Ultrasonic Phased Array Industrial Imaging Research with Compressed Sensing

Defects in welds can affect the structural safety and reliability of workpieces. Currently, the method of using phased array ultrasonic inspection technology for non-destructive testing of weld structures with high detection efficiency, good sensitivity, and good visualization of the results is widely used. However, the defective A-scan data collected by the ultrasonic phased array detector inevitably contain noise data, including the test piece material structure noise, equipment noise, and environmental noise, which undoubtedly affects the analysis of the A-scan signal. In addition, when defects are interpreted, the presence of noise also interferes with the process, which affects the accuracy of the interpretation. Therefore, to enhance the accuracy of defect identification based on phased array ultrasonic inspection technology, we must prevent the series of consequences caused by misjudgments. In this study, ultrasonic phased array inspection experiments were carried out, and the specific process flow of ultrasonic phased array inspection of flat plate butt welds was summarized. Utilizing pre-fabricated flat plate butt specimen blocks containing five types of typical defects, defect A-sweep signals based on ultrasonic phased array inspection were obtained. Combining the sparrow optimization algorithm (SSA), variational mode decomposition (VMD), and wavelet packet decomposition (WPD), a defect signal noise reduction method based on parameter optimization was studied. A noise reduction study was carried out using the noise-added simulated signal, and the results indicated that the noise reduction method proposed in this paper had a better noise reduction effect and the proposed method could effectively retain the detailed features of the ultrasonic phased array defective A-scan signal and realize the noise reduction processing of the defective A-scan signal.

With the development of ultrasonic technology, ultrasonic wave plays an increasingly important role in the field of nondestructive testing. Among all kinds of ultrasonic nondestructive testing technologie, ultrasonic phased array is widely used because of its high accuracy and flexibility. However, due to the existence of rayleigh limit, ordinary ultrasonic phased array technology cannot recover the space frequency greater than 2K, so it is impossible to achieve the resolution less than half of the wavelength of the super-resolution. In this paper, we introduce a method to realize super resolution imaging in multi-band phased array.In this method, the damage is detected by multiple phased arrays, and the received signals are processed by specific algorithms to obtain super-resolution imaging. The signal is excited by M exciter and then received by N receiver. The total signal can form an M*N matrix. After singular value decomposition of the collected signal matrix,T significant eigenvalues can be obtained. The T significant eigenvalues represent the number of injuries. The singular vector after singular value decomposition contains the information of noise space. The number of eigenvalues in the signal space is the number of damage. Using the randomness of noise subspace, special algorithm can be used to restore the spatial frequency greater than 2K to achieve super-resolution imaging.The more elements in this method, the more accurate and complicated it is. As long as the smallest value of M and N is greater than the number of injuries, each injury can be successfully distinguished under super resolution. Therefore, the appropriate number of matrix elements should be selected for different damages.

The recently proposed compressive sensing (CS) theory provides a new solution for multiple description coding (MDC) with fine granularity, by treating each random CS measurement as a description. The performance of CS-based MDC (CS-MDC) depends on the efficacy of the CS recovery algorithm. Existing CS recovery algorithms recover the signal in a fixed space (e.g., Wavelet, DCT, and gradient spaces) for the entire duration of the signal, even though a typical multimedia signal exhibits sparsity in time/space variant spaces. To rectify this problem and develop a better CS recovery algorithm for CSMDC, we propose a learning-based framework to conduct the CS recovery in locally adaptive spaces, and carry out a case study on image MDC. A set of prior image models are learned offline from a training set to facilitate the CS recovery in local adaptive bases. Experiments show that the learning-based CS recovery algorithm can significantly improve the performance of the previous CS-MDC technique in both PSNR and visual quality.

Ultrasonic phased array techniques are widely used for defect detection in structural health monitoring field. The increase in the element number, however, leads to larger amounts of data acquired and processed. Recently developed compressive sensing states that sparse signals may be accurately recovered from far fewer measurements, suggesting the possibility of breaking through the sampling limit of the Nyquist theorem. In light of this significant advantage, the novel use of the compressive sensing methodology for ultrasonic phased array in defect detection is proposed in this work. Based on CIVA software, we first present a simulated study on the effectiveness of the compressive sensing applied in ultrasonic phased array in defect detection through the average mean percent residual difference at varying compression rates. The results particularly show that the compressive sensing yields a breakthrough of the sampling limitation. We then experimentally demonstrate comparative analyses on the signals extracted from three types of artificial flaws (through-hole, flat-bottom hole, and electrical discharge machining notches) on two different specimens (made of aluminum and 20# steel). To find the optimal algorithm combination, the best sparse representation basis is chosen among fast Fourier transform, discrete cosine transform, and 34 wavelet kernels; the reconstruction performance is compared between five greedy algorithms; and the recovery accuracy is further improved via four sensing matrices selection. We also evaluate the influence of the sampling rate, and our results are comparable with the gold standard of signal compression, namely, the discrete wavelet transform.

