数字超声波信号中有色噪声的自适应滤波

针对测试环境中常存在的超声波频段的有色干扰噪声,设计了一种基于横向滤波器和最小均方误差自适应滤波算法的自适应对消器结构,并提出了固定步长和自适应步长相结合的自适应滤波算法流程。该方法增设了一个接收环境噪声的专用探头来自动跟踪噪声特性的改变,无需手动设置自适应滤波器参数和期望信号。通过自适应步长调整算法与固定步长方法结合,该方法能够在实现良好滤波效果的同时兼顾快速跟踪环境的变化。实验表明,提出的方法可以有效滤除目标超声波信号频带之外频率点处的有色干扰噪声,信噪比改善幅度可达16dB;时间复杂度为O(n),可实现实时处理。本文方法可以在无人工干预下自动、实时、有效地滤除与超声波信号频率接近的有色干扰噪声,已被成功地应用于气体超声波流量测量中。     

Sparsity enhancement for blind deconvolution of ultrasonic signals in nondestructive testing application

The received signal in ultrasonic pulse-echo inspection can be modeled as a convolution between an impulse response and the reflection sequence, which is the impulse characteristic of the inspected object. Deconvolution aims at approximately inverting this process to improve the time resolution so that the overlap between echoes from closely spaced reflectors becomes small. This paper presents a modified minimum entropy blind deconvolution algorithm for deconvolving ultrasonic signals. Enhancement of the resolution is achieved by using the presented method. In addition, the presented approach will, in many cases, lead to a faster computation. A nonlinear function is the key point to the efficiency of the modified blind deconvolution algorithm, which is used to increase the sparsity of the iteration output and to decrease the influence of the added noise by replacing each iteration output by output of the nonlinear function. Simulations showed the efficiency of the modification as compared with minimum entropy deconvolution when deconvolving synthetic ultrasonic signals. Experimental results using real ultrasonic data evaluated further that the exact solution consistently yields good performance. The thickness of a thin steel sample can be calculated by the modified blind deconvolution filter with a reasonable accuracy.     

机械裂纹无损检测方法综述

针对机械裂纹扩展以及检测的问题,对常用的裂纹无损检测方法进行了叙述,具体介绍了磁粉检测和渗透检测技术的发展现状。对近年来新兴的激光超声检测技术、电磁超声检测技术、超声红外热成像检测技术、脉冲涡流及涡流阵列检测技术的特点、作用原理进行了详细的说明,对比了相对传统检测技术的优势,对各新型无损检测技术的发展方向进行了总结分析。研究结果表明:未来新型裂纹无损检测方法的发展趋势将由人工向智能化、全自动化、图像化检测发展,复合模式检测在新技术中的应用愈加广泛,检测仪器设备的发展以降低能耗和提高信噪比为主,新型裂纹无损检测技术在特殊工程领域的应用将更加专业化。     

The possibility of using the maximum-entropy method in ultrasonic nondestructive testing for increasing the resolution of echo signals

The problem of deconvoluting echo signals via regularization according to the maximum entropy method followed by the reconstruction of 2D images via the Fourier transformation synthetic aperture focusing technique (FT-SAFT) is considered. Numerical and experimental simulations have been performed. The possibility of improving the ray resolution of echo signals and reducing the speckle-noise level is demonstrated. The results obtained are compared to the results of constructing an AR model of the spectrum of echo signals.     

新的超声立体视觉数据增强技术

针对超声成像噪声大、数据质量严重退化的特点,提出了一种新颖的非稳定度度量算法,该算法通过加强图像变化较大的部分来实现超声数据的增强.给出了输入信号信噪比不同情况下非稳定度算子与Deriche算子的输出仿真结果;通过兔子肝脏和12周胎儿的实际数据计算,得到了二者经非稳定度算子处理前后的超声立体视觉图像.研究结果表明,非稳定度数据增强技术对噪声不敏感,通过对比处理前后的图像可清晰地看出非稳定度算子能够有效地改善超声立体视觉成像的质量.     

