用极性阈值法降低铸钢超声探伤组织噪声的研究

采用超声波对铸钢件进行无损探伤时将产生较强的组织散射噪声，这对正确评价探测对象的质量十分不利。该项研究采用分离频谱法对探伤信号进行处理，再用极性阈值法作恢复运算，来达到降低组织噪声的目的。以水平连铸圆管坯为研究对象的实验结果表明，研究采用的方法对组织噪声有较好的抑制作用。     

金属内部裂纹的超声衰减特性与近表面缺陷识别

建立了包含裂纹缺陷的二维金属板模型.采用有限元方法,对具有不同深度裂纹的材料内部超声波场进行计算,获得了不同裂纹深度金属材料上表面的回波信号,分析了裂纹深度对超声波传播特性的影响规律.进一步分离提取不同阶次底面回波的频谱特征,获得了由裂纹缺陷引起的超声衰减系数随频率的变化关系.最后提出了通过底面回波频谱图辨识近表面裂纹缺陷的方法.      

基于小波包分解和支持向量机的石油套管缺陷智能识别

 针对石油套管缺陷超声无损检测(NDT)中缺陷回波的特点,提出了一种基于小波包分解和支持向量机(SVM)的缺陷智能识别新方法。分析了Gabor、小波和小波包3种信号时频变换分解方法的特点,并进行了基于3种方法生成的特征数据可分性比较,确定了小波包分解方法效果最好。根据SVM解决分类问题的原理,采用SVM法对3种时频分解提取的缺陷信号特征数据进行识别。试验表明,基于小波包分解局部熵的特征提取结合SVM模式智能识别的组合方法,可应用于石油套管上的4种典型缺陷的识别。     

金属材料小缺陷超声反射信号建模及识别

本文主要分析了给予散射声场与高斯回波理论的超声回波模型,并针对相关洗护发的金属材料微小缺陷识别方法进行了研究和探讨,以期正确识别出金属材料的微小缺陷回波。     

超声检测与特征分析在半固态铝合金产品中的应用

采用接触法和水浸聚焦法分别对平底孔、通孔、槽伤三类半固态用铝合金人工缺陷进行超声检测并提取特征参量进行分类识别。用频谱分析方法分析静态超声A扫信号,对缺陷信号段进行快速傅里叶变换,以偏度值、峰度值、主频率峰值、谐振频率间隔作为特征参量判断缺陷类型。槽伤的偏度值、峰度值最大,通孔次之,平底孔最小,随着缺陷埋深的增加频谱图趋于对称和正态分布的特征;主频率峰值通孔最大,平底孔次之,槽伤最小;谐振频率间隔平底孔最大,槽伤次之,通孔最小。分析动态超声C扫描信号随着缺陷埋深增加的衰减情况,根据图像边缘形状特征可判断出缺陷类型,并且测量值/实际值(ρ/ρ0)图表明,平底孔缺陷尺寸测量误差最小达到40μm,通孔最小误差达到30μm,槽伤误差最小达到50μm。人工缺陷检测结果为自然缺陷的类型识别提供了可靠的判断依据。     

基于HHT方法的微差爆破延时识别

基于HHT方法,利用EMD分解的自适应性和Hilbert谱平方的能量密度意义,提出微差爆破延时时间的幅值包络线识别法和瞬时能量识别法。先对爆破振动信号进行EMD分解并识别主震分量,然后作Hilbert变换,获取主震分量幅值包络线和信号瞬时能量,依据炸药能量的释放引发测点爆破振动信号速度或者能量突增原理,寻找主震分量幅值包络线和瞬时能量突峰点,便可计算微差爆破延时时间。工程实例分析表明：由幅值包络线和瞬时能量识别的延时时间都在理论值范围内,说明这2种方法识别微差爆破延时时间可行。     

金属材料内部非金属夹杂超声检测的数值模拟

在金属材料内部夹杂物的超声检测中,如何通过检测获得的回波信号辨识夹杂物的属性和位置,一直是其重点和难点问题.通过建立包含夹杂物缺陷的二维金属板模型,采用有限元数值模拟的方法,对材料内部超声波场进行计算,获得了两种最典型的夹杂物Al₂O₃和TiN,以及二者在材料内部不同深度时的超声回波信号.研究了夹杂物类型和夹杂物深度对超声回波时域波形以及对界面波、夹杂物缺陷回波和底面回波频谱分布的影响规律.      

基于多域流形的行星齿轮箱局部故障识别

行星齿轮箱振动信号包含多种频率成分和噪声干扰，频谱具有复杂的边带结构，容易对故障识别造成误导甚至引起错判.在不同故障状态下，行星齿轮箱振动信号的多域特征量将偏离正常范围且偏离程度不同，根据这一特点，提取振动信号的时域、频域特征参量用于故障识别.为了避免传统分析方法中负频率及虚假模态问题，增强对噪声干扰的鲁棒性，采用局部均值分解法将信号自适应地分解为单分量之和，提取时频域单分量瞬时幅值能量.针对多域特征空间构造过程中出现的高维及非线性问题，采用流形学习对数据进行降维处理.提出基于改进的虚假近邻点的本征维数估计及最优k邻域确定方法，并通过等距映射对多域特征空间进行降维分析.对于行星齿轮箱实验信号，根据样本流形特征聚类结果，分别识别出了太阳轮、行星轮和齿圈的局部故障，从而验证了上述方法的有效性.      

离散跟踪微分器在板形识别上的研究与应用

 实际生产过程中很多因素会对板形信号产生干扰,从而造成板形缺陷识别不准确。针对这一问题,在板形勒让德多项式回归分解识别方法基础上应用最速离散跟踪微分器对板形信号进行滤波处理,消除噪声干扰。仿真结果表明,两种方法相结合后在板形缺陷识别的精确度和抗干扰性方面都有很好的效果。     

基于集合经验模式分解和交叉能量算子的滚动轴承故障诊断

振动信号的周期性冲击及其重复频率是滚动轴承故障诊断的关键.本文提出了一种基于集合经验模式分解和交叉能量算子提取滚动轴承故障特征的方法.首先,应用集合经验模式分解方法将振动信号分解为本征模式函数以满足交叉能量算子对信号单分量的要求.然后根据相关程度和峭度从本征模式函数中选取敏感分量,计算敏感分量和原始信号的瞬时交叉能量及其傅里叶频谱.最后根据交叉能量的频谱结构和特征频率识别轴承故障.通过分析滚动轴承故障仿真信号和实验测试信号,诊断了滚动轴承元件故障,验证了该方法的有效性.     

SPLICE: sub-second diffusion-sensitive MR imaging using a modified fast spin-echo acquisition mode

Recent human studies for measuring of the apparent diffusion coefficient in tissue by magnetic resonance imaging have been conducted by time-consuming standard spin-echo acquisition sequences and phase correction with navigator echoes. Diffusion-weighted echo-planar sequences have been shown to be rapid alternatives for brain imaging. Both methods show inherent disadvantages in applications on thoracic or abdominal sites. A new approach combining single-shot diffusion-weighted imaging with a modified fast spin-echo acquisition mode is reported here. The modification is necessary, because normal fast spin-echo acquisition requires a particular phase relation between the magnetization and the refocusing pulses. Unfortunately, this phase relation is not provided after diffusion sensitive preparation. Therefore, the split echo acquisition mode was developed and is shown to be insensitive to the phase of the magnetization. The advantages of both fast spin-echo acquisition and diffusion weighting can be combined in the SPLICE sequence (split aqcuisition of fast spin-echo signals for diffusion imaging). The applicability of the new technique is shown by series of sub-second diffusion-weighted images from different parts of the body.     

