Problems and features of spatiotemporal signal processing in ultrasonic testing of products manufactured from complexly structured materials

The main principles of spatiotemporal processing of signals during ultrasonic testing of articles manufactured from complexly structured materials with high signal attenuation are considered. Features of ultrasonic low-frequency testing limiting the application of the simplest algorithms for spatiotemporal signal processing in both ultrasonic flaw detection and ultrasonic tomography of articles manufactured from complexly structured materials are analyzed.     

The fundamentals of the theory of spatiotemporal signal processing as applied to problems of ultrasonic flaw detection of articles from complexly structured materials

The basic propositions of spatiotemporal signal processing as applied to the problems of ultrasonic testing of complex-structure articles with a high attenuation of acoustic signals are considered. Different algorithms of extracting informational echo signals from white and structural noise during multichannel spatiotemporal signal processing are studied.     

Requirements for choosing the parameters of broadband transducers for testing objects with high damping of ultrasonic signals

The main concepts of the theory of optimal signal processing as applied to tasks of ultrasonic testing of articles with high integral damping of acoustic vibrations are considered. The conditions for ensuring the optimal transfer coefficient of the receiving section of an ultrasonic flaw detector’s electroacoustic channel are formulated. The requirements for the characteristics of broadband piezoelectric transducers aimed at the insurance of undistorted transmission of ultrasonic signals are formulated.     

Issues of ultrasonic testing of extended complexly structured items with strong attenuation of signals

These and subsequent articles present the results of the studies of interference resistant methods and devices for ultrasonic testing of extended items made of complexly structured materials. The presented results are based on the radio-engineering R &; D that have been conducted for over 30 years by the Department of Electronic Devices of the Moscow Power Engineering Institute. The studies are concurrently focused on the development of methods for separating echo signals from white and structural noise, on the application of complexly modulated signals, on the development of spatial and temporal methods for processing signals, on the development of broadband mosaic transducers, and on the design of multifunctional devices for ultrasonic testing. The necessity of such a comprehensive approach to ultrasonic testing is substantiated in this article by analysis of the problems of ultrasonic testing of complexly structured items with strong integral attenuation of ultrasound.     

Models of the formation of ultrasonic signals in image reconstruction problems

Theoretical concepts of the formation in articles of ultrasonic signals that are used in image reconstruction algorithms are considered. The approximations and limitations of these models are analyzed.Translated from Defektoskopiya, Vol. 41, No. 1, 2005, pp. 10–19.Original Russian Text Copyright © 2005 by Barkhatov.     

Effect of Surface Waves from a Moving Object on Its Image During Reconstruction using Aperture Synthesis

The reconstruction of an image of the cross section of a thin wire obtained by an ultrasonic detector in an aqueous medium at a frequency of 1.3 MHz with a monochromatic probing signal is considered. The image was reconstructed using a synthesized aperture by correlation processing of a trajectory Doppler signal with calculated reference trajectory signals from point objects. The disturbing effect of the ultrasonic wave reflected from the surface wave generated by the moving wire on the image reconstruction is taken into account. The results of reconstruction of the image of the wire cross-section from model and experimental trajectory signals in the presence of a surface wave are given.     

Image Processing-Based Mine Detection Techniques: A Review

Various mine detection techniques are reviewed with particular emphasis on signal and image processing methods. Based on the target, mines are classified into two types; anti-tank mine (ATM) and anti-personnel mine (APM). Because of the variety of mine types, current mine detection techniques are diversified. The assumption is made that most mine detection techniques consist of sensor, signal processing, and decision processes. For the sensor part, ground penetration radar (GPR), infrared (IR), and ultrasound (US) sensors are reviewed and their characteristics are summarized for the corresponding output signals. For the signal processing and decision parts, a set of image processing techniques including filtering, enhancement, feature extraction, and segmentation are surveyed. Segmentation is used to extract mine signal from various competing signals. For most image processing techniques covered by this paper, mine detection related experimental results are included or reproduced from existing works.     