This paper analyzes and compares the characteristics of conventional nondestructive testing method and ultrasonic phased array testing method, and introduces several ultrasonic phased array testing methods of power grid equipment. Ultrasonic phased array technology is a high-efficiency, intuitive and reliable new nondestructive testing technology. It is of great significance to apply ultrasonic phased array technology to the nondestructive testing of power industry equipment and explore the adaptability of its testing technology to ensure the reliable operation of equipment and the security of power grid.

Welding seams are prone to safety accidents and failures during actual operation, which has an adverse effect on the economic benefits of the enterprise. When using traditional ultrasonic inspection methods to inspect the pipe butt welds, the staff needs to use the inspection probe to move as needed, which makes the inspection process difficult to operate and is greatly affected by human factors. The beam of conventional ultrasound cannot be deflected and focused. It is difficult to detect parts with complex geometric shapes and large anisotropic welds. Ultrasonic phased array is a new type of non-destructive testing method, which makes up for the limitations of conventional ultrasonic testing, and has great advantages compared with conventional ultrasound. Therefore, in order to reduce the misjudgment of defects caused by humans, this paper studies the application method of ultrasonic phased array technology in weld inspection, discusses the principles and characteristics of ultrasonic phased array inspection technology in nondestructive testing, and the defects were tested. The test results show that the phased array technology can effectively detect weld defects.

Single‐element scanning techniques are widely used in the NDT industry and have seen a number of successful applications. They require moving the sensor in time‐consuming raster scan to create two‐dimensional scan patterns and several transducers are required to focus at different levels in the inspected material. However, phased array technology is an emerging NDI technology which offers means to focus the ultrasonic beam at different locations and steer it to reach defects at hidden parts in complex structures, hence, substantially reducing the scanning time and simplifying the scanning pattern by scanning electronically in milliseconds instead of scanning mechanically in a few seconds. The motivation of this work is to investigate and compare electronic and SAFT (synthetic focusing) of the ultrasonic waves using linear phased array transducers. Experimental tests were done on an aluminum block with side‐drilled holes to simulate defects. Reduction of calculation time for the SAFT algorithm was achieved using beam width limitation. Experimental SAFT results and results from phased array system were compared. Practical SAFT advantages and limitations are then highlighted and requirements for better performance are discussed.

Three-dimensional (3D) ultrasonic imaging enables the viewing of internal features in a more accurate way than cross-sectional imaging. 3D imaging requires two-dimensional (2D) ultrasonic phased arrays to resolve all three spatial dimensions through beamforming along azimuthal and elevation angles. 2D phased arrays pose a manufacturing and control challenge due to the requirement of large number of elements to satisfy the Nyquist sampling limit. This problem can be alleviated through the use of sparse ultrasonic array designs. The optimization process is critical, as this dictates the efficiency of suppression of grating lobes. The aim of this work is to establish a framework for design of optimized sparse 2D phased arrays. This is enabled by exploiting the reconfigurability of Laser Induced Phased Arrays (LIPAs). LIPAs are synthetic arrays produced by scanning one laser for ultrasound generation and another for ultrasound detection, independently of each other. The reconfigurability and decoupled ultrasonic generation and detection of this systems enables easy and fast implementation of any arbitrary array layout. The framework consists of an analytical model for parametric evaluation of designs. The model performs a parametric sweep on the generation and detection element positions for each array design in order to identify the optimal parameters, based on mean and maximum side-lobe level. In the presented framework, four array designs are utilized for the optimization process: matrix, random, Vernier and a novel array design the Rotated Array (RA).

Ultrasonic phased array has the functions of ultrasonic array, 3D imaging, and defect multi-signal characterization. However, there are problems in current detection such as effective parameter setting and inconsistent identification standards for defect characteristic signals. Based on the principle of ultrasonic phased array imaging, the experimental research on the setting of effective parameters for concrete cavity defect detection is carried out in this paper. The results show that the selection of wave velocity and frequency is the key factor to improve the accuracy of 3D imaging. For 20mm concrete cavity, when the frequency is less than 25kHz, the system cannot detect defects. When the working frequency is increased to 45KHZ, the defect imaging accuracy is gradually improved. When the frequency is increased to 60kHZ, the detection accuracy is reduced. The ultrasonic shear wave velocity is in direct proportion to the detection imaging depth. When the difference between the actual wave velocity and the set wave velocity is 10%, the influence of the detection imaging depth is small. When the difference between the actual wave velocity and the set wave velocity is greater than 20%, the detection imaging depth has a great impact, and the difference between the defect position and the actual value is too large, which may cause the system to be unable to detect the existence of defects.

