Static/Dynamic Actuation Technique Of Optothermal Microactuators Operated In Air And Liquid

Microactuator is a key component in micro-electromechanical systems(MEMS)and micro-opto-electromechanical systems(MOEMS),and has been one of the research hotspots in this field.Up to now,a variety of microactuation techniques have been developed based on electromagnetic,electrostatic,piezoelectric,electrothermal,and other different mechanisms.Among them,electrothermal actuating technique is a typical electric microactuation technique.It has the characteristics of large displacement and strong actuating force.However,as electrothermal actuation requires the built-in or external power supply or circuits,it is difficult to integrate or miniaturize the whole system.The heating current of the electrothermal microactuator may interfere with the microcircuit or microdevice in the microsystem,and it also prevents the actuation in the conductive liquid environment.This dissertation proposes and develops a laser-based optothermal microactuating technique for air and liquid environments,which uses a laser beam to actuate and control an optothermal microactuator(OTMA)through optothermal expansion effect.It has a novel principle,simple structure,flexible actuation(unidirectional and bidirectional actuation),and needs no wire connection,free of electromagnetic interference.The optothermal microactuation technique overcomes the limitations of electrothermal and other electric drive technologies,and has not only important scientific significance,but also broad practical application prospects in the above-mentioned fields.This dissertation presents a systematic theoretical and experimental study of the static and dynamic actuating properties of OTMA in different environments.The main contents of the dissertation are as follows:Theoretical studies on the effect of nano/microscale optothermal expansion in air and liquid environments are systematically conducted,and a new method for static and dynamic optothermal microactuation in air/liquid environments is proposed.The mechanism of light-matter interaction,heat transfer and thermal expansion are first investigated.Theoretical models of optothermal temperature rise and expansion are established.based on finite element analysis,heat balance equations,boundary conditions and partial differential equation solutions,the expressions for temperature rise,optothermal expansion and the amplitude are derived.The leverage relationship between the optothermal deflection and the expansion of the OTMA in air is then obtained through structural mechanics analysis.Taking into account the damping force by fluids,the damping-corrected deflection-expansion relationship for OTMA in the liquid environment is proposed,which provides a theoretical basis for realizing static and dynamic optothermal microdrives in air/liquid environment.Based on theoretical studies,simulations are carried out for the first time to study the actuating properties of the OTMA in air and liquid environments(water).Firstly,The two-dimensional temperature rise distributions of the expansion arm under laser spots of different shapes/sizes/power are simulated.Secondly,the optothermal expansion and its amplitude under laser pulse irradiation in air and water environments are calculated and analyzed.Using the multi-physics field simulation software Comsol Multiphysics with its solid heat transfer,solid mechanics,and laminar flow modules,the optothermal deflection characteristics of the OTMA and the temperature/stress changes of the microactuator,as well as the variation of the flow velocity and pressure in the water domain are further simulated and analyzed,revealing the optothermal microactuating properties of OTMA in different environments.OTMAs made of high-density polyethylene(HDPE)are designed and fabricated based on AutoCAD and excimer laser micromachining system.Using 248 nm KrF excimer laser,A series of OTMAs with a total length of 200?2000 ?m,a thickness of 20?60 ?m are machined,including two-armed symmetric and asymmetric OTMAs,OTMA switches,etc.,to realize optothermal microactuation in air and liquid environment.The optothermal microactuation controlling and measuring system is designed and built.It applies to the microactuation both in air and liquid environments and can realize microscopic measurement of the optothermal microacuation characteristics.The system consists of OTMA and air/liquid vessel,actuating control unit(including a laser control circuit,laser diode,beam splitter,and multi-dimensional stage),microscopic imaging module(including illumination,microscopic objective,and image sensor)and computer.Furthermore,a microscopic motion measurement software based on a sub-pixel matching algorithm is developed to measure the deflection and optothermal properties of OTMA.Using the microactuation controlling and measuring system,experimental studies of static and dynamic optothermal microactuation of OTMAs in air are carried out to verify the feasibility of optothermal microactuation and obtain optothermal actuating characteristics.The "on" and"off" states of a switched OTMA are achieved under the irradiation of a laser beam with 650 nm wavelength and 2 mW power,and a maximum deflection of 15.5 ?m is measured.Besides,the dynamic optothermal microactuation of an asymmetric OTMA is achieved using laser pulses with 2.5 mW and adjustable frequencies,and its maximum response frequency in air is measured to be about 19.6 Hz.Additionally,experiments are conducted on a two-armed symmetric OTMA,and bi-directional microactuations are realized by irradiating two arms alternatively.Systematic experimental studies of OTMA actuating in liquid(water)environment are carried out,and static/dynamic optothermal microactuations in liquid(water)environment are realized for the first time.Using a laser with a wavelength of 650 rm,520 nm and 450 nm,respectively,effective microactuations of OTMA in liquid are all observed,demonstrating the feasibiliy of the technique.Under the laser pulses with 9.9 mW power and 0.9-25.6 Hz frequencies,static and dynamic microactuating experiments of an asymmetric OTMA in water are then carried out,and the OTMA achieves deflection amplitude ranging from 3.9 to 3.2 ?m.A two-armed symmetric OTMA is also actuated in water,and the bi-directional actuating property of the OTMA in water is verified.To further investigate the high-frequency response characteristics of the OTMA,laser pulses with adjustable frequencies up to 200 Hz are used for microactuation,the highest response frequency of the OTMA in the water is between 1 50 and 200 Hz.The above experiments show that OTMA can achieve effective optothermal microactuation in water,and exhibits the dynamic response characteristics superior to air environment.The research work of this dissertation is summarized at the end.The optothermal microactuation technique proposed and developed in this dissertation can realize static and dynamic optothermal microactuation in air and liquid(water)environments,which has remarkable features and innovations.The research results provide the theoretical and technical basis for the application of optothermal microactuation in the field of MEMS,MOEMS,and micro-nanotechnology.