https://scholar.gist.ac.kr/handle/local/7961 Sat, 08 Aug 2026 10:13:17 GMT 2026-08-08T10:13:17Z https://scholar.gist.ac.kr/handle/local/19868 Title: Ultrathin Epitaxial Lift-off GaAs Solar Cell Array with Highly Flexible and Lightweight Characteristics Author(s): Sungbum Cho Abstract: Recent interests increasing in ultraflexible and ultralight solar cells with reliable and high efficiency for untethered power supply to electronic devices such as attachable, implantable, and miniaturized drones, etc. However, the structural limitation of material obstructs the coexistence between the ultraflexible characteristics and the high electrical performance. This dissertation proposes an ultrathin, ultralight solar cell array with high efficiency on an ultrathin polymer film. Framing of 1.4 μm thick ultrathin film and a series of processes of cold-welding, epitaxial lift-off (ELO), and microfabrication gives the GaAs solar cell array ultraflexible and ultralight characteristics. The mechanical characteristics of the ultrathin GaAs photovoltaic (PV) array were analyzed through finite element analysis and planar compression test. The PV array operates under extreme deformation and demonstrates the connectivity to diverse unconventional surfaces. Lastly, the ultralight characteristic was ensured with a specific power of 5.44 W/g. Fri, 31 Dec 2021 15:00:00 GMT https://scholar.gist.ac.kr/handle/local/19868 2021-12-31T15:00:00Z https://scholar.gist.ac.kr/handle/local/19855 Title: Transfer-Printed Optoelectronics for Cylindrical Concentrating Photovoltaics and Vascular Hemodynamics Monitoring Author(s): 이태연 Abstract: The transfer printing method, which selectively separates optoelectronic elements based on compound semiconductor thin films epitaxially-grown on wafers and integrates them onto foreign substrates, offers applicability in various fields such as photovoltaic energy harvesting, wearable and implantable sensors. Optoelectronic elements transfer-printed onto flexible film substrates overcome the structural and functional limitations of conventional rigid elements, enabling applications such as curved surface-attached flexible solar cells, vertically stacking the light emitting diodes (LEDs), and the heterogeneous integration of photodetector and LEDs. The main focus of this dissertation is to design a system that meets the required performance through systematic analysis, and to fabricate devices by integrating optoelectronic elements using transfer printing method, demonstrate the applications in various fields, including concentrating photovoltaics (CPV) and hemodynamics monitoring. In this doctoral dissertation, a planar-type cylindrical CPV module design to save energy required for solar tracking and a vertically stacked LED structure for localized hemodynamics monitoring are proposed. Notably, red and blue-colored LEDs were vertically stacked on a foreign substrate using the transfer printing method, and a photodetector capable of measuring the light emitted from these LEDs was heterogeneously integrated on the same substrate, allowing it to function as a hemodynamic sensor. Thus, transfer-printed optoelectronics is a key technology that can expand the functionality of traditional semiconductors Tue, 31 Dec 2024 15:00:00 GMT https://scholar.gist.ac.kr/handle/local/19855 2024-12-31T15:00:00Z https://scholar.gist.ac.kr/handle/local/32670 Title: Topology optimization of acoustic and vibroacoustic problems using the hybrid finite element-wave based method Author(s): Seongyeol Goo Abstract: To find an optimal solution in acoustic and vibroacoustic problems by topology optimization often requires a high computational cost. A common analysis in acoustic and vibroacoustic involves tens or hundreds of frequency components. Moreover, a fine resolution of the design domain leads to extremely heavy computational cost. The approximation technique such as reduced order modeling and Padé approximation can be applied to reduce computational cost. However, they still show unsatisfactory performances and also have unsolved issues regarding the accuracy of the solutions and sensitivities. To resolve these issues, a novel efficient topology optimization method that uses the hybrid finite element-wave based method is proposed in this dissertation. In the proposed method, the entire problem domain is divided into design and non-design domains. The finite element method is applied to the design domain for the material interpolation in topology optimization. The wave-based method, which is an efficient numerical scheme for acoustic problems, is applied to the non-design domain to reduce the computational cost. A direct coupling approach is used to construct the hybrid models for both acoustic and vibroacoustic problems. To use an efficient gradient-based optimizer, design sensitivities are computed by using the adjoint variable method that is presented in this dissertation. The performance evaluation of the proposed design method is conducted in 2D / 3D acoustic and vibroacoustic problems. The comparative studies for optimization results and computation cost are conducted for conventional topology optimization and the proposed method. In all numerical tests, the proposed design method significantly reduces the computational cost while maintaining identical results as those obtained from the conventional topology optimization method. Moreover, the efficiency of the proposed method further increases in 3D problems. The optimization results confirm that the proposed method can effectively handle largescale acoustic and vibroacoustic problems that conventional approach is infeasible due to huge computational burdens. Mon, 31 Dec 2018 15:00:00 GMT https://scholar.gist.ac.kr/handle/local/32670 2018-12-31T15:00:00Z https://scholar.gist.ac.kr/handle/local/19845 Title: Topology Design Optimization and Data-aided Analysis by Physics Informed Neural Networks for Additive Manufactured Structure Author(s): Dongjin Kim Abstract: This dissertation addresses methodologies for the design and analysis related to additive manufacturing. First, the design methodology is proposed to optimize the structural shape for stiffness maximization, and to generate the CAD file for its additive manufacturing. Specifically, open-source MATLAB code is developed for topology optimization of three-dimensional arbitrary design domains. In addition, the post-processing procedure is built to generate STL format file for the additive manufacturing of topology optimization result. The developed program enables the practical design process, which includes the loading of three-dimensional CAD file for setting the design domain, topology design optimization, and the additive manufacturing of design result. The effectiveness of the developed code is validated through various design examples, including a simply supported beam, a bridge, and an airplane bearing bracket. Subsequently, the data-aided analysis methodology is developed, which aims to reconcile the discrepancies between the analysis results by Computer-Aided Engineering (CAE), and the actual behavior of additive manufactured structures. Here, the discrepancies come from uncertainty in additive manufacturing processes. To overcome this problem, the distribution of material properties is included as the additional state variable, and the measured physical variables are added as the data. To treat material property as unknown variable and contain the data in the structural analysis, the physics-informed neural networks (PINNs) are utilized in this dissertation. For the stable analysis of additive manufactured structure with complex shapes, energy functional targeting loss function is proposed, and its effectiveness is validated by comparing with the result of existing PINN loss functions. In addition, the effect of data, i.e. data type among displacement and strain, and data domains, on the analysis result is investigated how to improve the accuracy of data-aided analysis results. The limitation of this work is as follows. The developed code for topology design optimization contains inaccuracies in geometry representation due to the use of an external, and discrepancies between the CAE model and the actual structure caused using isotropic properties of materials. The proposed data-aided analysis treats simplified two-dimensional geometries, and utilizes virtual data instead of the actual measured data of addictive manufactured structure. Sat, 31 Dec 2022 15:00:00 GMT https://scholar.gist.ac.kr/handle/local/19845 2022-12-31T15:00:00Z