Features of applying complexly modulated signals in ultrasonic flaw detection

The use of complexly modulated signals during ultrasonic testing of articles with high integral ultrasonic attenuation is substantiated. On the basis of concepts of the optimal-filtering theory, phase-manipulated and frequency-modulated signals most suitable for ultrasonic testing are chosen and the main characteristics of various complexly modulated signals are analyzed. The advantage of using phase-manipulated and frequency-modulated signals in ultrasonic flaw detection for ensuring a high testing resolution and a high sensitivity is shown. It has been revealed that the application of state-of-the-art circuitry components allows the use of various properties of complexly modulated signals and creation of new ultrasonic methods and devices on this basis.     

Ultrasonic tomography of metal structures using the digitally focused antenna array method

Physical principles and algorithms for reconstructing images of the inner structure of an object made of a solid material are considered. These are based on the pulsed echo method of ultrasonic testing using multielement antenna arrays focused on each point of the visualized region of the object by spatiotemporal processing of signals from a combination sounding of the object by all possible pairs of the antenna array. Substantial improvement of the image during testing of a plane-parallel object is obtained by using signals that are multiply reflected from the object boundaries; the use of different algorithms of image reconstruction is expedient for different types of discontinuity flaws.     

Investigation of deep neural network with drop out for ultrasonic flaw classification in weldments

Ultrasonic signal classification of defects in weldment, in automatic fashion, is an active area of research and many pattern recognition approaches have been developed to classify ultrasonic signals correctly. However, most of the developed algorithms depend on some statistical or signal processing techniques to extract the suitable features for them. In this work, data driven approaches are used to train the neural network for defect classification without extracting any feature from ultrasonic signals. Firstly, the performance of single hidden layer neural network was evaluated as almost all the prior works have applied it for classification then its performance was compared with deep neural network with drop out regularization. The results demonstrate that given deep neural network architecture is more robust and the network can classify defects with high accuracy without extracting any feature from ultrasonic signals.     

相敏检波在空气耦合超声检测中的应用

空气耦合超声检测信噪比低、脉冲余振长,需要采用合适的信号处理技术增强接收信号的信噪比。根据空气耦合超声检测过程中影响接收信号的因素,提出先采用相敏检波技术对接收信号进行处理,获取相位信号,然后计算得到超声检测信息。介绍了超声检测中的超外差接收、相敏检波原理,并阐述了在超声检测应用中需注意的问题。根据分析研究结果,构建了相敏检波空气耦合超声检测系统,在常规超声检测系统的基础上进行了相应改造,实现了超声成像检测。碳纤维增强复合材料板的成像检测结果表明:相敏检波可以有效提高系统信噪比和检测效果。     

Ultrasonic testing of complexly structured cast-iron articles using a multifunctional software-hardware measuring system

Problems of ultrasonic noise-immune testing of complexly structured cast-iron articles are considered. It is shown that the extraction of informative echo signals from noise and interference requires, in addition to the fulfillment of optimal signal-filtering conditions, the use of flexible multifunctional equipment for ultrasonic testing that allows formation of various signals, flexible variation of their parameters, and application of numerous radio-engineering operations to signals for adapting the parameters of the instrumentation to the characteristics of a tested object.     

基于PCI总线的超声检测虚拟仪器系统设计

为了实现超声检测的数字化、智能化、图像化以及自动化,开发了一种基于PCI总线的超声检测虚拟仪器系统.系统以计算机为核心,利用FPGA强大逻辑处理能力,PCI总线高速数据传输功能,实现了超声检测信号的发射接收,采集处理,数据存储、显示和输出,并运用小波变换对超声信号进行了降噪处理.实验结果表明,小波变换对超声信号具有良好的滤波效果,该系统具有数据传输速度快,信噪比高、性价比高等优点,为缺陷信号的准确定量和定性分析奠定了良好的基础.     

Maximum kurtosis principle for the parameter selection of Gabor wavelet and its application to ultrasonic signal processing

The noise suppression techniques with wavelet transform (WT) are widely used in nondestructive testing and evaluation (NDT&E), especially in ultrasonics. But the wavelet based filter has the property of equal Q-factor, so, it is impossible to choose the central frequency and the bandwidth arbitrarily at the same time. This paper develops a new technique using WT to eliminate this drawback. In this paper, a weak ultrasonic signals identification method by using the optimal parameter Gabor wavelet transform is proposed. We address the choice of the optimal central frequency and bandwidth of the Gabor wavelet using the kurtosis maximization algorithm. The central frequency and bandwidth of the optimal parameter Gabor wavelet matched that of the ultrasonic signal very well. Numerical and experimental results have been presented to evaluate the effectiveness of the optimal parameter Gabor wavelet transform on ultrasonic flaw detection. This technique is a simpler and effective technique for processing heavy noised ultrasonic signals.     

