Kristina Helena Valborg Hedengren

Decomposition of edge operators

Common 2-D kernels are decomposed into basic elements to minimize their complexity and to demonstrate how they are related. Decomposition of the popular SOBEL filter kernels shows that they can be replaced by functionally identical simpler kernels. This result is significant because it proves that the SOBEL filter can be implemented with faster software or hardware than is currently possible.<<ETX>>

Optimizing the Design of Multilayer Eddy Current Probes — A Theoretical and Experimental Study

General Electric developed a new eddy current probe technology in the early ‘90’s to address critical NDE needs in the aerospace industry. The technology utilizes lasers to trace out precise, multiple turn coils on a flexible substrate. The result is an eddy current probe that is capable of conforming to complex geometries and inspecting with a very high detection sensitivity. To cover large areas quickly, arrays of these coils were also fabricated and are currently in use with great success at GE inspection facilities. The newly developed probes, however, raised some unique questions and problems that needed to be addressed in order to determine the“best” probe configuration. In this paper we summarize these issues and through a combination of experimental and finite element results, we show how the design of the probe is“optimized” for various applications. Further details on the development of the technology are provided in a companion paper in these proceedings[1].

Information Fusion Methods For Coupled Eddy-Current Sensors

Though imaging techniques have been applied routinely for visual, x-ray, and ultrasound inspections, they are new to eddy-current testing. Over the past few years, such techniques have been developed and applied to eddy-current data to demonstrate their value for defect detection and system analysis. In eddy-current testing, changes are sensed in the impedance of a coil excited by an alternating current to detect surface defects in metal. In eddy-current imaging, a complex impedance is measured at each pixel and used to construct an image pair. Eddy-current measurements can also be made using multiple coils; this paper discusses complex impedance image pairs formed using coupled coils that provide information from the surface covered by the two coils. A phasor plot, which is a scatter diagram of the complex impedance image pair, is an effective tool for presenting, explaining, and analyzing the information. In these plots a defect and the background noise often map to different loci, and thus have distinct signatures. The phasor plot can be used to find an appropriate combination of the image pair to improve defect detection. This paper discusses the presentation and fusion of the two images for enhanced defect detection. Images are shown together with their phasor plots to demonstrate the effects of rotational transformations and different signal combinations. The described methods are generic and can also be applied to image pairs created by different modality imaging systems; this is demonstrated with a combined eddy-current and ultrasound pair of images.

Edge enhancement with image algebra

Illustrates an implementation method for edge enhancement algorithms, or other processes based on convolutions, through the application of image algebra. Standard convolution kernels are decomposed into orthogonal components to identify a small set of basis images that are combined to perform the desired functions. With this method, algorithms can easily be modified as they are not limited by the summation of fixed constants in convolution kernels. Though results are shown on a pixel basis, there is no effort in this paper to evaluate the relative performances of various algorithms. However, the image algebra approach naturally illuminates the fundamental properties of different algorithms. The approach is effective for software implementation as algorithms typically execute faster than implementations based on conventional convolutions.<<ETX>>

Eddy Current Arrays for Defect Detection

What was originally an inspection technique for large-scale defects has become an increasingly miniaturized method. Originally, the use of eddy currents for nondestructive evaluation was limited to gross defects in massive structures such as railroads and ship hulls; today, eddy current techniques are routinely used to detect sub-millimeter cracks. Unfortunately, the trend towards miniaturization creates a practical dilemma. To achieve greater resolution and sensitivity, eddy current probes must be made smaller. As probes become smaller, the amount of time needed to completely cover an inspection area escalates. As with other NDE modalities, one solution proposed to resolve the conflict between productivity and sensitivity is the use of eddy current arrays. An array of many elements could easily decrease the required inspection time by an order of magnitude without sacrificing the high-resolution capabilities of smaller probes. The advantages of array inspection are thus quite attractive, and interest is increasing. However, practical implementation of eddy current arrays requires careful attention to a number of details, including elementto-element uniformity, size versus sensitivity, and electrical interactions (crosstalk).

Eddy Current Probe Evaluation: Experimental Measurements and System Interaction

Eddy current testing is often considered an old and mature technology. However, the state of the art technology cannot meet the new stringent demands that the US Government has imposed on inspection of new aircraft engines under a program called ENSIP (engine structural integrity program). These demands require substantial improvements both in inspection sensitivity and speed — for instance, crack detection capability must improve by a factor of 3 over what is currently possible. In order to meet the new goals, all aspects of an eddy current inspection system must be addressed from probe selection and mechanical scanning noise to system electronics and signal processing. It has previously been shown [1,2] that imaging techniques provide improved flaw detection capability and also may be used to optimize system performance. This paper describes work that combines imaging with probe measurements to analyze eddy current probes and system performance from a practical point of view. Slightly different designs of a specific type of probe have been examined to evaluate differences in the designs and to determine how well the probe construction method is controlled. Parameters were calculated from electric measurements on the probes and plotted in an attempt to explain their significance and to provide a method for selection of probes with superior qualities. The probe/system interaction was also analyzed in order to learn why some probes with good electric properties did not perform well in the eddy current system. Finally, images were created and used to evaluate the impact of different imaging parameters on inspection performance.