Noncontact pulsed laser-scanning laser Doppler vibrometer (PL-SLDV) phased array imaging for damage detection in composites.

Guided wave phased array beamforming and imaging in composite plates

This paper presents the phased array beamforming and imaging using guided waves in anisotropic composite laminates. A generic phased array beamforming formula is presented, based on the classic delay-and-sum principle. The generic formula considers direction-dependent guided wave properties induced by the anisotropic material properties of composites. Moreover, the array beamforming and imaging are performed in frequency domain where the guided wave dispersion effect has been considered. The presented phased array method is implemented with a non-contact scanning laser Doppler vibrometer (SLDV) to detect multiple defects at different locations in an anisotropic composite plate. The array is constructed of scan points in a small area rapidly scanned by the SLDV. Using the phased array method, multiple defects at different locations are successfully detected. Our study shows that the guided wave phased array method is a potential effective method for rapid inspection of large composite structures.

Pulsed laser-scanning laser Doppler vibrometer (PL-SLDV) phased arrays for damage detection in aluminum plates

Ultrasound image quality is related to the receive beamformer's ability. Delay and sum (DAS), a conventional beamformer, is combined with the coherence factor (CF) technique to suppress side lobe levels. The purpose of this study is to improve these beamformer's abilities. It has been shown that extension of the receive aperture can improve the receive beamformer's ability in radar studies. This paper shows that the focusing quality of CF and CF+DAS in medical ultrasound can be increased by extension of the receive aperture's length in phased synthetic aperture (PSA) imaging. The 3-dB width of the main lobe in the receive beam related to CF focusing decreased to 0.55mm using the proposed PSA compared to the conventional phased array (PHA) imaging, whose FWHM is about 0.9mm. The clutter-to-total-energy ratio (CTR) represented by R20dB showed an improvement of 50 and 33% for CF and CF+DAS beamformers, respectively, with PSA as compared to PHA. In addition, simulation results validated the effectiveness of PSA versus PHA. In applications where there are no important limitations on the SNR, PSA imaging is recommended as it increases the ability of the receive beamformer for better focusing.

Phased array imaging for damage localization using multi-narrowband Lamb waves

The UK power industry is going through a difficult period, trying to balance the demand for electricity with conforming to the new environmental regulations. Because of overcapacity, it is no longer an attractive proposition to build new power stations but, instead, it makes economic sense to keep older power stations running beyond their design life. Structural integrity is increasingly demanding greater accuracy and repeatability from NDE inspections; new equipment and technology has been developed predominantly based on ultrasonic and eddy current technology. The development of information technology has been crucial for the improvement of ultrasonic imaging techniques. Advanced specialist inspections including phased array, time-of-flight diffraction and advanced eddy current, have been developed for evaluation of steam pipework, generator end-rings, steam chests, blade roots, rotor bore and rotor discs and many other plant items. The latest phased array techniques bring considerable benefits to the inspection of complex geometries. Ultrasonic inspections on components with complex geometries can give rise to confusing signal patterns which influence the speed and integrity of inspections. Additionally, access restrictions often limit probe movement, further affecting test integrity. The development and utilisation of phased array ultrasonic hardware and analysis software, has enabled high-integrity high-speed scanning and imaging of complex components. 'Sweep Scanning' can be carried out from a static position allowing coverage where access is restricted; the data can then be stored for future interrogation if required. The phased array probe contains multiple elements, and scanning can be mechanical (probe movement), electronic (pulsed beam sweep), or a combination of both. Component drawings and geometries can be overlaid on the phased array images, enabling both inspection design and ease of analysis. Advantages are gained through scanning complex geometries quickly with high integrity. Focusing of the optimal inspection angle gives improved defect detection and electronic data storage enables an auditable inspection fingerprint. This paper concentrates on three main applications: phased array and time-of-flight diffraction applications, rotor bore applications and generator retaining ring (end-ring) applications.

Lithium-ion batteries (LIBs) are widely used in electric vehicles and energy storage systems, making accurate state transition monitoring a key research topic. This paper presents a characterization method for large-format LIBs based on phased-array ultrasonic technology (PAUT). A finite element model of a large-format aluminum shell lithium-ion battery is developed on the basis of ultrasonic wave propagation in multilayer porous media. Simulations and comparative analyses of phased array ultrasonic imaging are conducted for various operating conditions and abnormal gas generation. A 40 Ah ternary lithium battery (NCMB) is tested at a 0.5C charge-discharge rate, with the state of charge (SOC) and ultrasonic data extracted. The relationship between ultrasonic signals and phased array images is established through simulation and experimental comparisons. To estimate the SOC, a fully connected neural network (FCNN) model is designed and trained, achieving an error of less than 4%. Additionally, phased array imaging, which is conducted every 5 s during overcharging and overdischarging, reveals that gas bubbles form at 0.9 V and increase significantly at 0.2 V. This research provides a new method for battery state characterization.

