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Showing papers on "Thermography published in 1997"


Journal ArticleDOI
TL;DR: It is demonstrated that IR thermography is an excellent method for studying ice nucleation and propagation in plants by monitoring of an array of plant species under different freezing conditions.
Abstract: We evaluated the use of infrared (IR) video thermography to observe directly ice nucleation and propagation in plants. An imaging radiometer with an HgCdTe long-wave (8-12 [mu]m) detector was utilized to image the thermal response of plants during freezing. IR images were analyzed in real time and recorded on videotape. Information on the videotape was subsequently accessed and analyzed utilizing IR image analysis software. Freezing of water droplets as small as 0.5 [mu]L was clearly detectable with the radiometer. Additionally, a comparison of temperature tracking data collected by the radiometer with data collected with thermocouples showed close correspondence. Monitoring of an array of plant species under different freezing conditions revealed that ice nucleation and propagation are readily observable by thermal imaging. In many instances, the ice nucleation-active bacterium Pseudomonas syringae placed on test plants could be seen to initiate freezing of the whole plant. Apparent ice nucleation by intrinsic nucleators, despite the presence of ice nucleation-active bacteria, was also evident in some species. Floral bud tissues of peach (Prunus persica) could be seen to supercool below the temperature of stem tissues, and ice nucleation at the site of insertion of the thermocouple was frequently observed. Rates of propagation of ice in different tissues were also easily measured by thermal imaging. This study demonstrates that IR thermography is an excellent method for studying ice nucleation and propagation in plants.

177 citations


Journal ArticleDOI
TL;DR: It is concluded that calculation of a reliable mean skin temperature must involve more than seven skin temperature measurement sites regardless of ambient temperature.
Abstract: To study the reliabiliity of formulas for calculating mean skin temperature (Tsk), values were computed by 18 different techniques and were compared with the mean of 10,841 skin temperatures measured by infrared thermography. One hundred whole-body infrared thermograms were scanned in ten resting males while changing the air temperature from 40° C to 4° C. Local, regional average and mean skin temperatures were obtained using an image processing system. The agreement frequency, defined as the percentage of the calculated Tsk values which agreed with the corresponding infrared thermographic Tsk within ±0.2° C, ranged for with the various formulas from 7% to 80%. In many sites, the local skin temperature did not coincide with the regional average skin temperature. When the local skin temperatures which showed the highest percentage similarity to the regional average skin temperature within ±0.4° C were applied to the formula, the agreement frequency was markedly improved for all formulas. However, the agreement frequency was not affected by changing the weighting factors from specific constants to individually measured values of regional surface area. By applying the physiologically reliable accuracy range of ±0.2° C in the moderate and ±0.4° C in the cool condition, agreement frequencies of at least 95% were observed in formulas involving seven or more skin temperature measurement sites, including the hand and foot. We conclude that calculation of a reliable mean skin temperature must involve more than seven skin temperature measurement sites regardless of ambient temperature. Optimal sites for skin temperature measurement are proposed for various formulas.

151 citations


Journal ArticleDOI
TL;DR: The found that the mean k value, and therefore the rate of decline in corneal temperature in patients with dry eye, was significantly less than that in normal subjects, and the k value may therefore reflect tear film layer stability.

110 citations


Patent
30 Oct 1997
TL;DR: In this paper, a non-destructive testing technique and system for locating flaws within an object is proposed. But the method is limited to transient depth thermography (TDPT).
Abstract: The present invention relates to transient depth thermography; a nondestructive testing technique and system for locating flaws within an object. The system, which comprises a heater for heating the surface of the object; a recorder for recording pixel intensity for each pixel on the heated surface; a means for determining pixel contrast from the pixel intensity; and a means for determining the size and location of flaws within the object based upon the pixel contrast; monitors each pixels' contrast for successive thermal images and utilizes those pixel contrasts determining the location of a flaw within the object. The object surface and the respective underlying flaws can then be depicted on a color spectrum image print which correlates the flaw depth with a particular color.

89 citations


Journal ArticleDOI
TL;DR: In this article, the use of infrared imaging methods for non-destructive evaluation (NDE) applications is discussed, and the benefits of thermal wave imaging systems are outlined, as well as their drawbacks.
Abstract: Examines the use of infrared imaging methods for non‐destructive evaluation (NDE) applications. Describes thermal wave imaging systems, outlining their benefits.

