Seungoh Han

Evaluation of the detectability of broken rotor bars for double squirrel cage rotor induction motors

Double squirrel cage rotor design is employed in induction motor applications that require high starting torque and high efficiency operation. The outer cage of double cage rotors is vulnerable to fatigue failure since it must withstand the large thermal/mechanical stresses experienced during a loaded startup due to the high starting current and long acceleration time. However, there are only a few publications that investigate broken bar detection for double cage induction motors. In this paper, the detectability of broken outer cage bars in double cage motors for the most commonly used rotor bar test methods is evaluated. A finite element and experimental study show that the sensitivity of on-line MCSA is significantly decreased, whereas that of off-line standstill tests is not influenced for broken outer cage bars. This suggests that one should be aware of the insensitivity of MCSA for double cage rotors, and there is a need for development of new on-line monitoring methods.

Novel NDIR CO/sub 2/ sensor for indoor air quality monitoring

This paper describes NDIR CO/sub 2/ gas sensor with novel optical cavities and two elliptical mirrors that are optimized for the optical path and light intensity. The new structures have two distinct features: one is focusing of infrared (IR) light onto the detector with the minimum cavity volume, and the other is an increased optical path length in order to enhance the sensitivity and accuracy. The developed sensor module shows about 360 mV voltage differences from 0 to 2000 ppm CO/sub 2/ concentration with 18,000 amplification gain. The response time of sensor module is around 30 sec.

Microelectromechanical-System-Based Variable-Focus Liquid Lens for Capsule Endoscopes

A liquid lens based on the electrowetting phenomenon was designed to be cylindrical to minimize dead area. The lens was fabricated with microelectromechanical-system (MEMS) technology using silicon thin film and wafer bonding processes. A multiple dielectric layer comprising Teflon, silicon nitride, and thermal oxide was formed on the cylinder wall. With a change of 11 Vrms in the applied bias, the lens module, including the fabricated liquid lens, showed a focal length change of approximately 166 mm. A capsule endoscope was assembled, including the lens module, and was successfully used to take images of a pig colon at various focal lengths.

Parameterized Simulation Program with Integrated Circuit Emphasis Modeling of Two-level Microbolometer

This paper presents a parameterized simulation program with integrated circuit emphasis (SPICE) model of a two-level microbolometer based on negative-temperature-coefficient thin films, such as vanadium oxide or amorphous silicon. The proposed modeling begins from the electricthermal analogy and is realized on the SPICE modeling environment. The model consists of parametric components whose parameters are material properties and physical dimensions, and can be used for the fast design study, as well as for the co-design with the readout integrated circuit. The developed model was verified by comparing the obtained results with those from finite element method simulations for three design cases. The thermal conductance and the thermal capacity, key performance parameters of a microbolometer, showed the average difference of only 4.77% and 8.65%, respectively.

Low voltage electrowetting on atomic-layer-deposited aluminum oxide

Electrowetting on dielectric (EWOD) is useful in manipulating droplets for digital (droplet-based) microfluidics, but its high driving voltage over several tens of volts has been a barrier to overcome. This paper presents the characteristics of EWOD device with aluminum oxide (Al2O3, εr≈10), deposited by atomic layer deposition (ALD), as the high-k dielectric for lowering the EWOD driving voltage substantially. The EWOD device of the single-plate configuration was fabricated by several steps for the control electrode array of 1 mm × 1 mm squares with 50μm space, the dielectric layer of 127nm thick ALD Al2O3, the reference electrode of 20μm wide line electrode, and the hydrophobic surface treatment by Teflon-AF coating, respectively. We observed the movement of a 2μl water droplet in an air environment, applying a voltage between one of the control electrodes and the reference electrode in contact with the droplet. Exponentially increasing droplet velocity with the applied voltage was obtained below 15V. The measured threshold voltage to move the droplet was as low as 3V which is the lowest voltage reported so far in the EWOD researches. This result opens a possibility of manipulating droplets, without any surfactant or oil treatment, at only a few volts by EWOD using ALD Al2O3 as the dielectric.

