Kee-Joe Lim

Design and Modeling of Piezoelectric Pump for Microfluid Devices

Recently, there has been increased incessantly an interest in research area on microfluidic pump for electronic and biological applications. The proposed pump takes an unobtrusive operation into the simple displacing mechanism using peristaltic traveling waves without the physical moving valves. However, this piezopump makes up a radical design, based on the operation of the stator on the piezoelectric motor. The ATILA simulation performs to estimate the operating frequency of the vibrating wave mode, and optimize the design conditions of piezopump such as pump structure, elastic materials, piezoelectric ceramics, and z-displacement on the elastic traveling wave of piezopump. The best measured value of the pumping rate is about 118 μ l/min under the following parameters: 4-wave mode, the operating frequency of 50 kHz and the peak voltage of 200 V.

Comparison of Classification Rate for PD Sources using Different Classification Schemes

Insulation failure in an electrical utility depends on the continuous stress imposed upon it. Monitoring of the insulation condition is a significant issue for safe operation of the electrical power system. In this paper, comparison of recognition rate variable classification scheme of PD (partial discharge) sources that occur within an electrical utility are studied. To acquire PD data, five defective models are made, that is, air discharge, void discharge and three types of treeinging discharge. Furthermore, these statistical distributions are applied to classify PD sources as the input data for the classification tools. ANFIS shows the highest rate, the value of which is 99% and PCA-LDA and ANFIS are superior to BP in regards to other matters.

Characteristics of Disk-type Linear Ultrasonic Motor for Application to x-y Stage

In this paper, a disk-type ultrasonic motor using a combination of radial and bending vibration modes is newly designed and fabricated. The characteristics of the test motor are also measured. By means of traveling elastic wave induced at the surface of circumference of the elastic disk, a steel bar in contact with the surface of circumference of the elastic disk bonded onto the piezoelectric ceramic disks is driven in both directions by changing the sine and cosine voltage inputs. The stator of the motor is composed of two sheets of piezoelectric ceramic disks to bond onto both surfaces of an elastic disk, respectively. As a result, the diameter of the elastic body is increased and the resonant frequency is decreased. The resonant frequency of the stator is about 92 ㎑, which is composed with piezoelectric ceramic disks of 28 ㎜ in diameter and 2 ㎜ in thickness, and an elastic body of 32 ㎜ in diameter and 2 ㎜ in thickness. A driving voltage of 20 Vpp produces 200 rpm with a torque of 1 Nm and an efficiency of about 10 %.

Vibration analysis of the stator in ultrasonic motor by FEM

A three-dimensional finite element method is proposed for the static and dynamic vibration of the stator in a piezoelectric motor which is comprised of an elastic body with slots bonded with piezoelectric ceramic elements. The validity of the computational technique is confirmed by comparison with experimental results measured by laser vibrometer. It is shown that the amplitude of the effective circumferential direction is dependent on the height of teeth cut out on the surface of the elastic body. If height of teeth is selected appropriately, the piezoelectric motor can be operated without slipping. These facts are useful for designing the shape of stator with high efficiency. The displacement in axial direction remains almost constant.

Design and Characteristics of Bar Type Piezoelectric Micropump

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 along the thickness direction. The proposed structure for the piezo-pump consists of the input and output ports the piezoelectric ceramic actuator, the actuator support, and the 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. Components of piezopump were made, assembled, and tested to validate the concepts of the proposed pump and confirm the simulation results.

Geometrical effects in the current measurement by Rogowski sensor

Rogowski coil is made having no ferromagnetic material in a core. So the coil cannot be driven into saturation. This result in that Rogowski coils may be calibrated at relatively low currents, and used with confidence at very high currents. However the lowest level of current that can be measured is limited by the sensitivity of the voltage measuring instrument and system noise. Therefore, geometrical effects were investigated in order to measure high sensitivity of low level current and the significant source of error was examined as well. In the results, the sources of error were associated with coil designs, i.e. shape, uniformity and a geometrical location of current source inside and outside of the Rogowski coil.