62 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed a method for the characterization of buried defects in building infrared thermography using a transient technique based on recording the image sequence in both the heating and cooling stages, with the thermal stimulus being delivered onto the surface with a Dirac or harmonic heat pulse.
Abstract: Building infrared thermography is a well-established but still qualitative technique that is used mostly for detecting insulation deficiencies, air leaks, moist areas, and thermal bridges in envelopes. Characterization of buried defects requires replacing steady-state thermography with a transient technique. It is proposed to borrow for this purpose the inspection methodology developed in the thermal nondestructive evaluation of materials. This methodology is based on recording the image sequence in both the heating and cooling stages, with the thermal stimulus being delivered onto the surface with a Dirac, square, or harmonic heat pulse. The dedicated image treatment allows the substitution of a sequence of any length with a pair of images called the maxigram and timegram. These images contain information needed for the characterization of defects. Some explicit inversion formulas discussed in the paper enable the determination of defect depth and thermal resistance. The proposed approach is illustrated with experimental results. Evaluation of internal corrosion in concrete and detection of underplaster delaminations are reported.

49 citations


Proceedings ArticleDOI
04 Apr 1997
TL;DR: In this paper, the advantages of phase sensitive modulation thermography (also called lockin thermography) are illustrated together with some applications of nondestructive evaluation (NDE) on advanced materials and large structures.
Abstract: The advantages of phase sensitive modulation thermography (also called lockin thermography) are here illustrated together with some applications of nondestructive evaluation (NDE) on advanced materials and large structures. Lockin thermography has shown to be a versatile tool for rapid inspection of large surfaces and detection of defects in materials where other NDE techniques are not able to give good results. Besides this, the phase angle image eliminates many undesired effects like inhomogeneous distribution of surface heating that make images obtained with pulse thermography difficult to interpret.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

37 citations


Journal ArticleDOI
TL;DR: In this article, the authors collected data on the wing temperature of flying bats using infrared thermal imaging to assess the thermoregulatory function of wing membranes and found small but significant changes in body temperature during flight.

35 citations


Journal ArticleDOI
TL;DR: In this article, a shape from shading (SDF) method is proposed to evaluate the shape of a nonplanar part and then apply a correction on subsequent thermograms in the time sequence to increase the reliability of defect detection.
Abstract: Pulse-transient IR thermography enables detection and quan- tification of subsurface defects. However, defect detection can be per- turbed by the geometry of the part, if not planar. A method is presented that, from a single IR image recorded at the end of the thermal pulse, enables one to evaluate the shape of a nonplanar part and then apply a correction on subsequent thermograms in the time sequence to increase the reliability of defect detection. The method uses some of the concepts of the ''shape from shading'' theory from the machine vision field. © 1997 Society of Photo-Optical Instrumentation Engineers.

32 citations


Journal ArticleDOI
Terumi Inagaki1, Yoshizo Okamoto1
TL;DR: In this article, the authors used infrared thermography in near ambient conditions to check the leakage point and its applicability is estimated by visualizing the temperature field generated around the point, which is not usually consistent with the surrounding temperature.
Abstract: It is important to check for leakage points of fluids on a surface to maintain and manage various structures satisfactorily. In particular, it is necessary that the leaking walls of a bank, dam, tunnel, pipeline and so on are diagnosed appropriately using some remote sensing technique and that they should be repaired immediately. Recently, infrared thermography for measuring temperature has become attractive in a wide variety of engineering applications. Infrared thermography in near ambient conditions is introduced to check the leakage point and its applicability is estimated by visualizing the temperature field generated around the point. The generated temperature around the leakage point is not usually consistent with the surrounding temperature. When using infrared thermography, we can detect the leakage point at the location where a marked temperature difference occurs.

