Showing papers on "Thermography published in 1991"

Thermography as an aid to the clinical lameness evaluation

Abstract: Thermography has been shown to be a practical aid in the clinical evaluation of lameness. This modality specifically increases the accuracy of diagnosis. Thermography represents skin temperature, usually pictorially. The techniques involve contacting and noncontacting modalities. Noncontacting thermography, which detects infrared radiation, is the most accurate. In order to be accurate, thermography must be performed in a temperature-controlled, draft-free area. The area should be protected from sunlight to avoid erroneous heating of the skin, and the hair length should be uniform. Thermography detects heat before it is perceptible during routine physical examination; therefore, it is useful for early detection of laminitis, stress fractures, and tendinitis. It offers a noninvasive means of evaluating the blood supply to an injured part and offers one of the only reliable means to evaluate blood flow to the foot of horses with navicular syndrome. Thermography also is useful for the early identification of stress injuries to the contralateral limb of convalescing orthopedic patients. Thermography is an excellent adjunct to clinical and radiographic examination. It is complementary to other imaging techniques such as ultrasonography and scintigraphy.

A quantitative analysis of pulsed video thermography

Abstract: The defect imaging capability of a pulsed video thermography system is assessed by detailed quantitative analysis of its performance in imaging a set of well characterized artificial defects in a steel test-piece. An analytical model is presented which provides an understanding of the imaging process. A method is proposed for the determination of defect depth by exploiting the temporal dependences of images.

Surface temperature/heat transfer measurement using a quantitative phosphor thermography system

Abstract: A relative-intensity phosphor thermography technique developed for surface heating studies in hypersonic wind tunnels is described. A direct relationship between relative emission intensity and phosphor temperature is used for quantitative surface temperature measurements in time. The technique provides global surface temperature-time histories using a 3-CCD (Charge Coupled Device) video camera and digital recording system. A current history of technique development at Langley is discussed. Latest developments include a phosphor mixture for a greater range of temperature sensitivity and use of castable ceramics for inexpensive test models. A method of calculating surface heat-transfer from thermal image data in blowdown wind tunnels is included in an appendix, with an analysis of material thermal heat-transfer properties. Results from tests in the Langley 31-Inch Mach 10 Tunnel are presented for a ceramic orbiter configuration and a four-inch diameter hemisphere model. Data include windward heating for bow-shock/wing-shock interactions on the orbiter wing surface, and a comparison with prediction for hemisphere heating distribution.

Infrared thermography in applied road climatological studies

Abstract: The aim of this paper is to describehow infrared thermography is used to analyse variation in road surface temperature during clear calm nights. Having knowledge of surface temperature variations along road stretches makes it possible to give an accurate survey of the risk of local slipperiness. The infrared equipment used is an Agema 870-system arranged on various kinds of platforms, stationary, car- and helicopter-mounted. Several factors are of importance in causing surface temperature variations, such as screening from the sun, variation in traffic intensity and construction materials of the road. This article reviews the influence of these factors on road surface temperature and how various platforms could be used to conduct detailed recordings. Sun screening by road rock cuts causes shadow patterns resulting in surface temperatures which are low when compared with sun exposed areas. Height and orientation of the screening object determine the intensity of the surface temperature difference....

A relative-intensity two-color phosphor thermography system

Abstract: The NASA LaRC has developed a relative-intensity two-color phosphor thermography system. This system has become a standard technique for acquiring aerothermodynamic data in LaRC Hypersonic Facilities Complex (HFC). The relative intensity theory and its application to the LaRC phosphor thermography system is discussed along with the investment casting technique which is critical to the utilization of the phosphor method for aerothermodynamic studies. Various approaches to obtaining quantitative heat transfer data using thermographic phosphors are addressed and comparisons between thin-film data and thermographic phosphor data on an orbiter-like configuration are presented. In general, data from these two techniques are in good agreement. A discussion is given on the application of phosphors to integration heat transfer data reduction techniques (the thin film method) and preliminary heat transfer data obtained on a calibration sphere using thin-film equations are presented. Finally, plans for a new phosphor system which uses target recognition software are discussed.

