 MHz and 4.3MHz, respectively. The piezoelectric coupling coefficient were about 38 and 37% and the mechanical quality factor were about 12.7 and 22. These value were very different from these of bulk PZT Plate.

• IEMEK Journal of Embedded Systems and Applications
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• v.6 no.2
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• pp.76-85
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• 2011

In conventional methods for measuring snow height, a graduated pole is installed on ground in an area of interest and the snow height is manually read from the pole. Recently, automated snow height measurement systems have been introduced to improve the conventional methods. The automated measurement systems, however, are quite expensive since they use the reflection of ultrasonic waves or laser beams. In addition, it is not easy to move the location of the automated measure systems. This paper proposes a snow height measurement system equipped with image sensors and wireless communication capability via a USN and the Internet. The proposed system has a resolution of 5 cm and easy to deploy without difficulties, which can be usefully used to monitor unforseen local snowfalls.