声呐信号的现场数据采集器

本文提出了一种不受微机采样速度的影响，采样频率仅仅只取决于Ａ／Ｄ器件的采样频率，只要选择高速Ａ／Ｄ，就能做成一个高速的数据采集系统。本文给出了该系统的工作原理框图以及时序关系图。并对其工作原理作了简单的介绍，并给出了实际应用时的图片和工作时的程序。     

新德克音频解码三剑客

新德克推出三款２４ｂｉｔ／９６ｋＨｚ数字音频解码器。 为了解决ＤＶＤ／ＶＣＤ播放机及低档ＣＤ机在播放ＣＤ碟时音质欠佳的遗憾，新德克在设计制造ＤＶＤ／ＣＤ双线路播放机获得成功的基础上，又推出了专门用于ＤＶＤ／ＶＣＤ及低档ＣＤ唱机升级的数码ＤＡＣ系列双声道音频解码器。该解码器具备独立的音频数字滤波及 ２４ｂｉｔ／９６ｋＨｚ的 Ｄ／Ａ转换，独立超低抖动（ＳｕｐｅｒＬｏｗ Ｊｉｔｔｅｒ）精确主时钟设计电路，其振荡核心部件选用了石英晶体振荡器，从而最大限度地降低了时钟抖动，有效地把Ｊｉｔｔｅｒ失真降低到可以忽…     

测量低信噪比电压的数学相敏解调算法及性能分析

本文研究了低信噪比正弦电压幅值及相位测量用的数字相敏解调（ＤＰＳＤ）算法，给出了ＤＰＳＤ算法的主要参数（数据长度，取样频率，Ａ／Ｄ转换器位数）与低信噪比电压测量的性能指标（测量精度，频率分辨力，动态储备及最小可测电压）之间的关系。对纳伏电压的实际测量表明，理论分析与测量结果是一致的，本文研究了结果可以用于数字式相敏解调程序的设计及应用。     

浅海多波束动态聚焦近场波束形成实现方法

讨论了一种动态聚焦波束形成实现方法,将聚焦波束形成的焦点时间结构与基阵空间结构相关联,得到时变焦点的高精度聚焦波束形成输出。通过实验数据的分析和处理,验证了方法的有效性。     

测量低信噪比电压的数字相敏解调算法及性能分析

本文研究了低信噪比正弦电压幅值及相位测量用的数字相敏解调（ＤＰＳＤ）算法，给出了ＤＰＳＤ算法的主要参数（数据长度、取样频率、Ａ／Ｄ转换器位数）与低信噪比电压测量的性能指标（测量精度、频率分辨力、动态储备及最小可测电压）之间的关系。对纳伏电压的实际测量表明，理论分析与测量结果是一致的。本文研究结果可以用于数字式相敏解调程序的设计及应用     

“未来音响”的先行者

介绍一款２４ｂｉｔ／９６ｋＨｚ的多轨数码录音机随着ＤＶＤ的大量流行,ＤＶＤＡｕｄｉｏ势必成为未来音频“ＣＤ”产品的新格式。一些专业录音师和拥有个人录音室的朋友都希望拥有一套能录制ＤＶＤＡｕｄｉｏ质量的多轨数字录音系统,能够快速、方便、高品质地完成录音工作。何谓ＤＶＤＡｕｄｉｏ的质量ＤＶＤＡｕｄｉｏ“ＣＤ”的音质是令人着迷的,那究竟何谓ＤＶＤ　Ａｕｄｉｏ的质量呢？我们知道,凡是数码音响都有一个模拟／数字（Ａ／Ｄ）;数字／模拟（Ｄ／Ａ）的转换过程,数字音频的质量有很大部分与Ａ／Ｄ、Ｄ／Ａ的转换质量有…     

双通道激光图像数据采集与通讯系统的研制

本文概述了在激光三维成像系统中的数据采集及其计算机通讯技术，介绍了高速Ａ／Ｄ转换器ＡＤ５７９与ＣＡ３３１８的功能及其在系统中的应用，探讨了系统各部分时序控制电路以及与计算机ＤＭＡ通讯的实现．     

超声相控阵扇扫诊断仪中提高帧频的新方法

文章通过仔细分析相控延时及超声波束的空间特征，导出了相邻波束指向与延时之间的相互关系；找出了其中的规律性及可用特征。提出一种提高帧频的新方法：多波束同时合成法，从而能有效地改善彩色超声成像质量。     

数字合成式波形发生器研制

本文介绍子使用Ｄ／Ａ转换器合成民压波形的原理,由Ｄ／Ａ转换器直接输出的电压波形是需合成波形的ＮＲＺ采样波形,为了得到所需波形,必须采用信号恢复电路。本文介绍了信号恢复的方法,并给出了一台实用的数字合成式波形发生器的设计思路。     

船体放样数据库系统设计与实现

主要讨论船舶ＣＡＤ／ＣＡＭ中的船体数学放样数据的计算机存取问题，并把讨论结果储诸实现。为了实现这一目标，首先把船体曲线光顺中需要处理的数据进行科学的分析，整理，编排，并此基础上给出数据库实现，方案。从而开发出适用于生产实践“船舶建造ＣＡＤ／ＣＡＭ一体系统”。     

Multidepth synthetic aperture processing of ultrasonic data

The characterization of the size, shape, and location of subsurface discontinuities in metals using multidepth synthetic aperture processing of ultrasonic data is considered. A technique is proposed to increase the lateral resolution and signal-to-noise ratio when metals of large thickness are tested. The first technique to achieve multidepth was dynamic focusing. The aperture in the proposed technique is simultaneously focused at several depths by means of a computer program, thus avoiding the fixed hardware required in the dynamic focusing technique. Experimental evidence is presented to indicate the improvement in resolution, due to multidepth processing, over the single-focus technique.     

