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1. Computational Design and 3D Weaving of 2D-Printable Conformal Flexible Electronics using Harmonic Foliation Theory

   Ye, Qian ; Guo, Yang ; Gu, Xianfeng David ; Chen, Shikui ( August 2021 , Proceedings of the International Design Engineering Technical Conferences & Computers and Information in Engineering Conference)

   null (Ed.)

   This paper proposes a new way of designing and fabricating conformal flexible electronics on free-form surfaces, which can generate woven flexible electronics designs conforming to free-form 3D shapes with 2D printed electronic circuits. Utilizing our recently proposed foliation-based 3D weaving techniques, we can reap unprecedented advantages in conventional 2D electronic printing. The method is based on the foliation theory in differential geometry, which divides a surface into parallel leaves. Given a surface with circuit design, we first calculate a graph-value harmonic map and then create two sets of harmonic foliations perpendicular to each other. As the circuits are processed as the texture on the surface, they are separated and attached to each leaf. The warp and weft threads are then created and manually woven to reconstruct the surface and reconnect the circuits. Notably, The circuits are printed in 2D, which uniquely differentiates the proposed method from others. Compared with costly conformal 3D electronic printing methods requiring 5-axis CNC machines, our method is more reliable, more efficient, and economical. Moreover, the Harmonic foliation theory assures smoothness and orthogonality between every pair of woven yarns, which guarantees the precision of the flexible electronics woven on the surface. The proposed method provides an alternative solution to the design and physical realization of surface electronic textiles for various applications, including wearable electronics, sheet metal craft, architectural designs, and smart woven-composite parts with conformal sensors in the automotive and aerospace industry. The performance of the proposed method is depicted using two examples. 

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2. Variational Level Set Method for Topology Optimization of Origami Fold Patterns

   https://doi.org/10.1115/1.4053925  

   Ye, Qian ; Gu, Xianfeng David ; Chen, Shikui ( August 2022 , Journal of Mechanical Design)

   Abstract With specific fold patterns, a 2D flat origami can be converted into a complex 3D structure under an external driving force. Origami inspires the engineering design of many self-assembled and re-configurable devices. This work aims to apply the level set-based topology optimization to the generative design of origami structures. The origami mechanism is simulated using thin shell models where the deformation on the surface and the deformation in the normal direction can be simplified and well captured. Moreover, the fold pattern is implicitly represented by the boundaries of the level set function. The folding topology is optimized by minimizing a new multiobjective function that balances kinematic performance with structural stiffness and geometric requirements. Besides regular straight folds, our proposed model can mimic crease patterns with curved folds. With the folding curves implicitly represented, the curvature flow is utilized to control the complexity of the folds generated. The performance of the proposed method is demonstrated by the computer generation and physical validation of two thin shell origami designs. 

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3. A proof by foliation that lawson's cones are $ A_{\Phi} $-minimizing

   https://doi.org/10.3934/dcds.2021077  

   Mooney, Connor ; Yang, Yang ( January 2021 , Discrete & Continuous Dynamical Systems)

   We give a proof by foliation that the cones over \begin{document}$ \mathbb{S}^k \times \mathbb{S}^l $\end{document} minimize parametric elliptic functionals for each \begin{document}$ k, \, l \geq 1 $\end{document}. We also analyze the behavior at infinity of the leaves in the foliations. This analysis motivates conjectures related to the existence and growth rates of nonlinear entire solutions to equations of minimal surface type that arise in the study of such functionals.

    

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4. Photonic crystallization of two-dimensional MoS 2 for stretchable photodetectors

   https://doi.org/10.1039/c9nr02173f  

   Kim, Richard Hahnkee ; Leem, Juyoung ; Muratore, Christopher ; Nam, SungWoo ; Rao, Rahul ; Jawaid, Ali ; Durstock, Michael ; McConney, Michael ; Drummy, Lawrence ; Rai, Rachel ; et al ( July 2019 , Nanoscale)

   Low temperature synthesis of high quality two-dimensional (2D) materials directly on flexible substrates remains a fundamental limitation towards scalable realization of robust flexible electronics possessing the unique physical properties of atomically thin structures. Herein, we describe room temperature sputtering of uniform, stoichiometric amorphous MoS 2 and subsequent large area (>6.25 cm 2 ) photonic crystallization of 5 nm 2H-MoS 2 films in air to enable direct, scalable fabrication of ultrathin 2D photodetectors on stretchable polydimethylsiloxane (PDMS) substrates. The lateral photodetector devices demonstrate an average responsivity of 2.52 μW A −1 and a minimum response time of 120 ms under 515.6 nm illumination. Additionally, the surface wrinkled, or buckled, PDMS substrate with conformal MoS 2 retained the photoconductive behavior at tensile strains as high as 5.72% and over 1000 stretching cycles. The results indicate that the photonic crystallization method provides a significant advancement in incorporating high quality semiconducting 2D materials applied directly on polymer substrates for wearable and flexible electronic systems. 

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5. “Seeing Is Believing”—In-Depth Analysis by Co-Imaging of Periodically-Poled X-Cut Lithium Niobate Thin Films

   https://doi.org/10.3390/cryst11030288  

   Reitzig, Sven ; Rüsing, Michael ; Zhao, Jie ; Kirbus, Benjamin ; Mookherjea, Shayan ; Eng, Lukas M. ( March 2021 , Crystals)

   null (Ed.)

   Nonlinear and quantum optical devices based on periodically-poled thin film lithium niobate (PP-TFLN) have gained considerable interest lately, due to their significantly improved performance as compared to their bulk counterparts. Nevertheless, performance parameters such as conversion efficiency, minimum pump power, and spectral bandwidth strongly depend on the quality of the domain structure in these PP-TFLN samples, e.g., their homogeneity and duty cycle, as well as on the overlap and penetration depth of domains with the waveguide mode. Hence, in order to propose improved fabrication protocols, a profound quality control of domain structures is needed that allows quantifying and thoroughly analyzing these parameters. In this paper, we propose to combine a set of nanometer-to-micrometer-scale imaging techniques, i.e., piezoresponse force microscopy (PFM), second-harmonic generation (SHG), and Raman spectroscopy (RS), to access the relevant and crucial sample properties through cross-correlating these methods. Based on our findings, we designate SHG to be the best-suited standard imaging technique for this purpose, in particular when investigating the domain poling process in x-cut TFLNs. While PFM is excellently recommended for near-surface high-resolution imaging, RS provides thorough insights into stress and/or defect distributions, as associated with these domain structures. In this context, our work here indicates unexpectedly large signs for internal fields occurring in x-cut PP-TFLNs that are substantially larger as compared to previous observations in bulk LN. 

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