Conformability of flexible sheets on spherical surfaces

Abstract

Three-dimensional surface-conformable electronics is a burgeoning technology with potential applications in curved displays, bioelectronics, and biomimetics. Flexible electronics are notoriously difficult to fully conform to nondevelopable surfaces such as spheres. Although stretchable electronics can well conform to nondevelopable surfaces, they need to sacrifice pixel density for stretchability. Various empirical designs have been explored to improve the conformability of flexible electronics on spherical surfaces. However, no rational design guidelines exist. This study uses a combination of experimental, analytical, and numerical approaches to systematically investigate the conformability of both intact and partially cut circular sheets on spherical surfaces. Through the analysis of thin film buckling on curved surfaces, we identify a scaling law that predicts the conformability of flexible sheets on spherical surfaces. We also quantify the effects of radial slits on enhancing conformability and provide a practical guideline for using these slits to improve conformability from 40% to more than 90%.

Monitoring Soft Shape Surface Deformation via Optical Images for the Distinction of Contact State

“…Note that spheres with perfect axisymmetry have been well studied in model problems of contact mechanics. [43,44] This set-up thus can be used to verify the effectiveness of our monitoring method in soft touch. During the contact process, the deformed region of the elastomer can be divided into a contact area and a noncontact area.…”

Mechanically-Guided 3D Assembly for Architected Flexible Electronics

“…Mechanically-guided 3D assembly methods exploit controlled mechanical deformations to transform planar electronic devices into 3D ones with various geometric configurations. Based on loading schemes and deformation characteristics, mechanically-guided 3D assembly methods are classified into rolling assembly, 15 − 17 , 91 − 94 , 108 , 109 , 115 − 119 , 123 , 136 , 137 , 141 − 164 folding assembly, 95 − 98 , 110 − 114 , 122 , 125 , 134 , 165 − 185 curving-induced assembly, 39 , 99 − 102 , 129 , 130 , 135 , 186 − 208 and buckling-guided assembly. 16 , 17 , 103 , 104 , 106 , 120 , 121 , 124 , 132 , 138 , 139 , 209 − 244 This section provides an overview of these four assembly approaches, emphasizing their distinct design principles.…”

“… 201 The high level of deformability of the above balloon stamp allows the assembly of flexible electronics on many complex 3D surfaces, such as the pyramid surface shown in the top panel of Figure 4 e. 201 The concept of kirigami was also introduced to improve the conformability of planar electronic circuits to nondevelopable curvy surfaces. 130 , 206 , 208 For example, an array of ultrathin silicon optoelectronic pixels with kirigami design was formed on a spherical cap by curving-induced assembly ( Figure 4 e, bottom panel). 130 Recently, a microscale transfer printing approach ( Figure 4 f) was developed using reflowable materials (e.g., sugar mixture) that can stretch to conform to surfaces with complex topographies and small curvature radii.…”

Low-impedance tissue-device interface using homogeneously conductive hydrogels chemically bonded to stretchable bioelectronics

“…Despite substantial progresses in the stretchable bioelectronics, including multifunctional sensor developments ( 11 , 12 ), stretchable device designs ( 13 , 14 ), and improved long-term user comfort ( 15 – 17 ), however, practical challenges still remain. One critical challenge is the microscale nonconformal contact between the device and the target tissue ( 18 ). Most of the stretchable devices have been fabricated with materials with high modulus, such as polymer films [polyimide: 2.5 GPa and parylene C: 3.2 GPa ( 19 )], metals [gold: 70 GPa and copper: 119 GPa ( 20 )], and oxide films [indium tin oxide: 89 GPa ( 21 ) and silicon dioxide: 65 GPa ( 22 )].…”