Investigation On Tunable Liquid Lens Actuated By Ferrofluid Droplet Deformation

Liquid lens is an optical component that uses light-transmitting droplets for imaging.Its advantages in high mirror smooth finish,light weight,wide zooming range and fast zooming speed can greatly reduce the weight and manufacturing cost of the optical imaging equipment in artificial satellites.This thesis focuses on the study of magnetic-controlled liquid lenses.Ferrofluid droplets are utilized as actuating fluid to drive micro lens droplet for zooming,in which the most critical issue is the effective manipulation of the droplets deformation in multiphase flows.As a result,this thesis conducts a basic study on the deformation of droplets in order to achieve a profound understanding of the deformation mechanism and zooming rule of the liquid lens.First of all,the deformation mechanism of non-wetting ferrofluid droplets is numerically studied under an external magnetic field.The analysis is focused on the distribution of flow field,magnetic field and the dynamic characteristic of the hanging droplets during deformation.In the numerical calculation,the level set method is used to capture the interface contour of the multiphase flow solved by coupling several physics modules.Based on the understanding of the coupling mechanism for non-wetting droplets,a full set of digital microfluidic platform is built to carry out relevant experimental studies on the deformation of sessile droplets.In addition,numerical studies are carried out for comparison and verification.With a moving contact line in the wetting droplet case,droplet deformation is investigated under the magnetic field.Furthermore,the magnetization curve of the water-based ferrofluid is fitted with high precision.Finally,on the basis of grasping the magnetic-fluid-solid coupling mechanism and the deformation rule of sessile droplets,a liquid lens is designed by using a ferrofluid sessile droplet driven by a magnetic field.At the same time,the optical path distribution and focusing rules of the lens are analyzed,which lays a theoretical foundation for the application of liquid lens in spacecraft.