Improved synthetic aperture focusing technique with applications in high-frequency ultrasound imaging

Synthetic aperture focusing using a virtual source was used previously to increase the penetration and to extend the depth of focus in high-frequency ultrasonic imaging. However, the performance of synthetic aperture focusing is limited by its high sidelobes. In this paper, an adaptive weighting technique based on a focusing-quality index is introduced to suppress the sidelobes. The focusing-quality index is derived from the spatial spectrum of the scan-line data along the mechanical scan direction (i.e., the synthetic aperture direction) after focusing delays relative to the virtual source have been applied. The proposed technique is of particular value in high-frequency ultrasound in which dynamic focusing using array transducers is not yet possible. Experimental ultrasound data from a 50-MHz imaging system with a single-crystal transducer (f-number=2) are used to demonstrate the efficacy of the proposed technique on both wire targets and speckle-generating objects. An in vivo experiment also is performed on a mouse to further demonstrate the effectiveness. Both 50-MHz fundamental imaging and 50-MHz tissue harmonic imaging are tested. The results clearly demonstrate the effectiveness in sidelobe reduction and background-noise suppression for both imaging modes. The principles, experimental results, and implementation issues of the new technique are described in this paper.     

Ultrasonic Imaging Algorithms With Limited Transmission Cycles for Rapid Nondestructive Evaluation

Imaging algorithms recently developed in ultrasonic nondestructive testing (NDT) have shown good potential for defect characterization. Many of them are based on the concept of collecting the full matrix of data, obtained by firing each element of an ultrasonic phased array independently, while collecting the data with all elements. Because of the finite sound velocity in the test structure, 2 consecutive firings must be separated by a minimum time interval. Depending on the number of elements in a given array, this may become problematic if data must be collected within a short time, as it is often the case, for example, in an industrial context. An obvious way to decrease the duration of data capture is to use a sparse transmit aperture, in which only a restricted number of elements are used to transmit ultrasonic waves. This paper compares 2 approaches aimed at producing an image on the basis of restricted data: the common source method and the effective aperture technique. The effective aperture technique is based on the far-field approximation, and no similar approach exists for the near-field. This paper investigates the performance of this technique in near-field conditions, where most NDT applications are made. First, these methods are described and their point spread functions are compared with that of the total focusing method (TFM), which consists of focusing the array at every point in the image. Then, a map of efficiency is given for the different algorithms in the nearfield. The map can be used to select the most appropriate algorithm. Finally, this map is validated by testing the different algorithms on experimental data.     

Model-based correction of diffraction effects of the virtual source element

A method for ultrasonic synthetic aperture imaging using finite-sized transducers is introduced that is based on a virtual source (VS) concept. In this setup, a focused transducer creates a VS element at its focal point that facilitates the use of synthetic aperture focusing technique (SAFT). It is shown that the performance of the VS method may be unsatisfactory due to the distortion introduced by the diffraction effects of the aperture used for creating the VS element. A solution to this problem is proposed that consists of replacing the classical SAFT by the extended synthetic aperature focusing technique (ESAFT) algorithm presented in our earlier works. In ESAFT, the full geometry of the VS is modeled, instead of applying the simplified point source approximation used when VS is combined with classical SAFT. The proposed method yields a substantial improvement in spatial resolution compared to that obtained using SAFT. Performance of the proposed algorithm is first demonstrated on simulated data, then verified on real data acquired with an array system.     

Finite element simulation of dynamic crack propagation process using an arbitrary Lagrangian Eulerian formulation

In this paper, the arbitrary Lagrangian Eulerian formulation is employed for finite element modelling of dynamic crack propagation problem. The application phase simulation of computational dynamic fracture is applied to model by which the crack propagation history and variation of crack velocity are predicted using the material dynamic fracture toughness. The dynamic solution of problem is accomplished using the implicit time integration method. The convective terms due to mesh‐material motion are taken into account via the convection equation. A robust and efficient mesh motion technique, that its equations need not to be solved at every time step, is employed in Eulerian phase. The mesh connectivity is preserved during the analysis. So, the successive remeshing of model is eliminated. When the dynamic fracture criterion is satisfied for crack growth, the presented algorithm allows the crack to advance by splitting the material particle at the crack tip. The dynamic energy release rate is calculated at each time step to determine dynamic stress intensity factor. The predicted results are compared with those obtained through the experimental study and remeshing technique cited in the literature. The proposed computational algorithm leads to an accurate and efficient simulation of dynamic crack propagation process.     

