Technique for imaging using virtual array of sources (tivas)
21 Jun 2011-Vol. 1335, Iss: 1, pp 1687-1694
TL;DR: In this article, the role of the depth of focus and the focal spot size on the performance of TIVAS were studied semi-analytically and through FDTD simulations.
Abstract: A new phased array inspection scheme, called Technique to Image using Virtual Array Sources (TIVAS), is proposed to image defects at deeper locations with good lateral resolution. An array of virtual focal spots using electronic beam forming and the expanded aperture through electronic linear scanning was employed to achieve significant increase in the focal depths, with improved SNR, when compared to single element array imaging or the conventional phased array focusing technique. The image reconstruction was performed using the well known synthetic focusing approach. In this paper, the role of the depth of focus and the focal spot size on the performance of TIVAS were studied semi‐analytically and through FDTD simulations. It was observed smaller virtual focal spot size provides improved lateral resolution and there is an optimum depth of focus for the smallest focal spot size achievable for a array transducer. Experiments were carried out to validate these findings.
Citations
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TL;DR: In this article, an angle beam virtual source FMC (ABVSFMC) method is proposed to enhance the sensitivity by increasing the transmitted energy with specific directivity, which utilizes apertures of a few elements to obtain a diverging beam by focusing very near to the top surface (virtual source).
Abstract: Full matrix capture coupled with total focusing method (FMC-TFM) is one of the most advanced and popular phased array ultrasonic techniques used to achieve simultaneous focusing at all depths in a specimen. In case of conventional FMC-TFM technique, a single element is used for transmission that limits the transmitted energy. This leads to reduced sensitivity at larger depths particularly in attenuating materials such as austenitic alloys. An Angle Beam Virtual Source FMC (ABVSFMC) method is proposed in the present paper to enhance the sensitivity by increasing the transmitted energy with specific directivity. The methodology utilizes apertures of a few elements to obtain a diverging beam by focusing very near to the top surface (virtual source). Further, as a group of elements is used in transmission, a divergent beam with specific directivity can be achieved without using a wedge. In reception, all the available channels are used and an algorithm similar to the Total Focusing Method (TFM) is used to reconstruct the image. The methodology is demonstrated by imaging the tip diffracted signals obtained from slot type planar defects at various depths in the range of 25–175 mm in a 200 mm thick nickel base alloy forging.
23 citations
TL;DR: In this paper, the development at Centre for Non-destructive Evaluation, Indian Institute of Technology Madras, of three different numerical methods, namely finite element, ray tracing and finite-difference time-domain methods for investigating the propagation of ultrasonic waves through polycrystalline media.
Abstract: The present article addresses the development at Centre for Non-destructive Evaluation, Indian Institute of Technology Madras, of three different numerical methods, namely finite element, ray tracing and finite-difference time-domain methods for investigating the propagation of ultrasonic waves through polycrystalline media. These methods are believed to aid in better understanding of ultrasonic wave interaction in materials exhibiting both simple and complex grain morphologies. The understanding is expected to provide an improved non-destructive assessment of material and defect characterisation.
7 citations
TL;DR: In this paper , the authors proposed a new phased array imaging technique called Arbitrary Virtual Array Source Aperture (AVASA) to image deeper defects with an improved SNR with fewer transmissions.
Abstract: In this paper, we propose a new phased array imaging technique called Arbitrary Virtual Array Source Aperture (AVASA) to image deeper defects with an improved SNR with fewer transmissions. The approach is to transmit the ultrasound waves by electronic beamforming at several arbitrary virtual source positions to achieve higher focal depth to increase the SNR of the received A-scans. Backscattered signals are recorded with all the array elements. A high-resolution image is obtained on reception by virtually focusing on every point in the region of interest by signal coherence summation. In this paper, the proposed AVASA and TFM methods are employed for scanning the larger thickness structure with an unknown defect nature to contrast the defect SNR and the number of defect imaging. Compared with TFM imaging, the AVASA method shows a significantly increasing defect-detecting range with higher amplitude. To further improve the imaging quality and reduce the reconstruction time, the influence of the virtual source parameters on the AVASA imaging and a scanning strategy is demonstrated. A good agreement between the AVASA and TFM is observed, and the number of transmissions is required to inspect the test specimen using AVASA reduced by a factor of four to eight.
TL;DR: In this paper , the authors proposed a framework to automate the process of defect characterizing for industrial structural component health monitoring by implementing automatic defect recognition (ADR) system consisting of a convolutional neural network (CNN) and an edge detection algorithm medial axis transform (MAT).
