Bo-Seon Kang

Application of the correlation coefficient method for determination of the focal plane to digital particle holography

The correlation coefficient (CC) method, which was proposed by our research group, is applied to digital particle holography to locate the focal plane of particles. It uses the fact that the CC is maximum at the focal plane. The factors influencing this method are discussed with a numerical simulation of holograms. For real holograms, the Wiener filter was proposed to process both recorded holograms and reconstructed images. The application results using the dot array target showed that the Wiener filter is a very effective tool for processing holography-related images. The effects of the dot size and the object distance on the errors in the determination of the focal plane by the CC method were investigated by using the calibration target.

Mechanical properties and nondestructive testing of advanced materials 2014

1Key Laboratory of Manufacture and Test Techniques for Automobile Parts, Ministry of Education, Chongqing 400054, China 2Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, BC, Canada V6T 1Z4 3Department of Bioengineering, University of Washington, Seattle, WA 98195-5061, USA 4Department of Mechanical System Engineering, Chonnam National University, Gwangju 500757, Republic of Korea

Measurement of the thermal conductivity of a water-based single-wall carbon nanotube colloidal suspension with a modified 3- ω method

A modified 3-omega method applied to a suspended platinum microwire was employed to measure the thermal conductivity and convective heat transfer coefficient of a water-based single-walled carbon nanotube (CNT) solution (metallic single-wall nanotubes with 1.33 nm diameter and 1.14 wt% concentration), and an expression for calculating the convective heat transfer coefficient in such a free convective fluid was introduced. The measurement technique was validated for three model systems including vacuum, air and deionized water. It is found that there is excellent agreement between these three model systems with theoretical predictions. In addition, the frequency dependence on the third harmonic response measured in deionized water reveals the existence of a very low working frequency below 60 mHz. The thermal conductivity and convective heat transfer coefficient of the nanofluid (water-based single-wall CNT solution) were determined to be 0.73 +/- 0.013 W m(-1) K(-1) and 14 900 +/- 260 W m(-2) K(-1), respectively, which correspond to an enhancement of 19.4% in thermal conductivity and 18.9% in convective heat transfer as compared to water.

Experimental Studies on Friction Factor and Heat Transfer Characteristics Through Wire-Woven Bulk Kagome Structure

Periodic cellular metals with open, periodic cell topologies have received much attention owing to their potential for multi-functionality such as load bearing, thermal dissipation, and actuation. Recently, a new technique, known as wire-woven bulk Kagome, has been introduced, which is used for fabricating multi-layered Kagome with truss periodic cellular metal. The fabrication of the wire-woven bulk Kagome is based on a concept where continuous helical wires are systematically assembled in six directions. Besides its excellent load-bearing capability with light weight, the wire-woven bulk Kagome has potential for a heat dissipation media because of the high ratio of surface area to volume and low flow resistance. This article presents the experimental results of the fluid flow and heat transfer characteristics of the multi-layered wire-woven bulk Kagome composed of aluminum 1100 helix wires. Under forced-air convection conditions, the friction factor and heat transfer rate of the wire-woven bulk Kagome specimen were investigated for two specimen orientations. The results showed that the friction factor of the wire-woven bulk Kagome was mainly affected by the flow blockage area, and the heat transfer characteristics depended on the open-area ratio. In addition, the results were compared with other heat dissipation media (e.g., open-celled foams, woven screens, lattice-frame materials, and cast Kagome structures). The results showed that the heat transfer performance of the multi-layered aluminum wire-woven bulk Kagome competed favorably with the best heat dissipation media currently available.

Experimental validation for the determination of particle positions by the correlation coefficient method in digital particle holography

The feasibility and the accuracy of the correlation coefficient (CC) method for the determination of particle positions along the optical axis in digital particle holography were verified by validation experiments. A translation system capable of high precision was used to move the particle objects by exact known distances between several different positions. The particle positions along the optical axis were calculated by the CC method and compared with their exact values to obtain the errors of the focus plane determination. The tested particles were two-dimensional (2D) dots in a calibration target along with different-sized glass beads and droplets that reflected and caused a three-dimensional (3D) effect. The results show that the CC method can work well for both the 2D dots and the 3D particles. The effect of other particles on the focus plane determination was also investigated. The CC method can locate the focus plane of particles with high precision, regardless of the existence of other particles.

Focal plane location in digital holography

The correlation coefficient method is introduced to locate the focal plane in digital particle holography. It uses the fact that the correlation coefficient is maximum at the focal plane. The factors influencing this method are discussed with a numerical simulation of holograms. For real holograms, the Wiener filter was first proposed to process both recorded holograms and reconstructed images. The application results using the dot array target showed that the Wiener filter is a very effective tool for processing holography-related images. The effects of the dot size and the object distance on the errors in the determination of the focal plane by the correlation coefficient method were investigated by using the calibration target.