Phased array ultrasonic testing (PAUT) has become a popular nondestructive technique for weld inspections in piping, pressure vessels, and other components such as turbines. This technique can be used both in manual and automated modes. PAUT is more attractive than conventional angle-beam ultrasonic testing (UT), as it sweeps the beam through a range of angles and presents a cross-sectional image of the area of interest. Other displays are also available depending on the software. Unlike traditional A-scan instruments, which require the reconstruction of B- and C-scan images from raster scanning, a phased array image is much simpler to produce from line scans and easier to interpret. Engineering codes have incorporated phased array technology and provide steps for standardization, scanning, and alternate acceptance criteria based on fracture mechanics. The basis of fracture mechanics is accurate defect sizing. There is, however, no guidance in codes and standards on the selection and setup of phased array probes for accurate sizing. Just like conventional probes, phased array probes have a beam spread that depends on the probe’s active aperture and frequency. Smaller phased array probes, when used for thicker sections, result in poor focusing, large beam spread, and poor discontinuity definition. This means low resolution and oversizing. Accurate sizing for fracture mechanics acceptance criteria requires probes with high resolution. In this paper, guidance is provided for the selection of phased array probes and setup parameters to improve resolution, definition, and sizing of discontinuities.

We describe methods for simultaneously acquiring and subsequently combining data from a multitude of closely positioned NMR receiving coils. The approach is conceptually similar to phased array radar and ultrasound and hence we call our techniques the "NMR phased array." The NMR phased array offers the signal-to-noise ratio (SNR) and resolution of a small surface coil over fields-of-view (FOV) normally associated with body imaging with no increase in imaging time. The NMR phased array can be applied to both imaging and spectroscopy for all pulse sequences. The problematic interactions among nearby surface coils is eliminated (a) by overlapping adjacent coils to give zero mutual inductance, hence zero interaction, and (b) by attaching low input impedance preamplifiers to all coils, thus eliminating interference among next nearest and more distant neighbors. We derive an algorithm for combining the data from the phased array elements to yield an image with optimum SNR. Other techniques which are easier to implement at the cost of lower SNR are explored. Phased array imaging is demonstrated with high resolution (512 x 512, 48-cm FOV, and 32-cm FOV) spin-echo images of the thoracic and lumbar spine. Data were acquired from four-element linear spine arrays, the first made of 12-cm square coils and the second made of 8-cm square coils. When compared with images from a single 15 x 30-cm rectangular coil and identical imaging parameters, the phased array yields a 2X and 3X higher SNR at the depth of the spine (approximately 7 cm).

Previously, we proposed compressed sensing based synthetic transmit aperture (CS-STA) to improve the contrast and frame rate of STA while maintaining its spatial resolution in linear array by choosing uniform random matrix as the measurement matrix and transmitting the plane waves (PWs). In this paper, to extend CS-STA for phased array imaging and further improve its performance, we design four types of CS-STA implementations with different combinations of measurement matrices (i.e., uniform random and Hadamard matrices) and transmitted waves [i.e., PW and diverging wave (DW)]. Through simulations and phantom experiments with a 3 MHz, 64-element phased array, we find that type-IV CS-STA with the combination of a Hadamard matrix and DW outperforms the other three implementations including the previously proposed type-I CS-STA in terms of image quality and reconstruction time. Specifically, PW transmission produces visible discontinuity and the reconstruction time with uniform random matrix is about 100-fold longer than that with the Hadamard matrix. Compared with STA, with eightfold higher frame rate, type-IV CS-STA achieves 8.2 and 12.3 dB higher contrast-to-noise ratio and signal-to-noise ratio in the simulations, respectively. These improvements are slightly lower in the phantom experiments, which are 6.2 and 6.6 dB, respectively. In addition, CS-STA does not deteriorate the spatial resolution of STA, with the maximum deterioration being smaller than 1/8 wavelength. These results demonstrate that type-IV CS-STA can achieve phased array imaging with high image quality at high frame rate and may be beneficial to cardiac imaging.

In this article, we present the challenges and achievements in development and use of a compact ultrasonic Phased Array (PA) module and imaging technology for autonomous nondestructive evaluation of composite aerospace structures. We analyse the state of composite components by processing full waveform (A-scan) information from PA, perform slicing and visualization of the data.We further accomplish the improvement of the axial (depth) resolution by proposing a new signal processing algorithm based on threshold improved wavelet transform (TIWT), that is able to separate overlapped echoes. This algorithm extracts a reference echo model from A-scans with no defect, and uses complex continuous wavelet transform and phase information of full waveform to estimate and localize echoes of each A-scan. The results of the proposed algorithm are validated by comparing them to the reference sample measures.