Abstract: In this paper, we propose a framework to automate the process of defect characterizing for industrial structural component health monitoring by implementing automatic defect recognition (ADR) system. The ADR system consists of a convolutional neural network (CNN) and an edge detection algorithm medial axis transform (MAT). The CNN learns the defect feature space from the training dataset to detect and classify the defect. The MAT algorithm is used upon post-validation of the ADR, and the predicted feature’s edges are extracted to size them. The ADR is trained using the simulation-assisted finite element (FE) simulation datasets consisting of side drilled holes (SDH) and crack defects images. The training datasets are generated by introducing virtual array source aperture (VASA), which is a full matrix capture (FMC) scanning strategy by activating the group of elements in an active aperture with predefined focal laws to form a focused beam at a virtual source in the material. The VASA technique uses multiple virtual sources and active aperture positions in a given transducer, which are determined using the Poisson point process. The ultrasound beam is excited in sequence on each virtual source, and the reflected wave is recoded using all the transducers in the array to create FMC A-scans signals. The total focusing method (TFM) technique is a postprocessing algorithm implemented on the FMC signal to generate an image. A large quantity of training datasets is created for each defect by modeling various FE models with varying defect morphology. To create nearly close to experimental images, the experimental noise is introduced in the simulated images. The three separate ADR systems are trained with individual defects class and combined defects. The effectiveness of the trained ADR system is validated by conducting experiments on the plates with laboratory-made SDH and crack defects, the casting components, and weldments with unknown defect types and sizes. The mAP of ADR training is 82%, and the F1-score on testing image classification is 89%. The ADR system could detect and size the smallest defect is 0.219 mm, which is λ L /5.
01 Nov 2021
TL;DR: In this article, an angle beam virtual source (ABVSFMC-TFM) is proposed to inspect thick attenuating materials such as nickel-base alloys, which leads to improved SNR due to increased energy with directivity during transmission using a group of elements and improved divergence as compared to the PWI due to a small virtual source near the sample surface.
Abstract: Ultrasonic nondestructive testing traditionally uses a conventional monolithic transducer. An approach similar to this comprising of independent single transmissions but with reception performed by all the elements in phased array ultrasonics is known as full matrix capture (FMC). The acquired data are processed by total focusing method (TFM). Conventional FMC-TFM has limitations in the inspection at large depth in attenuating materials due to single element transmission. To improve the beam forming process, coherent recombination of the plane wave with specific angles is utilized in transmission and the same aperture is used for the reception in plane wave imaging (PWI). A new methodology called angle beam virtual source FMC-TFM (ABVSFMC-TFM) is proposed to inspect thick attenuating materials such as nickel-base alloys. The ABVSFMC method leads to improved signal-to-noise ratio (SNR) as compared to the conventional FMC due to increased energy with directivity during transmission using a group of elements and improved divergence as compared to the PWI due to a small virtual source near the sample surface. In the present paper, FMC-TFM, PWI-TFM, and ABVSFMC-TFM methods are compared for the inspection of thick nickel-base superalloy (Alloy 617) with slots at various depths in the range of 25–200 mm. Optimization of the incidence angle has been performed by beam computation in CIVA software. Results obtained by CIVA simulations are discussed and also compared for the three methods.
References
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TL;DR: In this paper, Lamb's method has been adapted to furnish definite-integral representations of the field at an arbitrary point in a semi-infinite isotropic solid, due to prescribed periodic stresses on the free surface, the particular stress distributions considered here being such as would be produced by certain types of electro-mechanical transducers.
Abstract: The problem of wave-motion in a semi-infinite solid has been studied by several workers in connexion with seismological disturbances. In a classic paper (1904), Lamb investigated the propagation of vibrations over the surface of a semi-infinite isotropic solid, due to the application of force at a point or along a line in the free surface. A related problem is studied by Lapwood (I 949) who considers the case of an infinitely long dilating line-source situated parallel to and just below the free surface. Both authors obtain solutions in the form of definite integrals which they evaluate asymptotically to obtain the various components of the field at points on or near the surface at large distances from the source. In a more recent paper by Margery Newlands (I 952) this work has been extended to include the case of a source situated in a thin surface layer and propagating into a semi-infinite solid. The static problem of the distortion of a semi-infinite solid by stresses on the free surface was investigated by Boussinesq in a series of papers (1878-83) and by Love (1929). In the present paper Lamb's method has been adapted to furnish definite-integral representations of the field at an arbitrary point in a semi-infinite isotropic solid, due to prescribed periodic stresses on the free surface, the particular stress distributions considered here being such as would be produced by certain types of electro-mechanical transducer. Asymptotic formulae are obtained for the field at infinity, and the results for the various displacement components are presented in the form of polar diagrams. To obtain the radiation impedance integral expressions are derived for the mean displacement over the part of the surface which lies beneath the source; these expressions have been evaluated by numerical quadrature in a number of cases and a table shows the corresponding values of the radiation impedance.
516 citations
TL;DR: The use of the focus as a virtual element is examined, and the virtual source has been shown to exhibit the same behavior as an actual transducer element in response to synthetic aperture processing techniques.
