Showing papers on "Thermography published in 1998"

A reappraisal of the use of infrared thermal image analysis in medicine

Abstract: Infrared thermal imaging of the skin has been used for several decades to monitor the temperature distribution of human skin. Abnormalities such as malignancies, inflammation, and infection cause localized increases in temperature which show as hot spots or as asymmetrical patterns in an infrared thermogram. Even though it is nonspecific, infrared thermology is a powerful detector of problems that affect a patient's physiology. While the use of infrared imaging is increasing in many industrial and security applications, it has declined in medicine probably because of the continued reliance on first generation cameras. The transfer of military technology for medical use has prompted this reappraisal of infrared thermology in medicine. Digital infrared cameras have much improved spatial and thermal resolutions, and libraries of image processing routines are available to analyze images captured both statically and dynamically. If thermographs are captured under controlled conditions, they may be interpreted readily to diagnose certain conditions and to monitor the reaction of a patient's physiology to thermal and other stresses. Some of the major areas where infrared thermography is being used successfully are neurology, vascular disorders, rheumatic diseases, tissue viability, oncology (especially breast cancer), dermatological disorders, neonatal, ophthalmology, and surgery.

An infrared thermography imaging system for convective heat transfer measurements in complex flows

Abstract: An infrared thermography imaging system is described for spatially resolved convective heat transfer measurements when used in conjunction with thermocouples, energy balances, digital image processing, zinc-selenide windows, and unique in situ calibration procedures. The usefulness of the system and the techniques developed are demonstrated by measurements made in two different environments with complex, three-dimensional flow features. First, spatial variations of surface Nusselt numbers are measured along the concave surfaces of a swirl chamber whose geometry models an internal passage used to cool the leading edge of a turbine blade. Second, spatially resolved distributions of the adiabatic film-cooling effectiveness are measured downstream of film-cooling holes on a symmetric turbine blade in transonic flow.

NDT of polymer materials using lock-in thermography with water-coupled ultrasonic excitation

Abstract: We present an NDT method that uses lock-in thermography with ultrasonic heating. The acoustical damping causes the mechanical energy to be converted to thermal energy. In the defective regions the damping is stronger resulting in higher temperature generation. Thus the heating is selective to defects and gives good defect detectability. Because defects also affect the heat conduction, the method gives combined information of the change of the mechanical and thermal properties of the sample due to defects. The ultrasonic excitation is amplitude modulated and the magnitude and the phase of the temperature are measured by infrared camera and software lock-in detection. The applicability of the method was proved with several polymer and composite samples having delaminations, impact damages, voids, and inclusions.

Assessing building façades using infra‐red thermography

Abstract: The applicability of infra‐red thermography for assessing building facades was studied. Results from the laboratory experiments highlight the importance of the environmental conditions on the accuracy of technique. The thermograms were found effective in showing the simulated anomalies in test samples.

The infrared thermography diagnostic technique of high-voltage electrical equipments with internal faults

Abstract: Infrared thermography techniques have become an effective way of diagnosing electrical equipment faults As far as the location of these faults is concerned, they can be divided into internal and external faults Generally speaking, external faults are simple and internal faults are complex Therefore, external faults are easily discernible and internal faults are difficult to pinpoint To find internal faults by means of infrared thermography, one must know the law of internal fault attributes in relation to their infrared thermography characteristics This paper aims to discuss techniques of diagnosing electrical equipment with internal faults by way of infrared thermography, and to show some typical examples thermographs of electrical equipment with internal faults

Compared performances of four algorithms used for modulation thermography

Abstract: A theoretical analysis is presented about the performances of a series of four different algorithms for modulation thermography: standard lock-in method, 4-bucket method, variance method and leastsquares method. The precision on the amplitude and on the phase lag is evaluated versus the number of integrated images; depending on the input noise level, on the actual signal amplitude and on the quantisation level.

