After demonstrating recently the possibilities of scanning photothermal radiometry for wear crack detection (Bodnar et al.,
J. Phys. IV, 4 (1994) 591–594), we now study its possibilities for ...dimensional characterization of these kinds of flaws. In this respect, we present here the results obtained from our study of two types of emerging cracks, i.e. thin and shallow cracks in samples with a reflecting surface as well as wider and deeper cracks in samples with an absorbing surface.
Polymer composites with high thermal conductivity are used more frequently in thermal management of electronic packaging systems. In this study, conductive polymer composites were prepared by melt ...mixing of ethylene-vinyl acetate (EVA) copolymer with graphite at different volumetric concentrations up to 29.3%. Two kinds of graphite were used as reinforcement to prepare composites: untreated natural graphite (UG) having particle sizes ranging from 20 μm to 25 μm and expanded graphite (EG) having originally particle sizes ranging from 5 to 6 μm in length. Upon mixing at high shear forces EG exfoliates in thin sheets of a few nanometers in thickness. Due to this high aspect ratio of graphite sheets, nanocomposites filled with expanded graphite have a lower percolation threshold for electrical conductivity, about (5 to 6) vol.% compared to the composites filled with untreated graphite (UG) which have a percolation threshold of (15 to 17) vol.%. Thermal diffusivity of the samples was measured by photothermal radiometry. At similar concentrations, thermal diffusivity values for the nano-composites, EG-filled EVA, were significantly higher than those composites filled with UG.
The understanding of the problem of nonradiative energy conversion in solid-state laser materials is a key factor in improving the overall efficiency of solid-state lasers. Furthermore, the reduction ...of the heat generated in an optically pumped laser crystal can lead to several new applications of solid-state lasers, especially in the high-power region. To improve the quality of grown crystals, laser crystal growers require accurate techniques to perform the quality control that is so vital to improving the growth process. Using a time-domain approach and a time-domain theoretical treatment of the IR radiative emission signal, it was determined that one may probe nonradiative surface and bulk processes by monitoring different time ranges. Our results show that photothermal radiometry can be used as a single-ended technique to evaluate both the bulk and surface nonradiative energy conversion rates in a solid-state laser material. This technique was compared to the standard laser cavity technique and it was concluded that photothermal radiometry can provide additional information to the standard technique by identifying the sources of heat generation as either surface- or bulk-originating.
The thermal diffusivity of various types of aluminum has been measured, using a completely noncontact experimental configuration based on infrared photothermal radiometry. Photothermal response ...transients, conventional frequency scans, and pulse duration- or repetition rate-scanned rate windows have been investigated. It has been shown that the conventional frequency scan is not suitable for measurements of aluminum with a short thermal transport time such as foils, due to an extremely degraded signal-to-noise ratio (SNR). Also, it has been found that the conventional frequency scan method is less sensitive to the actual value of thermal diffusivity than the rate-window scan. The rate-window method, furthermore, gives superior SNR especially for thin metals and yields excellent agreement between the theory and the data. An advantage of the pulse duration-scanned rate window mode is that it does not require knowledge of the instrumental transfer function as an input. The transient response gives the worst SNR but is best for the physical interpretation of the photothermal signals. In addition, it has been shown that the infrared photothermal radiometric transmission mode is less sensitive to surface roughness than the reflection mode and, therefore, is preferable for thermal diffusivity measurements of aluminum and of good thermal conductors, in general.
Photothermal methods are well adapted to thin multilayer material analysis. In the particular case of biological materials, which are thermally fragile, low excitation power is required. We have ...studied whole human blood sedimentation by using photothermal radiometry and a photopyroelectric technique. Results obtained with random- and sine-modulated excitation are discussed. Evolution laws of plasma thicknesses and optical absorption coefficients during the process have been determined by identifying the parameters using different estimation methods. It appears that results are consistent with theoretical predictions of our 2D-thermophysical model and also with the values measured by the well-known Westergreen reference method, usually used in clinical analysis. Finally, in order to extend the investigation field of the pyroelectric method, particularly in the domain of biological materials, we have analysed the possibility of using the sensitive pyroelectric sensors without direct thermal contact with the sample and detecting the temperature changes at the sample surface through a thin air monolayer.
Les méthodes photothermiques sont particulièrement adaptées à l'analyse de matériaux minces stratifiés. Dans le cas particulier des matériaux thermiquement fragiles tels que les matériaux d'origine biologique, de faibles puissances d'excitation sont requises. À titre d'exemple, nous présentons une étude sur la sédimentation du sang total humain, réalisée tout d'abord par radiométrie photothermique, puis en utilisant une technique photopyroélectrique. Les résultats obtenus respectivement sous excitation aléatoire et sous excitation sinusoïdale sont discutés. Les lois d'évolution des épaisseurs de plasma et des coefficients d'absorption optiques durant le processus ont été déterminées par différentes méthodes d'estimation de paramètres. Les résultats obtenus sont conformes aux prédictions théoriques de notre modèle thermophysique 2D et aux valeurs mesurées par la méthode de référence dite de Westergreen habituellement utilisée en analyse clinique. Dans le but d'élargir le champ d'investigation de la méthode pyroélectrique, d'un intérêt particulier dans le domaine des matériaux biologiques, nous avons finalement proposé l'utilisation de capteurs pyroélectriques, non pas mis en contact direct avec l'échantillon, mais positionnés de manière à détecter les variations du champ de température à la surface de celui-ci au travers d'une fine couche d'air.
Alumina derivative ceramics and low temperature co-fired ceramic (LTCC) electronic multichip module (MCM) packaging substrates have been characterized using single- and double-sided inspection laser ...flash thermal diffusivity measurement techniques. The paper highlights problems associated with both the measurement system and associated data analysis for the single-sided measurement, and these data are evaluated with reference to that measured by an existing (double sided inspection) standard laser flash method. Finally, a preliminary single-sided measurement methodology is proposed.
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