Vegetative bacterial endocarditis on the prolapsing mitral valve. Echocardiographic evaluation

Vegetative endocarditis on the prolapsing mitral valve can be diagnosed with an echocardiogram and the response to therapy can be followed with this technique. A dense mass of fuzzy echoes was noted on the prolapsing posterior leaflet of an echocardiogram from a patient with endocarditis. Three months after the initiation of antibiotic therapy, the mass of echoes had disappeared and was replaced by a dense linear echo, suggesting fibrosis of the part of the mitral valve that had been infected previously. Persistence of the echocardiographic evidence of endocarditis, despite negative blood cultures, may indicate persistence of the risk of peripheral embolization.     

Endobronchial sonography: feasibility and preliminary results

Endobronchial sonography, a new ultrasound technique, has been evaluated for the assessment of normal lungs and bronchial carcinomas. The procedure was performed with ultrasound catheters, which were introduced into central and peripheral bronchi through the operating channel of fibreoptic bronchoscopes. The bronchial wall is highly echogenic and laminated. The lung parenchyma appears echo rich and patchy. Pulmonary arteries can be identified by the pulsatile changes and floating echoes within the echo free lumen. Echo poor bronchial carcinomas were detected in 69 out of 74 patients with endoscopically visible tumours and in 19 out of 26 patients with peripheral carcinomas. The correct implantation of metallic stents was facilitated by endobronchial sonography in nine patients. The sonographic examination carried no particular risk and caused little discomfort.     

Ruptured or intact: what can linear echoes within silicone breast implants tell us?

OBJECTIVE: During sonographic evaluation of silicone breast implants for possible rupture, we have frequently encountered several patterns of linear echoes within the implants. To our knowledge, the significance of this finding has not been established in the literature. The purpose of this study was to determine whether internal echoes are significant in predicting implant rupture. SUBJECTS AND METHODS: Thirty-three patients with 64 silicone implants were prospectively entered into a study that included gray-scale sonography of the implants and subsequent surgical removal. Echo patterns within the implants were retrospectively evaluated on hard-copy films and compared with the integrity of the implant at surgery. RESULTS: Three categories of internal echo patterns were identified: "thick linear echoes." "thin linear echoes," and "commas." One or more of these echo patterns were seen in 57 (89%) of the 64 implants. Thick linear echoes were seen in 23 (36%) of the 64 implants, thin linear echoes were seen in 33 (52%) of the 64 implants, and commas were seen in 47 (73%) of the 64 implants. All echo patterns were seen in intact and ruptured implants with nearly equal frequency. We found no statistical significance for any echo pattern in predicting whether an implant was ruptured or intact. Of the 64 implants, four were entirely free of internal echoes. All four implants were intact. CONCLUSION: A variety of linear echoes can be seen in most silicone breast implants on gray-scale sonography. The presence or absence of linear echoes is not useful in predicting implant rupture. Complete absence of internal echoes, while highly predictive of an intact implant, is infrequently seen.     

Human listeners provide insights into echo features used by dolphins (Tursiops truncatus) to discriminate among objects.

Echolocating bottlenose dolphins (Tursiops truncatus) discriminate between objects on the basis of the echoes reflected by the objects. However, it is not clear which echo features are important for object discrimination. To gain insight into the salient features, the authors had a dolphin perform a match-to-sample task and then presented human listeners with echoes from the same objects used in the dolphin's task. In 2 experiments, human listeners performed as well or better than the dolphin at discriminating objects, and they reported the salient acoustic cues. The error patterns of the humans and the dolphin were compared to determine which acoustic features were likely to have been used by the dolphin. The results indicate that the dolphin did not appear to use overall echo amplitude, but that it attended to the pattern of changes in the echoes across different object orientations. Human listeners can quickly identify salient combinations of echo features that permit object discrimination, which can be used to generate hypotheses that can be tested using dolphins as subjects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Procedure for estimating the correlation dimension of optokinetic nystagmus signals

In this study, optokinetic nystagmus (OKN) is hypothesized to be controlled by a low-dimensional deterministic and possibly chaotic generator. A procedure for quantifying the presumably low-dimensional structure of the OKN signal, based on the Singular Spectrum Approach and the Grassberger--Procaccia algorithm for estimating the correlation dimension, v, is described. The procedure developed showed robustness against noise. Applying this method to OKN signals from 10 healthy subjects and 10 patients suffering from vertigo showed a statistically significant lower mean v value for the patients.     

