EWOD Liquid Lens Dynamic Response Test And Wetting Mechanism Research

Electrowetting on dielectric(EWOD)is a phenomenon that the morphology of a small droplet on the surface of a dielectric be manipulated by applying the electric field between the droplet and the metal beneath the dielectric.Imaging principle of liquid lens based on EWOD is similar to that of human eyes,which has the advantages such as compact,fast response etc.Therefore,it has huge potential in designing portable digital devices.Researchers have conducted a lot of work on the dynamic response of wetting droplet.However,neither contact angle hysteresis nor contact angle saturation has been well explained.Moreover,the dynamic response of the interface encapsulated inside the liquid lens is very complicated.Therefore,it is of high necessity to study the dynamic response of EWOD based liquid lens.Traditionally,high-speed photography is utilized to record the dynamic process of the droplet,by which the contact angle can be measured frame by frame.But it is not applicable to the liquid lens because no transparent wall exists.Furthermore,the focal length and dynamic response of the interface not only just affected by the contact angle,but also the droplet oscillation modes.This paper provides a new method for characterizing the dynamic response of EWOD based liquid lens.The innovative content of the dissertation is as following:1.A test device for characterizing the dynamic process of focal length of the liquid lens is developed based on gaussian beam transmission theory.The dynamic process of the focal length of EWOD based liquid lens is studied.Reasonable signal waveforms are obtained by the detector.The focal length of the lens is found to be able to change with the polarity and amplitude of the excitation voltage.It is revealed that the characteristic peaks are caused by both the voltage polarities and oscillation modes of the interface.The experimental device has the advantages of simplicity,economy,convenient operation,high precision,wide working range and decreasing error.This method is with high time resolution and can explore more details of the process that cannot be achieved by high-speed camera.The testing system can be widely used in the testing of various zoom lenses.2.Typical response characteristics of luminous flux based on the test device are analyzed,which are asymmetric threshold voltages and stable response critical frequencies.The optimized test signals of EWOD liquid lens are proposed.It is concluded that the mechanism of EWOD is affected by the polarity of excitation voltage.3.Intelligent test systems for response time and focal length are developed,respectively.Based on the hardware platforms,interactive computer aided MATLAB based platforms are built.The response time of the liquid lens and the focal length can be automatically measured and recorded,and the testing precision is improved.Based on these two intelligent test systems,further research on transfer function and the performance optimization of EWOD liquid lens can be conducted.4.It is concluded that negative charges in the conductive solution are more easily to be bounded by a dielectric.Sine,bipolar pulse and pulse signals are utilized to stimulate EWOD liquid lens,and the positive and negative polarity of the driving voltage can cause large differences.Effect of lens driven by negative polarity is more apparent,which can be explained by dielectric charge bound theory reasonably.The conclusion benefit for the study of EWOD mechanism.