29 citations


Book ChapterDOI
TL;DR: In this paper, the authors recommend general procedures for reliable quantitative thermographic measurements in chambers operated for winter heating conditions, and use a temperature-controlled reference emitter to remove error appear to show accuracies of 0.5°C for flat specimens with low temperature gradients.
Abstract: Infrared (IR) imaging radiometers, which measure relative levels of thermal radiation energy, can be used for noninvasive surface temperature measurements of building thermal envelope components undergoing steady-state heat flow in laboratory thermal chambers. One advantage of IR measurement is that it provides large contiguous sets of surface temperature data which are useful for validating the accuracy of complex computer models that predict heat flow through thermally insulated systems. Because they give such detailed information about surface temperature, IR measurements complement hot-box measurements of heat flow. This paper recommends general procedures for reliable quantitative thermographic measurements in chambers operated for winter heating conditions. Actual surface temperature depends on heat flow, surface emittance, and environmental conditions such as air temperature, air flow field, and background thermal radiation. The infrared temperature measurements are affected by many of the same factors including surface emittance, air temperature, background thermal radiation, and air humidity. Equipment specifications for the absolute accuracy of infrared temperature measurements are typically ′1° to ′2°C. Measurements that use a temperature-controlled reference emitter to remove error appear to show accuracies of ′0.5°C for flat specimens with low temperature gradients.

Journal ArticleDOI
TL;DR: In this article, the authors used dynamic contact thermography to measure the local current flow through biased solar cells, which reveals the locations limiting the open circuit voltage and the fill factor of solar cells.
Abstract: The local current flow through biased solar cells can be monitored by measuring the local heating at the cell surface. Based on the discussion of heat diffusion phenomena and on practical aspects, optimum strategies for dynamic local current density measurements are derived. The practical realization of dynamic contact thermography is reviewed. Local inhomogeneities of the injected current density can be measured by this technique with a spatial resolution of down to 100 mm and a sensitivity of about 200 mA/cm 2 in forward direction of a silicon cell. Moreover, local I‐‐V characteristics can be measured thermally in a non-destructive way. The applicability of this technique is demonstrated by investigating shunts in multicrystalline silicon solar cells. Dynamic thermography is shown to be a useful supplement to LBIC and EBIC investigations, since it reveals the locations limiting the open circuit voltage and the fill factor of solar cells.

Journal ArticleDOI
TL;DR: In this paper, a technique for evaluating the wind environment around buildings in wind tunnel tests has been developed, which can be used effectively at an early design stage of a tall building development, e.g., when the cross sections and/or the arrangement of buildings are examined from the view point of the pedestrian level wind environment.

Journal ArticleDOI
TL;DR: In this paper, the ability of a thermographic imaging technique for detecting flat bottom hole defects of various diameters and depths was evaluated in four composite systems (two types of ceramic-matrix composites, one metalmatrix composite, and one polyamide-polyamide composite) of interest as high-temperature structural materials.
Abstract: The ability of a thermographic imaging technique for detecting flat-bottom hole defects of various diameters and depths was evaluated in four composite systems (two types of ceramic-matrix composites, one metal-matrix composite, and one polymer-matrix composite) of interest as high-temperature structural materials. The holes ranged from 1 to 13 mm in diameter and 0.1 to 2.5 mm in depth in samples approximately 2—3 mm thick. The thermographic imaging system utilized a scanning mirror optical system and infrared (IR) focusing lens in conjunction with a mercury—cadmium—telluride infrared detector element to obtain high-resolution infrared images. High-intensity flash lamps located on the same side as the infrared camera were used to heat the samples. After heating, up to 30 images were sequentially acquired at 70—150 ms intervals. Limits of detectability based on depth and diameter of the flat-botton holes were defined for each composite material. Ultrasonic and radiographic images of the samples were obtained and compared with the thermographic images. This study was done under a nonreimbursable Space Act Agreement between NASA—Lewis Research Center and Bales Scientific, Inc., to allow several heating configurations to be evaluated in a cost-effective and timely fashion.

Journal ArticleDOI
TL;DR: In this article, the possibilities and the main problems of thermography in VLSI circuits and power devices design and measurement are discussed, focusing on emissivity correction, noise and other measuring difficulties.