微分处理方法在漏磁检测信号分析中的应用研究

提出用微分方法处理含有趋势项和幅值相等的内外伤漏磁检测信号,对微分算法及其选取进行了深入探讨。试验结果表明,经过微分处理后,内外伤缺陷区别明显,内外伤信号的幅值与直接提取原始信号内外伤缺陷的幅值相比差别明显,分辨率大大提高。     

Complex sound analysis in the FM bat Eptesicus fuscus, correlated with structural parameters of frequency modulated signals

Big brown bats, Eptesicus fuscus, were presented with artificial frequency modulated (FM) echoes that simulated an object becoming progressively closer to the bat. A stereotyped approach phase behavioral response of the bat to the virtual approaching target was used to determine the ability of the bat to analyze FM signals for target distance information. The degree to which the bats responded with approach phase behavior to a virtual approaching target was similar when they were presented with either a naturally structured artificial FM echo or an artificial FM echo constructed from a series of brief pure tone steps. The ability of the bats to respond to an FM signal structured from a sequence of pure tone elements depended on the number of pure tone steps in the series; the bats required the presentation of tone-step FM signals containing about 83 or greater pure tone elements. Moreover, the duration of the individual tone steps of the tone-step FM signals could not exceed a specific upper limit of about 0.05 ms. Finally, it appears that the bats were able to independently resolve individual tone steps within the tone-step FM signals that were separated by about 450 Hz or more.     

Acoustic image representation of a point target in the bat Eptesicus fuscus: evidence for sensitivity to echo phase in bat sonar

Echolocating bats, Eptesicus fuscus, were trained in two distinct behavioral tasks to investigate the images they perceive of a sonar point target. In the first task, bats were trained in a two-alternative forced-choice procedure to detect electronically simulated target echoes at a range of approximately 57 cm. Half of the trials in the detection task contained echoes from a stationary target (simulated by a fixed echo delay) and half contained echoes from a jittering target (simulated by an echo delay alternating between two time values over successive sonar emissions). In the second task, bats were trained in a two-alternative forced-choice procedure to discriminate between electronically simulated stationary and jittering targets, centered about a range of 57 cm. Both target detection and target jitter discrimination performance were assessed as a function of jitter magnitude, with jitter values ranging from 0-60 microseconds (corresponding to a change in distance of 0 to 10.3 mm). In both detection and discrimination tasks, the bat's performance changed cyclically with the magnitude of echo jitter. Specifically, when the phase of the playback echoes was unchanged, performance levels were poorest at 0 and 30 microseconds, and when the phase of the echoes alternated by 180 deg from one to the next, performance levels were poorest at 15 and 40-50 microseconds. The results suggest that Eptesicus is sensitive to the phase reversal of echoes and thus have implications for assessing receiver models of echolocation.     

Recursive autoregressive spectral maps for ocular pathology detection

This article presents a new approach to the problem of obtaining topological maps for tissue characterization, based on spectral parameters extracted from radio frequency (RF) backscattered ultrasonic signals. The spectral parameter we deal with is the power spectral density centroid, since it is an efficient indicator of the tissue microstructure characteristics as far as the particle dimensions are concerned. The spectral analysis of RF ultrasonic echoes is performed using a recursive least-squares scheme with a variable forgetting factor, based on low-order autoregressive models. The proposed technique is particularly tailored to the differentiation of ocular pathologies; moreover, it is capable of tracking the spatial high-varying signal characteristics. The proposed approach was tested on simulated signals and on a gel suspension of calibrated latex spheres; finally, it was applied to signals scattered by in vitro eye specimens, giving satisfactory results in terms of frequency resolution and computational efficiency. The reduced computational burden allows an on-line implementation of the procedure. Topological spectral maps, combined with the conventional B-mode display, may offer a complete and integrated diagnostic tool, able to locally characterize the investigated tissue region in terms of amplitude and frequency shift of the corresponding echoes.