超声动态测距的一种直接数字解调处理方法

为了减少传统的相位差超声动态测距的复杂性,提出了一种基于直接数字解调的信号处理方法。运用STM32内部两路A/D同步采集超声测量信号与参考信号,对这两组信号数据通过最小二乘椭圆拟合方法,计算[-π,π]单周期范围内的实时相位差。在此基础上,对实时相位差进行解包裹运算,得到绝对相位差。最后,通过绝对相位差的变化量与距离变化量成正比的关系,计算出实时的动态变化距离值。实验结果表明:当目标速度不超过2.5 m/s时,该方法能够准确地将距离值直接解调出来,满足动态变化条件下跟踪测距要求。     

J-TEXT 偏振仪信号相位差实时计算方法研究

介绍了常用的相位差算法过零检测法、数字相关法和FFT 算法,对这三种算法的测试表明,三者均能在几十微秒量级的延时内较准确地获得计算结果,但所需的资源和时间开销有所不同。过零检测法占用的资源较多,但平均计算延时较小;FFT 资源占用率和延时均较大;而数字相关法资源占用率和延时均较小,但相位翻转的判断存在困难。     

Direct determination of bulk strain soliton parameters in solid polymeric waveguides

Bulk strain solitons in solids attract considerable attention in applications due to their very small decay, permanent bell shape and the wave parameter dependence on waveguide elasticity and geometry. One of the reasons of an evident gap between theory and numerical simulation of strain solitons propagation in various waveguides and comparatively rare experimental verification of rigorous results lies in extensive variability of physical constants data available for polymers. We show how a dramatic improvement of experimental setup provides new opportunities in solitary wave observation and its parameters measurements.Digital holography based on high-speed registration cameras allowed us to refine the accuracy of measurements, and precise pulse synchronization provided direct measurements of bulk strain soliton velocity with proper accuracy. It confirms the fact that the soliton parameters depend rather on the waveguide geometry and material, not on an initial pulse, which power provides either a single soliton or a soliton train.     

Scanning schemes in white light photoelasticity – Part II: Novel fringe resolution guided scanning scheme

Varied spatial resolution of isochromatic fringes over the domain influences the accuracy of fringe order estimation using TFP/RGB photoelasticity. This has been brought out in the first part of the work. The existing scanning schemes do not take this into account, which leads to the propagation of noise from the low spatial resolution zones. In this paper, a method is proposed for creating a whole field map which represents the spatial resolution of the isochromatic fringe pattern. A novel scanning scheme is then proposed whose progression is guided by the spatial resolution of the fringes in the isochromatic image. The efficacy of the scanning scheme is demonstrated using three problems – an inclined crack under bi-axial loading, a thick ring subjected to internal pressure and a stress frozen specimen of an aerospace component. The proposed scheme has use in a range of applications. The scanning scheme is effective even if the model has random zones of noise which is demonstrated using a plate subjected to concentrated load. This aspect is well utilised to extract fringe data from thin slices cut from a stereo-lithographic model that has characteristic random noise due to layered manufacturing.     

Exchanging digital video of laryngeal examinations

Laryngeal examinations, especially stroboscopic examinations, are increasingly recorded using digital video formats on computer media, rather than using analog formats on videotape. It would be useful to share these examinations with other medical professionals in formats that would facilitate reliable and high-quality playback on a personal computer by the recipients. Unfortunately, a personal computer is not well designed for reliable presentation of artifact-free video. It is particularly important that laryngeal video play without artifacts of motion or color because these are often the characteristics of greatest clinical interest. With proper tools and procedures, and with reasonable compromises in image resolution and the duration of the examination, digital video of laryngeal examinations can be reliably exchanged. However, the tools, procedures, and formats for recording, converting to another digital format ("transcoding"), communicating, copying, and playing digital video with a personal computer are not familiar to most medical professionals. Some understanding of digital video and the tools available is required of those wanting to exchange digital video. Best results are achieved by recording to a digital format best suited for recording (such as MJPEG or DV),judiciously selecting a segment of the recording for sharing, and converting to a format suited to distribution (such as MPEG1 or MPEG2) using a medium suited to the situation (such as e-mail attachment, CD-ROM, a "clip" within a Microsoft PowerPoint presentation, or DVD-Video). If digital video is sent to a colleague, some guidance on playing files and using a PC media player is helpful.     

CCD胶片点阵信息判读技术

本文论述了一种判读胶片点阵信息的新技术.CCD点阵信息判读技术采用面阵CCD实时采集点阵图象,并结合数字图系处理技术,使点阵判读达到了通用性强、误码率低、处理速度高的水平,同时系统结构简单、成本低.本文在分析CCD图象处理系统原理的基础上,重点讲述了点阵图象的处理方法.     

Quality assessment of speckle patterns for digital image correlation

Digital image correlation (DIC) is an optical–numerical full-field displacement measuring technique, which is nowadays widely used in the domain of experimental mechanics. The technique is based on a comparison between pictures taken during loading of an object. For an optimal use of the method, the object of interest has to be covered with painted speckles. In the present paper, a comparison is made between three different speckle patterns originated by the same reference speckle pattern. A method is presented for the determination of the speckle size distribution of the speckle patterns, using image morphology. The images of the speckle patterns are numerically deformed based on a finite element simulation. Subsequently, the displacements are measured with DIC-software and compared to the imposed ones. It is shown that the size of the speckles combined with the size of the used pixel subset clearly influences the accuracy of the measured displacements.     

Volume-grating phase-shifting digital speckle pattern interferometry used for measurement of out-of-plane displacement field

A new digital speckle pattern interferometry, called volume-grating phase-shifting digital speckle pattern interferometry, is discussed in this paper. The out-of-plane displacement field of a bent plate can be quantitatively measured using volume-grating phase-shifting digital speckle pattern interferometry proposed in this paper. Theoretical and experimental results, as well as absolute errors, are given.