Journal Article
TL;DR: In this article, a complete procedure for the calibration of a focal plane array in quantitative infrared nondestructive testing (NDT) is proposed, which includes vignetting correction and gray level conversion into temperature.
Abstract: In this paper, a complete procedure is proposed for the calibration of a focal plane array in quantitative infrared nondestructive testing (NDT). This procedure includes vignetting correction and gray level conversion into temperature. A noise analysis is also presented in the context of pulsed infrared thermography applied to NDT. In this analysis, the authors introduce a new parameter, the noise equivalent material loss (NEML). The NEML is a global figure of merit which allows the comparison of different experimental set-ups for infrared pulsed thermography. Theory, experimental validation of the proposed concepts, and comparison with a few infrared scanning thermal imagers are presented as well.

Journal ArticleDOI
TL;DR: In this article, a new experimental method using infrared thermography for the evaluation of wind impact at pedestrian level is described, which consists of a heated plate on which building models stand, an infrared video camera for detecting the surface temperature distributions on the heated plate, and a microcomputer for image processing and presentation.
Abstract: This paper describes a new experimental method using infrared thermography for the evaluation of wind impact at pedestrian level. The developed measurement system consists of a heated plate on which building models stand, an infrared video camera for detecting the surface temperature distributions on the heated plate, and a microcomputer for image processing and presentation. Since the heat loss from the heated plate can be related to air flow speeds by the principle of heat convection, the surface temperature pattern is used as an indicator of the wind impact at the pedestrian level. Results have been derived from thermal images around various buildings both on selected points and over entire affected areas that are quantified by the reduced temperature and the overall impact, respectively. The paper presents details of the experimental setup, operational principles, calibration results, application examples, and further thoughts on this technique. At the current stage, the infrared technique is capable of visualizing surface flow fields through color images, quantifying windy zones in terms of temperature variation, and evaluating the overall wind impact by further calculation.

Proceedings ArticleDOI
04 Apr 1997
TL;DR: In this paper, the authors discuss the possibilities of defect detection in terms of minimum diameter-to-depth ratio (D2R) in aluminum components and evaluate the performance of this approach on both academic and real corroded specimens from the aircraft industry.
Abstract: Recently, the fundamentals of the 'pulsed phase thermography' approach were described. As it is recalled, this approach somehow combines together practical advantages of both the well-known 'pulsed-transient thermography' and the 'lockin thermography' for which specimens are submitted to a periodical excitation. Some advantages of this novel approach were demonstrated as well. In the present paper, the discussion about 'pulsed phase thermography' includes theory and reviews the possibilities of defect detection in terms of minimum diameter-to-depth ratio in aluminum components. Experimental results include both academic and real corroded specimens from the aircraft industry.

Journal ArticleDOI
TL;DR: In this paper, the authors used infrared thermography as a two-dimensional method of measuring device temperatures and heat fields, compared with contacting thermometry or integration of thermally sensitive structures.

Journal Article
TL;DR: In this paper, the temperature distribution of a paper sheet during fracture toughness testing was successively observed as a series of color images by means of an infrared thermography system with close-up lens.
Abstract: The temperature distribution of a paper sheet during fracture toughness testing was successively observed as a series of color images by means of an infrared thermography system with close-up lens. No stress concentration accompanied by plastic deformation occurs within the deep double-edge notched tension specimen except around notch tips. A uniformly and plastically deformed region develops from notch tips at the second half of the testing period and becomes a circular plastically deformed region on the ligament just before final sheet failure, irrespective of beating degree. A stable crack has started to grow from notch tips at latest at the point of maximum load. Application: The thermography is a good tool to examine the new testing methods for strenghth properties.

Journal ArticleDOI
TL;DR: In this article, the utility of infrared thermography applied to the study of moisture in builiding materials or in buildings, including those cases in which the water content is very high, is shown.

Proceedings ArticleDOI
30 Oct 1997
TL;DR: The development of an image-processing program capable of producing images of the temperature difference between the affected side and the corresponding contralateral healthy side of the living body is described.
Abstract: The most common and most effective method for using thermography to detect abnormalities is to compare the thermographic image of the affected area with that of the corresponding contralateral healthy area, even though this method can be applied to cases with only hemilateral involvement. This paper describes the development of an image-processing program capable of producing images of the temperature difference between the affected side and the corresponding contralateral healthy side of the living body. The feasibility of the image-processing program was demonstrated by employing it for diagnostic purposes with actual clinical patients.

