Showing papers on "Thermography published in 2004"
TL;DR: The most relevant experiences devoted to the use of infrared thermography in three main fields, i.e. thermo-fluid dynamics, technology and cultural heritage, which have been performed in the department the authors belong to are described in this article.
Abstract: Infrared thermography transforms the thermal energy, emitted by objects in the infrared band of the electromagnetic spectrum, into a visible image. This feature represents a great potentiality to be exploited in many fields, but this technique is still not adequately enclosed in industrial instrumentation because of a lack of adequate knowledge; at first sight, it seems too expensive and difficult to use. The aim of the present paper is to shortly overview existing work and to describe the most relevant experiences devoted to the use of infrared thermography in three main fields, i.e. thermo-fluid dynamics, technology and cultural heritage, which have been performed in the department the authors belong to. Results may be regarded from two points of view, either as validating infrared thermography as a full measurement instrument, or as presenting infrared thermography as a novel technique able to deal with several requirements, which are difficult to perform with other techniques. This study is also an attempt to give indications for a synergic use of the different thermographic methods and sharing experiences in the different fields.
414 citations
TL;DR: In this article, a fuel cell has been designed that combines three methods of spatially resolved measurements, which allows simultaneous evaluation of current, temperature and water distribution in a polymer electrolyte fuel cell under operation.
311 citations
TL;DR: A general review of the Pulsed Phase Thermography technique is presented and the different types of uncertainties related to data acquisition and processing are identified.
Abstract: Pulsed Phase Thermography has considerably evolved since it was originally introduced in 1996. In this paper, a general review of the technique is presented. The different types of uncertainties related to data acquisition and processing are identified. Equivalence between discrete and continuous Fourier Transforms when applied to thermographic data is discussed in detail. As will be pointed out, the optimal solution for a Pulsed Phase problem, qualitative or quantitative, arises from a compromise between sampling rate, truncation window size and the available computer power. The theoretical concepts introduced here are reinforced with a variety of experimental results.
223 citations
TL;DR: Thermography is shown to be more than just a method for obtaining pretty pictures; it has particular advantages for the quantitative analysis of spatial and dynamic physiological information.
Abstract: The applications of remote temperature sensing of plants by infrared thermography and infrared thermometry are reviewed and their advantages and disadvantages for various purposes discussed. The great majority of applications of thermography and of infrared thermometry depend on the sensitivity of leaf temperature to evaporation rate (and hence to stomatal aperture). In most applications, such as in the early or pre-symptomatic detection of disease or water deficits, what is actually being studied is the effect of the disease on stomatal behaviour or membrane permeability to water. Other applications of thermography in plant physiology include the study of thermogenesis as well as the characterisation of boundary layer transfer processes. Thermography is shown to be more than just a method for obtaining pretty pictures; it has particular advantages for the quantitative analysis of spatial and dynamic physiological information. Its capacity for large throughput has found application in screening approaches, such as in the selection of stomatal or hormonal mutants. The use of wet and dry reference surfaces for the enhancement of the power of thermal imaging approaches, especially in the field is reviewed, and the problems and potential solutions when applying thermography in the field and in the laboratory discussed.
222 citations
TL;DR: In this article, an overview of infrared thermography and its applications relating to the investigation of historic structures is presented. But this work is limited to the case of buildings and does not cover the application of non-destructive testing and evaluation on the materials and structures.
220 citations
TL;DR: Investigation of the capability of infrared thermography as a non-invasive, early detection method for identifying animals with a systemic infection found it to be effective in detecting bovine viral diarrhoea virus infection in calves.
Abstract: Early detection and/or prediction of disease in an animal is the first step towards its successful treatment. The objective of this study was to investigate the capability of infrared thermography ...
192 citations
TL;DR: The Monte Carlo method was implemented to solve the transient three-dimensional bio-heat transfer problem with non-linear boundary conditions and space-dependent thermal physiological parameters and indicated that the thermal states of biological bodies, reflecting physiological conditions, could be correlated to the temperature or heat flux mapping recorded at the skin surface.
188 citations
TL;DR: In this article, the thermal diffusivity of yttria-zirconia (Y2O3-ZrO2) single crystals, with YO1.5 concentrations in the range of 0-60 mol%, has been determined using a new method that is based on spatially resolved (20 μm) infrared mapping of a modulated thermal field.
