高速光截法三维面形重建

在高速光截法三维面形测量中,由于光截面之间距离增加,物体表面的不连续性将容易导致错误的三角网格化,引起面形重建的畸变。由此,提出了一种新的快速面形重建方法。这种方法在三角网格化时考虑截面中心的移动,并通过引入权值函数来调整连接状态;用连接加权法构造三角网格,提高了网格连接的准确性;通过调整光截面中心消除了由三角网格化错位造成的影响。理论分析和实验结果表明,该方法具有与其它快速方法相同的运算复杂度O(N),而面形恢复的准确度明显优于传统方法。     

Comparative analysis of low-pass filters for the demodulation ofprojected gratings in 3-D adaptive profilometry

In 3-D adaptive profilometry based on structured light projection, the choice of the low-pass filter to he used in the deformed pattern demodulation is crucial. In this paper, we have studied the performance of a typical finite impulse response (FIR) and of an infinite impulse response (IIR) Butterworth low-pass filter. Adaptiveness of the filters to both coarse and small variations of the grating frequency has been investigated. The ability of the filters to adapt to coarse changes of the grating frequency has been quantified in terms of their speed of synthesis, while the ability of the filters to tolerate small variations of the grating frequency has been quantified by measuring the residual phase errors. The analysis shows that the IIR Butterworth filter performs better than the FIR filter both in the coarse and in the fine grating frequency variation cases     

采用标记条纹跟踪的冲击过程三维轮廓术

针对在冲击、爆轰等快变化过程的三维轮廓术中,CCD拍摄速度低于物体的运动速度而导致对动态条纹的时间采样不足和物体表面发生破裂而分成数块的动态过程,提出一种采用标记条纹进行跟踪的动态过程三维轮廓术.以傅里叶变换轮廓术为基础,通过采用标记条纹进行跟踪锁定变形条纹中同级次条纹的变化以及Gerchberg迭代算法在破裂区域迭代生成伪条纹,对破裂表面分块进行处理,有效地解决了在快变化动态过程的三维重建中因时间采样不足和条纹断裂对三维相位场的展开所带来的问题,获得了物体正确的面形分布.实验证实了此种方法的正确性.     

Dual beam light profile microscopy: a new technique for optical absorption depth profilometry

Light profile microscopy (LPM) is a recently developed technique of optical inspection that is used to record micrometer-scale images of thin-film cross-sections on a direct basis. In single beam mode, LPM provides image contrast based on luminescence, elastic, and/or inelastic scatter. However, LPM may also be used to depth profile the optical absorption coefficient of a thin film based on a method of dual beam irradiation presented in this work. The method uses a pair of collimated laser beams to consecutively irradiate a film from two opposing directions along the depth axis. An average profile of the beam's light intensity variation through the material is recovered for each direction and used to compute a depth-dependent differential absorbance profile. This latter quantity is shown from theory to be related to the film's depth-dependent optical absorption coefficient through a simple linear model that may be inverted by standard methods of numerical linear algebra. The inverse problem is relatively well posed, showing good immunity to data errors. This profilometry method is experimentally applied to a set of well-characterized materials with known absorption properties over a scale of tens of micrometers, and the reconstructed absorption profiles were found to be highly consistent with the reference data.     

A class of data structures for 2-D and 3-D adaptive mesh refinement

A ‘family’ of tree data structures for adaptive mesh refinement is described and details concerning the associated logic are provided. The data structures encompass triangular elements and quadrilateral elements in two dimensions and quadrilateral bricks in three dimensions. Furthermore, both linear (bilinear) and quadratic (biquadratic) element types, respectively, are developed. Representative refinement results are given for the bilinear, trilinear and biquadratic types and associated performance studies made for the refinement procedure.     

光栅投影三维形貌测量低通滤波器的设计

分析在光栅投影三维形貌测量中,用于对变形光栅像解调的低通滤波器的性能。分别设计了脉冲响应为9点的FIR低通滤波器和IIR4阶Butterworth低通滤波器。处理1×512大小的光栅图像,FIR滤波器需要16128次加法和2304次乘法,位相测量平均误差为0.0356rad;4阶Butterworth滤波器只需4096次加法和4096次乘法,位相测量平均误差为0.0043rad。仿真试验结果表明,IIR的Butterworth低通滤波器具有更高的测量精度和计算速度。     

