A Method for Scanning the Internal Structure of an Object by a Synthesized Aperture using a Doppler Signal

A method for constructing the image of an object from a Doppler signal reflected by the object using a synthesized antenna aperture is proposed. The technique is based on the known property of a synthesized aperture to focus to a certain range. Cartograms of the objects reconstructed by using Doppler signals are presented.     

Determination of the reflector type from an image reconstructed using echo signals measured with ultrasonic antenna arrays

The application of the digital image focusing (DFA) method to the determination of the types of detected reflectors is considered. For this purpose two antenna arrays (AAs) are used, which are placed on opposite sides of the reflector and using which echo signals are recorded in three acoustic channels in the double-scanning mode. The first and second acoustic channels transmit and receive echo signals using the first and second AA, respectively, and the third channel is tuned so that the first AA transmits pulses and the second AA receives echo signals. Using signals in each channel, many partial images can be reconstructed in a common coordinate system according to different acoustic schemes with allowance for both multiple reflections from irregular boundaries of a tested object and effects of transformation of the wave types. Combining partial images makes it possible to obtain a high-quality image, in which the entire boundary of the reflector is seen and using which an attempt to automate the procedure of evaluating the reflector size and determining its type was made. Such an approach allows one to reduce the subjective influence of an operator on the testing results. It is shown that in order to increase the image resolution, the spectrum of echo signals can be extrapolated by the spectrum splitting method jointly with the construction of an AR model of their spectrum. The results of model experiments that confirm the possibility of determining the reflector type are presented.     

Increasing the signal-to-noise ratio in ultrasonic testing of repair welds using the technology of thinned antenna arrays

To test objects of materials with a high level of structural noise, use of thinned antenna arrays (TAAs) that have a large spatial aperture and consist of a small number of elements that are positioned from one another at a distance larger than the wavelength is proposed. A TAA moves over the surface of a tested object and echo signals are recorded during transmission and reception by different pairs of piezoelectric plates. For each transmitter-receiver pair, the measured echo signals are used to reconstruct partial images, which are then coherently added together to form the final image, by the SAFT method. A procedure for calibrating each piezoelectric plate of the TAA in order to determine the coordinates of its center for efficient coherent summation of partial images has been developed. The calibration procedure reduces the requirements for the accuracy of the arrangement of the piezoelectric plates of the TAA on a prism. The use of the technology of TAAs allows one to obtain images of flaws in repair welds with a signal-to-noise ratio (SNR) that is 12 dB higher than the SNR for an image obtained using the technique for a single-element transducer. The results of testing specimens of 800 pipelines with repair welds in weld seams are presented. The efficiency of this method is shown in comparison to the method in which a single-element piezoelectric transducer is used.     

Automated Acquisition and Processing of 3D GPR Data for Object Detection and Characterization

To improve image resolution of GPR data, proper data acquisition is the first key part of the whole imaging sequence. Obtainable down and cross range resolutions, insofar as they are related to acquisition, are determined by the frequency bandwidth of the GPR equipment, the temporal and spatial sampling rates and the accurate knowledge of the antenna positions. The key parameters for three-dimensional imaging algorithms are wave velocity distribution in the domain of interest, radiation (polarization and amplitude) characteristics of the antenna system and emitted waveform. To this end we have designed and manufactured a measurement frame with high horizontal position accuracy of the antennas, by using a servomotor that automatically moves the antennas over the whole area of the measurement frame for a fixed vertical position of the antennas. When acquisition is completed, the data needs to be processed such that object detection and characterization is most easily accomplished. In most cases, object detection can be carried out on the preprocessed data itself, but in some cases and certainly for characterization purposes improved image resolution is required. This is realized using imaging algorithms, preferably those that take into account the polarization and amplitude characteristics of the antennas.Now with Shell International Exploration and Production B.V.     

Comparison of systems for ultrasonic nondestructive testing using antenna arrays or phased antenna arrays

This paper considers the features of forming the images of reflectors using phased antenna array technology and the images obtained by the C-SAFT method by echo signals measured in by double-scanning mode. It is shown that in some cases the images obtained by the phased antenna array technology are less informative, while the images obtained by the C-SAFT method have a higher frontal resolution over the entire area of image restoration; the partial images restored at different positions of the antenna array can be coherently combined to obtain a high and homogeneous resolution throughout the entire volume of thickwalled articles and increasing the signal/noise ratio. For the sake of brevity, the registration of echo signals in the double-scanning mode and restoration of the images of reflectors by the C-SAFT method will be called digital focusing by an antenna array (DFA). The ability to restore the partial images of reflectors by once measured echo signals according to many acoustic schemes with their consequent combination into one high-quality image should provide reliable automation of the process of recognition and dimensioning of scatterers. Another advantage of the images obtained by the C-SAFT method with three-dimensional focusing is the possibility of restoring images in the same coordinate system when using antenna arrays on prisms of different configurations. This facilitates the joint analysis of the images. Speeds of forming the images by the technology of phased-antenna arrays and the images obtained by the C-SAFT method are comparable. If the testing technique is based on the use of nonlinear effects, then in this case PA flaw detectors have a distinct advantage over DFA flaw detectors. However, within the framework of linear acoustics, PA flaw detectors have no fundamental advantages over DFA flaw detectors. It is fairer to say that PA flaw detectors have drawbacks. This article shows images that illustrate the features of the images that were obtained by PA and DFA flaw detectors.     