Abstract: The thermal diffusivity of yttria–zirconia (Y2O3–ZrO2) single crystals, with YO1.5 concentrations in the range of 0–60 mol%, has been determined using a new method that is based on spatially resolved (20 μm) infrared mapping of a modulated thermal field. The decreasing trend of the thermal conductivity (K), as a function of the YO1.5 content (up to 20 mol%), can be described using a model based on a Debye approach that has been modified by introducing a cut-off length for the phonon mean free path. At higher concentrations, K increases, as a result of a possible ordering of the point defects.
154 citations
TL;DR: In this article, an infrared thermography technique using a transient surface temperature acquisition is described which determines both the heat transfer coefficient and film effectiveness (non-dimensional adiabatic wall temperature) from a single test.
Abstract: In film cooling situations, there is a need to determine both local adiabatic wall temperature and heat transfer coefficient to fully assess the local heat flux into the surface. Typical film cooling situations are termed three temperature problems where the complex interaction between the jets and mainstream dictates the surface temperature. The coolant temperature is much cooler than the mainstream resulting in a mixed temperature in the film region downstream of injection. An infrared thermography technique using a transient surface temperature acquisition is described which determines both the heat transfer coefficient and film effectiveness (non-dimensional adiabatic wall temperature) from a single test. Hot mainstream and cooler air injected through discrete holes are imposed suddenly on an ambient temperature surface and the wall temperature response is captured using infrared thermography. The wall temperature and the known mainstream and coolant temperatures are used to determine the two unknowns (heat transfer coefficient and film effectiveness) at every point on the test surface. The advantage of this technique over existing techniques is the ability to obtain the information using a single transient test. Transient liquid crystal techniques have been one of the standard techniques for determining h and η for turbine film cooling for several years. Liquid crystal techniques do not account for non uniform initial model temperatures while the transient IR technique measures the entire initial model distribution. The transient liquid crystal technique is very sensitive to the angle of illumination and view while the IR technique is not. The IR technique is more robust in being able to take measurements over a wider temperature range which improves the accuracy of h and η. The IR requires less intensive calibration than liquid crystal techniques. Results are presented for film cooling downstream of a single hole on a turbine blade leading edge model.Copyright © 2004 by ASME
119 citations
TL;DR: In this paper, the authors assess the usefulness of infrared thermography as a technique for the detection of the thermal performance of rural buildings in Spanish rural areas, using two common housing prototypes of existing buildings.
101 citations
TL;DR: In this paper, the authors highlight the help provided by infrared thermography in the characterization of materials, and demonstrate the capability of modulated lockin thermography (MT) to discriminate between materials very similar and this feature can be advantageously exploited to evaluate modifications that occur in material characteristics as consequence of ageing, or exposure to adverse environmental conditions.
TL;DR: In this article, an analysis of different techniques to measure thermal diffusivity is presented, resulting from a collaboration between two laboratories, and the agreement between the results obtained by applying the six techniques appears satisfactory from a practical point of view.
Abstract: In this work, resulting from a collaboration between two laboratories, an analysis of different techniques to measure thermal diffusivity is presented. First, a brief description of the laser flash method, thermal wave interferometry photothermal techniques, and four different thermographic techniques in terms of experimental setups and in data processing algorithms is given. After that, results obtained on samples cut from the same block of stainless steel AISI 304 are reported. Uncertainty evaluations of the measurements are reported together with a discussion on the pros and cons of the related techniques. The agreement between the results obtained by applying the six techniques appears satisfactory from a practical point of view.
TL;DR: A complete set of automated techniques for the computerised assessment of thermal images to assess pain-related thermal dysfunction is developed and compared favourably against Wiener and other wavelet-based denoising methods.