Airfoil transition and separation studies using an infrared imaging system

Abstract: An infrared imaging system was used to detect the thermal signature of boundary-layer flow regimes on a NACA 0012 airfoil from zero angle of attack up to separation. The boundary-layer transition from laminar to turbulent flow and the onset of separation could be seen on the airfoil thermograms. The findings were compared against the behavior of aluminum foil tufts observable both visually and with the infrared imaging system. This arrangement offers the option of using the infrared imaging system both for flow regime detection through surface thermography and flow visualization by the aluminum foil tufts. Ultimately the surface temperature changes due to variation in the angle of attack of a lifting surface provide a means for interpretation of the boundary-layer flow regimes.

The utilization of contact liquid crystal thermography in the evaluation of temporomandibular dysfunction.

Abstract: A previously diagnosed patient population of 109 volunteers having temporomandibular dysfunction agreed to undergo pretreatment and post-treatment thermographic examination. In 1988, at the time of this study, a contact liquid crystal thermographic unit was utilized in accordance with the protocol advocated by the Academy of Neuro-Muscular Thermography. The examination consisted of pretreatment and post-treatment thermograms repeated in a series of three sets, i.e., in triplicate, incorporating four different views per set, namely, frontal face, right lateral face, left lateral face, and posterior cervical. This study revealed that the application of contact liquid thermography in the evaluation of temporomandibular dysfunction was a reliable, valid, and efficacious diagnostic tool in approximately 95% of the cases. Resolution of thermographic asymmetry and/or decrease in Delta T was demonstrated in approximately 81% of the post-treatment population. Thermography also proved to be a reliable indicator of pretreatment duration of dysfunction (chronicity pattern) in approximately 78% of the cases.

A review of factors influencing defect detection in infrared thermography: Applications to coated materials

Abstract: Infrared thermography is a technique that is used to nondestructively inspect parts for the presence of subsurface defects. The technique normally consists of applying heat to one surface of the part and observing the thermal response, using heat-sensing devices such as infrared cameras, as the part cools. Internal defects such as voids modify the thermal response and produce local hot or cold spots on the specimen surface. For the detection of subsurface defects, the sensitivity of the technique to different parameters such as defect depth, material properties, and heating methods has not been established due in part to the complex nature of the heat/flaw interaction. A finite element model is used here to examine the influence of these parameters on defect dectability. The model shows that the defect detectability decreases with increasing defect depth beneath the surface, and that the technique is most sensitive to the inspection of low thermal diffusivity coatings bonded to high thermal diffusivity substrates. The results also show that the heat pulse duration should be made as short as possible to maximize defect detectability.

Accurate temperature measurement in thermography: an overview of relevant features, parameters, and definitions

Abstract: This paper presents an overview of what features a state-of-the-art thermal imaging system needs to posses to be an accurate temperature measurement system. In thermography one of the major problems is a consequence of the fact that the surface temperature is not measured directly but is computed from the radiation received by the detector. This radiation consists not only of radiation emitted from the object but also from the surroundings, the atmosphere and the thermal imager itself. A thermal imaging system which compensates for this unwanted radiation is described. The influences from the surroundings, the atmosphere and the thermal imager is treated. The use of temperature references in the optical path, temperature sensors for measuring the imager temperature for compensation of its own radiation is described. Spatial resolution, calibration and accuracy of the imager are also discussed.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

New Applications of Liquid-Crystal Thermography in Rotating Turbomachinery Heat Transfer Research

Abstract: Two new liquid-crystal thermography techniques developed for use in rotating heat transfer experiments are described In one experiment steady-state heat transfer data were obtained on the exterior surface of rotating turbine airfoil models In the second study a transient technique was employed to obtain interior-surface heat transfer data in a rotating turbine blade coolant passage model Sample data are presented in the form of photographs of the liquid-crystal temperature patterns and as contour maps and distributions of heat transfer on the rotor and coolant passage surfaces