利用CPM实现自适应OFDM系统研究

在正交频分复用(OFDM)系统中应用自适应技术能有效地提高系统性能。正交频分复用-连续相位调制(OFDM-CPM)通过CPM相关相位状态引入记忆,从而获得比传统OFDM更好的误码性能。文章提出了一种利用单一的CPM调制方式实现自适应OFDM-CPM系统的新方案。仿真结果表明,选取最佳的CPM参数组合,通过改变CPM的参数来实现自适应OFDM-CPM调制,能够获得比传统调制方式要低的门限值,同时系统硬件实现更为简单。     

First-time investigation on crystal growth,optical, thermal,electrical and third-order non-linear optical activities of novel thiosemicarbazide single crystals for non-linear optical applications

Journal of Materials Science: Materials in Electronics - This present communication reports the crystal growth and characterization of organic novel thiosemicarbazide (TSC) single crystals grown by...     

星载自适应光学系统信标技术与理论

由于重力场、温度场、光学器件等产生波前误差,造成航空详查相机的分辨力和测量精度降低,用自适应光学钠导星信标系统对这种波前误差进行校正是一种理想的方法。通过对钠导星信标产生原理进行分析,提出了钠导星信标理论模型,并且在该模型的基础上进行了仿真实验,在实验中得到相机高度在250-400km高空时激光器最佳脉冲能量值在597-1530mJ之间,激光脉宽则在5.4-7.1ns之间,这些实验数据对实际应用有一定的参考价值。     

A miniaturized catheter 2-D array for real-time, 3-D intracardiac echocardiography

The design, fabrication, and characterization of a 112 channel, 5 MHz, two-dimensional (2-D) array transducer constructed on a six layer flexible polyimide interconnect circuit is described. The transducer was mounted in a 7 Fr (2.33 mm outside diameter) catheter for use in real-time intracardiac volumetric imaging. Two transducers were constructed: one with a single silver epoxy matching layer and the other without a matching layer. The center frequency and -6 dB fractional bandwidth of the transducer with a matching layer were 4.9 MHz and 31%, respectively. The 50 omega pitch-catch insertion loss was 80 dB, and the typical interelement crosstalk was -30 dB. The final element yield was greater than 97% for both transducers. The transducers were used to acquire real-time, 3-D images in an in vivo sheep model. We present in vivo images of cardiac anatomy obtained from within the coronary sinus, including the left and right atria, aorta, coronary arteries, and pulmonary veins. We also present images showing the manipulation of a separate electrophysiological catheter into the coronary sinus.     

2-D array for 3-D ultrasound imaging using synthetic aperture techniques

A two-dimensional (2-D) array of 256 X 256 = 65,536 elements, with total area 4 X 4 = 16 cm2, serves as a flexible platform for developing acquisition schemes for 3-D rectilinear ultrasound imaging at 10 MHz using synthetic aperture techniques. This innovative system combines a simplified interconnect scheme and synthetic aperture techniques with a 2-D array for 3-D imaging. A row-column addressing scheme is used to access different elements for different transmit events. This addressing scheme is achieved through a simple interconnect, consisting of one top, one bottom single-layer, flex circuits that, compared to multilayer flex circuits, are simpler to design, cheaper to manufacture, and thinner so their effect on the acoustic response is minimized. We present three designs that prioritize different design objectives: volume acquisiton time, resolution, and sensitivity, while maintaining acceptable figures for the other design objectives. For example, one design overlooks time-acquisition requirements, assumes good noise conditions, and optimizes for resolution, achieving -6 dB and -20 dB beamwidths of less than 0.2 and 0.5 mm, respectively, for an F/2 aperture. Another design can acquire an entire volume in 256 transmit events, with -6 dB and -20 dB beamwidths in the order of 0.4 and 0.8 mm, respectively.     

A probabilistic fracture mechanics analysis for cracked pipe using 3-D model

For the purpose of probabilistic fracture mechanics (PFM) estimation based on elastic-plastic fracture mechanics (EPFM) in the field of reliability analysis of pressure vessels and piping, a 3-D EPFM database of fully plastic solutions for surface cracks and a PFM code for the integrity evaluation of nuclear structural components based on the above database are given. As an example, a comparison study of the PFM analysis is then performed between the 2-D and the 3-D solutions to demonstrate the 3-D effects on the solutions.     

