Wave-based Tomographic Reconstruction for Enhanced Ultrasonic Phased Array Imaging

Discretized tensor-based model of total focusing method: A sparse regularization approach for enhanced ultrasonic phased array imaging

The application of total focusing method (TFM) for imaging of Carbon fiber reinforced plastics (CFRP) with ultrasonic phased array is particularly challenging due to the layered structure and anisotropy of CFRP. To improve the TFM imaging performance, the precise knowledge of complex ultrasonic paths in anisotropic CFRP laminates should be obtained for accurate calculation of time of flights (TOFs), which makes the inspection process complicated and time-consuming. In this work, an adaptive TFM is developed for full-matrix imaging of CFRP laminates using ultrasonic phased array. Based on the acquired full matrix data, the elastic constants, including C 11, C 22, C 55, and C 13, can be directly derived using TOFs of A-scan signals. Based on the measured elastic constants, group velocity profiles of quasi-pressure (QP) wave were then calculated for different stacking sequences, from which the TOFs were corrected. To verify the effectiveness of proposed method, simulations and experiments are demonstrated on the CFRP laminates with different stacking sequences. As a representative example, the delamination defects are showcased. Compared with isotropic TFM, the SNR of proposed method is increased by 10.2-18.0 dB. The simulated and experimental results agreed well with each other, indicating that the feasibility of proposed method in full matrix imaging of anisotropic CFRPs.

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.

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.

The marriage of welding and Non-Destructive Testing (NDT) processes at the point of manufacture has enabled the detection and correction of defects during the welding process. This has demonstrated clear financial and production benefits by reducing weld rework and ensuring schedule certainty, however this is yet to be demonstrated for use with narrow-groove welding practises. Narrow-groove welds are notoriously difficult to inspect using traditional Phased Array Ultrasonic Testing (PAUT) techniques due to large thicknesses and the vertical nature of Lack-of-Sidewall Fusion (LOSWF) defects. This is further complicated by the presence of partially-filled weld geometries during in-process inspection, which cause geometric reflections which can mask or falsely indicate the presence of a defect. A solution to this is proposed in this work, by adapting a dual-tandem phased array imaging system for the imaging of LOSWF defects in a partial weld geometry. This considers a two array system utilising a phased array probe on each weld side, coupled with an advanced dual-aperture Full Matrix Capture (FMC) acquisition technique. Advanced multi-mode image processing algorithms such as the Total Focusing Method (TFM) and Phase Coherence Imaging (PCI), with adaptive delay law calculation, have shown high sensitivity to LOSWF defects in a mock partial weld geometry. Additionally, an adaptive Probe Centre Spacing (PCS) technique is defined for in-process inspection based on amplitude and phase coherence sensitivity in partial weld geometries, with the effects of partial weld reflections analysed and discussed. These results have demonstrated the effectiveness of a dual-tandem phased array approach to imagine LOSWF defects during the in-process inspection of narrow-gap welds.

Ultrasonic defect detection of high-density polyethylene pipe materials using FIR filtering and block-wise singular value decomposition

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.

Ultrasonic arrays are increasingly widely used in nondestructive evaluation (NDE) due to their greater flexibility and potentially superior performance compared to conventional monolithic probes. The characterization of small defects remains a challenge for NDE and is of great importance for determining the impact of a defect on the integrity of a structure. In this paper, a technique for characterizing reflectors with subwavelength dimensions is described. This is achieved by post-processing the complete data set of time traces obtained from an ultrasonic array using two algorithms. The first algorithm is used to obtain information about reflector orientation and the second algorithm is used to distinguish between point-like reflectors that reflect uniformly in all directions and specular reflectors that have distinct orientations. Experimental results are presented using a commercial 64-element, 5-MHZ array on two aluminum test specimens that contain a number of machined slots and side-drilled holes. The results show that the orientation of 1-mm-long slots can be determined to within a few degrees and that the signals from 1-mm-long slots can be distinguished from that from a 1-mm-diameter circular hole. Techniques for quantifying both the orientation and the specularity of measured signals are presented and the effect of processing parameters on the accuracy of results is discussed.