Infrared-thermography-based pipeline leak detection systems

Abstract: Computerized Infrared Thermographic pipeline inspection is now a refined and accurate process having been thoroughly proven to be an accurate, cost effective, and efficient technology during a 10 year development and testing process. The process has been used to test pipelines in chemical plants, water supply systems, steam lines, natural gas pipelines and sewer systems. Its non-contact, nondestructive ability to inspect large areas from above ground with 100% coverage and to locate subsurface leaks as well as the additional capability to locate voids and erosion surrounding pipelines make its testing capabilities unique. This paper will detail the development of computerized infrared thermographic pipeline testing along with case histories illustrating its implementation problems and successes and innovations anticipated for the future.

Quantitative measurement of thermal parameters over large areas using pulse-video thermography

Abstract: Illustrative examples are presented of the quantitative results obtainable from pulse-video thermography (PVT) for a variety of fields, emphasizing the character of the pictorial representations which is anticipated to be most useful for quality-assurance management. The ability to obtain sequential frame-grabbed thermal images has greatly improved PVT data, opening the way for digital processing of thermal-transient images, as well as the determination of thermal diffusivity and effusivity over large areas.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Infrared thermal-wave studies of coatings and composites

Abstract: We present applications of our infrared thermal wave imaging system which was described in detail at Thermosense XII. In brief, the system consists of an infrared video camera and a real time image processor under the control of a computer workstation, together with various time- dependent heat sources. The heat sources are used to launch pulsed or periodic thermal waves into the target, and the camera is used to record the thermal waves scattered back to the surface by sub-surface thermal features (cracks, coating substrate boundaries, inter-ply delaminations, etc.). Recently we have succeeded in developing an additional capability for this instrumentation, namely the ability to make quantitative depth and thickness measurements. Furthermore, some of the authors, together with V. Vavilov of Tomsk Polytechnic, have demonstrated a capability of carrying out thermal wave tomography. We have recently extended this technique to real time with our system. We describe these recent developments and present several applications to the study of thickness variations and adhesion defects in coatings and composites.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Quantitative heat transfer measurements in hypersonic wind tunnels by means of infrared thermography

Abstract: A description of infrared thermography, as this is used in a hypersonic blowdown wind tunnel for the acquisition of high-quality two-dimensional heat transfer data over aerodynamic surfaces, is given. The emphasis is on the accuracy of the measurements, and the advantages and limitations of the technique relative to standard discrete point heat transfer gauges. Following on outline of the experimental setup, the performance capabilities of the measurement system are discussed and illustrated through a selection of results. >

Temperature Recovery and Contrast Computations in NDE Thermographic Imaging Systems

Abstract: Thermographic imaging systems find application in many nondestructive evaluation problems However, because of the inherent nature of the image-formation process, several degradations arise which preclude a more generalized use of thermographic NDE In this paper, we analyze radiometric and noise degradations and propose a calibration process for the imaging systems which allows recovery of object surface temperature evolution Moreover, a constrast computation technique which combines both the time and spatial reference techniques is shown to increase the defect visibility and make possible a more quantitative (sizing) defect evaluation

Future applications of electronic thermography.

Abstract: Drs. Barton M. Gratt and Edward A. Sickles explain how electronic thermography uses facial heat emissions to paint colorful diagnostic pictures.

Subsurface flaw detection in reflective materials by thermal-transfer imaging

Abstract: In this paper a thermal imaging apparatus is described for the nondestructive detection of subsurface defects in materials that would not usually lend themselves to thermal imaging because of their low emissivity and high susceptibility to background reflection noise. This is accomplished by transferring the thermal image produced by surface temperature perturbation of the workpiece material to a high emissivity material with which it is continuously brought in contact. The transferred thermal image may be observed by a suitable infrared device, resulting in a high radiance image with minimum reflectivity or variable emissivity noise. Numerical simulations, as well as experimental results, are presented.