Focal laws fast calculation is one of the key technologies in ultrasonic phased array (UPA). To improve the real-time of the focal laws applied in the UPA. In the paper, we designed a focal laws calculator by FPGA technology to calculate the time delays for the ultrasonic waves between multi-element ultrasonic sensors attached a wedge and the focus to realize the beam focusing. Allowing the time delays are associated with a series of one-element higher-order equations. And n-time interval search and CORDIC algorithm are further presented for solving the equations to calculate the time delays in real time. Experiments show that the n(n=12)-time interval search and CORDIC algorithm to calculate the focal laws can achieve a maximum relative error value of 0.434% by FPGA technology. The real-time and validity of the focal laws calculator are proved through application of the UPA, which is of great importance significances in engineering application.

In this paper, channel overhead is reduced by exploiting channel sparsity for multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) system. Where, compressive sensing (CS) based dictionary design algorithms has been adopted as a channel estimation technique in high mobile systems with minimal number of pilots, such as high-speed train (HST) systems. A novel framework design of the dictionary-based CS was proposed considering both delay and Doppler effects in order to correctly recover the channel response. The channel under consideration is a 2 by 2 space-time block code (STBC) MIMO channel. Simulation tests according to the international telecommunication union (ITU) channel model demonstrated the suitability of the proposed dictionary for estimating the channel impulse response (CIR) of a liner time varying (LTV) channel with a mobility approaches 675 Km/h related to a Doppler frequency of 1500 Hz and 2.4 GHz carrier frequency. Two CS recovery algorithms were applied; orthogonal matching pursuit (OMP) and basis pursuit (BP), where by about 7 dB gain in signal to noise ratio (SNR) was achieved with mobility of 675 Km/h using OMP as compared to BP at a bit error rate (BER) of with 128 OFDM subcarriers.

The influence of the grain structure of titanium alloys, used for additive manufacturing (AM), on the propagation of ultrasonic beams is of great significance for the non-destructive testing of components manufactured from this material. In order to explore the issues related to ultrasonic testing, such as low signal-to-noise ratio (SNR) and large imaging error of internal defects, an ultrasonic phased array C-scan image was obtained and the measurements of ultrasonic noise level and defect distortion caused by columnar crystals were analysed. Ultrasonic wave theory was combined with the Voronoi algorithm to establish a finite element (FE) model of the AM titanium alloy with a columnar crystal structure. The focusing and scattering of ultrasonic beams in different grain structures was studied and the defect echo signals from the FE model and the experimental results were extracted and compared. Comparisons of the signal-to-noise ratio and the background noise of three typical sections were in good agreement, which shows that the proposed simulation model can be used to analyse the propagation and scattering of beams for the inspection of AM titanium alloys. Finally, suggestions to improve the ultrasonic detection results of AM titanium alloy components and the applicability of the wave simulation model for other polycrystalline materials are discussed.

With the increasing use of high-density polyethylene (HDPE) piping for nuclear applications, nondestructive evaluation is an important tool for evaluation of the integrity in fused joints. This paper will discuss the method of using ultrasonic phased array for inspecting butt-fusion (BF) joints in HDPE piping. The benefit of phased array is the ability to perform a volumetric inspection using multiple angles, which greatly increases the probability of detection of defects and allows the data to be analyzed using a representative two-dimensional image of the joint. It has been determined that successfully producing BF joints is highly dependent on environmental and mating-surface conditions. The primary defects of concern are lack-of-fusion, an area of the joint where there is no bond, cold fusion, an area of partial bond, and inclusion. Phased array has successfully demonstrated the ability of detecting and characterizing these defects using low frequency ultrasound. Factors addressed include joint location, wall thickness, material temperature, transducer wedge material, and manual versus automated data acquisition.

Ultrasonic phased arrays are well suited to weld inspections. Phased arrays can perform electronic scanning (where a scan pattern is rapidly multiplexed across a component), sectorial scanning (where the angle of inspection is varied), and combinations of these two. Electronic scanning increases inspection speed using linear scanning, while sectorial sweeping permits the beams to be precisely targeted at selected portions of the welds. The combination permits customized, high speed scans, which create high quality, tailored inspections. This paper describes some of the weld inspections using phased arrays.

The article deals with the internal defects identification and characterization in butt weld joints by non-destructive ultrasonic Phased Array and X-ray technique. Basics of ultrasonic and X-ray testing are described in the theoretical part of manuscript. Phased Array and X-ray technique are volume nondestructive methods that can detect internal defects without breaking of construction. Ultrasonic Phased array and X-ray test procedures and test results obtained in non-destructive testing of butt weld are shown in experimental part. Ultrasonic record, X-ray record and weld macrostructure are given for each identified weld deffect. Advantages and disadvantages as well as comparison of ultrasonic and X-ray testing resulting from experimental measurements are described in the end of this article.