基于正交球面波源边界点法的声学灵敏度分析

提出采用正交球面波源边界点法作为声学灵敏度算法,计算空间任意点的声学量关于设计变量的灵敏度,克服基于边界元的声灵敏度分析中所固有的各阶奇异积分和非唯一性问题,降低数值处理难度和工作量.提出近场声全息与声学灵敏度的组合分析方法,利用声全息重建出表面法向振速及其导数,然后再进行灵敏度分析,解决表面声学量获取困难的问题.数值仿真的结果充分证明该声学灵敏度分析方法的正确性和可行性.     

Reducing speckle artifacts in digital holography through programmable filtration

We propose a speckle reduction technique in electronic holographic display systems, where digital micro‐mirror array devices are used as spatial light modulators. By adopting a programmable filtration in a general 4‐f optic configuration, it is shown that the signal spectrum components in the frequency domain of a viewing‐window‐based holographic display system can be selectively filtered. Compared to the widely utilized single‐sideband filtration techniques in electronic holographic display systems, our proposed programmable filtration can be utilized to effectively reduce the speckles in the reconstruction of point‐cloud‐based computer‐generated holograms. Experimental results are presented to verify our proposed concept.     

JPEG Pleno: Providing representation interoperability for holographic applications and devices

Guaranteeing interoperability between devices and applications is the core role of standards organizations. Since its first JPEG standard in 1992, the Joint Photographic Experts Group (JPEG) has published several image coding standards that have been successful in a plethora of imaging markets. Recently, these markets have become subject to potentially disruptive innovations owing to the rise of new imaging modalities such as light fields, point clouds, and holography. These so‐called plenoptic modalities hold the promise of facilitating a more efficient and complete representation of 3D scenes when compared to classic 2D modalities. However, due to the heterogeneity of plenoptic products that will hit the market, serious interoperability concerns have arisen. In this paper, we particularly focus on the holographic modality and outline how the JPEG committee has addressed these tremendous challenges. We discuss the main use cases and provide a preliminary list of requirements. In addition, based on the discussion of real‐valued and complex data representations, we elaborate on potential coding technologies that range from approaches utilizing classical 2D coding technologies to holographic content‐aware coding solutions. Finally, we address the problem of visual quality assessment of holographic data covering both visual quality metrics and subjective assessment methodologies.     

基于二代小波算法的数字全息显微成像自动对焦方法

针对传统数字全息显微重建方法难以获取最佳重建距离,且依赖于传统PC平台难以便携化等问题,设计了一种嵌入式数字全息显微自动对焦系统。该系统不仅能方便的完成数字全息显微成像的自动对焦,获取最佳重建效果,而且具有便携化的特点。该系统采用同轴全息光路配合图像传感器获取全息图,利用优化后的角谱算法实现全息重建,再结合二代小波算法对重建结果进行图像质量评价,根据评价结果找到最佳重建距离,同时获取最佳重建结果,完成自动对焦。利用该系统采集一批分辨率板全息图进行自动对焦测试。实验表明,系统的重建速度为0.6s,分辨率为3.48um,自动对焦准确率达到90%以上,实验结果验证了系统的有效性。     

强干扰环境下声源可视化重建方法的研究进展

准确识别噪声源是机电产品噪声控制的关键,其中,近场声全息和波束形成是两种常用的声源可视化重建方法,分别适用于近场低频和远场高频声源重建的情况。传统的声全息和波束形成方法基于自由场假设,即适用于目标声源辐射声与干扰噪声之间的信噪比大于10 dB的情况。然而很多机电产品的噪声测试只能在工作现场进行,不满足自由场条件。为此,从声学传播方程和信号处理两个方面出发,回顾了强干扰环境下声源可视化重建方法的研究发展历程,评点了每种方法的特点和适用范围。重点介绍了强干扰环境下的近场声全息方法,包括声场分离法和逆块传递函数法。另外,还介绍了混响环境下的声源重建方法以及基于信号处理的信号噪声分离方法。最后,讨论了强干扰环境下声源重建有待解决的问题及其发展趋势。     