A coherent array imaging method is described that uses small groups of adjacent array elements called subarrays. For each firing event, only one subarray is used for transmit and receive, and all elements of the subarray transmit and receive in parallel. Phased array processing is used to focus and steer the subarray beam in transmit and receive. A sufficient number of beams are acquired such that the Nyquist sampling criteria is met for the subarray. The beams acquired from each subarray are upsampled, filtered, and combined with beams from all the other subarrays to form the final high-resolution image. A subarray-dependent reconstruction and restoration filter is applied to the subarray beams. The method significantly reduces the front-end hardware complexity compared to full phased array imaging. Experimental results demonstrate the performance of the proposed method.

IntroductionBoth curvilinear and phased array transducers are commonly used to perform lung ultrasound (LUS). This study seeks to compare LUS interpretation accuracy of images obtained using a curvilinear transducer with those obtained using a phased array transducer.MethodsWe invited 166 internists and trainees to interpret 16 LUS images/cineloops of eight patients in an online survey: eight curvilinear and eight phased array, performed on the same lung location. Images depicted normal lung, pneumothorax, pleural irregularities, consolidation/hepatisation, pleural effusions and B‐lines. Primary outcome for each participant is the difference in image interpretation accuracy scores between the two transducers.ResultsA total of 112 (67%) participants completed the survey. The mean paired accuracy score difference between the curvilinear and phased array images was 3.0% (95% CI: 0.6 to 5.4%, P = 0.015). For novices, scores were higher on curvilinear images (mean difference: 5.4%, 95% CI: 0.9 to 9.9%, P = 0.020). For non‐novices, there were no differences between the two transducers (mean difference: 1.4%, 95% CI: −1.1 to 3.9%, P = 0.263). For pleural‐based findings, the mean of the paired differences between transducers was higher in the novice group (estimated mean difference‐in‐differences: 9.5%, 95% CI: 0.6 to 18.4%; P = 0.036). No difference in mean accuracies was noted between novices and non‐novices for non‐pleural‐based pathologies (estimated mean difference‐in‐differences: 0.6%, 95% CI to 5.4–6.6%; P = 0.837).ConclusionsLung ultrasound images obtained using the curvilinear transducer are associated with higher interpretation accuracy than the phased array transducer. This is especially true for novices interpreting pleural‐based pathologies.

Fiber Bragg gratings are known being immune to electromagnetic interference and emerging as Lamb wave sensors for structural health monitoring of plate-like structures. However, their application for damage localization in large areas has been limited by their direction-dependent sensor factor. This article addresses such a challenge and presents a robust damage localization method for fiber Bragg grating Lamb wave sensing through the implementation of adaptive phased array algorithms. A compact linear fiber Bragg grating phased array is configured by uniformly distributing the fiber Bragg grating sensors along a straight line and axially in parallel to each other. The Lamb wave imaging is then performed by phased array algorithms without weighting factors (conventional delay-and-sum) and with adaptive weighting factors (minimum variance). The properties of both imaging algorithms, as well as the effects of fiber Bragg grating’s direction-dependent sensor factor, are characterized, analyzed, and compared in details. The results show that this compact fiber Bragg grating array can precisely locate damage in plates, while the comparisons show that the minimum variance method has a better imaging resolution than that of the delay-and-sum method and is barely affected by fiber Bragg grating’s direction-dependent sensor factor. Laboratory tests are also performed with a four–fiber Bragg grating array to detect simulated defects at different directions. Both delay-and-sum and minimum variance methods can successfully locate defects at different positions, and their results are consistent with analytical predictions.

Crack closure stress (CCS) is an important parameter that affects crack propagation rate. However, the method for measuring CCS in practical fields has yet to be developed. In this study, we propose a practical method of estimating CCS. In our experiment, a closed fatigue crack was imaged by a linear phased array (PA) method during crack opening by global preheating and local cooling (GPLC). Here, we assumed that the crack appears in PA images after the thermal stress induced by GPLC exceeds CCS. Therefore, we calculated the thermal stress induced by GPLC using an analytical solution and thereby estimated CCS. Then, to validate the CCS estimation method, we simulated the PA images by a finite difference time domain (FDTD) method with a damped double node (DDN) model, where CCS was relieved by the calculated thermal stress. Consequently, the temporal variation in crack depth observed in the PA image was successfully reproduced in the simulation. Thus, the CCS estimation method was verified by comparing experimental results with analysis results.