Mechanics And Applications Of Serpentine Structures In Flexible Devices

Serpentine structures have the characteristics of strong stretchability,good ductility,low bending stiffness,and small tensile stiffness,which are widely used in two-dimensional/three-dimensional flexible electronic devices.The study of the mechanical behavior of serpentine structures is of great significance to enhance the understanding of the mechanical properties and to further apply it to flexible electronic systems to bring more characteristics that are difficult to achieve by traditional electronics.In this paper,the mechanical response behaviors of in-plane/out-of-plane serpentine structures and the advantages and characteristics brought about in some applications are studied by combining theoretical analysis and numerical simulation,and the buckling-guided assembly method by which two-dimensional serpentine structures are transformed into three-dimensional structures are analyzed and improved.Specific research and innovations are as follows:Firstly,based on energy method and bending beam theory,the mechanical model of serpentine structure under tensile strain and thermal load in real working environment is established,and the analytical solution of true stretchability and equivalent stiffness is obtained and verified by numerical simulation results.The influence of thermal load and geometric parameters on real ductility and equivalent stiffness is quantitatively studied.In addition,a finite deformation model of modified serpentine structure with large in-plane tensile strains is established.Combined with numerical simulation,the effect of structural parameters on the mechanical response of equivalent strain-stress is analyzed.Further apply it as the basic unit of triangular lattice network.Results reveal that the network materials have evident increase in negative Poisson ratio effect and notable reduction in maximum strain level.It has potential application in the cellular substrate bonded with biological tissues with negative Poisson ratios.Secondly,a new strategy is proposed for the layout structures and substrate structures in flexible electronics.A novel out-of-plane wave-shaped flexible layout is proposed.The analytical solutions of stretchability and compressibility are obtained based on strain limitation and critical buckling.The effects of geometric and material parameters on stretchability and compressibility are systematically studied,revealing its good stretchability and compressibility.In addition,considering the phenomenon of strong adhesion in the three-dimensional assembly by soft substrate,it is proposed to replace the traditional uniform substrate with a cellular substrate.The theoretical modeling shows that the cellular substrate can significantly expand the design space of the globally-buckled three-dimensional serpentine structures and has certain application value in three-dimensional microelectronics.Thirdly,based on the low bending stiffness characteristics of 3D serpentine structure,it is applied to 3D serpentine ferromagnetic robot and 3D scaffolds for muscle ring strain gauge.Through theoretical modeling and numerical simulation,it is found that the 3D serpentine structure robots increase efficiency in unfolding deformation and locomotion speed by two orders of magnitude compared with the ordinary 3D arch-shaped ribbon structure under magnetic field.For 3D scaffolds of muscle ring strain gauge,the scaling law of the structure/material parameters corresponding to the mechanical constraint is established,and the influence of the relevant parameters is clearly shown.It is found that the use of the 3D serpentine structure in the strain gauge supports greatly reduces the mechanical constraint on the muscle ring actuator and provides the possibility for a sufficiently compliant support for muscle ring.Finally,combined with the actuation method by Lorentz forces,the mechanical behavior of in-plane/out-of-plane deformation of planar serpentine structure and its grid structure is studied.By establishing a simple circular structure model,the expressions of the critical current of compression buckling and Joule heating are obtained by numerical simulation and parametric analysis,and the applicable current range is determined.Based on the linear relationship of the critical current to the cubic power of the structure thickness,a suitable electromagnetic actuation method is proposed for the 3D assembly of thin,low-stiffness structures,and discussion is developed by demonstrating an in-plane four-petal rose with four independent currents and switching in various deformation states when subjected to compressive Lorentz forces.In addition,based on numerical simulation and parametric analysis,the displacement of serpentine mesh network out of the plane is studied.A numerical method of inverse design is established for the 3D surface formed by the raised nodes in the mesh structure.The application of this method in tuning 3D surface and applications in optical and acoustic systems is demonstrated by finite element simulations.