Lock-in contact thermography investigation of lateral electronic inhomogeneities in semiconductor devices

Abstract: Dynamic precision contact thermography (DPCT) is a thermal scanning probe technique with pulsed heating of the sample and lock-in signal detection. It enables the lateral imaging of weak leakage- and injection currents in large-area electronic devices. After summarizing the basic principles of this investigation technique, recent results of investigating a silicon solar cell and MOS wafers are presented.

Pathophysiological expression and analysis of far infrared thermal images

Abstract: Clinical far infrared (FIR) imaging is a measurement technique applied to images of temperature distribution on the skin surface. It is a noninvasive analysis tool for physiological functions related to skin-temperature control. The imaging modality has been termed thermography, tele-thermography, or infrared thermography. FIR image processing for medical use has been developed independently in each thermography system because each sensor and scanning system was developed independently. The lack of standardized image handling has been a great barrier to the popular use of FIR imaging systems in clinical medicine. However, recent FIR sensor technology has brought forth some standard output protocols. Therefore, there is now a better opportunity to develop standard FIR image-processing software for medical imaging. This article is the first proposal for such trials. Computer processing methods have been developed and tested that make it possible to reduce diagnostic ambiguity and complexity. This article proposes eight thermophysiological expressions, called thermatomes, as well as standardized analytical procedures using computed image processing. These methods have demonstrated the possibility of a standardized thermographic image diagnosis procedure.

Progress in ultrasound lockin thermography

Abstract: Ultrasound lock in thermography (UL T) is based on thermal wave imaging as a local response to periodical heat deposition. The substantial difference as compared to photothermal imaging and optical lockin thermography (OL T) is that the heat source generating a thermal wave is provided by the defect itself due to the attenuation of amplitude modulated ultrasound. While friction effects heat areas with defects selectively, the slow amplitude modulation provides a periodicity of heating that results in the emission of long ranging thermal waves from defects. This way one has a dark field method to display defects in various materials even in the presence of complicated structures related with intact samples.

Thermal diffusivity imaging of aerospace materials and structures

Abstract: Thermographic imaging is increasingly being utilized for inspection and characterization of materials and structures. Thermal diffusivity imaging provides a means for quantitative characterization of a materials which is independent of apparatus and measurement configuration. This enables more precise imaging of variations in the material or structure needed to track changes resulting from fatigue or aging processes.

Evaluating asymmetrical thermal distributions through image processing

Abstract: In order to use thermography for clinical diagnosis, it is necessary to determine the location of the abnormal thermal areas as well as the degree of the change in body-surface temperature This necessitates an evaluation of the distribution of the deviation in skin temperature from a standard skin-temperature distribution of the healthy subject However, there is no standard distribution of the body-surface temperature of a healthy subject because it is affected by so many factors, such as the ambient and internal thermal conditions, age, sex, body weight, etc Further, it also differs widely with individuals One of the best ways to eliminate this variability, and to detect and evaluate the change in the body-surface temperature, is to measure the body-surface temperature of each thermograph pixel in the affected area and subtract from it the body-surface temperature of the corresponding pixel in the symmetrically located contralateral healthy area The aim of this study is to develop a program for a computerized thermographic system that will produce images of the distribution of temperature differences between the affected side and the contralateral healthy side, and also to investigate the feasibility of the program in a clinical setting

Mine detection by means of dynamic thermography: simulation and experiments

Abstract: We present a study on detection of buried anti-personnel mines (APM) by means of infrared imaging. First, an analytical study of a theoretical thermal model is presented. Then we describe an original approach towards the simulation of an extended model and summarize the results. These are then compared with results obtained from experiments in laboratory and real environment conditions. In order to use the whole dynamic information contained in the image sequences, two methods for extracting the difference in dynamic temperature response between objects in a scene are introduced and applied.

