【作者】 程腾；

【导师】 张青川；

【作者基本信息】 中国科学技术大学 ， 固体力学， 2010， 博士

【摘要】 目前,红外成像技术已在军事、工业、商业等广泛的领域发挥了重要的应用,其中,非制冷红外成像技术因其体积小、成本低、性能高而备受关注。本文在课题组已有工作基础上,对基于MEMS技术的新型光学读出非制冷红外成像系统进行了深入的研究,主要在无基底FPA的仿真分析和结构设计、光学读出方法的优化、红外成像系统的小型化和工程化等方面进行学习和研究,取得的主要成果如下：(1)在无基底FPA的仿真分析方面,通过有限元方法,开发了像素数为80×80的无基底FPA和有基底FPA的三维有限元仿真分析平台,并通过ANSYS软件分析热应力问题时的间接法,详细分析了它们在热学性能、热机械性能上的差异。分析发现：(a)在热学性能方面,由于支撑框架的热导大幅度减小,无基底FPA具有和有基底FPA完全不同的热学特性。一方面,支撑框架等效于一段与热隔离梁串联的热阻,它有效降低了感热单元的总热导,提高了感热单元的温升效果,另一方面,支撑框架通过热扩散使相邻单元产生了“预温升”现象,它通过线性叠加大幅度提高了感热单元的温升。这些特性使得无基底FPA的能量转换效率大幅度提高,甚至有数量级的提升。(b)在热机械性能方面,由于无基底FPA的支撑框架是变温结构,各感热单元的双材料变形梁的温升几乎相等,因此,其热变形效率与有基底FPA相比,最大可提高约33%。根据上述有限元分析结果,修正了基于恒温基底假设的物理模型,具体涉及感热单元的总热导和热变形效率公式。(2)在无基底FPA的结构设计方面,设计了增强型的支撑框架。它可在保持感热单元热学性能的基础上有效提高支撑框架的结构性能,从而解决在大阵列的无基底FPA(≥1024×1024)中,支撑框架的Z向刚度比较薄弱的问题。(3)在光学读出方法的优化方面,根据傅里叶光学的近场夫琅和费衍射理论,建立了反光板弯曲时的光学检测灵敏度的理论分析模型,发现系统的光学检测灵敏度是关于反光板板长、曲率半径和刀口滤波器位置的函数。通过建立的理论分析模型,提出了一种针对弯曲反光板的光学优化方法。它可以最大化地提高系统的光学检测灵敏度,将由反光板弯曲引起的灵敏度损失降低到最小程度。(4)在红外成像系统的小型化和工程化方面,通过FPGA+DSP架构,设计并实现了第一代小型化的图像采集处理系统,并组装了光学读出非制冷红外成像系统的原理样机,虽然其成像效果与放置在防震台上的实验系统有明显差距,但仍获得了室温物体的红外图像。更多还原

【Abstract】 Currently, infrared imaging has been a key technology in variety of military, in-dustrial, and commercial applications, especially uncooled infrared imaging has drawn substantially increased attention for its small dimension, low cost and high performance. Based on past achievements, this dissertation primarily studied a novel MEMS based optical readout uncooled infrared imaging system. The chief contents include:the finite element analysis and structural design of substrate-free focal plane array (FPA), the optimization of optical readout method, the miniaturization and in-dustrialization of uncooled infrared imaging system. The main achievements of this dissertation are as follows:(1) Based on the finite element method, the three-dimensional (3-D) finite ele-ment models of substrate/substrate-free FPA with 80×80 pixels were developed, and then using the sequential approach of multiphysics analysis in ANSYS software, the thermal and mechanical characterizations of substrate/substrate-free FPA were inves-tigated and found that:(a) As compared with the substrate FPA, because of the large decrease in thermal conductance, the supporting frame is a temperature-variable one. This brings out a unique thermal characteristic:(i) the supporting frame functions as a’thermal isola-tion’ frame which reduces the thermal conductance and therefore increases the tem-perature change; (ii) the supporting frame also functions as a‘thermal diffusion’frame which certainly results in the temperature pre-change in the ones not absorbing radia-tion. The linear superposition of the temperature pre-change by the other ones thus will greatly increase the temperature change. This characteristic will significantly in-crease the energy conversion efficiency, even with a magnitude of one order.(b) Because the supporting frame is a temperature-variable structure, the temper-ature change in the bi-material microcantilevers is almost in the same level, therefore, a potential of 33% improvement in thermo-mechanical efficiency is envisionedBased on the finite element analysis, the theoreticl model which assumes that the substrate is a temperature constant structure was corrected, namely the calculation of total thermal conductance and thermo-mechanical efficiency of each microcantilever.(2) An enhanced supporting frame was developed for substrate-free FPA. This design would not only increase the structure performance of supporting frame but also maintain an excellent thermal performance, and therefore is much suitable for large scale substrtate-free FPA (≥1024×1024).(3) Based on the Fraunhofer diffraction pattern of each reflector in Fourier Op-tics, and the theoretical model of the optical readout sensitivity was established and found to be a function of reflector length, curvature radius and position of knife-edge filter. Using this theoretical model, an optical resolution to the reflector deformation was developed. This optical solution can efficiently maximize the optical readout sen-sitivity, and the sensitivity loss induced by the deformed micro-reflector can be re-duced to minimum level.(4) Using FPGA and DSP, the first generation image acquisition and processing system based on miniaturization design was developed, and the prototype machine of optical readout uncooled infrared imagings system was aslo established. This proto-type machine could obtaion thermal image at room temperature but with a decrease in performance, as compared with the experimental platform.更多还原