Young Moon Kim

CHARACTERISTICS OF BaTiO3-PVDF 0-3 COMPOSITE FILM FOR INORGANIC ELECTRO-LUMINESCENCE DEVICE

ABSTRACT In order to increase the brightness, the relative dielectric constant of the dielectric layer inserted between rear electrode and phosphor layer should be high. We manufactured BaTiO3-PVDF 0-3 type composite film for the application of the dielectric layer in the high brightness inorganic electro-luminescence (EL) device. The pastes for the BaTiO3-PVDF composite film were made with various mixing ratio by using 3-roll milling mixer. The pastes were coated on the phosphor layer by screen-printing method. The phosphor layer was also coated on a substrate by using the same screen-printing system. The substrate is an indium tin oxide (ITO) film deposited on PET (polyethylene terephthalate) polymer film. The others of rear electrode and insulating layer were also coated by the screen-printing method. Both the relative dielectric constant and the brightness of the fabricated EL device were increased with increasing the weight percent of BaTiO3 dielectric material in the composite films. The brightness was also increased with decreasing the thickness of the dielectric layer. The brightness was enough to be applied to the backlight of the keypad in mobile phones.

Effects of La2O3 on the Piezoelectric Properties of Lead-Free (Bi0.5Na0.5)0.94Ba0.06TiO3 Piezoelectric Ceramics

In an approach to acclimate ourselves to the recent ecological consciousness trends, a lead free piezoelectric material, bismuth sodium barium titanate (Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBT), was considered as an environment-friendly alternative to the PZT system. A perovskite BNBT was synthesized by the conventional bulk ceramic processing technique.La2O3 as a dopant was incorporated into the BNBT system up to 0.025 mol, and the doping effects on subsequent piezoelectric and dielectric properties were systematically investigated. In the case of La2O3 addition, the formation of grain boundary coherency was remarkably increased, and the sintered density was increased with increasing La2O3 contents. Piezoelectric and dielectric properties were shown to have the maximum value at 0.02 mol of La2O3 addition. La3+ ions were believed to act as a softener in the BNBT system and to enhance dielectric and piezoelectric properties in this study.

Active Control of Along-Wind Response of a Tall Building with AMD Using LQR Controller

Most of modern tall buildings using lighter construction materials are more flexible so could be excessive wind-induced vibrations resulting in occupant discomfort and structural unsafety. The optimal control technique for reducing along-wind vibration of a tall building based on the linear quadratic regulator (LQR) is presented in this work. Actively controlled reduced along-wind vibration response is obtained from the tall building installed in an active mass damper (AMD) with a LQR controller. Fluctuating along-wind load is generated using numerical simulation method, which can formulate a stationary Gaussian white noise process. Simulating wind load in the time domain using known spectra data of fluctuating along-wind load is particularly useful for estimation of windinduced vibration which is more or less narrow banded process such as a along-wind response of a tall building. In this work, fluctuating along-wind load acting on a tall building treated as a stationary Gaussian white noise process is simulated numerically using the along-wind load spectra proposed by G. Solari in1992. And using this simulated along-wind load estimated the reduced along-wind vibration response of a tall building installed in an AMD with a LQR controller.

Active Control of Along-Wind Response of Tall Building Using LQG Controller

Most of modern tall buildings using lighter construction materials which have high strength and less stiffness are more flexible so could be excessive wind-induced excitations resulting in occupant discomfort and structural unsafety.It is necessary to predict such a wind-induced vibration response and seek to find out the metho to mitigate such an excessive win-induced vibration. Active control method using actuator control force for mitigating along-wind vibration of a tall building with linear quadratic Gaussian (LQG) controller is investigated. Fluctuating along wind-load acting on a tall building which can be treated as a stationary Gaussian white noise process could be simulated numerically in time domain using along-wind load spectra. And using this simulated alongwind load calculated along-wind response of a tall building without and with LQG controller.

Grain Size and Orientation Control in Lead-Free (Bi,La)4Ti3O12 Thin Film Deposited by Spin-On Method for High Density FeRAM Device

A 16Mb 1T1C FeRAM device was successfully fabricated with the lead-free BLT capacitors. The average value of the switchable polarization obtained in the 32k-array (unit capacitor size: 0.68 μm2) BLT capacitors was about 16 μC/cm2 at the applied voltage of 3V and the uniformity within an 8-inch wafer was about 2.8%. But random bit failures were detected during the measuring the bit-line signal of each cell. It was revealed that the grain size and orientation of the BLT thin film were severely non-uniform. Therefore, the grain size and orientation was optimized by varying the process conditions of nucleation step. The random bit failure issue was solved by adopting the optimized BLT film. The cell signal margin of the optimized FeRAM device was about 340 mV.

