The Foundations of Statistics By Prof. Leonard J. Savage. (Wiley Publications in Statistics.) Pp. xv + 294. (New York; John Wiley and Sons, Inc.; London: Chapman and Hall, Ltd., 1954.) 48s. net.

Probability and Statistical Inference

The Journal of the Acoustical Society of America

Ultrasonic testing of materials: Josef and Herbert Krautkramer Springer-Verlag Publishing Company, Berlin, Heidelberg, New York (1975) 669 pp, $63.00

Review of progress, QNDE

In this review, the use of x-ray computed tomography (XCT) is examined, identifying the requirement for volumetric dimensional measurements in industrial verification of additively manufactured (AM) parts. The XCT technology and AM processes are summarised, and their historical use is documented. The use of XCT and AM as tools for medical reverse engineering is discussed, and the transition of XCT from a tool used solely for imaging to a vital metrological instrument is documented. The current states of the combined technologies are then examined in detail, separated into porosity measurements and general dimensional measurements. In the conclusions of this review, the limitation of resolution on improvement of porosity measurements and the lack of research regarding the measurement of surface texture are identified as the primary barriers to ongoing adoption of XCT in AM. The limitations of both AM and XCT regarding slow speeds and high costs, when compared to other manufacturing and measurement techniques, are also noted as general barriers to continued adoption of XCT and AM.

/pdf/x-ray-computed-tomography-for-additive-manufacturing-a-1ouio0owzb.pdf

X-ray computed tomography for additive manufacturing: a review


 Recently there is much interest in metamaterial based super resolution imaging. Several demonstrations have been reported using sources or slits as targets for imaging. However, in the context of non-destructive evaluation, imaging of defects and discontinuities within a sample are of more interest. Such defects, unlike sources or slits, induce wave scattering which could potentially impact image generation. This paper studies the effects of wave scattering by subwavelength spaced defects in holey structured metamaterial based super resolution imaging using numerical (finite element) models. In these models, the ultrasonic waves are assumed to impinge on the defects in a normal incidence through transmission configuration, and a line-scan image at the receiver location is generated based on the captured waves past the metamaterial. The influence of defect position within the specimen sample (object plane) and the receiver location (image plane) with respect to the metamaterial on the output images are investigated. The results show that the defect-induced wave scattering processes produce intensity and spatial artefacts that have a signature on imaging. For various parametric cases, the changes in the output images are quantified and discussed in the context of metamaterial based super resolution imaging in the field of non-destructive evaluation and non-invasive diagnostics.

A Study on the Influence of Wave Scattering in Metamaterial-Based Super-Resolution Imaging of Defects in Materials

S0 Lamb mode scattering studies in laminated composite plate structures with surface breaking cracks; insights into crack opening behavior.

Ultrasonic inspection is commonly used for Non-Destructive Evaluation (NDE). Phased array ultrasonic transducers (PAUT) enable beamforming and beam steering by implementing electronic time delays. By providing appropriate delays in exciting individual elements, PAUTs can generate a curved wavefront. The authors propose a metamaterial device made of Gradient Refractive Index Phononic Crystals to transform curvature of a wavefront generated from a single element transducer. The manipulation of the wavefront as it passes through holey region, is simulated using the finite element method. Results from experimental studies carried out on a holey plate, designed using this approach are comparable to simulation results. The authors suggest that add-on devices can be designed using this approach for tailoring wave incidence in ultrasonic inspection.

Manipulating curvature of plane wavefront using holey plates

With rapidly improving computational power numerical models are being developed for ever more complex problems that cannot be solved analytically, making them more and more computationally intensive. Parallel computing has emerged as an important paradigm to speed up the processing of such models. In recent years graphics processing units (GPU) are among the massively parallel devices widely available to the commodity market. General purpose computing on these devices went mainstream after the introduction of NVIDA ‘compute unified device architecture’ (CUDA). Here we develop CUDA implementations of the finite difference time domain (FDTD) scheme for three-dimensional problems of acoustic and two-dimensional problems of ultrasonic NDE. Simulations are run on the commodity GPU GeForce 9800GT. Results show a strong improvement in the speed of computation as compared to that of a serial implementation on a CPU. We also discuss the accuracy of GPU-based computation.

Graphical Processing Units (GPU)-based modeling for Acoustic and Ultrasonic NDE

In recent years, various types of acoustic metamaterials have been proposed with capabilities for overcoming the diffraction limit. However, typically such developments only consider the acoustic regime [1] or imaging in liquid media [2]. In this paper we demonstrate the application of a holey structured metamaterial lens for sub-wavelength imaging of defects in a metallic sample, in the ultrasonic regime. Finite Element (FE) simulations are used to study longitudinal wave interaction with ideal cracks in isotropic elastic materials. Holeystructured meta-lenses are then used to transmit the scattered waves. We experimentally demonstrate a subwavelength resolution of λ/7 with a sub-wavelength notch in an aluminium block, which to the best of our knowledge this is the highest resolution achieved in the ultrasonic regime.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=4869&context=qnde

Prabhu Rajagopal

Papers

A Study on the Influence of Wave Scattering in Metamaterial-Based Super-Resolution Imaging of Defects in Materials

S0 Lamb mode scattering studies in laminated composite plate structures with surface breaking cracks; insights into crack opening behavior.

Manipulating curvature of plane wavefront using holey plates

Graphical Processing Units (GPU)-based modeling for Acoustic and Ultrasonic NDE

Subwavelength Resolution of Cracks in the Metallic Materials