Showing papers on "Thermography published in 1996"

Pulse phase infrared thermography

Abstract: An approach is proposed which combines simultaneously advantages both of pulse (PT) and modulated infrared thermography. In a nondestructive evaluation perspective, the specimen is pulse heated as in PT and the mix of frequencies of the thermal waves launched into the specimen is unscrambled by performing the Fourier transform of the temperature evolution over the field of view. Of interest is the maximum phase image with many attractive features: deeper probing, less influence of surface infrared and optical characteristics, rapid image recording (pulse heating, surface‐wide inspection), and the possibility to inspect high thermal conductivity specimens. Several results are presented and the theory is discussed as well.

Amplitude-Modulated Lock-In Vibrothermography for NDE of Polymers and Composites

Abstract: We present a nondestructive testing method based on lock-in thermography with mechanical heat excitation. Stresses are generated in the sample by vibrating it with a mechanical shaker. The mechanical energy is converted to thermal energy due to the acoustical damping. The defected regions have a stronger damping and also a stress concentration next to them, both of which result in a higher temperature generation. Because of the changes of the thermal properties, the defects also affect the heat conduction. These phenomena result in thermal anomalies due to the defects. The high-frequency vibration used for excitation is amplitude-modulated with a low frequency. The magnitude and phase of the sample temperature with respect to the modulation are measured with an infrared camera and a software lock-in technique. The use of phase information increases the reliability of the defect detection, and the application of high vibration frequencies results in a good thermal signal even at low stress levels,...

Infrared thermovision of damage processes in concrete and rock

Abstract: Infrared thermography has been used as a nondestructive and noncontact technique to examine the progressive damage processes and failure mechanisms of concrete and rock specimens subjected to given static unconfined compressions and to a superimposed vibratory excitation. The parameter investigated in this paper is the heat generation due to intrinsic dissipation caused by anelasticity and/or inelasticity of the material which has been excited beyond its stable reversible limit. This useful technique allows accurate illustration of the onset of unstable crack propagation and/or flaw coalescence when increasing irreversible microcracking is activated by vibratory loading.

Comparative effectiveness of videothermography, contact thermography, and infrared beam thermography for scanning relative skin temperature.

Abstract: Videothermography (Video TRM), infrared beam thermography (IRTHRM), and contact thermography (Contact TRM) are utilized to detect asymmetries in temperatures between paired limbs. This information is controversially used in many diagnostic procedures in rehabilitation medicine. In this study, the effectiveness of the above techniques for scanning skin heat patterns and detecting asymmetries is compared. The skin over both lower limbs was imaged with each technique sequentially on 139 male and 15 female patients reporting lower limb pain. Images were also made of an electronic heat producer in order to determine relative accuracy. Contact TRM was unable to accurately image many areas with curved surfaces and was unable to produce accurate recordings when several sensors with differing temperature ranges had to be used on the same subject. It was also relatively inaccurate when imaging the heat producer. Video TRM was easy to use and produced excellent recordings but was difficult to transport. IRTHRM used in conjunction with a grid map of the body was the simplest and least expensive system to use for scanning and was as accurate as Video TRM.

In Situ Calibration for Quantitative Infrared Thermography

Abstract: This paper presents a method to correct temperatures obtained by infrared thermography using thermo­ couples as reference temperatures. The raw signal values of the infrared detector are compared to the temperatures measured with thermocouples. The relation between raw thermal value and body tempera­ ture includes three parameters which allow to determine a best-fit approximation between detector signal and body temperature. The resulting non-linear system of equations is solved numerically using the Levenberg-Marquardt procedure. These parameters are then used to calculate the corrected tempera­ tures of the body. 1 Introduction Infrared thermography is a powerful method for temperature measurement in turbomachinery research. At the 'Institut fOr Thermische Stromungsmaschinen' at the 'Universitat Karlsruhe' the infrared camera has been used in numerous investigations on heat transfer phenomena. So far, the results achieved were mainly used for qualitative reviews of complex surface temperature distributions. To allow for any quantitative analyses the data have to undergo some further cor­ rection or calibration procedure. This procedure has to account for many different effects (e.g. reflected radiation, gas radiation, translucency of the window) which have an impact on the thermography results. In most experimental set-ups matching real engine conditions, these effects are difficult to quantify. Therefore, any correction procedure on a pure theoretical basis is not very promising. Better accuracy can be achieved with a case specific calibration of the thermography system which is obtained experimentally. Various authors have proposed calibration procedures for thermography systems which rely on calibration experiments. Among them Koschel et al. [1] used an external system to calibrate a pyrometer which was used to measure the temperatures on the surface of turbine blades. In this way the influence of the observation angle and thE: distance between blade surface and detector on the IR-signal could be studied precisely. Nevertheless, the surface emissivity could not be determined accurately and reflection effects could not be simulated in the calibration setup. Carlomagno et al. [2] used a little black body to calibrate an IR-camera under real test conditions. The black body was placed in the test rig at the location at which the surface tem­ perature had to be determined later on. The calibration parameters obtained with the black body were then used in the surface temperature measurements with an additional correction for gray body. This method can only be applied if the test surface can be dealt as a gray body, i.e. its emissivity is independent of temperature, and if the test section allows for the insertion of a black body. Reflected radiation, which occurs in the case of any gray body, cannot be taken into account. Meyers at al. [3] performed temperature measurements on film cooled combustor walls. During the heating-up of the combustor, temperature data were recorded from both the infrared scanner and from the embedded thermocouples. These data were then paired and used for a best fit approximation for the calibration parameters of the camera. Thus, all tem­ perature dependent properties of the system are taken into account. Nevertheless thermal im­ age recording during the heating-up period leads to slightly shifted operating conditions be­ tween calibrating and testing. The calibration method presented in this paper uses a similar approach but thermocouple temperature and thermal image recording takes place at steady state and the 'best-fit' approximation includes three parameters instead of two for higher accu­ racy.