Increasing Damping Ratios in a Tuned Liquid Damper Using Damping Bars

Wind-induced vibration of tall buildings have been of interest in engineering for a long time. Wind-induced vibration of a tall building can be most effectively controlled by using passive control devices. The tuned liquid damper(TLD) is kind of a passive mechanical damper, which relies on the sloshing liquid in a rigid tank. TLD has been successfully employed in practical mitigation of undesirable structural vibrations because it has several potential advantages: low costs, easy installation in existing structures, and effectiveness even against small-amplitude vibrations. Shaking table experiments were conducted to investigate the characteristics of the shallow water sloshing motion in a rectangular tank. To increase the damping ratio of the rectangular water tank, triangle sticks were installed at the bottom of water tank. This installation increased the damping ratio by amaximum of 40-70%.

Structural Analysis of Boom System in 42m Aerial Platform Truck

In the study, the development of aerial platform truck of 42m boom system has been completed to be satisfied with working in much higher place. To avoid the rollover accident of vehicles while working, 3D FEA is applied to verify the 3D design, stress concentration, stress distribution, deflection, natural frequencies etc. In these analyses, traction load of Boom System, 700 Kg and traction degree analyzed to 0° ~ 85°. Analysis result, when Boom Systems angle is 0°, could know that stress concentration and deflection are obtained to maximum. We could predict that maximum point of Stress concentration is 3.275 as safety factor and deflection of Boom system end part is max. 78.5Cm. Also could know that natural frequency and mode shape of boom system are stable in correlation with aerial platform trucks operation area. With these results, the structural stability of boom system in 42m aerial platform truck is obtained, then finally trying to find an optimum design of aerial platform truck.

Damage Detection and Quantitative Assessment for the Cracked Beam Structures

Beam structures are a common form in many large structures, and therefore the real-time condition monitoring and active control of beams will improve the reliability and safety of many structures. However, the incipient damage, i.e. cracks, is not easy to be detected with using the traditional methods, such as modal analysis, etc. Piezoceramic (PZT) sensors offer special opportunities for the health monitoring of structures constructed by beams. The change of mechanical impedance of structures along with the occurrence of damage is sensitively indicated by the change of electro-impedance of PZT sensors. This paper presents work done on developing and utilizing PZT sensors to detect and quantitatively assess the extent and locations of cracks occurred in simulated structures. The PZT sensors are conducted particularly to generate the longitudinal wave along the beam specimen, and systematic experiments conducted on statistical samples of incrementally damaged specimens were used to fully understand the method, the cracks with different length and location are simulated to indicate the feasibility of the detection and assessment. To estimate the damage conditions numerically, in this paper, we propose the evaluation method of impedance peak frequency shift F and CC (Correlation Coefficient), Cov (Covariance). The results of experiments verify that the impedance peak frequency shift Δ F uniformly assesses the location of cracks, and as well CC. and Cov assesses the size of cracks efficiently. The study presents the method that is satisfied for much higher frequencies, alternate power, and minute damages.

Aerodynamic Across-wind Response According to Damping Ratios of a Tall Building Using Tuned Liquid Column Damper

Tuned liquid column damper (TLCD) is more advantageous in terms of space than TLD for instance in the installation on the actual building. The aeroelastic experiment installation of TLCD, however, it is more difficult to relate the natural frequency of scale model of TLCD to aero elastic model and the evaluation of wind control performance. Aeroelastic experiment is achievable only for low damping ratio. This study installs TLCD with different lengths of horizontal pipes at the top floor of aeroelastic model, which is similar to the actual structure. Through aeroelastic experiment at different damping ratios, the vibration response (displacement) in across-wind direction establishment is important in order to figure out the vibration of the wind control effects to damping rate changes.

A Study on the Types of Snowdrifts in Domed Stadium Using Snow Wind Tunnel

The necessity of a dome stadium is increasing with the continued increase in sport interests. In tune with such trend, southwestern region baseball stadium, the first domed stadium in the nation, is being constructed. The roof is composed of membrane structure, which is significantly affected by snow loads. The Metrodome of Minnesota, which had a roof designed as a membrane structure had its roof collapse due to heavy snowdrift in 2011. For this reason, snow load is increasingly important. Nevertheless, studies on snowdrift experiment, which is considered important in estimating snow load, are insufficient in reality. This paper focused on snowdrift experiment that was performed on southwestern region baseball stadium that happens to be the first domed stadium in the nation. Snow wind tunnel, the use of the measured result, the maximum depth of fresh snowdrift, and the maximum depth of snowdrift were predicted in the experiment. As result, it is anticipated that snow will heap up on the roof of the stadium in 2.9cm to 32.2cm range if maximum depth of fresh snowdrift is applied and in 3.4cm to 37cm range.