Journal Article
TL;DR: In this article, the authors developed laboratory tests for paper structure using an infrared camera for passive measuring methods, which adds mechanical or thermal energy to a sample to effect a temperature change.
Abstract: Recently developed laboratory tests for paper structure use an infrared camera for passive measuring methods. The technique adds mechanical or thermal energy to a sample to effect a temperature change. The new test methods help to characterize the structure and functional properties of paper. Application : measurements with an infrared camera can provide information about the structure of paper.

Proceedings ArticleDOI
04 Apr 1997
TL;DR: In this article, a new experimental technique using an infrared stress measurement system and an infrared transmitting material is proposed for the visualization of a contact stress distribution, which is employed as one of two contacting materials, and is brought into contact with a cyclically loaded sample.
Abstract: A new experimental technique using an infrared stress measurement system and an infrared transmitting material is proposed for the visualization of a contact stress distribution. An infrared transmitting material is employed as one of two contacting materials, and is brought into contact with a cyclically loaded sample. Infrared emissions from the contact surface are measured through the infrared transmitting material, and thermoelastic stress analysis (TSA) is applied to measure the contact stress distribution. First, a flat contact is investigated, in which a barium- fluoride window is in contact with an embossed plastic letter. Stress distribution on the contact area in the letter can be measured accurately. Further, a spherical Hertz contact is examined by using an infrared transmitting sapphire convex lens and a flat plastic plate. The obtained contact stress distribution is compared with the stress distribution predicted by the Hertz theory. An excellent correspondence is found between those stress distributions, indicating the feasibility of quantitative analysis using the present technique.

Journal ArticleDOI
TL;DR: In this paper, a small-scale filament winding apparatus was built so that surface temperature distributions could be determined during actual filament winding runs and the resulting temperatures could be compared to those predicted by a numerical model.
Abstract: A small-scale filament winding apparatus was built so that surface temperature distributions could be determined during actual filament winding runs and the resulting temperatures could be compared to those predicted by a numerical model. Several experimental runs were performed using various combinations of infrared energy input and prepreg tape velocities. Infrared thermography was used to determine the surface temperature of the composite during each experiment. The field of view of the infrared camera included approximately 90 degrees of the mandrel in the angular direction and two-thirds of the axial length of the composite on the mandrel.The numerical and experimental results in this paper suggest that varying the position of the infrared lamp, changing the prepreg tape velocity (winding speed), or the heat flux incident on the composite have a major impact on the temperature distribution throughout the composite; these factors may therefore be used to alter the physical properties and overall quali...

Proceedings ArticleDOI
04 Apr 1997
TL;DR: In this paper, a new variation of Forced-Diffusion Thermography, Coating Tolerant Forced Diffusion Tmography (CTDTFT), is described. The technique is specifically designed to inspect large steel bridge structures.
Abstract: A new variation of Forced-Diffusion Thermography, Coating Tolerant Forced Diffusion Thermography, is described.This new thermal method. is specifically designed to inspect large steel bridge structures. To increase effectiveness inthe field Coating Tolerant Thermography separates the effects of structural defects from variations in emissivity. Thetechnique is a derivative of Forced Diffusion Thermography which uses patterned radiation to force heat flow in-planeto specifically target cracks. This paper presents the fundamentals of Coating Tolerant Forced Diffusion Thermographyincluding the mathematical bases for the separation of thermal gradients and emissivity gradients. Also, presented arecase studies including the inspection of a bridge girder samples at FHWA Turner Fairbanks Lab.Keywords: Thermography, NDE, Crack, Bridge, Coating Tolerant, Forced Diffusion Thermography 1.0 INTRODUCTION A very sizable investment has been made in steel highway bridges, the integrity of which is often taken for granted. Itis vital that the Federal Highway Administration has the tools necessary to assess and monitor the health of keystructures quickly and accurately. Thermal methods have been recognized above other NDI methods for rapidinspection of large structures. Thermal methods are safe, convenient and relatively inexpensive tools; however, thetechniques' dependence on emissivity makes them sensitive to field conditions such as chipped paint. This paperdescribes an exciting new crack detection technology: Coating Tolerant Thermography, which is specifically designedto meet the demands of more challenging field conditions. The paper shows that Coating Tolerant Thermographyexhibits high probability of detection, low false signals, easy interpretation, speed and portability.