Processing of Backscattered Signal in Ultrasonic Testing

A method for processing backscattered signals in the ultrasonic testing of thick-walled articles is proposed. The method is based on normalizing the intensity of recorded signal to the energy per one cycle from the moment of signal emission to the first reflected bottom signal. The method allows one to take account of the level of probing signal, the effect of the acoustic contact, the reception-path gain, and the damping of the propagating signal as well as produce the profile of the cross section of backscattering of ultrasound by the material along the signal propagation path. The backscattering cross-section profile provides a basis for identifying scattered damage in the bulk of the material. Results of experimental testing of the method are provided. A technique for determining the minimum gain required for the “correct” reception of backscattered signals has been developed.     

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.     

Application of super-resolution techniques to expert testing of welded joints in pipelines of nuclear power plants

Utilization of super-resolution techniques in processing reflected signals in ultrasonic testing has proved to be useful with a view to improve expert estimates of defect dimensions and shapes with the help of theAvgur holographic facility. In particular, the improvements in the image quality mostly due to athree-fold increase in the beam coordinate resolution has allowed more accurate determination of defect dimensions and more reliable classification of defects.A lower intensity of the speckle noise due to the broader frequency band can also be considered as a favorable feature of the extrapolation techniques. The signal-to-noise ratio in the images of flaws in materials with an intense structural noise isa factor of about 1.7 higher when super-resolution techniques are used. The paper describes some results of practical utilization of super-resolution techniques in estimating dimensions of flaws detected in welded joints of DU-300 pipelines (an effective diameter of 300 mm) of nuclear power plants.     

Ultrasound Imaging of Pipeline Crack Based on Composite Transducer Array

Cracks, especially small cracks are difficult to be detected in oil and gas transportation pipelines buried underground or covered with layers of material by using the traditional ultrasonic inspection techniques. Therefore, a new composite ultrasonic transducer array with three acoustic beam incidence modes is developed. The space model of the array is also established to obtain the defect reflection point location. And the crack ultrasound image is thus formed through a series of small cubical elements expanded around the point locations by using the projection of binarization values extracted from the received ultrasonic echo signals. Laboratory experiments are performed on a pipeline sample with different types of cracks to verify the effectiveness and performance of the proposed technique. From the image, the presence of small cracks can be clearly observed, in addition to the sizes and orientations of the cracks. The proposed technique can not only inspect common flaws, but also detect cracks with various orientations, which is helpful for defect evaluation in pipeline testing.     

Development of passive ultrasonic tomography techniques

Passive ultrasonic tomography is described. Results of developing, modeling, and testing some key techniques in passive ultrasonic tomography are provided. The techniques include an algorithm for determining arrival times of noisy acoustic signals with sloping leading edge; a method for determining the source coordinates and onset times of acoustic signals and estimating the accuracy of those; and regularizing procedures for tomographic reconstruction of nonuniform distributions of propagation speed of acoustic signals. The results of modeling the effect of measurement noises on the accuracy of source location and the mutual influence of the source location accuracy and the soughtfor nonuniform distribution of propagation speed of acoustic signals are described. Results of experimental testing of the developed techniques are also provided.     

应用微分算法处理特种管道测厚激光超声信号

为了实现特种管道在高温、高压、辐射等特殊环境下管壁厚度的非均匀性检测,提出一种基于微分算法的管道壁厚激光超声测量及特征信号处理方法。采用脉冲激光激励和激光干涉探测的激光超声方法,实验测得管道试件的宽频带激光超声信号。采用数字平均算法对宽带激光超声信号进行去噪处理,提高原始激光超声信号的信噪比。采用微分算法对激光超声信号进行特征提取处理,得到表征管壁厚度的激光超声特征信号。根据管道材料声速和激光超声传播时间反演计算得到管道试件的壁厚值,管壁厚度测量值与实际值的误差小于5%。研究表明,基于微分算法的管道壁厚激光超声测量及特征信号处理方法具有良好的信噪比、准确的信号特征量和较高的测量精度,可用于管道壁厚的在线实时检测以及因腐蚀、应力引起的管道壁厚不均匀性检测。