准规则生物组织超声背散射信号的仿真

超声背散射信号能提供反映组织微结构的有用信息.本文在原有的生物组织超声背散射信号仿真模型基础上,将影响平均散射元间距(MSS)估计的组织特性具体为4个主要参数,为检测各种平均散射元间距估计方法的性能提供了方便.文中用AR倒谱方法对仿真信号4个参数的合理性进行反向测试,实验结果表明,仿真信号的4个参数能表示影响平均散射元间距估计性能的组织特性.通过仿真信号与人体脾组织的背散射信号以及相关文献中组织信号的比较,证明仿真信号与具有准周期性的生物组织背散射信号基本类似.     

Frequency multiplexer for ultrasonic Doppler blood flow signals

An instrument is described which uses single-sideband techniques to combine two channels of Doppler flow signals into a form suitable for simultaneous processing by a single-channel real-time spectral analyzer. The maximum input frequency range is 50 Hz to 10 kHz.     

超声表面强化技术的研究进展

介绍了目前发展较为成熟的几种超声表面强化技术,如超声喷丸、超声挤压、超声滚压和超声振动辅助电火花脉冲放电等的基本原理、技术特点和研究进展,指出了各类超声表面强化技术研究中尚待解决的问题,并提出了超声表面强化技术的发展趋势。     

管道对接焊缝超声检测爬行器的研制

介绍了一种用于管道对接焊缝内部缺陷检测的自动检测爬行器的工作原理、系统结构和工作特点。该系统在PC机的控制下相对焊缝运动，实现了超声检测的自动化。试验结果表明，该系统在灵活性和易于使用等方面取得了较满意的结果，具有较广泛的适用性。     

Efficiency of noise-resistant coding of ultrasonic signals

Advantages of noise-resistant coding in ultrasonic instruments are considered. Rarefied pulse-phase codes are investigated, and experimental results are presented.     

Image enhancement and post-processing for low resolution compressed video

This research paper recommends the point spread function(PSF)forecasting technique based on the projection onto convex set(POCS)and regularization to acquire low resolution images.As the environment for the production of user created contents(UCC)videos(one of the contents on the Internet)becomes widespread,resolution reduction and image distortion occurs,failing to satisfy users who desire high quality images.Accordingly,this research neutralizes the coding artifact through POCS and regularization processes by:1)factoring the local characteristics of the image when it comes to the noise that results during the discrete cosine transform(DCT)and quantization process;and 2)removing the blocking and ring phenomena which are problems with the existing video compression.Moreover,this research forecasts the point spread function to obtain low resolution images using the above-mentioned methods.Thus,a method is suggested for minimizing the errors found among the forecasting interpolation pixels.Low-resolution image quality obtained through the experiment demonstrates that significant enhancement was made on the visual level compared to the original image.     

Zigzag pattern of Brillouin OF sensor for spatial resolution enhancement

Brillouin optical fiber (OF) sensing technology shows superior potential for structural health monitoring with the advantages of distributed strain and temperature measurement, immunity of electromagnetic interference and so on. However most of current commercial Brillouin OF sensing systems have encountered spatial resolution bottleneck, which cannot deal with local high-precision measurement. A zigzag pattern of Brillouin OF sensor is developed explicitly for spatial resolution enhancement in this paper, and a relative zigzag optical fiber sensor is produced and packaged by fiber reinforced polymer (FRP). Their characteristics are studied by using the strain measurement of one small-size uniform strength beam. From the experiments, the zigzag pattern exhibits excellent performance for strain measurement with high-precision and enhances the spatial resolution to a certain degree without changing the Brillouin sensing instrument’s performance itself.     

Adaptive modelling of transient vibration signals

Conventional vibration signal processing techniques are most suitable for stationary processes. However, most mechanical faults in machinery reveal themselves through transient events in vibration signals. Time-series modelling, including autoregressive moving average (ARMA) modelling and autoregressive (AR) modelling, is an efficient approach for transient signal analysis. Based on the adaptive prediction technique, this paper applies the principle of the adaptive line enhancer (ALE) to the modelling of transient vibration signals. The time-series models, adaptive algorithms and the rational time–frequency transfer function are investigated in the paper. Simulation and experimental studies with different time–frequency–amplitude distributions and transient vibration responses are described. The results show that the adaptive modelling method can trace the time–frequency signal and extract dynamic features such as time–frequency distributions and time–amplitude distributions from sample signals. Given the simple programming and potentially easy implementation in on-line applications, this method should have application in machine monitoring and fault diagnosis.     