Abstract: A new imaging technique has been proposed that combines conventional B-mode and synthetic aperture imaging techniques to overcome the limited depth of field for a highly focused transducer. The new technique improves lateral resolution beyond the focus of the transducer by considering the focus a virtual element and applying synthetic aperture focusing techniques. In this paper, the use of the focus as a virtual element is examined, considering the issues that are of concern when imaging with an array of actual elements: the tradeoff between lateral resolution and sidelobe level, the tradeoff between system complexity (channel count/amount of computation) and the appearance of grating lobes, and the issue of signal to noise ratio (SNR) of the processed image. To examine these issues, pulse-echo RF signals were collected for a tungsten wire in degassed water, monofilament nylon wires in a tissue-mimicking phantom, and cyst targets in the phantom. Results show apodization lowers the sidelobes, but only at the expense of lateral resolution, as is the case for classical synthetic aperture imaging. Grating lobes are not significant until spatial sampling is more than one wavelength, when the beam is not steered. Resolution comparable to the resolution at the transducer focus can be achieved beyond the focal region while obtaining an acceptable SNR. Specifically, for a 15-MHz focused transducer, the 6-dB beamwidth at the focus is 157 /spl mu/m, and with synthetic aperture processing the 6-dB beamwidths at 3, 5, and 7 mm beyond the focus are 189 /spl mu/m, 184 /spl mu/m, and 215 /spl mu/m, respectively. The image SNR is 38.6 dB when the wire is at the focus, and it is 32.8 dB, 35.3 dB, and 38.1 dB after synthetic aperture processing when the wire is 3, 5, and 7 mm beyond the focus, respectively. With these experiments, the virtual source has been shown to exhibit the same behavior as an actual transducer element in response to synthetic aperture processing techniques.
313 citations
TL;DR: If identical physical aperture dimensions are used and other parameters held to identical values, the synthetic‐aperture sonar gives higher signal‐to‐ratio than does the nonsynthetic‐aperno sonar primarily because the latter must operate at higher acoustic frequencies for which signal attenuation becomes extremely large.
Abstract: A comparison is made of the signal‐to‐noise characteristics of synthetic‐aperture sonar and conventional sonar. For the synthetic‐aperture sonar case a design procedure is described which makes possible the choice of essentially any unambiguous range and any resolution. Often multiple beam receivers are required. It is shown for the synthetic‐aperture sonar case that the horizontal aperture is the major factor affecting area coverage rate. The comparisons are made with as many parameter values as spossible identical for both the synthetic‐aperture cases and the nonsynthetic‐aperture cases. If identical physical aperture dimensions are used and other parameters held to identical values, the synthetic‐aperture sonar gives higher signal‐to‐ratio than does the nonsynthetic‐aperture sonar primarily because the latter must operate at higher acoustic frequencies for which signal attenuation becomes extremely large. If the sonar systems are operated at the same frequency, then the nonsynthetic aperture sonar can give a higher signal‐to‐noise ratio only when its physical aperture is larger than that used in the synthetic‐aperture case.Subject Classification: 30.82; 60.20.
174 citations
TL;DR: In this article, the authors derived the pressure distribution for beam focusing, and showed that the directivity of focusing converges to that of steering in the far field of the array.
Abstract: One of the fundamental features of phased arrays is the ability to focus the propagating waves to a specific point within the load material by inducing a parabolic time delay. This required focusing time delay has been modified from the current formulation to incorporate either an odd or even number of elements. A brief procedure leading to the derivation of the pressure distribution for beam focusing is described, which gives rise to an unclosed form. Consequently, a numerical method is desirable for the analysis of beam focusing. Using this approach, beam directivity and pressure distributions are studied to predict the behavior of focusing as compared to steering. This shows a benefit of focusing over steering within the near field of the array, and that the directivity of focusing converges to that of steering in the far field.
173 citations
TL;DR: A two-dimensional (2-D) finite-difference model for elastic waves in the ground has been developed and it is seen that the presence of an air-chamber within the mine gives rise to resonant oscillations that are clearly visible on the surface above the mine.
Abstract: A two-dimensional (2-D) finite-difference model for elastic waves in the ground has been developed. The model uses the equation of motion and the stress-strain relation, from which a first-order stress-velocity formulation is obtained. The resulting system of equations is discretized using centered finite-differences. A perfectly matched layer surrounds the discretized solution space and absorbs the outward traveling waves. The numerical model is validated by comparison to an analytical solution. The numerical model is used to study the interaction of elastic waves with a buried land mine. It is seen that the presence of an air-chamber within the mine gives rise to resonant oscillations that are clearly visible on the surface above the mine. The resonance is shown to be due to flexural waves being trapped within the thin layer between the surface of the ground and the air chamber of the mine. The numerical results are in good qualitative agreement with experimental observations.
66 citations