Light intensity and image visualization of GDI injector sprays according to nozzle hole arrangements

Kim, H.J.,Park, S.H.,Lee, C.S. Wissenschaftliche Verlagsgesellschaft m. b. H 2014 OPTIK -STUTTGART- Vol.125 No.12

The light intensity measurement and image visualization of multi-hole injection spray due to different hole arrangements and hole numbers were investigated. The light intensities and behavior characteristics of the GDI spray were analyzed through the axial and diagonal spray penetration, cone angle, and spray area from the spray images by using the image visualization system and image analysis system. The atomization performance of GDI injectors was analyzed by the local and overall Sauter mean diameter (SMD) measurement. It is revealed that the higher injection pressure shows higher light intensity levels due to the strong vortices and collision by a high injection pressure. The light intensity level at the outer and end region of the spray shows lower value compared to that at the center spray region. In all of test injectors, the increased injection pressure leads to the decrease of the droplet size distribution in the initial spray. But, there is little difference of the droplet size at low and high injection pressure in middle and latter period after the injection. The overall SMD of GDI injectors showed from 14 to 23.14μm.

Light enhancement of surface nano-textured GaN based light emitting diodes using self-assembled Ni nano-masks

Mustary, M.H.,Ryu, B.D.,Han, M.,Yang, J.H.,Lysak, V.V.,Hong, C.H. Wissenschaftliche Verlagsgesellschaft m. b. H 2016 Optik Vol.127 No.4

<P>Light enhancement of GaN based light emitting diodes (LEDs) has been investigated by texturing the top p-GaN surface. Nano-textured LEDs have been fabricated using self-assembled Ni nano mask during dry etching process. Experimental result was further compared with simulation data. Three types of LEDs were fabricated: Conventional (planar LED), surface nano-porous (porous LED) and surface nano-cluster (cluster LED). Compared to planar LED there were about 100% and 54% enhancement of light output power for porous and cluster LED respectively at an injection current of 20 mA. Moreover, simulation result showed consistency with experimental result. The increased probability of light scattering at the nano-textured GaN-air interface is the major reason for increasing the light extraction efficiency. (C) 2015 Elsevier GmbH. All rights reserved.</P>

Highly accurate film thickness measurement based on automatic fringe analysis

Abdelsalam, D.G.,Baek, B.J.,Abdel-Aziz, F.,Chegal, W.,Kim, D. Wissenschaftliche Verlagsgesellschaft m. b. H 2012 OPTIK -STUTTGART- Vol.123 No.16

This paper describes an automated multiple-beam interferometry for measuring a calibrated step height of (27.00+/-3.00) nm nominally. The fringes captured from the multiple-beam Fizeau-Tolansky interferometer were thinned by using a written program to obtain accurate measurement. We claim that multiple-beam interferometry based on automatic fringe thinning process can provide a real time solution for calibrating step heights precisely and with high accuracy. The uncertainty budget of the multiple-beam interferometry method due to incomplete parallelism of the incident beam and the inhomogeneity of the reflecting layers was calculated automatically with a written ray tracing program. The uncertainty budget in multiple-beam interferometry was estimated to be of the order of 3.00nm.

Application of background oriented Schlieren (BOS) method for visualization of evaporating impinged spray

Bang, S.H.,Lee, C.S. Wissenschaftliche Verlagsgesellschaft m. b. H 2015 OPTIK -STUTTGART- Vol.126 No.18

The background oriented Schlieren (BOS) method for the visualization of impinged evaporating spray is presented to analyze macroscopic spray characteristics and evolution processes. The spray characteristics of dimethyl ether (DME), DME blends, biodiesel and diesel on the impinged wall in a pressurized chamber are effectively visualized for the spray evolution processes, spray depth, and spray area at various elapsed times. The visualization results of impinged spray on the wall by BOS method compared those with the scattering method. It is confirmed that the BOS method is an effective method for measurement and visualization of impinged evaporating sprays. The spray depth for the impinged wall increased with the increase of DME mixing fraction and the evolution patterns showed the stepped increasing due to impinged effect of plane wall.

Development of image reconstruction algorithm with iterative method using maximum-likelihood expectation-maximization (MLEM) for chest digital tomosynthesis (CDT) X-ray system

Lee, S.,Kang, S.H.,Heo, Y.C.,Lee, Y. Wissenschaftliche Verlagsgesellschaft m. b. H 2017 OPTIK -STUTTGART- Vol.150 No.-

<P>Digital tomosynthesis system (DTS) has been increasingly used in chest X-ray imaging with a limited-projection angle image reconstruction method. Image reconstruction methods in chest digital tomosynthesis (CDT) have fundamental impacts on image characteristics. Among these methods, iterative algorithm provides the additional benefits of chest X-ray imaging. However, there is almost no research that maximum-likelihood expectation-maximization (MLEM) method in CDT system. Thus, the purpose of this study was (1) to develop MLEM reconstruction algorithm based on CDT system and (2) to quantitatively compare the image characteristics with respect to the total angular range and iteration number as applied this system. For that purpose, we performed both simulation using MATLAB program and experimental studies. Tomography was performed linearly with a maximum +/- 30 degrees total angular range and then we acquired Shepp-Logan and PMMA-Aluminum (Al) phantom images using 120 kVp X-ray source for simulation and experiment, respectively. We evaluated and compared the MLEM reconstructed image characteristics using root-mean-square error (RMSE) and signal difference-to-noise ratio (SDNR) with various total angular ranges and iteration numbers. According to the results, we can acquire improved image characteristics as the number of iterations and the number of projections increased. Also, we found optimized iteration number for 20 iteration numbers in our CDT system geometry because there were few changes of image characteristics over 20 iteration numbers. In conclusion, we have presented usefulness and effectiveness of developed CDT image reconstruction algorithm. (C) 2017 Elsevier GmbH. All rights reserved.</P>