An ultrasonic phased array imaging system is provided which includes a normal mode and an adaptive mode of operation. The adaptive mode adjusts the delay associated with each element in the transducer such that the average image brightness of the region of interest is maximized. A motion detector is provided for determining when the transducer has been moved a distance sufficient to render the previous adaptive measurements possibly invalid whereupon the system automatically reenters the normal mode. A method of operating the ultrasonic phased array imaging system is also provided.

this study presents an eight array ultrasonic signal phased array sparse sampling experiment system based ultrasonic phased array technology and Compressed Sensing (CS). Proposed system considers recovery ultrasonic beam signal received eight phased array elements with sparse samples captured using sub-Nyquist model in CS recovery algorithm. We have the block defect detection test in the system. The test result approximated the actual block defect position. Based on block defect detection test, We compared sparse sampling value using spectrum estimation to Compressed Sensing recovery algorithm imaging, and no focus and focus detection effect, proved the phased array experiment system based on Compressed Sensing .it can greatly improve the detection signal to noise ratio (SNR) and sensitivity. So we verify the phased array focus can improve the detection ability.

Phased array ultrasonic total focusing method (TFM) imaging has attracted much attention due to its high detection image resolution and large dynamic range. However, due to the small emission energy of its single element, the echo signal is weak and susceptible to noise interference, resulting in a relatively low signal-to-noise ratio (SNR). Especially when detecting high sound attenuation carbon fiber reinforced polymer (CFRP) composites, the signal amplitude can decrease with depth to a level lower than the electronic noise introduced by the signal acquisition system. To solve this problem, a new imaging algorithm was proposed that combines the Golay code excitation using linear frequency modulation (LFM) signal as the carrier with the TFM algorithm (LFM-Golay TFM). Meanwhile, in order to further overcome the disadvantage of the LFM-Golay code encoding excitation method requiring two excitations, an AB code encoding excitation conversion factor was introduced, two sets of echo data were obtained through processing single excitation, TFM imaging based on LFM-Golay code single excitation (IMP-LFM-Golay TFM) is realized. Simulation and experimental studies were conducted to compare the TFM imaging performance of single-pulse excitation (Pulse TFM), Barker coding excitation (Barker TFM), LFM excitation (LFM TFM), and improved LFM-Golay coding excitation. The results show that IMP-LFM-Golay TFM has the best SNR, axial resolution, and depth resolution.

Low-frequency ultrasonic array imaging for detecting concrete structural defects in blind zones

<p>key components of large industrial equipment for manufacturing need regular maintenance. The health state<br> of these components are evaluated during maintenance, then future maintenance plan is continuously updated according<br> to the latest health state. However, the health state of some components is difficult to evaluate since internal flaws are<br> invisible and cannot be detected with passive inspection methods. Ultrasonic testing (UT) is an active non-destructive<br> testing(NDT) method to inspect internal defects. But the use of UT in maintenance for machinery in manufacturing<br> industry is limited due to the limited quality of result, i.e., the depth of inspection is limited, the resolution is not<br> sufficient, and the complicated defects are difficult to interpret from 2D images. To overcome these problems, a<br> multi-element synthetic aperture focusing technique (SAFT) algorithm with filtering and a novel weighting factor with<br> linear array is studied. It can improve the quality of conventional ultrasonic non-destructive testing (UNDT) and prepare for future 3D model reconstruction. In the proposed algorithm, filters are implemented to denoise the acquired images, weighting factor can make the acquired image more balanced comparing to conventional algorithm, which simply sums received signal from all receiving elements at each pixel. The proposed algorithm is simulated using FIELD Ⅱ in Matlab software and compared with single-element, multi-element SAFT and total focusing method (TFM) algorithms. An aluminium specimen is used as the simulation object. The results show that the proposed algorithm has clearer boundaries of defects, better contrast resolution (CR), contrast-to-noise ratio (CNR) and better overall result of the acquired image. The computational complexity of the proposed algorithm is higher than single element SAFT but lower than TFM. In the future study, 3D reconstruction of defective components can be implemented based on the results of this study.</p>

As a critical structural component within pressure vessels, weld can be frequently found with harmful defects during service, such as microcracks with different orientations. Therefore, regular inspections of welds from pressure equipment are very important. Compared to traditional ultrasonic NDT, ultrasonic phased array total focusing method is a new postprocessing imaging method that is more accurate for defect localization. The inspection of defects in the weld often necessitates prior knowledge to scan multiple times using different inspection surfaces and angles to increase detection coverage, which is time-consuming and labor-intensive. In this study, a multi-mode ultrasonic phased array total focusing method (TFM) for crack-like defects with different orientation is proposed, and the multi-mode imaging method is applied to the inspection of butt welds and fillet welds to achieve effective and quantitative detection of defects in different orientations. In addition, according to the actual size of the detection object, the sound beam incident state and imaging parameters are calculated based on intelligent algorithms, and the optimum imaging view is selected. As a result, a multi-mode imaging method that can comprehensively cover the weld area is obtained. Experimental results show that the multi-view method delivers different sensitivity to different defect orientations, which can better suppress noise than single-view imaging, and improve the probability of detection for crack-like defect.

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.