Stephen W. Kercel

In-process detection of weld defects using laser-based ultrasound

Laser-based ultrasonic (LBU) measurement shows great promise for on-line monitoring of weld quality in tailor-welded blanks. Tailor-welded blanks are steel blanks made from plates of differing thicknesses and/or properties butt- welded together, they are used in automobile manufacturing to produce body, frame, and closure panels. LBU uses a pulsed laser to generate the ultrasound and a continuous wave laser interferometer to detect the ultrasound at the point of interrogation to perform ultrasonic inspection. LBU enables in-process measurements since there is no sensor contact or near-contact with the workpiece.

Characterization of gas pipeline flaws using wavelet analysis

As U.S. natural gas supply pipelines are aging, non-destructive inspection techniques are needed to maintain the integrity and reliability of the natural gas supply infrastructure. Ultrasonic waves are one promising method for non-destructive inspection of pipeline integrity. As the waves travel through the pipe wall, they are affected by the features they encounter. In order to build a practical inspection system that uses ultrasonic waves, an analysis method is needed that can distinguish between normal pipe wall features, such as welds, and potentially serious flaws, such as cracks and corrosion. Ideally, the determination between “flaw” and “no-flaw” must be made in real-time as the inspection system passes through the pipe. Because wavelet basis functions share some common traits with ultrasonic waves, wavelet analysis is particularly well-suited for this application. Using relatively simple features derived from the wavelet analysis of ultrasonic wave signatures traveling in a pipe wall, we have successfully demonstrated the ability to distinguish between the “flaw” and “no-flaw” classes of ultrasonic features.

Novel Methods for Detecting Buried Explosive Devices

Oak Ridge National Laboratory and Quantum Magnetics, Inc. are exploring novel landmine detection technologies. Technologies considered here include bioreporter bacteria, swept acoustic resonance, nuclear quadrupole resonance (NQR), and semiotic data fusion. Bioreporter bacteria look promising for third-world humanitarian applications; they are inexpensive, and deployment does not require high-tech methods. Swept acoustic resonance may be a useful adjunct to magnetometers in humanitarian demining. For military demining, NQR is a promising method for detecting explosive substances; of 50,000 substances that have been tested, one has an NQR signature that can be mistaken for RDX or TNT. For both military and commercial demining, sensor fusion entails two daunting tasks, identifying fusible features in both present-day and emerging technologies, and devising a fusion algorithm that runs in real-time on cheap hardware. Preliminary research in these areas is encouraging. A bioreporter bacterium for TNT detection is under development. Investigation has just started in swept acoustic resonance as an approach to a cheap mine detector for humanitarian use. Real-time wavelet processing appears to be a key to extending NQR bomb detection into mine detection, including TNT-based mines. Recent discoveries in semiotics may be the breakthrough that will lead to a robust fused detection scheme.

Wavelet and wavelet-packet analysis of Lamb wave signatures in laser ultrasonics

Laser-based ultrasonic (LBU) measurement shows great promise for on-line monitoring of weld quality in tailor-welded blanks. Tailor-welded blanks are steel blanks made from plates of different thickness and/or properties butt-welded together; they are used in automobile manufacturing to provide body, frame, and closure panels. LBU uses a pulsed laser to generate the ultrasound and a continuous wave laser interferometer to detect the ultrasound at the point of interrogation to perform ultrasonic inspection. LBU enables in-process measurement since there is no sensor contact or near-contact with the workpiece. The authors are using laser-generated plate waves to propagate form one plate into the weld nugget as a means of detecting defects.

Wavelet-based acoustic recognition of aircraft

We describe a wavelet-based technique for identifying aircraft from acoustic emissions during takeoff and landing. Tests show that the sensor can be a single, inexpensive hearing-aid microphone placed close to the ground. The paper describes data collection, analysis by various techniques, methods of event classification, and extraction of certain physical parameters from wavelet subspace projections. The primary goal of this paper is to show that wavelet analysis can be used as a divide-and- conquer first step in signal processing, providing simplification and noise filtering. The idea is to project the original signal onto the orthogonal wavelet subspaces, both details and approximations. Subsequent analysis, such as system identification, nonlinear systems analysis, and feature extraction, is then carried out on the various signal subspaces.

Bayesian separation of Lamb wave signatures in laser ultrasonics

Laser-based ultrasonic (LBU) measurement shows great promise for on-line monitoring of weld quality in tailor-welded blanks. Tailor-welded blanks are steel blanks made from plates of differing thickness and/or properties butt-welded together; they are used in automobile manufacturing to produce body, frame, and closure panels. LBU uses a pulsed laser to generate the ultrasound and a continuous wave laser interferometer to detect the ultrasound at the point of interrogation to perform ultrasonic inspection. LBU enables in-process measurements since there is no sensor contact or near-contact with the workpiece. The authors are using laser-generated plate waves to propagate from one plate into the weld nugget as a means of detecting defects.

