TOF estimation for eddy current problems

Eddy Current Testing (ECT) is an NDE technique that has found widespread use in practice. Due to the frequencies and the conductivity of the materials involved, ECT is often mathematically best described by a “quasi-static” approximation to Maxwell’s Equations. These approximate equations describe a parabolic system and as such has no notion of time of flight. The Q transform, a parabolic to hyperbolic transform first derived by Bragg et al (SIAM J. Appl. Math, 16, (1968), 459-467),has been shown to be very useful in extracting Time of Flight (TOF) data from ECT schemes. The technique is well studied in homogenous media. However the presence of material interfaces complicates matters and the extraction of a TOF is no longer trivial. I work on developing interface removal transformations to handle this problem. Specifically, we have developed transformations that remove the effect of material boundaries for a planar geometry. We are currently working on experimental validations of these techniques.

Sensor Development for Eddy Current Inspection of Aircraft Structures

 One of the more common problems with aging aircraft are cracks that occur around fastener holes in multi-layer wing structures. The large number of potential flaw sites has contributed to interest in the development of fast and reliable NDE techniques for detecting such cracks. Magneto-Optic Imaging (MOI) was proposed as a possible solution to the problem several years ago. In this scheme, a copper foil is used as a “sheet” current source to induce eddy currents in the test specimen. When there are no anomalies present in the specimen, the normal component of the field near the center of the current source vanishes. However, in the presence of a defect, a normal component exists and is imaged using the Faraday rotation effect. The MOI system returns an analog image of this magnetic field. The lack of any special processing requirements makes this system extremely fast and simple to use. The primary disadvantage of this technique is the lack of a quantitative measure of the field. Alternative approaches are needed in applications where a quantitative measure of the field is desired. We are currently designing a system that combines the advantages offered of both quantitative field measurement and MOI. In particular, we intend to retain the speed of inspection of the MOI scheme while being able to quantitatively measure the field. To this end, the sheet current excitation scheme of the MOI system is retained in our design but the optical sensor is replaced with a Giant Magneto Resistive (GMR) based field sensor. The GMR sensor is an instantaneous field sensor and consequently sampling the signal directly would require the use of a high bandwidth data acquisition and processing system. As an alternative, we use an analog inphase/quadrature (I/Q) detection scheme that directly computes the amplitude and the phase of the GMR signal, resulting in a baseband signal whose bandwidth is only a function of the scanning speed and flaw characteristics. This amplitude and phase can then be easily sampled using a very low frequency A/D card. This simplifies the data acquisition process significantly.

Nondestructive Evaluation of Sprayed on Foam Insulation (SOFI) using Terahertz Waves

The objective of the project is to improve the effectiveness of the terahertz inspection of the Sprayed on Foam Insulation (SOFI) of the space shuttle external tank by developing advanced signal processing tools. Specifically, we are involved in the development of signal processing algorithms for interpreting the data. We have come up with several signal processing algorithms to enhance the image quality of the data obtained from SOFI. In addition we are also involved in the modeling of the inspection process using Ray-Tracing techniques.

Some (more) Qoutes I Like

Steal from one and it is plagarism, Steal from many and it is research.
-Albert Einstein (1879 - 1955)

2+2 = 4, except when 2 is very large
-Anon

There was once a man called Maxwell,
Four equations, he once did tell,
Why ? No one knows...
But at 28 my graying hair shows,
He has made my life a living hell.
-Ich (1980-)