The Mechanism Of Micro Photo-thermal Expansion And The New Method Of Photo-thermal Micro Actuator

Micro/nano-technology is a newly developed interdisciplinary subject in recent years, and micro electro-mechanical systems (MEMS) are one of its important branches. Micro actuators are a kind of MEMS which can implement micro/nano order drive and operation; they can be divided to kinds of types according to different realizing method. Thermal actuators are a kind of micro actuators that utilize thermal expansion to realize micro drive, and have became a focus of current micro actuator research. The photo-thermal micro actuators (PTA) introduced in this dissertation for the first time, take laser as power source, utilize photo-thermal expansion to output micro/nano order displacement; they have advantages of simple structure, easy fabrication, remote control, high degree of miniaturization and integration, are a kind of innovate micro actuator with comprehensive application prospect.This dissertation carries out complete and systematic research on micro scale photo-thermal expansion mechanism. Photo-thermal expansion is a kind of complex mechanism that involves several physical phenomenons, including photo-thermal energy transformation, thermal conductivity, convective heat transfer, irradiative heat transfer and thermal expansion. We analyze all these inner mechanisms theoretically, study their functions and influences on photo-thermal expansion. Based on these theoretical analyses, three-dimensional static model is built. Then it is reasonably simplified to a two-dimensional model on the condition that Biot number is much less than 1, and two-dimensional temperature distribution is calculated numerically. According to two-dimensional calculation result, the model is further simplified to a one-dimensional model. By deducing its analytical solution, we get general expressions of static temperature distribution of PTE and its static length increment. Using these expressions, we implement theoretical calculation and analysis on an instantial micro expansion arm. A one-dimensional dynamical model is provided on the basis of one-dimensional static model, it brings up expressions of transient temperature distribution and transient length increment of photo-thermal actuators. We study vibratory response of expansion arm while actuated by periodic laser pulse, and also dependencies of vibration amplitude on repetition frequency and duty ratio of laser pulse.According to above theoretical analyses, we design and produce several types of PTE for the first time. Basic micro expansion arm utilize length increment to realize micro drive directly. Optimized micro expansion arm improves structure of basic micro expansion arm. Double arm symmetric PTA transforms length increment of heated arm to deflection at the free end and improves its performance. Double asymmetric PTA is a further improvement type with more elaborate structure and higher degree of mobility. Using black plastic of large expansion and low thermal conductivity can give PTE better and more stable performance. Excimer laser workstation is applied to produce photo-thermal actuators, whose predominant advantages in cold-working fields can guarantee high machining accuracy, smooth machining edge and high efficiency.A photo-thermal control system is studied and developed. It consists of laser source, optical path system, electrical circuit system and mechanical system. The optical path system and electrical circuit system cooperate together to control instant laser power, pulse frequency and duty ratio of laser pulse using electro-optic modulating method. The optical path system is also responsible for focusing heating laser. Mechanical system is responsible for adjusting injection angle and injection position of driving laser. To observe and measure micro displacement output of micro actuators, we design a special apparatus composed by CCD and stereoscopic microscope. Using this device, we can not only observe micro actuators, but also measure their deformations and record them. Meanwhile, we modify atomic force microscope (AFM) to get an apparatus which can get vibration curve of PTA while actuated by periodic laser pulse.We practically carry out experimental study of photo-thermal expansion and photo-thermal micro actuator technology, put photo-thermal micro actuator into practice for the first time. We use our self-designed apparatus to study our self-realized photo-thermal actuators experimentally. The experiments prove that simple expansion arm can output micro scale displacement while actuated by laser of milliwatt order. Although optimized expansion arms have shorter length, narrower width and smaller volume than simple expansion arm, they can give the same output performance. Double arm symmetric PTA improve their own displacement output without increasing heating laser power; they can also realizing micro drive of two opposite directions. Double arm symmetric PTA optimize symmetric type, reduce their size and increase their mobility while they can only output micro displacement at one direction. The performances of several modification types of asymmetric actuators are studied and compared through experiment, the result shows how structure changes influence performance of actuators. The vibration curve is acquired using modified AFM system, and it proves the feasibility of persistent drive. We also study photo-thermal vibration of several PTA, and analyze the relationship between vibration amplitude and repetition frequency.The achievements of this whole subject are concluded at the end of this dissertation: analyzing inner mechanisms of photo-thermal expansion through theoretical study and experiment, proving feasibility of photo-thermal micro actuator, practically measuring and optimizing performance of PTA. Meanwhile some insufficient points of our works are pointed out, and some directional advices on how to continuing future work are provided as well.