Abstract: The skin temperature distribution of a healthy human body exhibits a contralateral symmetry. Some nociceptive and most neuropathic pain pathologies are associated with an alteration of the thermal distribution of the human body. Since the dissipation of heat through the skin occurs for the most part in the form of infrared radiation, infrared thermography is the method of choice to study the physiology of thermoregulation and the thermal dysfunction associated with pain. Assessing thermograms is a complex and subjective task that can be greatly facilitated by computerised techniques. This paper presents techniques for automated computerised assessment of thermal images of pain, in order to facilitate the physician's decision making. First, the thermal images are pre-processed to reduce the noise introduced during the initial acquisition and to extract the irrelevant background. Then, potential regions of interest are identified using fixed dermatomal subdivisions of the body, isothermal analysis and segmentation techniques. Finally, we assess the degree of asymmetry between contralateral regions of interest using statistical computations and distance measures between comparable regions. The wavelet domain-based Poisson noise removal techniques compared favourably against Wiener and other wavelet-based denoising methods, when qualitative criteria were used. It was shown to improve slightly the subsequent analysis. The automated background removal technique based on thresholding and morphological operations was successful for both noisy and denoised images with a correct removal rate of 85% of the images in the database. The automation of the regions of interest (ROIs) delimitation process was achieved successfully for images with a good contralateral symmetry. Isothermal division complemented well the fixed ROIs division based on dermatomes, giving a more accurate map of potentially abnormal regions. The measure of distance between histograms of comparable ROIs allowed us to increase the sensitivity and specificity rate for the classification of 24 images of pain patients when compared to common statistical comparisons. We developed a complete set of automated techniques for the computerised assessment of thermal images to assess pain-related thermal dysfunction.
TL;DR: In this article, a grid-like mask is placed in front of the flash lamp so that heat is absorbed over a series of periodic parallel strips and the signal-to-noise ratio is increased thereby.
TL;DR: Induction-Lockin-Thermography (ILT) as discussed by the authors uses a thermography camera with a detector array to monitor induction heated areas, which allows for fast phase angle imaging of defects in larger areas.
Abstract: A new lockin thermography method is presented where inductive heating by eddy current is used for periodical sample excitation. In conventional eddy current testing damages like cracks in metals are detected with a coil which changes its impedance over defect areas. The disadvantage of this method is its time consuming point-by-point scanning over the surface of the sample. Induction-Lockin-Thermography (ILT), however, uses a thermography camera with a detector array to monitor induction heated areas. Temperature patterns and their time dependence responding to the coded excitation allow for fast phase angle imaging of defects in larger areas.
TL;DR: In this article, the aid provided by infrared thermography for non-destructive evaluation of three types of joints: aluminum adhesively bonded joints, stainless steel laser welded joints and Glare® mechanical fastened joints.
TL;DR: In this paper, an experimental study is presented to gain information about limits in detection of defects in composites by infrared-thermography, and the results are presented in terms of difference of temperature (pulse), or difference of phase angle (lockin), between damaged zones and sound material.
Abstract: The aim of the present experimental study is to gain information about limits in detection of defects in composites by infraredthermography. Specimens are manufactured of either carbon/epoxy, or glass/epoxy, and withinclusions of foreign materials to simulate defects of different size and positioned at different depths. Tests are carried out by using both pulse and lockin techniques. Results are presented in terms of difference of temperature (pulse), or difference of phase angle (lockin), between damaged zones and sound material. It seems that, apart from diameter and depth, thethickness is very crucial for defects visibility.
TL;DR: In this paper, the junction temperature of multiquantum well (MQW) LEDs in InGaN-GaNsapphire structure is measured using a high power laser beam to enhance the contrast of the thermal image.
Abstract: In this letter, we present a new configuration with laser illumination to measure the temperature of visible light-emitting diode (LED) chips using nematic liquid crystals. This method is applied to measuring the junction temperature of multiquantum well (MQW) LEDs in InGaN-GaN-sapphire structure. A color filter is inserted in the optical path to attenuate the overwhelming LED light. A high-power laser beam is used as the sensing light to enhance the contrast of the thermal image on LED chips. This technique is nondestructive and can be performed in real-time during device operation. One objective is to investigate the effect of the junction temperature on the electrical and optical performance of the LED devices. For the LEDs measured, the conversion efficiency decreases by 67% when the junction temperature rises from 22/spl deg/C to 107/spl deg/C. The new measurement configuration is a valuable tool to study the thermal performance of GaN-based LED devices and subsequently to investigate the degradation on electrical and optical performance due to junction temperature increase.
TL;DR: In this paper, a 2D-technique for temperature visualization of single droplets and sprays is presented, where laser induced emission from thermographic phosphor seeded to the investigated liquid was detected by a fast framing camera.
