• Journal of the Korea Convergence Society
• /
• v.12 no.12
• /
• pp.267-272
• /
• 2021

This study would like to propose a certification of aviation components manufactured through 3D printing. Currently, many types of 3D printers are being used in various industries. Among them, a lot of research is being done in the aviation sector to manufacture drones and aviation components. However, the current level of 3D printer technology and the application of aviation components using it are lacking in many problems and related airworthiness certification standards. Furthermore, clear certification criteria for conformity and coherence are rarely presented. Therefore, we would like to propose matters related to certification of 3D printed equipment for application as aviation components. It is expected that 3D printing equipment will improve precision, reduce defect rate, sagging problem, and bed leveling problem will be solved in the future, and certification standards will be clearly established. In addition, we hope that the reliability of aviation components applied with 3D printing technology will be improved and the relevant certification standards will be further developed.

• The Journal of the Korea Contents Association
• /
• v.19 no.7
• /
• pp.220-233
• /
• 2019

Hitherto there have been by and large three different approaches to the installation works of Olafur Eliasson; a soma-aethetic, politico-aesthetic and techno-aesthetic. But none of these provides us with the aesthetic descriptions of the light effect. This failure seems to arise from the lack of the conceptual tools suit for describing the atmospheric effect of 'light'. The symbolism of light, or the theological optics of Middle Age may help us to compensate for the lack of appropriate concepts needed for theorizing the effect of light used very frequently by contemporary installation artists. And this medieval aesthetics of light can also of service to elucidate some essential characteristics of the digtal visual culture in general.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.30 no.3
• /
• pp.243-251
• /
• 2019

Recently, several studies were conducted on the micro-Doppler(MD) phenomenon to identify a warhead from decoys. Both, the warhead and decoy, can be modeled as various shapes and maneuver with their own micro-motion. Their MD phenomenon can be demonstrated by amplitude modulation and phase modulation. Most studies have utilized approximate solutions to express the amplitude modulation regardless of various warhead and decoy shapes. However, the exact solution of the amplitude modulation is required for more effective warhead identification. In this study, we proposed a new modeling method of receiving radar signals from warheads and decoys based on physical optics. The proposed solution was evaluated using an electromagnetic prediction technique and computer-aided design models.

• Current Optics and Photonics
• /
• v.2 no.6
• /
• pp.499-507
• /
• 2018

For the spatiotemporally aligned observation of photothrombosis induction and transient variations of in vivo brain stroke, we developed a novel photothrombosis inducing system compatible to a magnetic resonance imaging (MRI) system using nonmagnetic stereotaxic equipment. From the spatial point of view, the system provides a more reliable level of reproducibility of the photothrombosis in each brain. From the temporal point of view, from T1- and T2-weighted in vivo MR (magnetic resonance) images, the transient variations such as incidence, location, and size of the thrombosis are measured quantitatively. In addition, the final variation is observed in the ex vivo brain by TTC (Triphenyltetrazolium chloride) staining based on histological assay and utilized for the verification of the MR images. From the experimental result of the rat brain, the proposed system shows more reliable characteristics for transient variations of brain strokes.

• Current Optics and Photonics
• /
• v.3 no.1
• /
• pp.66-71
• /
• 2019

Application of liquid crystal (LC) materials to a flexible device is challenging because the bending of LC displays easily causes change in thickness of the LC layer and orientation of LCs, resulting in deterioration in a displayed image quality. In this work, we demonstrate a prototype device combining a flexible polymer substrate and an optically isotropic LC-polymer composite in which the device consists of interdigitated in-plane switching electrodes deposited on a flexible colorless polyimide substrate and the composite consisting of nano-sized LC droplets in a polymer matrix. The device can keep good electro-optic characteristics even when it is in a bending state because the LC orientation is not disturbed in both voltage-off and -on states. The proposed device shows a high potential to be applicable for future flexible LC devices.

• Current Optics and Photonics
• /
• v.3 no.1
• /
• pp.46-53
• /
• 2019

Monte Carlo simulations were performed for a three-dimensional tissue model with and without an embedded large vessel, to understand how varying vessel geometry affects surface light distribution. Vessel radius was varied from 1 to 5 mm, and vessel depth from 2 to 10 mm. A larger difference in surface fluence rate was observed when the vessel's radius increased. For vessel depth, the largest difference was seen at a depth of approximately 4 mm, corresponding to human wrist region. When the vessel was placed at depths greater than 8 mm, very little difference was observed. We also tested the feasibility of using two source-detector pairs, comprising two detectors distinctly spaced from a common source, to noninvasively measure blood-scattering changes in a large vessel. High sensitivity to blood-scattering changes was achieved by placing the near detector closer to the source and moving the far detector away from the source. However, at longer distances, increasing noise levels limited the sensitivity of the two-detector approach. Our results indicate that the approach using two source-detector pairs may have potential for quantitative measurement of scattering changes in the blood while targeting large vessels near the human wrist region.