非接触式喷嘴旋流槽测量系统的搭建与实现

针对航空发动机燃油喷嘴组件的旋流槽特征的精密快速检测难题,本文采用锥光偏振全息采样技术与多轴联动定位技术相结合的方式,搭建了非接触式的喷嘴旋流槽测量系统,可以实现喷嘴旋流槽的槽深、旋流角度和槽宽等几何参数的扫描测量。该系统主要由机械本体、光学测头、运动控制系统和喷嘴专用夹具等构成,其机械本体设计为紧凑的立柱式结构,运动机构包括三个直线轴和一个回转轴,控制系统采用主流工控机与通用坐标测量机控制器相结合的二级位置闭环数字复合控制方式,并应用高精度的免校准加工及检测专用夹具来实现被测喷嘴零件的安装和定位。最后,应用该系统对某喷嘴样件的旋流槽特征进行了多次重复测量。实验结果表明,本文所搭建的非接触式喷嘴旋流槽测量系统能够完成既定的测量任务,而且系统的重复性测量精度能够满足检测任务需求,因而可以作为一项喷嘴结构尺寸检测的技术解决方案。     

基于新型传感器阵列的声全息测试分析方法研究

针对声全息技术在实际工程应用中的扫描相位误差和有限测量孔径的问题,通过改进测试阵列和算法优化两种途径对其进行分析和解决.使用基于数字麦克风的面阵进行快照法测量,代替了传统的扫描测量,规避了扫描引入的相位误差;从理论上分析了有限孔径下近场声全息重构误差产生机理,并提出了"有限孔径空间扩展+波数域迭代滤波"的声全息算法,选用简谐激励作用下四周为无限大障板的简支钢板为对象,与传统声全息算法结果对比,验证了算法的有效性,并分析了全息面数据空间补零长度和迭代循环次数对声场重构的影响;使用转子台作为被测设备,模拟已知故障,通过单参考源下传感器阵列扫描测量结果验证了算法可以准确地定位模拟故障的空间位置.     

Patch nearfield acoustic holography based on the equivalent source method

On the basis of nearfield acoustic holography (NAH) based on the equivalent source method (ESM), patch NAH based on the ESM is proposed. The method overcomes the shortcoming in the conventional NAH that the hologram surface should be larger than the source surface. It need not to discretize the whole source and its measurement need not to cover the whole source. The measurement may be performed over the region of interest, and the reconstruction can be done in the region directly. The method is flexible in applications, stable in computation, and very easy to implement. It has good potential applications in engineering. The numerical simulations show the invalidity of the conventional NAH based on the ESM and prove the validities of the proposed method for reconstructing a partial source and the regularization for reducing the error effect of the pressure measured on the hologram surface. Supported by the National Natural Science Foundation of China (Grant Nos. 10504006 and 50675056) and the Research Fund for the Doctoral Program of Higher Education (Grant No. 20060359003)     

基于计算全息技术的彩色CT真三维可视化

不同于现有的用计算机软件合成的CT 图像的伪 三维可视化,本文提出了一种基于计算全息技术的彩色CT 图像的真三维可视化技术。首先,利用计算全息技术对彩色CT图像进行三维重建,将一组 彩色CT图像的空间 二维信息融合成三维信息,并以计算全息图(CGH)的形式进行保存;然后,设计了彩色CT图 像光电再现与三维显示系 统,以液晶空间光调制器(LC-SLM)作为CGH的显示载体,通过计算机同时输入 3幅CGH,通过光电再现获得 三原色三维再现像,利用合色棱镜将三原色再现像合成为彩色图像,用雾屏作为彩色三维再 现像的显示载体,获 得彩色真三维CT图像。在全息图的计算过程中,基于CT图像的二维属性,采用了快速傅里 叶变换(FFT)算法,大大加快了计算速度。给出了理论分析与实验结果。     

编码孔径和解码孔径的设计

基于光学外差扫描全息术 3D成像的基本原理和编码孔径成像技术 ,设计了用于正在研制的“近红外扫描全息光学层析成像系统”中的编码孔径和解码孔径。当编码函数非负时 ,设计能取正负值的解码函数可以改善系统的点扩散函数 ,使其更接近于理想的二维 δ函数。在点扩散函数分布中的均匀或起伏较小的背景将降低重建图像的对比度。计算机模拟结果表明 ,采用对比度增强技术可以减少菲涅耳波带板和非冗余小孔阵列编码孔径重建图像的背景噪音 ,提高图像的对比度