Ultrasonic control of welded joints in a Du800-type pipeline. Part I: Restoring reflector images by digital focusing with an antenna

The reliability of ultrasonic nondestructive testing can be improved by acquiring reflector images that can be used to solve the defectometry problem, that is, to determine the type, size, and coordinates of a reflector deep in the sample. Welded pipelines with a diameter of 840 mm (Du800 type) are used at nuclear power facilities in Russia; ultrasonic testing of these pipelines is thus a topical problem. In model experiments, echo signals were registered by two antenna arrays, situated on the opposite sides of a welded joint (the N- and P-sides). The arrays performed scanning along and across the welded joint. The following techniques were used to reconstruct reflector images by the DFA method in a homogeneous isotropic medium: registering echo signals for all emission–reception combinations of elements in the two antenna arrays with the aim of merging partial images into a single image by different methods; reconstructing images on different acoustic schemes with allowance for wave-type transformation; and registering echo signals in a triple-scanning mode with subsequent coherent summation of partial images. It has been shown that the above techniques are insufficient for producing high-quality images.     

Application of an ultrasonic antenna array for registering echo signals by the double-scanning method for obtaining flaw images

The prospects for applying the double-scanning mode in ultrasonic nondestructive testing for recording echo signals are considered. A variant of implementing the double-scanning mode using a phased antenna array is proposed. Algorithms for reconstructing flaw images by the method of projection in the spectral space and the combined SAFT (C-SAFT) method are presented. It is shown that, to obtain high-quality flaw images, the ultrasound propagation velocity in a tested object must be known to within a high accuracy (at least 0.5%). The results of numerical and model experiments in which images were obtained by these methods are presented.     

Obtaining flaw images that take the effect of multiple ultrasonic pulse reflections from the boundaries of a test object into account

The problem of obtaining flaw images from echo signals multiply reflected from the boundaries of a test object and modifications of the FT-SAFT and SAFT algorithms for obtaining flaw images in a test object with plane-parallel boundaries are considered. The reason that a transducer operating on transverse waves in the transceiver mode cannot yield information on flaw location depth is stated. It is shown that the detecting signals in the double-scanning mode, obtaining a set of partial images by the SAFT method, and combining them into a final image allow one to solve this problem. To obtain a combined image, the moduli of partial images were summed and their median was calculated. Because of difficulties in determining the velocity of sound and the thickness of a particular object, the coherent summation, which is potentially the most efficient combining technique among the considered ones, does not allow one to obtain a high-quality image. The results of a numerical simulation of the procedure of obtaining images of point defects are presented. The results of model experiments aimed at obtaining an image of a 1-mm-deep groove in a 20-mm-thick metal slab are presented as well. It is shown that measuring echo signals in the double-scanning mode and obtaining images by the DS-M-SAFT method make it possible to determine the flaw location depth.     

Estimating the object image velocity against background

Synthesis and analysis of maximum likelihood algorithms for estimating the velocity of a spatially extended object image under different contents of a priori information on the background and object image intensities are carried out. The efficiency of the algorithms and the scope of applicability of the found asymptotical expressions for the velocity estimate characteristics are determined by statistical computer modeling.     

Features of applying the method of focusing to a point in ultrasonic testing of products manufactured from complexly structured materials

The well-known method of focusing ultrasonic signals to a point implemented using phased antenna arrays is considered as applied to problems of tomography of products manufactured from complexly structured materials. The features of applying broadband ultrasonic complexly modulated signals in phased antenna arrays and the limits of applicability of this method in constructing an image of a reflecting surface are discussed.     

The use of an ultrasonic flaw detector with a phased antenna array for the recording of echo signals to reconstruct the images of reflectors by the method of projection in the spectral space

A method of automated ultrasonic testing based on the use of a PAA flaw detector for the recording of echo signals followed by the reconstruction of the image of reflectors by applying the 3D variant of the method of projection in the spectral space (3D-PSS) is considered. Customized setting of the PAA flaw detector makes it possible to simulate the operation of many single-element transducers with different angles of incidence. This approach allows one to obtain the images of reflectors with a high resolution and a high signal-to-noise ratio at a depth of more than 100 mm. A procedure for the calibration of an antenna array on a prism operating in the mode of emulation of several piezoelectric transducers with different angles of incidence is discussed. The results of a testing a fragment of the support billet for the ITER diverter when obtaining the images by the classical PAA method and with the use of 3D processing, which demonstrate the efficiency of the developed testing technology, are presented.     

