TY - CONF A1 - Thiel, Erik A1 - Studemund, Taarna A1 - Ziegler, Mathias T1 - Spatial and temporal control of thermal waves using spatial light modulators N2 - Active thermography has been developed into a well-established non-destructive testing method and is used to detect cracks, voids, or material properties. The spatial-temporal structure of the external heating: spatially: planar (e.g., halogen lamp) or local (e.g., focused laser), and temporally: pulsed (e.g., flash lamp) or periodical (e.g., halogen lamp), has led to different testing modalities, as for instance flash and lock-in thermography. In this work, we combine a high-power laser with a spatial light modulator (SLM) allowing us to merge all degrees of freedom into a spatially and temporally controlled heat source. This approach allows us to launch a set of individually controlled and fully coherent high-energy thermal waves into the sample volume. As one possible application, we demonstrate the interference of two phase shifted thermal wave patterns in order to detect the position and depth of hidden defects, which is still a challenging task in thermographic and photothermal techniques. The patterns are positioned with a certain distance and a phase shift of pi to each other, creating an amplitude depletion zone that is centered between them. Now, when a defect is brought into the depletion zone, the destructive interference is disturbed and the defect can be recognized. This approach means that we intentionally exploit the vertical and lateral propagation directions of the thermal waves. In a more general view, controlling simultaneously control of phase and amplitude of a set of thermal waves enables us to have a defined propagation of the thermal wave field within the sample, which means that thermal waves can be controlled almost like acoustical or optical waves. However, in contrast to optical or acoustical waves, thermal waves are highly damped due to the diffusive character of the thermal heat flow and therefore limited in penetration depth in relation to the achievable spatial resolution. Nevertheless, the coherence length of thermal waves can be chosen in the mm-range for modulation frequencies below 10 Hz which is perfectly met by present SLM technology. Eventually, this offers the opportunity to transfer known technologies from wave shaping techniques to thermography methods and to exploit the possibilities of coherent thermal wave shaping. T2 - 57th Course on Photoacoustic & Photothermal Phenomena CY - Erice, Italy DA - 19.10.2016 KW - Infrared thermography KW - Thermal Wave KW - DMD PY - 2016 AN - OPUS4-37954 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Altenburg, Simon A1 - Bernegger, Raphael A1 - Krankenhagen, Rainer T1 - Absorption coefficient dispersion in flash thermography of semitransparent solids JF - International Journal of Thermophysics N2 - Pulse and flash thermography are experimental techniques which are widely used in the field of non-destructive testing for materials characterization and defect detection. We recently showed that it is possible to determine quantitatively the thickness of semitransparent polymeric solids by fitting of results of an analytical model to experimental flash thermography data, for both transmission and reflection configuration. However, depending on the chosen experimental configuration, different effective optical absorption coefficients had to be used in the model to properly fit the respective experimental data, although the material was always the same. Here, we show that this effect can be explained by the wavelength dependency of the absorption coefficient of the sample material if a polychromatic light source, such as a flash lamp, is used. We present an extension of the analytical model to describe the decay of the heating irradiance by two instead of only one effective absorption coefficient, greatly extending its applicability. We show that using this extended model, the experimental results from both measurement configurations and for different sample thicknesses can be fitted by a single set of parameters. Additionally, the deviations between experimental and modeled surface temperatures are reduced compared to a single optimized effective absorption coefficient. T2 - 19th International Conference on Photoacoustic and Photothermal Phenomena CY - Bilbao, Spain KW - Absorptance KW - Dispersion KW - Flash thermography KW - Infrared thermography KW - NDT KW - Semitransparency PY - 2018 DO - https://doi.org/10.1007/s10765-018-2474-0 SN - 0195-928X SN - 1572-9567 VL - 40 IS - 1 SP - 13, 1 EP - 13 PB - Springer Nature AN - OPUS4-47105 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Moskovchenko, A. I. A1 - Vavilov, V. P. A1 - Bernegger, Raphael A1 - Maierhofer, Christiane A1 - Chulkov, A. O. T1 - Detecting Delaminations in Semitransparent Glass Fiber Composite by Using Pulsed Infrared Thermography JF - Journal of Nondestructive Evaluation N2 - Thanks to its good strength/mass ratio, a glass fibre reinforced plastic (GFRP) composite is a common material widely used in aviation, power production, automotive and other industries. In its turn, active infrared (IR) nondestructive testing (NDT) is a common inspection technique for detecting and characterizing structural defects in GFRP. Materials to be tested are typically subjected to optical heating which is supposed to occur on the material surface. However, GFRP composite is semitransparent for optical radiation of both visual and IR spectral bands. Correspondingly, the inspection process represents a certain combination of both optical and thermal phenomena. Therefore, the known characterization algorithms based on pure heat diffusion cannot be applied to semi-transparent materials. In this study, the phenomenon of GFRP semi-transparency has been investigated numerically and experimentally in application to thermal NDT. Both Xenon flash tubes and a laser have been used for thermal stimulation of opaque and semi-transparent test objects. It has been shown that the Penetration of optical heating radiation into composite reduces detectability of shallower defects, and the signal-to-noise ratio can be enhanced by applying the technique of thermographic signal reconstruction (TSR). In the inspection of the semi-transparent GFRP composite, the most efficient has been the laser heating followed by the TSR data processing. The perspectives of defect characterization of semi-transparent materials by using laser heating are discussed. A neural network has been used as a candidate tool for evaluating defect depth in composite materials, but its training should be performed in identical with testing conditions. KW - Infrared thermography KW - Thermal testing KW - GFRP KW - Semi-transparent composite KW - Laser heating PY - 2020 DO - https://doi.org/10.1007/s10921-020-00717-x VL - 39 SP - 69 PB - Springer Science+Business Media, LLC, part of Springer Nature 2020 AN - OPUS4-51179 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -