Blur Reduction in Ultrasonic Images Using Pseudo Three-Dimensional Wiener Filtering

The ability to quantitatively image material anomalies with ultrasonic methods is severely restricted by the axial and lateral resolution of the interrogating transducer. Axial resolution is controlled by the pulse duration of the transducer with shorter pulse durations yielding better axial resolution. Lateral resolution is controlled by the width of the interrogating beam with narrower beams providing better lateral resolutio

Marr-Hildreth Enhancement of NDE Images

Previous publications [1–5] have demonstrated the usefulness of digital image enhancement techniques for improving visual detection and resolution of features in NDE images. Many of the techniques are high-pass spatial domain convolution filters [6] which are used to enhance the appearance of edges by removing blur. Two of the major advantages of the more popular edge enhancement operators are their ease of implementation and their rapidity of execution [7]. This makes them very useful for rapid “screening” of images. Their major disadvantages are that they emphasize “noise” as well as edges, and some are directionally dependent operators which tend to suppress features that are not aligned in the “preferred” direction

Leaky Plate Wave Inspection of Biaxial Composites

The utilization of leaky plate waves in a scanning arrangement has exhibited improved reliability and increased sensitivity to important defects in unidirectional material [1,2,3].The application of frequency modulation to the usual tone burst signal used to generate plate waves has also been shown to enhance defect discrimination [2,3].In the current work, leaky plate wave techniques have been applied to the inspection of biaxially laminated graphite-epoxy composites.Test samples having 8, 16, and 24 plies, respectively, are studied.Test specimens contain several types of defects — simulated delaminations, porosity, and ply cuts.In addition, a series of impact-damaged samples are examined to study the method’s sensitivity to this type of delamination.All simulated defects were detected, and comparisons with conventional normal-incidence C-scan measurements have shown that the plate wave technique is more sensitive to both porosity and ply cuts, consistent with our observations on uniaxial composites [3]. Novel gating methods have been applied to the plate wave spectra to improve defect detection in biaxial composites.</p

Notes on Chang Ping-lin

Nondestructive evaluation (NDE) techniques are widely used in manufacturing and service industries for quality assurance and related applications [1]. Depending on the sophistication of a given NDE procedure, the inspection result can be in a form of a simple go/no-go indication, an amplitude readout, a list or a table of measurements, a two- dimensional figure, or an image which correlates test results with material and defect parameters. An image presentation which directly correlates measured NDE parameters with component coordinates is generally the preferred way of displaying results. Recent advances in computer and electronic technology have also facilitated the development and operation of image acquisition, processing, and presentation for many NDE techniques

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Ultrasonic signal analysis and image processing play important roles in the field of NDE. Many methods of ultrasonic imaging such as A-scan, B-scan and C-scan are available. Using such images, NDE tests and analysis can be performed. However, the images are limited by the resolution limits of the imaging system which are established by many factors such as the bandwidth of the transducer, frequency of interrogation, diffraction effects, etc. One of the results of such resolution limits is the blurring of the images

Improved Performance of Laser-Ultrasonic F-SAFT Imaging

The spatial resolution of laser-ultrasonics depends upon the spot sizes of the generation and detection lasers and may be inadequate for detecting small and buried flaws. The use of a broad laser spot at the surface of the specimen to produce an ultrasonic beam with little divergence gives a spatial resolution limited by the spot size. In the opposite case, focusing the laser beam to a small laser spot yields a strongly diverging acoustic wave, leading also to poor spatial resolution. As in conventional ultrasonics, spatial resolution can be greatly enhanced by the use of the Synthetic Aperture Focusing Technique (SAFT) [1,2]. In addition, the coherent summation performed by SAFT yields an improved signal-to-noise ratio (SNR). Originally developed in the time domain, SAFT can be advantageously implemented in the frequency domain (F-SAFT). F-SAFT is based on the angular spectrum approach [2–4], which allows a significant reduction in processing time as compared to time-domain SAFT