Abstract: A novel 2D-technique for temperature visualization of single droplets and sprays is presented. Laser induced emission from thermographic phosphor seeded to the investigated liquid was detected by a fast framing camera. The subsequent phosphorescence images measured by seven consecutively gated CCD detectors allowed pixel-to-pixel lifetime evaluation of the phosphorescence emission. The temperature at each pixel position was evaluated using a calibration procedure of temperature against lifetime. These measurements were applied first to a free falling water based droplet, then to a suspended droplet in an ultrasonic levitator. Finally, the technique was applied to spray.
TL;DR: In this article, transient-pulsed thermography was used as a through skin imaging technique with the intention of locating anchoring points beneath the outer skins of aircraft structures, and a representative test structure, comprising a thin skin positioned over a thick strut fixture, was investigated experimentally and analysed using finite difference thermal modelling software.
TL;DR: In this article, a spatially resolved image of leakage currents in solar cells is obtained by using illuminated lock-in thermography, which is directly proportional to the local power losses in the solar cell.
Abstract: The spatially resolved evaluation of power losses in solar cells is a key issue in identifying technological and material quality problems and realistically judging their influence on solar cell performance. Up to now a spatially resolved image of leakage currents could only be obtained by lock-in thermography measuring the distribution of the dark leakage current in solar cells. However, it is well known from simulations that the dark and illuminated current paths in solar cells may differ considerably. In this article spatially resolved images of the power losses in solar cells measured under realistic operation conditions, that is at the maximum power point and under illumination, are presented. This improvement was made possible by the development of a measurement technique called illuminated lock-in thermography. The underlying physics of this technique are discussed and it is shown that this method gives an image, which is directly proportional to the local power losses in the solar cell. Different ...
TL;DR: In this paper, the authors used transient thermography (TT) for the non-destructive assessment of repaired aircraft carbon or boron composite panels, as well as composite patches enclosing a fibre optic across their width.
TL;DR: In this paper, the applicability of infrared thermography in two particular situations is considered -the delamination of external wall finishes and a roofing system condition survey and the factors influencing the IR imaging.
Abstract: The application of infrared thermography has provided a reliable and accurate assessment method for the inspection of buildings and structures. The principle of the infrared thermography technique is the detection of energy by an infrared scanner and mapping the temperature contours over the surface of a target object to provide an appropriate measure of the damaged building or structure. This paper reviews the background of infrared thermography and the factors influencing the IR imaging. The applicability of infrared thermography in two particular situations is considered – the delamination of external wall finishes and a roofing system condition survey.
12 Apr 2004
TL;DR: In this article, the authors present some practical solutions developed by CEDIP infrared systems to perform non uniformity and thermal drift corrections, as well as their performance and limits are reviewed.
Abstract: In the last decade, a technology of thermal imagers was developing on the basis of new infrared detectors, as well for civil and military uses. These imagers implement miniaturised infrared detectors laid out in a matrix placed in the optical focal plane of the imager. The technology of the FPA associates the detector matrix to specific electronics allowing detection and addressing on each pixel. This technology allowed a fast improvement of the performance of the thermal imager. Nevertheless, their use in thermography measurement requires some metrological care. The principal problem is both the uniformization of the pixel’s response and the temporal stability of this uniformization. The second problem consists in the compensation of the thermal drift. In this paper, we present some practical solutions developed by CEDIP infrared systems to perform non uniformity and thermal drift corrections. Performance and limits are reviewed.
TL;DR: In this article, a wide range of applications of illuminated lock-in thermography (ILT) in identifying the causes of power losses in solar cells are presented. But the main focus of this paper is to demonstrate the wide range and application of ILT in identifying and quantifying power losses of solar cells.
Abstract: The principles of a recently introduced measurement technique for power losses in solar cells, illuminated lock-in thermography (ILT), are reviewed. The main advantage of ILT over dark lock-in Thermography (DLT) is measurement under realistic operational conditions of solar cells. The main focus of this paper is to demonstrate the wide range of applications of ILT in identifying the causes of power losses in solar cells. For this purpose different evaluation methods are presented. A method for the evaluation of improvement potentials within a given cell technology is demonstrated. It is shown that different types of series resistance may be localized. Small areas of recombination losses (e.g., grain boundaries) can routinely be detected, which is not possible in dark lock-in thermography. Good correspondence with light-beam-induced current images is found. A realistic evaluation of the impact of recombination losses on solar cell performance is demonstrated on two examples. Finally, process- or treatment-induced recombination losses are investigated. In summary ILT is shown to be an extremely powerful tool in localizing, identifying and quantifying power losses of solar cells under realistic illumination conditions.