Electrical properties of paraelectric PLT(28) thin films deposited by dc magnetron sputtering

Abstract Paraelectric [Pb, La]TiO3 (PLT, La = 28 mol%) thin films were prepared by dc magnetron sputtering using a multi-element metal target. In order to crystallize the as-deposited PLT thin films into the cubic perovskite structure, a heat treatment was applied at annealing temperatures ranging between 450 and 750°C. The electrical measurements such as dielectric properties, polarization-electric field (P-E), and current-voltage (I–V) were investigated with the change of annealing temperature. The dielectric constant and dissipation factor of paraelectric PLT film annealed at 750°C were 1216 and 0.018, respectively. The charge storage density was approximately 12.5 μC/cm2. The leakage current density in PLT film annealed at 650°C was around 0.1 μA/cm2 at the electric field of 0.25 MV/cm.

SiGe Synthesis by Ge Ion Implantation

We report here the successful synthesis of SiGe by Ge ion implantation into Si-on-insulator (SOI) substrates. The fundamental principle for our SiGe synthesis is a chemical reaction preference by nature; oxygen molecules preferentially combine with Si atoms rather than Ge atoms since the formation energy of SiO2 is lower than GeO/GeO2, and the chemical bond strength of SiO2 is higher. This phenomenon consequently retards the diffusion of implanted Ge ions from the desired area, offering them sufficient time and chances to homogeneously unite with Si atoms and curing implantation damage during O2 gas annealing. Thus, the result is practical synthesis of SiGe that can flexibly create various Ge concentrations along with high crystalline quality. Ge ions with a dose of 1017 cm-2 are implanted at 100 keV into 193-nm-thick top Si layers of SOIs at room temperature. The Ge-implanted samples are subsequently annealed at 1100 or 1200 °C in an O2 gas ambient for 5 to 180 min. It is found that the implanted Ge ions mostly remain in the desired area during O2 gas annealing. An apparent increase in Ge concentration and a significant decrease in defect density by increasing annealing time are also observed. A theoretical basis and useful simulation for this material synthesis method are presented in this study, being supported by evidential experimental data and comparison of theoretical calculation and measured values.

High Voltage Dielectric Characteristics of Epoxy Nano-Composites in Liquid Nitrogen for Superconducting Equipment

Cryogenic dielectric insulation skills play a significant role in the development of superconducting electric equipment for transmission and distribution electric network. Nowadays, newly developed nano-composites have shown enhanced electrical, thermal, and mechanical properties of polymer insulation materials. And the application of nano-composites in high voltage power systems could be implemented in the near future. Among the various nano-composites, epoxy nano-composites have been paid much attention as a new insulating material for high voltage insulation. In this paper, we presented experimental results of epoxy nanocomposites in liquid nitrogen and determined the possible applications of nano-composites as insulating material for superconducting equipment. In order to determine their dielectric breakdown properties in liquid nitrogen, various kinds of epoxy based nano-composites have been made by mixing SiO2, Al2O3, TiO2 fillers, respectively. AC withstand voltage test and partial discharge (PD) inception voltage tests have been performed to verify the insulation breakdown characteristics of nano-composites in cryogenic environment. Consequently, it was deduced that the breakdown strength of epoxy nano-composites have been improved compared to epoxy with micro-fillers in cryogenic environment. And epoxy nano-composites immersed in liquid nitrogen showed a similar breakdown voltage characteristic when compared with that of insulating oil. In addition, the effects of nano-composites have been varied according to the concentration of nano-fillers and their content of fillers.

Classification of defects and evaluation of electrical tree degradation in cable insulation using pattern recognition method and weibull process of partial discharge

The purpose of this paper is to recognize partial discharge (PD) sources and evaluate of electrical treeing degradation for cable insulation. To acquire PD data, three defective tree models were made. And the data are shown by the phase-resolved partial discharge method (PRPD). As a result of PRPD, tree discharge sources have their own characteristics. If other defects (void, metal particle) exist at internal power cable, their characteristics are shown very differently. This result is related to the time of breakdown and this is important point of cable diagnosis. To apply PD data classification, methods of different type are selected. Those are, multi layer perceptions (MLP-BP), adaptive neuro-fuzzy inference system (ANFIS) and principle component analysis-linear inference system(PCA-LDA). As a result, ANFIS shows the highest rate which value is 100 %. Finally, we performed classification of tree progress using ANFIS and that result is 99 %. To evaluate degradation of electrical tree, weibull distribution was used. The time of each degradation stage (initiation, middle, breakdown) was measured to classify electrical tree degradation with each model by. Using the result, parameters are presumed by the each model and stage and it is possible to calculate time difference of each degradation stage and estimate the lifetime.