Microwave enhanced infrared thermography

Abstract: A detection apparatus (10) incorporating microwave-enhanced infrared thermography for providing the detection, location and identification of underground devices Microwave energy at a wavelength determined by the depth of the object (60) and the soil conditions is utilized to heat the underground target and the surrounding ground (80) The contrast in dielectric properties of the object with respect to the ground produces a contrast in absorbed energy of the underground device with respect to the surrounding soil This contrast in absorbed energy as well as the contrast in thermal conductivity and specific heat of the underground object (60) with respect to the surrounding soil result in a concomitant contrast in the temperature at the surface of the ground (70) This contrast in temperature at the surface of the ground is detected and recorded by a device (40) such as an infrared camera from which the underground device can be precisely located and identified

Thermographic detection and quantitative characterization of corrosion by application of thermal line source

Abstract: Recent advances in thermal imaging technology have spawned a number of new thermal nondestructive evaluation (NDE) techniques that provide quantitative information about flaws in aircraft structures. Thermography has a number of advantages as an inspection technique for aircraft. It is a totally noncontacting, nondestructive, imaging technology capable of inspecting a large area in a mater of a few seconds. The development of fast, inexpensive image processors have aided in the attractiveness of thermography as an NDE technique. These image processors have increased the signal to noise ratio of thermography and facilitated significant advances in post-processing. The resulting digital images enable archival records for comparison with later inspections thus providing a means of monitoring the evolution of damage in a particular structure. NASA Langley Research Center has developed a thermal NDE technique designed to image and quantitatively characterize the thickness of thin aluminum sheets. The technique involves the movement of a thermal line source across the outer surface of a sample followed by an IR imager at a fixed distance behind the line source. Images of the material loss due to corrosion are reconstructed from measurements of the induced surface temperature variations. This paper will present a discussion of the development of the thermal imaging system as well as the techniques used to reconstruct images of flaws. The application of the thermal line source coupled with the analysis technique represents a significant improvement in the quantification of flaws over conventional thermal imaging. Results of laboratory experiments on specimens with fabricated material loss region swill be presented to demonstrate the capabilities of the technique. An integral part of the development of this technology is the use of analytic and computational modeling to optimize the technique and reduce the data. The experimental results will be compared with simulations to demonstrate the utility of such an approach.

Infrared thermography for examination of paper structure

Abstract: The paper industry has used IR cameras primarily for troubleshooting, where the most common examples include the examination of the condition of dryer fabrics and dryer cylinders and the analysis of moisture variations in a paper web. Another application extensively using IR thermography is non-destructive testing of composite materials. This paper presents some recently developed laboratory methods using an IR camera to examine paper structure. Specific areas include cockling, moisture content, thermal uniformity, mechanism of failure, and an analysis of the copying process.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Non-Destructive Evaluation of Wind Turbine Blades Using an Infrared Camera

Abstract: The use of a digital infrared as a non-destructive evaluation thermography camera (NDE) tool was ex- plored in two separate wind turbine blade fatigue tests. The fwst test was a fatigue test of part of a 13.1 meter wood-epoxy-composite blade. The second test was on a 4.25 meter pultruded fiber glass blade section driven at several mechanical resonant frequencies. The digital infrared camera can produce images of either the static temperature distribution on the surface of the specimen, or the dynamic temperature distribution that is in phase with a specific frequency on a vibrating specimen. The dynamic temperature distribution (due to thermoplastic effects) gives a measure of the sum of the principal stresses at each point on the surface. In the wood- epoxy-composite blade fatigue test, the point of ultimate failure was detected long before failure occurred. The mode shapes obtained with the digital infrared camera, from the resonant blade tests, were in very good agree- ment with the finite-element calculations. In addition, the static temperature images of the resonating blade showed two areas that contained cracks. Close-up dy- namic inf%red images of these areas showed the crack structure that agreed with subsequent dye-penetrant analysis.

NDE of frescoes by infrared thermography and lateral heating

Abstract: The lateral heating procedure is applied to frescoes. A dedicated algorithm is proposed to reconstruct conventional thermograms and to identify detachments of the plaster and cracks. Then a map of defect location and extension is produced. Two numerical models have been implemented to simulate tests. A prototype equipment was also developed and applied both in laboratory and in situ.