TL;DR: In this paper, an investigation has been made of the potential of pulsed-transient thermography for identifying the location of fixtures beneath aircraft skins to facilitate accurate automated assembly operations.
Abstract: In this work, an investigation has been made of the potential of pulsed-transient thermography for identifying the location of fixtures beneath aircraft skins to facilitate accurate automated assembly operations. Representative test structures, comprising of aircraft skin (i.e. aluminium (Al) or carbon fibre reinforced plastic (CFRP)) positioned over a thick strut fixture of Al or CFRP, were investigated experimentally and analysed using finite difference thermal modelling software, taking into account the size and depth of the features, as well as the thermal properties of the investigated materials. The ability of the technique to detect a subsurface fixing and to provide information about its location was analysed. Results from the modelling and the experimental analysis are presented and discussed.
TL;DR: In this paper, a light-modulated lock-in thermography (LimoLIT) method was proposed to detect photovoltaic conversion of modulated light, which can be used for defect analysis of solar cells.
Abstract: Lock-in thermography (LIT) is a well-established tool for defect analysis of solar cells, but so far has been restricted to the measurement of metallized samples. The new light-modulated lock-in thermography (LimoLIT) described in this paper overcomes this restriction by generating the voltage modulation needed for detection from photovoltaic conversion of modulated light. Thus wafers can be measured during all stages of fabrication, a pn-junction provided. The contactless LimoLIT method shows a stronger measurement signal and invokes a current flow close to illuminated operating conditions of solar cells, whereas conventional LIT is only comparable to a dark I–V measurement. Copyright © 2004 John Wiley & Sons, Ltd.
01 Jan 2004
TL;DR: This research explores the relationship between the characteristics (location and power) of an embedded heat source and the resulting temperature distribution on the surface and determined that a genetic algorithm based approach is well suited for the estimation problem since both the depth and the heat generation rate of the heat source were accurately predicted.
Abstract: Breast cancer is the most common cancer among women. Statistics released by American Cancer Society (1999) show that every 1 in every 8 women in the United States is likely to get breast cancer during her lifetime. Thermography, also known as thermal or infrared imaging, is a procedure to determine if an abnormality is present in the breast tissue temperature distribution, which may indicate the presence of an embedded tumor. In the year 1982, United States Food and Drug Administration (FDA) approved thermography as an adjunct method of detecting breast cancer, which could be combined with other established techniques like mammography. Although thermography is currently used to indicate the presence of an abnormality, there are no standard protocols to interpret the abnormal thermal images and determine the size and location of an embedded tumor. This research explores the relationship between the physical characteristics of an embedded tumor and the resulting temperature distributions on the skin surface. Experiments were conducted using a resistance heater that was embedded in agar in order to simulate the heat produced by a tumor in the biological tissue. The resulting temperature distribution on the surface was imaged using an infrared camera. In order to estimate the location and heat generation rate of the source from these temperature distributions, a genetic algorithm was used as the estimation method. The genetic algorithm utilizes a finite difference scheme for the direct solution of Pennes bioheat equation. It was determined that a genetic algorithm based approach is well suited for the estimation problem and that thermography can prove to be a valuable tool in locating tumors if combined with such an algorithm.Copyright © 2004 by ASME
TL;DR: The study revealed that thermography fails to meet the criteria of high level of evidence and cannot be recommended for routine use as a diagnostic technique to identify TMJ disorders.
Abstract: This paper presents a review of the use of infrared thermography in diagnosis of temporomandibular joint (TMJ) arthralgia. The question examined was whether the infrared thermography could be reliably used as a tool to diagnose arthralgia by objectively assessing the site of origin and the degree of irritation. Controlled studies were performed by using advanced thermographic devices to show both diagnostic validity and reliability of infrared thermography as a screening test for selecting healthy subjects from patients with unilateral TMJ arthralgia. The study revealed that thermography fails to meet the criteria of high level of evidence. Further studies are required to confirm these results in order to specify analysis of facial thermal patterns and to better understand the relationship between TMJ arthralgia and regional temperature changes. Until then infrared thermography cannot be recommended for routine use as a diagnostic technique to identify TMJ disorders.
TL;DR: In this article, the Peltier effect was used to estimate the diffusivity of a thermal signal, where the wavefront of the temperature oscillation within the sample becomes plane and perpendicular to the main surfaces of the sample.