Ceramic dry-phantom and its application to SAR estimation

Abstract: A dry-phantom material having the same microwave properties as biological tissues was developed. The new phantom, composed of ceramics, overcomes various problems incidental to the conventional jelly phantom. Experiments were performed to estimate specific energy absorption rates of human heads exposed to microwave sources by using the thermography method. >

Using infrared thermography for the study of heat transfer through building envelope components

Abstract: Heat transfer through building envelope components is typically characterized by one number, the conductance. Such a characterization is best suited for homogeneous samples since it does not quantify or illustrate spatial variations within a sample. However, the growing use of advanced wall and window insulations with existing framing materials has increased the importance of understanding spatial heat transfer effects within building envelope components. An infrared thermography laboratory has been established to provide detailed quantitative and qualitative information on the spatial heat transfer effects of building envelope materials. The use of this facility for more effective product development and more accurate product development and more accurate product characterization is discussed.

Analysis of emissivity effects on target detection through smokes/obscurants

Abstract: The magnitude of target thermal contrast is used as a key parameter in determining whether observers using thermal-imaging systems can detect military targets. The effects of differences in target and background emissivities on thermal contrast estimates are evaluated, and the effects these differences have on the estimate of the transmittance attenuation thresholds required to obscure a target viewed with a thermal imager are examined. Target-background radiometric difference in the thermal infrared bands is first computed in terms of target-background emissivities and thermodynamic temperatures; the result is then used to compute a difference function for brightness temperature relative to thermodynamic temperature as a function of the target-background emissivity ratio. The effect of emissivity differences between targets and backgrounds on smoke/obscurant attenuation required to obscure a target viewed with a thermal imager is then examined using an expression derived from the Center for Night Vision and Electro-Optics Static Performance model. Results of the analysis show that smoke screen requirements for obscuring targets from thermal imager detection can change by factors of 10 as the ratio of target-to-background emissivity changes by less than 25%.

Thermographic detection of cracks in thin sheets

Abstract: A thermographic inspection technique for crack detection based on a 2D filter convolved with the thermal temperature images is presented. The filter is designed to approximate operating on the temperature images with a Laplacian operator. This operation yields an image which approximates changes in the heat flux in a thin plate. This filtering method results in an enhanced contrast due to the presence of cracks. Measurements have been performed on samples with fabricated electrical discharge machining (EDM) notches (both through-the-thickness and surface notches) and closed fatigue cracks around rivets. It is shown that the technique is effective for the detection of various crack lengths down to the resolution limits of the imager used.

A new transducer for thermography to observe the electric field distributions in a microwave oven

Abstract: The electric field pattern in a microwave oven is often observed as a heat pattern using thermography by using an appropriate transducer. In this article, a new type of observing plate is proposed as a transducer of the electric field into heat.

Qualitative and quantitative evaluation of moisture in thermal insulation by using thermography

Abstract: Exploitation reliability of porous thermal insulation depends strongly on its moisture because the excess water leads to its destruction under extreme conditions. Active and passive thermographic methods are described to estimate the distribution and quantity of water inside the insulation by using the Soviet thermoviser TV - O3 and IR pyrometer.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Infrared/microwave correlation measurements

Abstract: An infrared (IR) measurement technique for determining two-dimensional (2-D) and three- dimensional (3-D) microwave field distributions is presented. This IR technique is used to verify predictions made by various numerical electromagnetic (EM) codes. The experimental technique is based on IR thermal measurements of the Joule heating induced in a lossy dielectric or resistive material used as a calibrated IR detection screen when microwave energy is absorbed by the screen. An IR scanning system records the thermal radiation from the screen. The intensity of the microwave field is related to variations in the surface temperature distribution. The detection screen material is of a thin, planar construction and, thus, produces a 2-D map of the microwave field. By moving the screen along the normal to its plane, samples of the 3-D field are obtained. This experimental approach has been applied to several 2-D and 3-D scattering and coupling problems. Comparisons are made between the theoretical and experimental results for various hollow slit cylinder configurations. The advantages, disadvantages and limitations of this IR thermal technique for validation of EM theoretical predictions are discussed.