By using relationships between wave propagation and thermal diffusive propagation, it was shown that that one can transform from diffusive propagation into an equivalent wave field. The transformation results in sharper reflections with time delay proportional to the distance. I have built a low cost system based on IR camera designed as a smartphone add on. I have tested the performance of the system on flat bottom holes both in polycarbonate and carbon composite samples using incandescent quartz halogen light bulb as excitations. The images are as good as or better than any of the common techniques in use. Application of delay and sum back projection was also demonstrated. The combined use of the equivalent wave field transform and delay and sum back projection improves both depth and lateral resolution above any existing methods. The technique is very efficient in term of computational load.
The purpose of this work is to introduce a new analytical inversion method for three-dimensional (3D) sub-surface imaging beneath the skin from time sequenced infrared (IR) thermography images. The work was motivated by advances in thermal nondestructive evaluation methods. Using relationships between wave propagation and thermal diffusive propagation, transformation from diffusive propagation into an equivalent wave field is performed. This transformation results in well-defined reflections with time delay proportional to the distance. We apply the algorithm to a dynamic thermogram of histologically confirmed breast carcinoma obtained from the Brazilian breast thermal imaging set. Inversion of the raw data reveals intensities that correspond to heat conduction, most notable is presence of hyperintense, aberrant vascularization in the diseased breast in comparison with the non-diseased breast. Equivalent wave field transform (EWFT) serves as a computationally efficient method of extracting depth resolved anatomical and physiological information from skin surface thermogram data for research purposes.
By using relationships between wave propagation and thermal diffusive propagation, it was shown that that one can transform from diffusive propagation into an equivalent wave field. The transformation results in sharp reflections with time delay proportional to the distance. The performance of the transform was tested on carbon composite samples using either xenon flash or incandescent quartz halogen light bulb excitations. The images are as good as any of the common techniques in use. The method can detect artificial damage locate at the depth of the 12<sup>th</sup> carbon mats. Application of back projection was also demonstrated. The combined use of the equivalent wave field transform and back projection improves both depth and lateral resolution. The technique is very efficient in term of computational load.
Quartz halogen lamps have highly desirable properties for use in transient thermography including low cost, high power, and low weight. Those properties make them attractive for inexpensive portable systems. On the flip side, halogen lamps have slow turn-on and turn-off times, which can exceed the response time of the tested samples. Their slow response results in inefficient use of power. An additional problem is the large inrush current during turn-on. Considering the intermittent mode of operation – a few seconds on and then a few seconds off, this is a severe limitation. The inrush current can overload the power line and restrict available power. When using the newly introduced equivalent wave field thermography, it is important to know the exact heating profile of the lamp. Methods to extract this profile from the lamp parameters or the thermography data are presented. In this presentation I will introduce a lamp model based on the physics of the filament. The model has an analytical solution during the cooling phase and it was solved numerically during the active heating phase. The model compares very well with the measured data. Using the model, it is possible to analyze electronic lamp drivers and the lamp parameters and their effect on total system performance.
Pulse thermography or thermal wave imaging are commonly used as nondestructive evaluation (NDE) method. While the technical aspect has evolve with time, theoretical interpretation is lagging. Interpretation is still using curved fitting on a log log scale. A new approach based directly on the governing differential equation is introduced. By using relationships between wave propagation and the diffusive propagation of thermal excitation, it is shown that one can transform from solutions in one type of propagation to the other. The method is based on the similarities between the Laplace transforms of the diffusion equation and the wave equation. For diffusive propagation we have the Laplace variable <i>s</i> to the first power, while for the wave propagation similar equations occur with s<sup>2</sup>. For discrete time the transformation between the domains is performed by multiplying the temperature data vector by a matrix. The transform is local. The performance of the techniques is tested on synthetic data. The application of common back projection techniques used in the processing of wave data is also demonstrated. The combined use of the transform and back projection makes it possible to improve both depth and lateral resolution of transient thermography.
Electromagnetic signals propagate underwater following a diffusion equation. Using similarities between the diffusion equation and wave propagation, a transformation between the diffusion and the wave propagation can be performed employing the equivalent wave field (EWF). Using EWF, it is possible to apply enhancements developed for wave propagation to diffusive propagation. Synthetic Aperture Radar (SAR) is one of the enhancements used in a conventional wave field. Using wide- band electromagnetic transmission and the EWF, it is possible to detect and localized underwater conductivity anomalies. SAR is known to improve the signal-to-noise ratio and the resolution. SAR together with EWF was applied to synthetic data of a conducting sphere embedded in an infinite ocean. Noise was added to the signal. A major improvement in the detection and resolution was demonstrated.
By using similarities between the diffusion equation and the wave equation it is shown that one can transform between solutions in one type of propagation to the other. The method is based on the similarities of the Laplace transform between the diffusive and the nondiffusive cases. In the diffusive case, the equation involves the Laplace variable s in the first power while for the nondiffusive cases, similar equations occur with s<SUP>2</SUP>. Four alternative implementations are developed. The first implementation is based on substitution s<SUP>2</SUP> for the Laplace transform variable s using forward and inverse numerical Laplace transform. The second implementation is based on expanding the diffusive time response on exponential time base and replacing it with its image function in the wave case, namely sinusoidal function. The third implementation is based on direct transformation in the time domain using exponential time interval sampling. The fourth one which is optimized for thermal NDE is performed by singular value decomposition.
Presented herein is a method for the interpretation of electromagnetic (EM) response in sea- water. The method is based upon similarities between the EM wave equation in lossless media, and the EM diffusion equation in conductive media. The technique allows for the transformation between the solution in the two propagation modes. The advantages of the technique are its simple implementation and its generality to a wide variety of cases. Application to mine hunting including conducting and nonconducting mines are simulated. Advantages and limitations of the method are discussed. The technique is also applicable to interpretation of time-dependent heat flow.