Design Of Cross-shaped Bistable Structures And Its Applications In Microfluidic Switch

Multistable structures are the structures which have multiple equilibrium stable states and can switch between stable states.Multistable structures are widely used in science and engineering such as micro electromechanical systems(MEMS),flexible electronics,biomedicine and robotics.The multistable structures realized by buckling-guided assembly has many advantages.It can fabricate large amount of meso-structures at a time and capable of diverse materials.The commonly used design strategy for these multistable structures is finite element analysis(FEA)with trial-and-error method,which consumes lots of computational resources.This thesis aims to establish the theoretical model for the stability analysis of a typical bistable cross-shaped structure and provide guidelines for the design of the bistable crossshaped structure.Based on the bistable cross-shaped structure,we designed a microfluidic switch device capable of reconfiguring the micro channels dynamically on demand.The main research contents and conclusions include:Based on the finite deformation beam theory,a theoretical model for post buckling analysis of bistable cross-shaped structures is established.Based on an energy criterion,a theoretical model for stability analysis of buckled cross-shaped structures is established.The deformed configuration and stability of the buckled cross-shaped structures are studied by experiment and FEA.The results show that the theoretical model can predict the deformed configuration and stability of the buckled cross-shaped structures.Using the theoretical model,the effect of the geometric design parameters of the creases(including the amount,the position and the width of the creases)on structure stability is studied.The phase diagrams of the stability of buckled configuration with respect to crease design parameters are constructed.The stability of the buckled configuration in different regions on the phase diagram is verified by experiment and FEA.The results indicate that in order to obtain bistability in cross-shaped structure,the crease should be set in a specific position and the crease width should be narrow enough.A two-channel microfluidic switch device is designed based on the bistable cross-shaped structure.When the device is under different buckled configurations,the on/off state of the micro channels inside the device differs.The influence of the channel design parameters on the switching characteristics of the device is studied by FEA.The channel design parameters include the shapes(rectangular and arc-shaped),the dimensions and the position of the channel.The device load to close the channels is studied.The switching characteristics of the device is studied by FEA and verified by experiments.Based on structural optimization,an arc-shaped channel with enhanced closing characteristics is designed and studied.The fabrication process of the flexible microfluidic switch device is studied,including the polydimethylsiloxane(PDMS)replica fabrication process and UV-light sealing process.Based on the fabrication process,the two-channel cross-shaped microfluidic switch device is fabricated.The switching performance of the device is tested.By combining single switch devices into a 3 × 1 switch array,a three-channel microfluidic switch is designed,fabricated and tested.