B-scan

A Scan at 7mm depth B Scan at 10mm depth C Scan at 13mm depth Fig. 11 Tomography scans of an internal shrinkage at different depths (A B C)... 

A novel approach for suppression of grain noise in ultrasonic signals, based on noncoherent detector statistics and signal entropy, is presented. The performance of the technique is demonstrated using ultrasonic B-scans from samples with coarse material structure. 

Experimental results on real ultrasonic B-scan data, acquired from samples with coarse material structure, are presented to demonstrate the power of the novel approach. 

The 45° transducer was used to inspect side drilled holes, with their centres located 40 mm below the surface. Due to the coarse material structure the echoes from the holes were totally masked by clutter. An example of an ultrasonic response signal, emanating from a hole with a diameter of 8 mm, is shown in the left part of Figure 3. Scanning the surface above the 8 mm and 10 mm holes resulted in the B-scan image shown in the upper part of Figure 4. 

Homogeneity of data. Homogeneous data will be uniform in structure and composition, usually possible to describe with a fixed number of parameters. Homogeneous data is encountered in simple NDT inspection, e.g. quality control in production. Inhomogeneous data will contain various combinations of indications from construction elements, defects and noise sources. An example of inhomogenous data are ultrasonic B-scan images as described in [Hopgood, 1993] or as encountered in the ultrasonic rail-inspection system described later in this paper. 

A Novel Method for Off-Line Defect Characterization and Sizing from Standard b-Scan Data. 

We present a novel method, called VIGRAL, to size and position the reflecting surface of a flaw. The method operates on standard B-scan recorded with traditional transducers, to extract Time-of-Flight (ToF) information which is then back-projected to reconstruct the reflecting surface of the flaw and characterize its radiation pattern. The VIGRAL method locates and sizes flaws to within k/2, and differentiates between flat and volumetric defects. 

The VIGRAL approach represents the reflecting surface of a defect as an ensemble of virtual point sources. At every measurement point of the B-Scan, the detecting transducer responds... 

The upi-SO screen display ( Figure 7 ) shows the A-scan signal (top) and the resulting B-scan image (bottom) for the tandem arrangement of Figure 6. The flaw reflection is seen on the left. 

To evaluate the VIGRAL method, we scanned steel blocks with simulated flaws using a Flexilrak and a upi-50 instrument. This system allows for rapid and accurate acquisition of the desired data, including the A-scan, B-scan, and C-scan data, and serves to evaluate, offline, the V-scan image (Figure 8). 

G.Krug, R.Aharoni, V.Orjelik, A novel method for sizing defects from off- line B-scan data . Proceedings of Ultrasonic World Congress,Yokogama, 1997, 122-124. 

In this paper, discontinuities in cylindrical specimens were studied by ultrasonic reflection tomography. The aim was threefold. First, to localize discontinuities from circular C-scan images. Second, to reconstruct quantitative cross-sectional images from circular B-scan profiles (i.e., reflection tomograms). Finally, to obtain three-dimensional information (i.e., discontinuity location, dimension and type) by stacking these reflection tomograms in multiple planes, in the third dimension. 

In order to ensure perpendicular beam incidence on the cylindrical specimen, the circular B-scan profiles were acquired by high frequency (narrow beam) transducers in a synthetic circular aperture array. From these profiles two-dimensional reflection tomograms were reconstructed using a filtered backprojection technique. Straight line propagation was assumed. Several artificial discontinuity types in a cylindrical Plexiglas (Perspex) specimen were compared with similar artificial discontinuities in a cylindrical A/Si-alloy [2]. Furthermore, examples of real discontinuities (an inclusion and a feed head) in the cylindrical AlSi-alloy are presented. 

Some discontinuities may be identified by a conventional two-dimensional ultrasonic technique, from which the well-known C-scan image is the most popular. The C-scan technique is relatively easy to implement and the results from several NDE studies have been very encouraging [1]. In the case of cylindrical specimens, a circular C-scan image is convenient to show discontinuity information. The circular C-scan image shows the peak amplitude of a back-scattered pulse received in the circular array. The axial scan direction is shown as a function of transducer position in the circular array. The circular C-scan image serves also as an initial step for choosing circular B-scan profiles. The latter provides a mapping between distance to the discontinuity and transducer position in the circular array. 

More recently, the circular array was proposed to assess the reflectivity of cylindrical specimens [3]. First, a circular C-scan image was obtained. The total scan time was about 25 min., which does not include a relatively time consuming alignment of the specimen. From the circular C-scan image, circular B-scan profiles were chosen in specific planes. The transducer was a focused high frequency transducer with a center frequency of 25 MHz of the transducer bandwidth. This frequency corresponds to a wavelength of 0.11 mm and 0.25 mm in the Plexiglas specimen and the AlSi-alloy, respectively. Additional experimental parameters are presented in Table 1. 

The results are illustrated by figure 5 B-Scan, C-Scan and D-Scan representations show that there are two types of defects. On the left part of the weld, we remark a lack of fusion, while on the right part, we observe a nest of blow hole. 

B-Scan X-Rays Images Segmentation Using Co-Occurrence Matrix. 

Automatic thresholding by dividing the matrix in several blocks to segment B-Scan images. 

A TOFD or B-Scan image is a discrete image defined as a function/of two variables on a finite and discrete domain D of dimensions MxN. 

B-scan view of a flat bottom hole in an aluminium plate of thickness 2 mm. 

Fig. 7 B-scan views of the artificial slots of height 1.7 nun left image) and 0.6 mm (right image) in a split configuration for gold-nickel alloy.

The testing-system used here allows computer-aided monitoring of the data in a B-scan. 

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