Time-varying, 3-D echocardiography using a fast-rotating probe

A fast continuous rotating ultrasound scan-head transducer was used to perform three-dimensional (3-D) echocardiography with 2-D images acquired during a single cardiac cycle. The 3-D images were reconstructed by interpolating 2-D data acquired with the probe. Two experiments were carried out to validate the image reconstructions. A dynamic cardiac phantom was used as a known reference to compare the minimal and maximal volumes estimated manually on the reconstructed 3-D images. The left ventricle (LV) volume of 30 healthy volunteers also were estimated using a semiautomatic ellipse approach and compared to measurements obtained with standard 2-D examination. Results showed a good agreement between 3-D and reference measurements.     

Multi-user adaptive orthogonal frequency-division multiplexing system for indoor wireless optical communications

An adaptive orthogonal frequency-division multiplexing (OFDM) system is proposed for multi-user communications over indoor wireless optical channels. The designed system uses multi-user least-squares detection techniques applied to space-division multiple access and OFDM schemes, in conjunction with angle-diversity reception. The system, which does not present an excessive increase in complexity with respect to the previous schemes, can support high bit rates for multiple users, beyond 100 Mbits/s. It also mitigates the channel fluctuations induced when either the space distribution or the number of emitters and receivers varies. The performance of the new proposed scheme is compared with that of a non-adaptive multi-user system and an adaptive single-user system, both described in the previous works, when they face similar environmental situations. The obtained results show a significant enhancement with respect to both the previous multi-user system and the adaptive single-user one, since the new scheme allows adaptively managing the system throughput on a multi-user environment     

A hybrid humidity sensor using optical waveguides on a quartz crystal microbalance

In this study, slab and ridge optical waveguides (OWGs) made of fluorinated polyimides were deposited on a quartz crystal microbalance (QCM), and hybrid sensors using OWG spectroscopy and the QCM technique were prepared. Polyvinyl alcohol (PVA) film with CoCl₂ was deposited on the OWGs, and the characteristics of humidity sensing were investigated. A prism coupler was used to enter a He–Ne laser beam (λ = 632.8 nm) to the slab OWG. The output light intensity markedly changed due to chromism of the CoCl₂ as a result of humidity sorption, and this change was dependent on the incident angle of the laser beam to the slab OWG. During the measurement of output light, the QCM frequency was simultaneously monitored. The humidity dependence of the sensor with the slab OWG was also investigated in the range from 15 to 85%. For the sensor with the ridge OWG, white light was entered by butt-coupling, and the characteristics of humidity sensing were investigated by observing the output light spectrum and the QCM frequency.     

A brain-based system for adaptive automation

Adaptive automation refers to technology that can change its mode of operation dynamically. Further, both the technology and the operator can initiate changes in the level or mode of automation. One of the important issues surrounding this technology concerns the method for initiating changes in the state of automation. The present paper considers the potential of using brain activity to drive an adaptive automation system. Relevant research on EEG is presented followed by a review of several experiments in which EEG is used to trigger changes among system modes in an adaptive automation system. The system moderates operator task load based upon an index derived from a ratio of EEG power bands. The research shows that it may be feasible to build an adaptive automation system and use this index of brain activity to drive the system. The paper concludes with a discussion of several issues that still need to be addressed before this approach can move beyond the laboratory.     

A novel broadband terahertz filter for photonic crystal

Abstract

The influence of the change of the radius of point defect cylinders, scattering dielectric cylinders, dielectric cylinders on both sides of line waveguide on S parameter is studied. According to the resonant coupling principle between micro-cavity and waveguide, a novel broadband terahertz filter is designed. The novel filter is formed by introducing scattering dielectric cylinders into the resonant microcavity, and the point defect cylinders are composed of HgTe material and adjusting the radius of dielectric cylinders on both sides of line waveguide. Results show that the 3 dB bandwidth reaches 74.2 GHz, the return loss is less than ?12.02 dB, the maximum insertion loss in-band reaches 0.35 dB and its drop efficiency is up to 96.79%. The novel terahertz filter has flat passband, sharp rejections at out-bands and its central frequency is 0.338THz. The good performances show that it can meet the requirements of high speed and broadband in terahertz atmosphere communication I window.     

自适应光学系统中高精跟踪回路性能在线分析

在自适应光学系统中,高精跟踪回路的闭环误差由未完全补偿的跟踪残余误差和倾斜噪声误差组成。利用高精跟踪回路闭环残余倾斜数据和电压数据,可以计算高精跟踪回路的跟踪残余误差、倾斜噪声以及开环倾斜误差。基于此种方法对1．2m望远镜61单元白适应光学系统中高精跟踪回路的性能进行了在线分析。分析结果表明,系统引入的噪声随着所观测恒星星等的增加而增加．