Single image-based spatially adaptive dynamic range extension using combined color-channels transmission map

Im, J.,Yoo, Y.,Paik, J. Wissenschaftliche Verlagsgesellschaft m. b. H 2015 OPTIK -STUTTGART- Vol.126 No.9

In this paper, a novel dynamic range extension method is presented by detecting under-exposed regions and performing spatially adaptive contrast enhancement. More specifically, a combined color-channels transmission (CCT) map is proposed to detect low-contrast regions, and spatially adaptive gain computation is used to enhance the contrast of the under-exposed regions. As a result, the proposed method can extend the dynamic range of a single input image by changing the brightness of under-exposed regions with preserving the brightness of background. Moreover, the proposed method requires less computational load than existing multiple frames-based high dynamic range (HDR) imaging methods without color distortion. For these reasons, the proposed method can be applied to various imaging devices, such as mobile phone cameras, compact digital cameras, and video surveillance systems.

Influence of the collimation of the reference wave in off-axis digital holography

Abdelsalam, D.G.,Baek, B.J.,Kim, D. Wissenschaftliche Verlagsgesellschaft m. b. H 2012 OPTIK -STUTTGART- Vol.123 No.16

In digital holography, the novel concept of the digital reference wave has opened in numerous opportunities for various fields to which digital holography may be applied. Oftentimes, a plane wave is utilized in digital holography experiments to operate as the reference wave; thus, the simulation of the plane wave is necessary for performing a numerical reconstruction. Conventionally, perfect collimation producing a perfect plane wave impinging on the reference should be carefully adjusted with a shear interferometer in order to obtain acceptable results. In this paper, we claim that it is not necessary to use a perfect plane wave in digital holography experiments. We experimentally proved that by using the Michelson interferometer, no influence of imperfect collimation of the reference wave in an off-axis digital holography exists, as has been previously claimed. Our deductions were verified by applying perfect and imperfect collimations to three different surfaces (flat, spherical and step) for height inspection and the results were almost consistent. The consistencies of the measured height values for the three tested surfaces at both perfect and imperfect collimations prove that there is no influence of imperfect collimations in off-axis digital holography.

The optical simulation of an air-guide edge-lit

Kim, S.J.,Joo, B.Y.,Kim, B.M. Wissenschaftliche Verlagsgesellschaft m. b. H 2014 OPTIK -STUTTGART- Vol.125 No.19

The air-guide edge-lit without a light guide panel has been developed to meet the low manufacturing cost of a surface illuminator. The performance of the light guide inside the air layer between the curved reflector, used as the rear surface, and a flat light diffuse plate, at the front surface, depends on the shape of reflector curve and the BRDF (bidirectional reflectance distribution function) of the material of reflector. The goal of this study is to develop a ray-tracing simulation model in order to design the curve shape of the air-guide edge-lit meeting the luminance uniformity. In the present study, the BRDFs of reflector materials were measured and calibrated. The simulation accuracy in the luminance uniformity of the model was examined, and the influence of BRDF at the high angle of incidence on simulation accuracy was discussed.

Multiple moving object segmentation using motion orientation histogram in adaptively partitioned blocks for high-resolution video surveillance systems

Lee, S.,Kim, N.,Jeong, K.,Paek, I.,Hong, H.,Paik, J. Wissenschaftliche Verlagsgesellschaft m. b. H 2015 OPTIK -STUTTGART- Vol.126 No.19

We present an efficient, robust moving object segmentation method that fully utilizes block motion information for high-resolution video surveillance systems. A high-resolution video surveillance system should satisfy two conflicting goals: (i) higher computational efficiency to manage the increasing amount of data and (ii) enhanced functionality in analyzing moving objects. In pursuit of both efficiency and functionality, we first quantize the orientation of motion vectors and then segment moving objects using adaptive block partitioning algorithm. We also present motion orientation histogram-based moving direction estimation. Major contribution of this work is the fully utilization of block motion information provided by either an image signal processing (ISP) chip or a digital signal processor (DSP) built-in software and the optimal representation of moving objects by the block divide-and-merge algorithm. Comparative experiments with the conventional video analysis algorithms show that the proposed method provides better segmentation results with the regular, efficient computational structure that can be easily embedded in an ISP chip or DSP software.

Investigations on the effect of the electric fields inside the wigglers on the trajectory of the electron beam in the miniaturized FEL module

Kim, Y.C.,Ahn, S.J.,Kim, H.S.,Kim, D.W.,Jeong, J.W.,Ahn, S. Wissenschaftliche Verlagsgesellschaft m. b. H 2013 Optik Vol.124 No.17

In the free electron laser (FEL) module, it is important to maintain the symmetrical profile of the e-beam propagation to obtain high-quality EM waves since the electromagnetic (EM) waves are generated directly from the acceleration of the electrons in the FEL module. We have investigated the motion of the electrons in the various types of wigglers of the miniaturized FEL module by using a 3D simulation tool. In the ring-type wiggler, we could obtain the e-beam profile bearing circular symmetry with respect to the optic axis. In the conventional planar-type wiggler, the e-beam went out of the optic axis as it propagated through the wiggler. We have demonstrated that such a deviation could be removed by applying the symmetrical bias to the electrode pairs, which is useful to improve the characteristics of the EM radiation.