Proceedings ArticleDOI
04 Apr 1997
TL;DR: In this paper, a mathematical model is proposed to describe the energy balance of the surface where evaporation is present, and the model has been applied to the fresco to correlate the temperature to the evaporic rate.
Abstract: Damage due to moisture and particularly to evaporation is one of the major causes of decay of wall surfaces in ancient buildings. The evaporative rate of water in building materials can be related to the alteration (chips, gallets) caused by salts crystallization when the water evaporates through the surface of the wall. Current and future usage of NDT heavily depends on the possibility to precisely measure physical variables which present large sensitivity to small variations of water content. A NDT thermography allows us to exactly determine the evaporation rate because of both the high value of water latent heat and the high sensibility of thermographic devices. The research has been carried out both in the laboratory and on the field measuring relative humidity and temperature in a frescoed wall of the castle of Malpaga (Northern Italy). In laboratory a climatic room has been set up using a thermovision system and a temperature & RH% probes, to analyze the evaporative phenomena. A mathematical model, although approximate, is proposed to describe the energy balance of the surface where evaporation is present. The model has been applied to the fresco to correlate the temperature to the evaporation rate. This method allows us to correlate the decay, due to the capillary raise of water in the masonry, to the transpiration phenomena.

Book ChapterDOI
01 Jan 1997
TL;DR: In this article, an interesting example of thermographic inspection using an ultrasonic heating source is illustrated, where some material features are selectively heated, so that the interpretation of the image can be straightforward.
Abstract: Infrared thermography is a powerful, fast and non contact method for non destructive testing of materials, based on heat conduction. While techniques like pulse or lockin thermography are based on external heat sources, other thermographic techniques, like vibro-lockin thermography, use internal sources of heat, where loss angle effect is involved. One advantage of these latter techniques is that some material features are selectively heated, so that the interpretation of the image can be straightforward. Another advantage is that the heat is generated directly on the defect, allowing to reach greater depths. Some interesting examples of thermographic inspection using ultrasonic heating source are here illustrated.

Journal ArticleDOI
TL;DR: In this article, the authors proposed a determination scheme of the true temperature of such objects in an explicit form of equation to be solved by combining the readout temperature of the camera with a response function of a camera to a blackbody.
Abstract: In conventional infrared (IR) thermographic cameras it is normally assumed that the ambient temperatures of optical objects are the same as the temperature determined at the camera head. In increasing cases of application of thermography, this assumption is not always satisfied, and often leads to erroneous results. In this article, we propose a determination scheme of the true temperature of such objects in an explicit form of equation to be solved by combining the readout temperature of the camera with a response function of the camera to a blackbody. The equation can be used to determine optical properties of components in an IR system. It also works to evaluate the contribution coming from each element along the optical path. Though the scheme is written in a form applicable to a specific camera among commercial products, it can be modified so that conventional IR cameras are conveniently used for thermographic determination of the temperature of gray objects in exotic environments.

Journal ArticleDOI
TL;DR: In this paper, the influence of rotation on the color response of encapsulated liquid crystals attached to a flat rotating surface was investigated for a rotational speed range from 0 to 7500 rpm using two different coatings displaying red at 30° and 45°C under stationary conditions.
Abstract: Liquid crystal thermography is an effective method widely employed in transient and steady-state heat transfer experiments with excellent spatial resolution and good accuracy. Most of the past studies in liquid crystal thermography deal with stationary conditions. The present investigation deals with the influence of rotation on the color response of encapsulated liquid crystals attached to a flat rotating surface. A general methodology developed for the application of thermochromic liquid crystals in rotating systems is described for the first time. The investigation is performed for a rotational speed range from 0 to 7500 rpm using two different coatings displaying red at 30° and 45°C, under stationary conditions. Local liquid crystal color on the surface ofa rotating disk is correlated with local temperature as measured by a non-intrusive infrared sensor at various rotational speeds. A complete and general experimental methodology including rotating surfaces with non-axisymmetric temperature distribution is presented.