Monitoring of Thermal Energy Distribution in Abrasive Waterjet Cutting Using Infrared Thermography

Abstract: Thermal energy distribution in the workpiece cut with abrasive waterjet (AWJ) is analyzed using the technique of infrared thermography through isotherms and linescans. Variation in workpiece temperature with thermal conductivity and cutting conditions is studied. The feasibility of visualization of AWJ cutting mechanisms in opaque materials using infrared thermography is investigated. A novel technique of AWJ nozzle wear monitoring through infrared thermography is proposed. A comparative study of infrared thermography results with the readings of thermocouples and the two-dimensional moving line heat source model show a close correspondence indicating that infrared thermography is a good technique for the above application.

Method of detecting defects in materials using infrared thermography

Abstract: A method of detecting defects in materials using infrared thermography, includes placing the rear surface of an object to be inspected close to the front surface of a thermoplate controlled by a temperature controller, and the front surface of the object in a vacuum chamber. At the other end of the vacuum chamber, on the outside, an infrared camera is arranged facing the object, so that a vacuum is maintained between the object and the camera. Defects are detected from thermal images of the object, obtained with the infrared camera.

Infrared thermography. Its role in dental research with particular reference to craniomandibular disorders.

Abstract: The use of infrared thermography in dentistry has been minimal, principally due to technological inadequacies of previous thermal imaging systems. However, with the ever-developing advancement in technology, current systems are capable of producing real-time, highly sensitive digitized thermal images. This development has led to an increased use of infrared imaging within both medical and dental research. The present paper describes these techniques and their previous applications within dentistry, and, through the use of a pilot study, highlights possible future applications in the assessment of craniomandibular disorders.

An experimental investigation of defect sizing by transient thermography

Abstract: Details are presented of an experimental and theoretical investigation of the defect sizing capabilities of the transient thermography technique. Back-drilled hole artificial defects, of diameters from 2 to 10 mm and at depths between 0.5 and 1.7 mm, in bakelite plates, were thermographically imaged. Full-width at half maximum (FWHM) of a defect image is shown to be accurately related to defect diameter. These measurements are also shown to be in excellent agreement with finite-difference simulations of the response of this type of defect. The temporal dependences of the images are shown to provide an indication of defect depth.

Lock-in thermography with mechanical loss angle heating at ultrasonic frequencies

Abstract: In this paper the mechanical loss angle heating as an internal thermal wave source is described. Acoustic energy at high frequency (ultrasound) can be coupled into the sample. The high hysteresis loss in the defect region results in increased heating of the defect. When the intensity of the ultrasound is modulated at a low frequency the defect itself emits a thermal wave at this low frequency. The range of this thermal wave is large enough for detection at the surface with lock-in thermography tuned to the intensity modulation. This technique combining ultrasonic waves and lock-in thermography provides a fast imaging of imaginary part of Young's modulus in materials. Results obtained with this selective heating on various real components are presented.

A hot-foil infrared technique for studying the temperature field of a wall

Abstract: An infrared technique is used to investigate the temperature field on the surface of heated walls in turbulent boundary layers. This method is based on measurement of local temperatures on the surface of a heated film, fixed on a solid frame, by means of infrared thermography. The behaviour of such a sensor is considered in connection with the variation of flow characteristics, film geometric parameters, physical properties of its material, etc. The advantages of the present method are illustrated in its application in the analysis of temperature fields on the surface of a wall in a turbulent boundary layer, under various flow conditions.