Inverse analysis of ultrasonic signals of ceramics based on ultrasonic self-compensating technique

An ultrasonic self-calibrating technique for the characterization of a ceramic which was fabricated by change pressing time during the HIP process has been applied by using the ratio of the reflection and transmission coefficients of normal incidence longitudinal waves. The ratio is self-compensated, in that it is independent of the characteristics for transmission and reception of ultrasound by the transducer and the condition of the couplant. The insensitive direction in parameter space is defined as the direction in which the variation of the ratio to changes of two parameters vanishes. For inverse problem the distribution of minima in an error surface is investigated.     

Using ultrasonic pulse-echo B-scan signals for estimation of time of flight

Time of flight based methods are extensively used for detecting, locating and sizing faults in ultrasonic non-destructive testing and evaluation. In this paper, we investigate model-based estimation of the ultrasonic time of flight using B-scan signals. The Cramer–Rao bounds on the time of flight estimator for B-scan signals are derived and then compared to the Cramer–Rao bounds on the time of flight estimator for A-scan signals. Through this theoretical analysis, we show that the estimation based on B-scan signals significantly reduces the Cramer–Rao bound on the time of flight estimator. In addition, the resulting theoretical equation allows evaluating the improvement in the accuracy of estimating the time of flight. The theoretical lower bound is then compared to the variance of a maximum likelihood estimator which is obtained using a Monte Carlo simulation. The results show that the maximum likelihood estimator can achieve the lower bound on the variance of the time of flight estimator and hence it is an efficient estimator. This numerical result will complement the theoretical analysis by showing that the Cramer–Rao bound can be reached if a proper estimator is selected.     

Electrical tuning for sensitivity enhancement of a piezo-electric ultrasonic transducer: Simulation and fabrication

Journal of Mechanical Science and Technology - In this study, two simple electrical impedance tuning methods derived from Krimholtz, Leedom, and Matthaei (KLM) modeling were proposed for increasing...     

A system for detecting weak light signals with nanosecond resolution

A simple method for detecting time-resolved weak light signals with a digital oscilloscope, which allows detection of several photons per one excitation period, is described. A system for detecting low-temperature photoluminescence with a resolution of 15 ns has been implemented on the basis of this technique and a method for attaining a resolution of 1–3 ns has been developed. The luminescence kinetics of Si/Ge _x Si_{1 ? x} /Si quantum wells was measured in the near-IR region.     

小波图像融合改善超声图像分辨率

针对超声图像分辨率较低,尤其足横向分辨率低的特点,采用基于插值和小波图像融合相结合的方法对相控阵超声图像进行了多种方式的对比试验.结果表明:采用区域能量大小判定的设计思想改善超声图像的分辨率是可行的,其中利用小波分解将经过插值放大的待融合图像分解为低频部分和高频部分,然后对低频部分采用平均法,高频部分采用区域能量最大的融合方式,由此,极大地改善了超声图像的分辨宰.     

A program for 3D simulation of signals for ultrasonic testing of specimens

Optimization of the parameters of schemes using multichannel ultrasonic flaw detectors for sonic testing of rails (sonic test schemes), as well as development of algorithms for processing test signals, are considered. The efficiency of the RAIL-3D computer code proposed for the 3D simulation of the propagation and formation of echo signals during ultrasonic testing is tested by comparing real signals and simulation results for a CB-2 calibration block. The comparison is performed for the complex conditions under which rails are tested. The code can also be used for simulating signals of ultrasonic nondestructive testing in other metal products.     

A new signal processing technique for detecting flaw echoes close to the material surface in ultrasonic NDT

A new signal processing technique for separating the reflection of a flaw near a surface from the surface reflection itself is proposed. The method is based on ultrasonic scattering energy function model of flaw close to the material surface. Flaw sensitive component in the model, which corresponding to the low frequency signal, is remained by using a low pass digital filter. In order to make the recognition procedure easier and enhance the recognition effect, a reference signal is introduced to avoid the influence of the surface echo. Thus, the surface flaw is easily and clearly recognized. The good performance of the approach is experimentally verified in laboratory on a steel sample with different man-made surface flaws.