Ultrasonic testing on a singly reflected beam using sparse antenna arrays and 3D echo-signal processing

Testing of welded joints in the main shutoff valves (MSVs) of the first circuit of a ВВЭР-440 reactor plant is impeded due to the high structural-noise level and the necessity of using pulses that are singly reflected from the tilted bottom of a branch pipe. Testing on a longitudinal wave leads to the appearance of false reflections, which are formed by pulses at a transverse wave, in the reconstructed image. Since the amplitude of false reflections can be commensurable with the amplitude of reflections that were obtained at longitudinal waves, the analysis of such images may be hampered. To increase the quality of an image, it is proposed to record echo signals using sparse antenna arrays and use 3D processing of echo signals. Numerical and model experiments showed that this approach increases the frontal resolution in the additional plane by several times and reduces the amplitude of false reflections, thus making it possible to increase the sensitivity and reliability of expert ultrasonic testing of the principal shutoff valve.     

Reducing the Level of Weakly Changing Noise by the Decorrelation Method during Ultrasonic Monitoring Using Antenna Arrays

Russian Journal of Nondestructive Testing - In ultrasonic testing with antenna arrays, the measured echo signals may contain interference echo signals that, after reconstructing the image of...     

Determining the flaw type from images obtained by the C-SAFT method with account for transformations of wave types upon reflections of ultrasonic pulses from the irregular boundaries of a test object

The application of antenna arrays (AAs) for obtaining flaw images during automated non-destructive testing is considered. The conventional technique of using an AA as a phased AA has a number of drawbacks. An alternative approach is proposed in which echo signals are registered using an AA operating in the double scanning mode, and a modified algorithm of the combined SAFT, which takes into account multiray ultrasound propagation with consideration of transformations of wave types upon reflections from irregular boundaries of a test object, is used to obtain flaw images. The results of testing a specimen with a model of a volumetric flaw in the form of a 2-mm-diameter side hole drilled at a depth of 12 mm and a specimen with a crack model with a tip at a 12-mm depth are presented. Both specimens have rough bottoms. The obtained images allow determination of not only the dimensions and locations of flaws, but also their type.     

机器人抓取对象硬度触觉感知研究

物体硬度感知对于机器人进行物体灵巧操作具有重要意义。针对物体硬度感知中传感信号复杂、物体压缩量大而导致的系统鲁棒性差以及容易损伤物体的问题,提出了一种基于触觉传感的机器人抓取对象硬度感知方法。该方法使用两指夹持器轻微挤压物体,通过安装在两指指尖的柔性触觉传感器阵列采集压力序列信号。将压力序列信号进行多项式处理得到非线性特征序列,使用基于决策树的Adaboost算法处理非线性特征序列,实现抓取物体在线硬度等级分类。将基于决策树的Adaboost算法和其他各种算法进行比较,并进行实际物体硬度识别实验。实验结果表明所提方法能够准确实时识别不同抓取对象的硬度。     

Nonlinear signal processing techniques in ultrasonic tomography of concrete structures

Questions of using various techniques for processing echo signals in ultrasonic tomography instruments for extended complexly structured concrete articles are considered. Various algorithms are discussed for constructing tomograms of tested articles, techniques for radio engineering processing of ultrasonic signals, and different variants of nonlinear image transformations intended for increasing the signal-to-structural noise ratio and improving image quality.     

一种新型旋转体信号测量方法的研究

通过利用环形泄漏缝隙天线阵 ,对安装在旋转体表面的声表面波传感器施加激励 ,经偶极子天线耦合后作为传感器的激励源 ,产生的测量信号由外置环形缝隙天线阵接收 ,从而建立起一种天线耦合测量模型 ,解决了旋转体信号无线、无源、持续测量的难题     

Reconstruction of flaw images by the C-SAFT method from echo signals measured by an antenna array in the triple-scanning mode

The application of antenna matrices (AMs) for obtaining flaw images during automated nondestructive ultrasonic testing is considered. The conventional technique of using an AM as a phased AM (PAM) has a number of drawbacks. One of them is related to the small number of AM elements and consists in a low frontal resolution of the thus-formed images. Scanning with an AM operating in the double scanning mode, viz., the so-called triple-scanning mode, allows coherent summation of partial images for each position and obtaining a resulting image with a frontal resolution that cannot be attained with a PAM. In order to test the serviceability of the proposed algorithm in the CIVA program, echo signals reflected from a crack model with a height of 6 mm and a length of 30 mm in a tested object, which simulated a welded joint of a pipeline with a conventional diameter of 800 mm (дy800), were calculated. The results of the reconstruction of images of model objects in the form of a drilled side hole with a diameter of 6 mm at a depth of 15 mm in a CO-2 specimen and a fatigue crack in a welded joint of a д y800 pipeline are presented. To reduce the influence of reverberation noise, a B-type median template was subtracted from echo signals. The flaw images that were reconstructed in numerical and model experiments demonstrate the efficiency of the proposed algorithm.     

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.     

图像增强技术在超声成像检测中的应用

研究图像增强技术在粗晶材料超声成像检测中的应用。为了克服粗晶材料检测时噪声对成像质量的影响 ,利用中值滤波的快速算法和小波变换的分解重构算法来降低噪声的干扰 ,提高超声图像增强技术的实用性。实验结果表明 :在粗晶材料超声成像检测时采用这两种算法能够得到高质量的超声检测图像