Electronic infrared thermography as a dental research technique

Abstract: Electronic infrared thermography is an imaging modality for the accurate quantification of surface temperature. It has been used in medicine since the 1960s but its use in dentistry has been limited. Its use in dentistry could, however, be very useful, for example in objectively quantifying post-surgical inflammation and studying the effects of treatment with agents such as analgesics and anti-inflammatory drugs.

A study of infrared thermographic assessment of liquid nitrogen cryotherapy

Abstract: Objectives To assess whether infrared thermography can accurately predict the area of soft tissue necrosis that resultsfrom liquid nitrogen cryoprobe therapy. Study design Eight rats received cryosurgery on the shaved abdomen with a liquid nitrogen cryoprobe in a triple-freezetechnique. The therapy was monitored with infrared thermography and thermocouple probes. The temperature reached was correlated with the area of tissue necrosis found on histologic examination at sacrifice 1 week after the cryotreatment. A parallel study was carried out on pieces of beefsteak to assess the depth and shape of freeze. Results The −20°C isotherm, which is felt to correspond to the cell lethal zone, occupied the inner 70% of the area ofthe iceball produced. Histologically, the −20°C isotherm corresponded well to the area of tissue necrosis. In depth, the iceball takes on a semicircular shape. Conclusions Infrared tomography is expensive to use clinically and cannot be readily used in the oral cavity. However,this study does show that one can clinically estimate that the inner 70% of the area of an iceball produced by liquid nitrogen on soft tissues will ultimately undergo necrosis.

Quantitative determination of impact damage and other defects in carbon fiber composities by transient thermography

Abstract: A quantitative assessment has been made of the performance of the transient thermography NDE method in the evaluation of defects in carbon-epoxy composite panels. Images have been obtained of artificial defects and their sizes are compared with the modeling predictions. Images have also been obtained of impact damage defects, impact energies up to 5 joules, and these results have been compared with defect images produced by ultrasonic c-scan.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Noncontact determination of thermal diffusivity in biomaterials using infrared imaging radiometry

Abstract: A noncontact method to determine the thermal diffusivity of biomaterials is derived theoretically and demonstrated experimentally. Assuming that the initial three-dimensional temperature distribution in the biomaterial immediately following pulsed laser irradiation can be separated into lateral and longitudinal factors, a convolution equation is derived that relates a pair of infrared emission images to the lateral thermal point spread function. Pairs of infrared emission images recorded following pulsed laser irradiation are used in combination with a nonlinear least-squares algorithm to determine the lateral thermal point spread function and thus the thermal diffusivity of the biomaterial. Sequences of infrared emission images recorded following pulsed laser irradiation are used to determine thermal diffusivity (0.10360.007 mm2/s) of an in vitro type I hydrated collagen film. Application of the method to in vivo tissues is discussed.

Observation window for checking the temperature of objects

Abstract: Observation window, especially for checking the temperature of objects using infrared thermography, including a parallel-faced transparent insert made of a single crystal suitable for radiation to pass through without being substantially modified and/or attenuated, which radiation, whose wavelength may range from the visible to the relatively far infrared emanates from an object whose temperature is to be monitored, housed in a screened cabinet provided with a door or panel against which the window is arranged, wherein the insert is fitted into a support which surrounds it at its periphery and is immobilized with respect to the support, this support being applied in a sealed manner against an aperture made in the door and then locked in position by means which are only accessible from inside the cabinet, the support comprising an external protective cover capable of pivoting about a pin connecting it to this support, so as to reveal the insert and allow observation through it of the object to be monitored by an infrared camera.

Thermal ellipsometry in steady-state and by lock-in thermography. Application to anisotropic materials characterization

Abstract: A technique for lock-in thermography that we recently developed was applied for the measurement of the in-plane principal diffusivities of orthotropic materials. The surface is point heated with a modulated laser beam and a 2-D synchronous detection is performed of the elliptical thermal field which develops around it. Diffusivities are inferred from the slope of the phase lag profiles. The approach was first validated with a duralumin (isotropic) sample. It was then applied on a unidirectional C/epoxy sample. The aspect ratio of the surface isotherms is imposed by the anisotropy of the considered material. Therefore, possible in-depth variations of the anisotropy unavoidably modify the aspect ratio distribution at the surface. Based on this observation, an inversion method was recently proposed to monitor the internal fibre orientation changes in composites. Results obtained with a continuous fibres C/epoxy sample and with an injection moulded short fibres sample are reported.