• Korean Journal of Materials Research
• /
• v.29 no.9
• /
• pp.567-577
• /
• 2019

Aluminum nitride (AlN) has versatile and intriguing properties, such as wide direct bandgap, high thermal conductivity, good thermal and chemical stability, and various functionalities. Due to these properties, AlN thin films have been applied in various fields. However, AlN thin films are usually deposited by high temperature processes like chemical vapor deposition. To further enlarge the application of AlN films, atomic layer deposition (ALD) has been studied as a method of AlN thin film deposition at low temperature. In this mini review paper, we summarize the results of recent studies on AlN film grown by thermal and plasma enhanced ALD in terms of processing temperature, precursor type, reactant gas, and plasma source. Thermal ALD can grow AlN thin films at a wafer temperature of $150{\sim}550^{\circ}C$ with alkyl/amine or chloride precursors. Due to the low reactivity with $NH_3$ reactant gas, relatively high growth temperature and narrow window are reported. On the other hand, PEALD has an advantage of low temperature process, while crystallinity and defect level in the film are dependent on the plasma source. Lastly, we also introduce examples of application of ALD-grown AlN films in electronics.

• Current Optics and Photonics
• /
• v.3 no.4
• /
• pp.342-349
• /
• 2019

We present a theoretical research concerning terahertz (THz) wave generation with $KTiOPO_4$ (KTP) by collinear phase matching (CPM) stimulated polariton scattering (SPS). Both CPM and corresponding nonzero nonlinear coefficients can be simultaneously realized with $s{\rightarrow}f+f$ in yz plane, $s{\rightarrow}f+s$ with ${\theta}$ < ${\Omega}$ in xz plane and $s{\rightarrow}f+f$ with ${\theta}$ < ${\Omega}$ in xz plane. The effective nonlinear coefficients including electronic nonlinearities and ionic nonlinearities are calculated. Based on the parameter values of refractive indices, absorption coefficients and effective nonlinear coefficients, we simulate THz wave intensities generated with CPM SPS by solving coupled wave equations and give the relationship among the maximum THz wave intensity, optimal crystal length and the angle ${\theta}$. The calculation results demonstrate that CPM SPS with KTP can generate THz waves with high intensities and quantum conversion efficiencies.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.32 no.3
• /
• pp.141-147
• /
• 2019

In this paper, a systematic beam splitter design for multi-beam forming is proposed. The objective of this research is to a design beam splitter that splits and focuses scattering microwaves into intense beams in multiple directions. It is difficult to split multi-beam to non-specific directions with theoretical approaches. Therefore, instead of using transformation optics(TO), which is a widely used process for controlling electromagnetic wave propagation, we used a systematic design process called the phase field design method to obtain an optimal topological structure of beam splitter. The objective function is to maximize the norm of electric field of the target areas of each direction. To avoid island structure and obtain the structure in one body, volume constraint is added to the optimization problem by using augmented Lagrangian. Target frequency is set to X-band 10GHz. The optimal beam splitter performed well in multi-beam forming and the transported electric energy of target areas improved. A frequency dependency test was conducted in the X-band to determine effective frequency range.

• Current Optics and Photonics
• /
• v.3 no.2
• /
• pp.119-127
• /
• 2019

A new secret-key-sharing cryptosystem using optical phase-shifting digital holography is proposed. The proposed secret-key-sharing algorithm is based on the Diffie-Hellman key-exchange protocol, which is modified to an optical cipher system implemented by a two-step quadrature phase-shifting digital holographic encryption method using orthogonal polarization. Two unknown users' private keys are encrypted by two-step phase-shifting digital holography and are changed into three digital-hologram ciphers, which are stored by computer and are opened to a public communication network for secret-key-sharing. Two-step phase-shifting digital holograms are acquired by applying a phase step of 0 or ${\pi}/2$ in the reference beam's path. The encrypted digital hologram in the optical setup is a Fourier-transform hologram, and is recorded on CCDs with 256 quantized gray-level intensities. The digital hologram shows an analog-type noise-like randomized cipher with a two-dimensional array, which has a stronger security level than conventional electronic cryptography, due to the complexity of optical encryption, and protects against the possibility of a replay attack. Decryption with three encrypted digital holograms generates the same shared secret key for each user. Schematically, the proposed optical configuration has the advantage of producing a kind of double-key encryption, which can enhance security strength compared to the conventional Diffie-Hellman key-exchange protocol. Another advantage of the proposed secret-key-sharing cryptosystem is that it is free to change each user's private key in generating the public keys at any time. The proposed method is very effective cryptography when applied to a secret-key-exchange cryptosystem with high security strength.