Extraction of sizes and velocities of spray droplets by optical imaging method

In this study, an optical imaging method was developed for the measurements of the sizes and velocities of droplets in sprays. Double-exposure single-frame spray images were captured by the imaging system. An image processing program was developed for the measurements of the sizes and positions of individual particles including separation of the overlapped particles and particle tracking and pairing at two time instants. To recognize and separate overlapping particles, the morphological method based on watershed segmentation as well as separation using the perimeter and convex hull of image was used consecutively. Better results in separation were obtained by utilization of both methods especially for the multiple or heavily-overlapped particles. The match probability method was adopted for particle tracking and pairing after identifying the positions of individual particles and it produced good matching results even for large particles like droplets in sprays. Therefore, the developed optical imaging method could provide a reliable way of analyzing the motion and size distribution of droplets produced by various sprays and atomization devices.

Measurements of three-dimensional velocities of spray droplets using the holographic velocimetry system

The Holographic Particle Velocimetry system can be a promising optical tool for the measurements of three dimensional particle velocities. In this study, the holographic particle velocimetry system was used to measure the sizes and velocities of droplets produced by a commercial full cone spray nozzle. As a preliminary validation experiment, the velocities of glass beads on a rotating disk were measured with uncertainty analysis to identify the sources of all relevant errors and to evaluate their magnitude. The error of the particle velocity measured by the holographic method was 0.75 m/s, which was 4.5% of the known velocity estimated by the rotating speed of disk. The spray droplet velocities ranged from 10.3 to 13.3 m/s with average uncertainty of +-1.6 m/s, which was +-14% of the mean droplet velocity. Compared with relatively small uncertainty of velocity components in the normal direction to the optical axis, uncertainty of the optical axis component was very high. This is due to the long depth of field of droplet images in the optical axis, which is inherent feature of holographic system using forward-scattering object wave of particles.

Focused Ion Beam in Thermal Science and Engineering

Laboratory of Thermodynamics, ETH Zurich CH-8092 Switzerland In this paper, utilizing a focused ion beam source for applications in thermal science is demonstrated. Focused-ion-beam (FIB) nanolithography has been used to make electrical contacts on nanometer-sized materials. However, a foreseeable damage occurring in these materials by highly energetic ion bombardment during metal deposition restrains its use. The appearance of the dual beam (conventional FIB with a scanning electron microscope) has facilitated the use of dual-beam FIB nanolithography owing to the possibility of acquiring electron beam images in situ and dissociating metalorganic compounds, giving rise to electron-beam-induced metal deposition [1]. Because interaction between electrons and the sample is less destructive than using ions, performing an electron-assisted deposition on the nanostructure can minimize undesired surface damage and structure modification of the nanostructure. The thermal properties of individual multi-walled carbon nanotubes was measured by utilizing the 4-point-probe 3-ω method, based on the fact that the third harmonic amplitude and phase as a response to applied alternate current at fundamental frequency, ω, can be expressed in terms of thermal conductivity and diffusivity. To this end, a microfabricated device composed of four metal electrodes was modified to manufacture nanometer-sized wires by using a focused ion beam source as shown in Fig. 1a. A carbon nanotube could then be suspended over a deep trench milled by the focused ion beam, preventing heat loss to the substrate (Fig. 1b). To deposit individual carbon nanotubes, we utilized the principle of dielectrophoresis (DEP). The dielectrophoresis has been considered as an excellent method for CNT manipulation. Herein, we applied a high-frequency (5 MHz) ac field combined with dc offset between the pads, 1 and 4. When a CNT touches the electrodes, it will stick to them and stays there by Van der Waals force [2]. Finally, to minimize the electrical contact resistance between carbon nanotubes and the metal electrodes, electron beam “soldering” was performed. The pads 1 and 4 have round shapes on the tip, which aids carbon nanotube deposition. Fig. 2 shows three different measurements of 3-ω signals for carbon nanotubes submerged in vacuum, air and deionized water. To this end, the 4-wire configuration (Fig. 1c) was utilized for measuring the 3

A Study on Determination of the Focal Plane of Particle in Digital Particle Holography

The correlation coefficient method, which was proposed by our research group, is applied to digital particle holography to locate the focal plane of particles. It uses the fact that the correlation coefficient is maximum at the focal plane. The factors influencing this method are discussed with a numerical simulation of holograms. For real holograms, the Wiener filter was proposed to process both recorded holograms and reconstructed images. The application results using the dot array target showed that the Wiener filter is a very effective tool for processing holography-related images. The effects of the dot size and the object distance on the errors in the determination of the focal plane by the correlation coefficient method were investigated by using the calibration target.