Analysis methods for full-field time-resolved infrared radiometry

Abstract: A data analysis procedure is described to enable quantitative information about defect depth and surface and subsurface thermal properties to be obtained from the time series of images acquired in a time-resolved infrared radiometry (TRIR) measurement. While the approaches described have been previously considered for single point measurements, in this work the algorithms are applied to full field images. As a result, images presenting defect depth and amount of thermal mismatch at subsurface interfaces can be constructed. Results are presented for composite test panels with flat-bottomed holes milled to different depths, two-layer specimens with differing thermal properties between the top layer and the substrate and a graphite/epoxy-honeycomb composite panel with simulated delaminations.

Experimental investigations of defect sizing by transient thermography

Abstract: Details are presented of an experimental and theoretical investigation of the defect sizing capabilities of the transient thermography technique. Back-drilled hole artificial defects, of diameters from 2 to 10 mm and at depths between 0.5 and 1.7 mm, in bakelite plates, were thermographically imaged. Full-width at half maximum (FWHM) of a defect image is shown to be accurately related to defect diameter. These measurements are also shown to be in excellent agreement with finite-difference simulations of the response of this type of defect. The temporal dependences of the images are shown to provide an indication of defect depth.

Digital infrared imaging for medicine. Recent advances in I.R. focal plane array imaging technology

Abstract: Thermal imaging has been in use for defence, scientific and industrial applications for more than 25 years. During the most recent five years, however, the rate of change of technology in this field has increased exponentially. As one would always like to see with technological developments, the result has been higher levels of performance, improved ease of use, and lower cost. In the field of medical thermography, the most significant new technological achievement is the commercialization of the staring focal plane array (FPA) detector and its incorporation in a calibrated thermography system. This paper describes the development of the ThermaCAM(R) calibrated digital FPA thermography system and its application to the technique of thermal coronary angiography (TCA). The use of the ThermaCAM for TCA in a multiroom cardiac surgical suite is also described.

Spatially resolved infrared spectroscopy : a novel technique for in situ study of spatial surface coverage during CO oxidation on supported catalysts

Abstract: A spatially resolved infrared (IR) imaging technique to monitor the linear adsorbed CO coverage on supported catalyst surface combining an IR bandpass filter and an IR thermography camera has been developed. Images acquired during the CO adsorption/desorption and ignition indicate that the technique provides an excellent method to image the change of surface coverage with a spatial resolution. It is expected that the combination of infrared thermography with spatially resolved imaging of surface coverage will provide a deeper insight in the dynamics of spatio-temporal patterns on heterogeneous catalysts.

Lockin thermography for imaging of modulated flow in blood vessels

Abstract: While conventional thermographic applications to the human body aim at revealing local temperature changes normally related with the beginning of a pathologic process, this paper shows how lockin thermography can be modified in order to meet medical needs in the visualization of functionality of blood vessels. A compression cuff is used in connection with the lockin system to create a modulation in the blood flow. The amplitude and phase images thus obtained can provide infonmation about the blood flow in the vessels.

Development of an urban thermal environment measurement system using a new spherical thermography technique

Abstract: The present paper describes a newly developed thermal environment measurement system that incorporates 'spherical thermography.' Spherical thermography is a new application of conventional thermography in which the visual plane is extended to a spherical field (4(pi) sr). Spherical thermography is highly effective for performing three- dimensional (3D) analysis of the thermal environment in an urban area containing large and/or tall buildings.

Phase measurements of electromagnetic fields using infrared imaging techniques and microwave holography

Abstract: Complex (magnitude and phase) measurements of the near field of a radiating antenna over a known surface (usually a plane, cylinder, or sphere) can be used to determine its far-field radiation pattern using near-field to far-field Fourier transformations. Standard gain horn antennas are often used to probe the near field. Experimental errors are introduced into the near-field measurements by mechanical probe position inaccuracies and electrical probe interactions with the antenna under test and probe correction errors. A minimally perturbing infrared (IR) imaging technique can be used to map the near fields of the antenna. This measurement technique is much simpler and easier to use than the probe method and eliminates probe position errors and probe correction errors. Current IR imaging techniques, which have been successfully used to rapidly map the relative magnitude of a radiating field at many locations (mXn camera pixels per image captured) over a surface, however, suffer from an inability to determine phase information. Absolute magnitude and relative phase data can be obtained by empirical or theoretical calibration of the IR detector screens (used to absorb the radiated energy over the measurement plane) and by using techniques from microwave holography. For example, magnitude only measurements of the radiating field of an antenna at two different locations (over two different surfaces) in the near field of the antenna can be used to determine its complex (magnitude and phase) far-field radiation pattern using plane-to- plane (PTP) iterative transformations. This paper discusses the progress made to data in determining both magnitude and phase information from IR imaging data (IR thermograms); thus, enabling near-field and far-field measurements of antenna patterns using IR thermal imaging techniques.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.