Autonomous target tracking and following mobile robot

Tracking and following a moving target in real time is a very challenging task in autonomous mobile robot applications, due to the unstructured and unknown environment. In this article, a real time, autonomous, dynamic, whole-field target tracking system (360° coverage) is developed based on a pan/tilt/zoom CCD vision system. The vision system scans and locks the pose of the moving target and commands the tracking mobile robot to follow the target while avoiding obstacles. Bayes’ theorem-based foreground–background segmentation algorithm is applied for motion detection. The color-based particle filter algorithm is used to track the moving object. The system steers the tracking mobile robot toward the moving target based on the angular difference obtained from the tracking module. Fuzzy logic is applied and a sensor data fusion algorithm is developed to reduce the ultrasonic phantom effect of obstacle detection using eight ultrasonic sensors. Multiple behaviors are integrated through the proposed system. Experimental results show the proposed system can successfully track and follow a moving target and avoid obstacles in real time. The tracking accuracy is higher than 80%.     

基于高速A／D卡的全波形采集超声自动检测系统

设计了一种全波形采集超声自动检测系统,实现了A,B,C 3种扫描方式且具有记录被检材料上所有检测点超声A扫描波形的功能,支持材料超声检测、评价技术研究.该系统由高速A/D卡、超声检测仪、自动扫描器、运动控制系统和CSCAN软件等组成,作为核心部件的高速A/D卡选用PCI-9820型,负责从超声检测仪采集A扫描波形信号.自动扫描过程中,A/D卡与超声检测仪、运动控制系统之间通过硬件信号实现同步,使A扫描波形数据的采集与被检材料上声传播的渡越时间、预定测量点位置相对应,采集得到的A扫描波形数据通过A/D卡的板载SDRAM及DMA功能异步传输至计算机内存,并由CSCAN软件进一步实现数据压缩、滤波、存储以及不同方式成像等处理.测试结果证明,该系统运行速度快,成像精度高且性能稳定. 更多还原     

ICARUS: imaging pulse compression algorithm through remapping of ultrasound

In this work we tackle the problem of applying to echographic imaging those synthetic aperture focusing techniques (SAFT) in the frequency domain commonly used in the field of synthetic aperture radars (SAR). The aim of this research is to improve echographic image resolution by using chirp transmit signals, and by performing pulse compression in both dimensions (depth and lateral). The curved geometry present in the unfocused radio-frequency (RF) ultrasonic image is the main cause of inaccuracy in the direct application of frequency domain SAFT algorithms to echographic imaging. The focusing method proposed in this work, after pulse compression in the depth dimension, performs lateral focusing in the mixed depth-lateral spatial frequency domain by means of a depth variant remapping followed by lateral pulse compression. This technique has the advantage of providing a resolution that is uniform in nonfrequency selective attenuation media, and improved with respect to conventional time domain SAFT, without requiring the acquisition and processing of channel data necessary for the most advanced synthetic transmit aperture techniques. Therefore, the presented method is suitable for easy real-time implementation with current generation hardware.     

Ultrasonic beam focusing through tissue inhomogeneities with a timereversal mirror: application to transskull therapy

Time reversal of ultrasonic fields allows a very efficient approach to focus pulsed ultrasonic waves through lossless inhomogeneous media. Time reversal mirrors (TRMs) are made of large transducer arrays, allowing the incident field to be sampled, time reversed, and reemitted. Time reversal method corrects for phase, amplitude, and even shape aberration and thus, is more efficient than time shift compensation techniques. However, this technique needs the knowledge of the Green's function of a dominant scatterer available in the medium. Aberration correction for ultrasonic hyperthermia could be achieved by combining TRM with an artificial acoustic source or sensor implanted inside the treatment volume. In this paper, time reversal method has been experimentally applied to the focusing through the skull bone. It is shown that the skull induces severe attenuation of ultrasound and reduces the efficiency of the time reversal approach. Then, an amplitude correction method is proposed to focus through an attenuating layer located close to the array. This method consists in inversing the amplitude modulation and then time reversing these signals. Finally, this method is combined with numerical backpropagation to compensate for an attenuating layer located some distance away from the transducer array     

Low-power split-path data-driven dynamic logic

Data-pre-charged dynamic logic, also known as data-driven dynamic logic (D3L), is very efficient when low-power constraints are mandatory. Differently from conventional dynamic domino logic, which exploits a clock signal, D3L uses a subset of the input data signals for pre-charging the dynamic node, thus avoiding the clock distribution network. Power consumption is significantly reduced, but the pre-charge propagation path delay affects the speed performances and limits the energy?delay product (EDP) improvements. This study presents a new dynamic logic named split-path D3L (SPD3L) that overcomes the speed limitations of D3L. When applied to a 16 X 16 bit Booth multiplier realised with STMicroelectronics 65 nm 1V CMOS technology, the proposed technique leads to an EDP 25 and 30% lower than standard dynamic domino logic and conventional D3L counterparts, respectively.