Dual structure of cholesteric liquid crystal device for high reflectance

The structure of cholesteric liquid crystal (CLC) undergoes a helical distortion which is left-handed or righthanded. By the right-hand CLC layer, Left-handed polarized light is reflected and vice versa. The color reflected by the selective reflection depends on the chiral pitch and the anisotropy of the refractive index. However, the reflectance of the single CLC layer is theoretically limited to 50% because only one of right- or left-handed circularly polarized light is reflected. In this paper, we demonstrate the enhanced reflectance of a dual-CLC device which can reflect both right- and left-handed circularly polarized light.

MEMS-based liquid lens for capsule endoscope

The capsule endoscope, a new application area of digital imaging, is growing rapidly but needs the versatile imaging capabilities such as auto-focusing and zoom-in to be an active diagnostic tool. The liquid lens based on MEMS technology can be a strong candidate because it is able to be small enough. In this paper, a cylinder-type liquid lens was designed based on Young-Lippmann model and then fabricated with MEMS technology combining the silicon thin-film process and the wafer bonding process. The focal length of the lens module including the fabricated liquid lens was changed reproducibly as a function of the applied voltage. With the change of 30V in the applied bias, the focal length of the constructed lens module could be tuned in the range of about 42cm. The fabricated liquid lens was also proven to be small enough to be adopted in the capsule endoscope, which means the liquid lens can be utilized for the imaging capability improvement of the capsule endoscope.

Fabrication of truly 3D microfluidic channel using 3D-printed soluble mold

The field of complex microfluidic channels is rapidly expanding toward channels with variable cross-sections (i.e., beyond simple rounded channels with a constant diameter), as well as channels whose trajectory can be outside of a single plane. This paper introduces the use of three-dimensional (3D) printed soluble wax as cast molds for rapid fabrication of truly arbitrary microfluidic polydimethylsiloxane (PDMS) channels that are not achieved through typical soft lithography. The molds are printed directly from computer-aided design files, followed by simple dissolution using a solvent after molding PDMS, making rapid prototyping of microfluidic devices possible in hours. As part of the fabrication method, the solubility of several build materials in solvents and their effect on PDMS were investigated to remove the 3D-printed molds from inside the replicated PDMS microfluidic channels without damage. Technology limits, including surface roughness and resolution by comparing the designed channels with fabricated cylindrical channels with various diameters, are also characterized. We reproduced a 3D image of an actual human cerebral artery as cerebral artery-shaped PDMS channels with a diameter of 240 μm to prove the developed fabrication technique. It was confirmed that the fabricated vascular channels were free from any leakage by observing the fluorescence fluid fill.

Threshold voltage model of fast-moving ball actuator

We clarified underlying physics and thereby developed threshold voltage model of a fast-moving ball actuator (FMBA) for reflective electronic paper display. The proposed threshold voltage model starts from considering all the related forces of Coulomb force, dielectrophoretic (DEP) force, frictional force, and adhesion caused by van der Waals force, where frictional force consists of vertical Coulomb and DEP forces, buoyance, and gravity. Considering 3-dimensional geometric effect, Coulomb and DEP forces were analyzed through numerical simulations while all the remaining forces were analytically modeled. As a result, DEP force, buoyance, and gravity were concluded negligible compared to Coulomb force and van der Waals force. With the simplified threshold voltage model, the required driving voltage of 39.54 V was obtained, which matched well to the measured voltage of 40 V.

Electro-thermal Feedback Effects on the Signal in a Pulse Voltage Biased μ-bolometer Focal Plane Array

In this paper, the analytical models for the electrothermal feedback of a -bolometer focal plane array(FPA) are proposed and applied to the conceptually designed FPA to investigate the electrothermal feedback effect on bolometer FPA signal. The temperature and resistance change of the -bolometer by the electrothermal feedback(ETF) model are increased upto 20 and 35.7 % of those of no feedback case, respectively, while those by the effective thermal conductance(ETC) model increased 8.5 and 15.1 %. The integration current and output voltage of a CTIA used as an column amplifier of FPA are also increased upto 41.6 and 32.4 % by the ETF model, while increased upto 17.2 and 13.5 % by the ETC model. The proposed models give more accurate temperature change, accordingly larger signal than no feedback considering case. Electrothermal feedback effect should be considered to design a high performance and high density -bolometer FPA. The proposed models are very useful to investigate the transient thermal analysis, also considered to be useful to predict the responsivity and dynamic range of -bolometer FPAs.