Thermal tomography characterization and pulse-phase thermography of impact damage in CFRP, or why end users are still reluctant about practical use of transient IR thermography

Abstract: Results of inspecting a CFRP specimen with the impact damage defect are reported. The accent is made on dedicated data processing including the so-called defect maps production which are of special interest for end-users. Comparison of thermal tomography and pulse phase thermography is made while applying these methods to both defect detecting and characterizing.

Infrared Thermography as a Tool for Thermal Surface Flow Visualization

Abstract: Infrared (IR) thermography is a two-dimensional, non-contact technique of temperature measurement which can be usefully exploited in a vast variety of heat transfer industrial applications as well as research fields. The present work focuses attention on thermal surface flow visualizations of several types of fluid flow studied by means of the IR imaging system and in particular: the flow over a delta wing at angle of attack; the flow generated by a disk rotating in still air; air jets impinging on a flat wall; the flow inside a 180deg turn in a static channel with, or without, turbulence promoters; the flow inside a 180deg turn in a rotating square channel. Each flow visualization is illustrated through thermographic images and/or Nusselt number maps. The emphasis is on the capability of the infrared system to study: laminar-to-turbulent transition and location of primary and secondary vortices over the delta wing at angle of attack; the spiral vortical structure developing at transition over the disk; azimuthal structures arising for certain jet conditions; the influence of the channel aspect ratio (width to height ratio) on the heat transfer coefficient distribution along the 180deg turn, as well as the influence of ribs, in the case of static channel; the influence of rotation for the rotating channel.

Infrared Thermography for Flow Visualization and Heat Transfer Measurements

Abstract: The paper intends to discuss the use of IR thermography as a new technology tool in various heat transfer and fluid dynamics problems. Different operating modes and their implementation are presented. Particular emphasis is given to the measurement of convective heat transfer coefficients. The development of appropriate software is also presented. Basic Principles of Infrared Thermography Thermography is a measurement technique of thermal maps. Accurate quantitative analysis of thermal images acquired in real time is an essential performance requirement of a thermographic system. The technology of modern infrared (IR) thermography can currently attain this goal to a considerable extent. Basically an IR thermal imager is a camera which detects the electromagnetic energy radiated in the IR spectral band from an object (whose temperature has to be measured) and converts it into an electronic video signal. In particular, starting from the object, IR energy is first radiated through a medium (typically the atmosphere). It then enters the sensing system, passing through a lens, an aperture (or a filter), and finally impinges on a single IR detector or a focal plane array (FPA) sensor, which transduces the radiation into an electrical signal. The IR systems of the first generation, which are typically are equipped with a single detector, need also a scanning mechanism (see later) ; for this reason they are termed conventionally IR scanning radiometers (IRSRs). IR (staring) cameras based on FPA sensing elements do not generally require any scanning device; nevertheless, since the image may be still thought of as the output from an electronic scanning, hereafter they will be also referred to as IRSRs. The standard instantaneous output is represented generally by a matrix of data having a number of elements typically of the order of 20-60k or more. Consequently, it is necessary to treat the data by means of numerical techniques. As a result, the procedures and the algorithms generally referred to as digital image processing may be conveniently applied; in particular, image enhancement and image restoration. Monochromatic radiation intensity Eλ, emitted by a surface having an absolute temperature T, is given by Planck's law: ) 1 ( / 5 1 0 2 − = = T C e C E E λ λ λ λ λ λ e e (1) where eλ is the spectral hemispherical emittance, C1 and C2 are the first and second radiation constants respectively; λ is the wavelength of the radiation being considered, and Eλ0 is the blackbody monochromatic radiation intensity. By integrating Planck's law over the entire spectrum the total radiation intensity E is obtained (Stefan-Boltzmann law):