A hardware implementation of multiresolution filtering for broadband instrumentation

The authors have constructed a wavelet processing board that implements a 14-level wavelet transform. The board uses a high-speed analog-to-digital (A/D) converter, a hardware queue, and five fixed-point digital signal processing (DSP) chips in a parallel pipeline architecture. All five processors are independently programmable. The board is designed as a general purpose engine for instrumentation applications requiring near real-time wavelet processing or multiscale filtering. The present application is the processing engine of a magnetic field monitor that covers 305 Hz through 5 MHz. The monitor is used for the detection of peak values of magnetic fields in nuclear power plants. This paper describes the design, development, simulation, and testing of the system. Specific issues include the conditioning of real-world signals for wavelet processing, practical trade-offs between queue length and filter length, selection of filter coefficients, simulation of a 14-octave filter bank, and limitations imposed by a fixed-point processor. Test results from the completed wavelet board are included.

Wavelet and wavelet-packet analysis of Lamb wave signatures in real-time instrumentation

A persistent problem in the analysis of Lamb wave signatures in experimental data is the fact that several different modes appear simultaneously in the signal. The modes overlap in both frequency and time domains. Attempts to separate the overlapping Lamb wave signatures by conventional signal processing methods have been unsatisfactory, As might be expected, the transient nature of Lamb waves makes them readily tractable to wavelet analysis. The authors have used the discrete wavelet transform and the wavelet packet transform to untangle the Lamb wave signature. Furthermore, both techniques are realizable in the highly parallel cascaded-lattice architecture, and are well suited for on-line real-time instrumentation. For signatures of Lamb waves captured in laser ultrasonic data in tailor-welded blanks, this has led to straightforward detection of weld defects and demonstration of principle that weld defects can be classified according to the type of defect as revealed by features in wavelet space. This technique has considerable commercial value for online monitoring of manufacturing processes. For example, laser-based ultrasonic (LBU) measurement shows great promise for on-line monitoring of weld quality in tailor-welded blanks. Tailor-welded blanks are steel blanks made from plates of differing thickness and/or properties butt-welded together; they are used in automobile manufacturing to produce body, frame, and closure panels.

Why should engineers be interested in bizarre systems

Examines the shortcomings of conventional analysis when applied to complex processes, and considers the consequences of ignoring process behaviors simply because they do not conveniently project on to lists of numbers. Complex behavior is bizarre, but not absurd. Bizarre systems are counter-intuitive, and yet bizarre behavior is logically tractable. The inferential linkages within a bizarre systems epistemological model are congruent with the causal linkages that govern its ontological behavior. From the perspective of neurophysiology, the behaviors that we normally consider to be intelligent are irreducible to a list of numbers. This being the case, no list of numbers, no matter how big, can emulate intelligent behavior. To discuss intelligence other than by empirical observation, some logical description of it must be found that is not limited to predicative inferential structures. Mathematics abounds with such alternatives; impredicative mathematical entities provide powerful ways of describing complex behavior. They do so at a cost, being non-algorithmic. Engineering decisions based on predictions made by attempting to reduce complex behaviors to algorithms cannot be trusted; the projection ignores key aspects of the behavior. Present-day computers only work for algorithmic processes. An engineered artifact that exhibits intelligent behavior requires at least one, and possibly both, of the following developments: a more powerful model of computation than the Turing machine, and/or a computing element that has entailments similar to those observed in complex processes.

Wavelet-based enhancements to nuclear quadrupole resonance explosives detectors

Nuclear Quadrupole Resonance (NQR) is effective for the detecting and identification of certain types of explosives such as RDX, PETN and TNT. In explosive detection, the NQR response of certain 14N nuclei present in the crystalline material is proved. The 14N nuclei possess a nuclear quadrupole moment which in the presence of an electric field gradient produces an energy level splitting which may be excited by radio-frequency magnetic fields. Pulsing on the sample with a radio signal of the appropriate frequency produces a transient NQR response which may then be detected. Since the resonant frequency is dependent upon both the quadrupole moment of the 14N nucleus and the nature of the local electric field gradients, it is very compound specific. Under DARPA sponsorship, the authors are using multiresolution methods to investigate the enhancement of operation of NQR explosives detectors used for mine detection. For this application, NQR processing time must be reduced to less than one second. False alarm response due to acoustic and piezoelectric ringing must be suppressed. Also, as TNT is the most prevalent explosive found in land mines NWR detection of TNT must be made practical despite unfavorable relaxation times. All three issues require improvement in signal-to-noise ratio, and all would benefit from improved feature extraction. This paper reports some of the insights provided by multiresolution methods that can be used to obtain these improvements. It includes results of multiresolution analysis of experimentally observed NQR signatures for RDX response and various false alarm signatures in the absence of explosive compounds.