Showing papers on "Thermography published in 2001"

Theory and Practice of Infrared Technology for Nondestructive Testing

Abstract: Preface. Getting Started with Thermography for Nondestructive Testing. FUNDAMENTAL CONCEPTS. Introduction to Thermal Emission. Introduction to Heat Transfer. Infrared Sensors and Optic Fundamentals. Images. Automated Image Analysis. Materials. Experimental Concepts. ACTIVE THERMOGRAPHY. Active Thermography. Quantitative Data Analysis in Active Thermography. ACTIVE AND PASSIVE THERMOGRAPHY: CASE STUDIES. Applications. References and Bibliography. Appendix A: Computer Model. Appendix B: Smoothing Routing. Appendix C: Parabola Computations. Appendix D: Higher-Order Gradient Computations Based on the Roberts Gradient. Appendix E: Properties of Metals and Nonmetals. Appendix F: Matlab M-Scripts Available. Index.

Advances in pulsed thermography

Abstract: The use of pulsed thermography as an NDE solution for manufacturing and in-service applications has increased dramatically in the past five years, enabled by advances in IR camera and computer technology. However, the basic approaches to analysis and processing of pulsed thermographic data have remained largely unchanged. These methods include image averaging, subtraction, division, slope calculation and contrast methods (e.g. peak contrast and peak slope time mapping). We have developed an alternative approach to analysis of pulsed thermographic data, based on developing a parametric equation for the time history of each pixel. The resulting synthetic image provides increased spatial and temporal resolution, and significantly extends the range of defect depths and sample configurations to which pulsed thermography can be applied. In addition, our approach reduces the amount of data that must be manipulated and stored, so that an entire array of image sequences from a large structure can be processed simultaneously.

The role of thermography in the management of equine lameness.

Abstract: Equine thermography has increased in popularity recently because of improvements in thermal cameras and advances in image-processing software. The basic principle of thermography involves the transformation of surface heat from an object into a pictorial representation. The colour gradients generated reflect differences in the emitted heat. Variations from normal can be used to detect lameness or regions of inflammation in horses. Units can be so sensitive that flexor tendon injuries can be detected before the horse develops clinical lameness. Thermography has been used to evaluate several different clinical syndromes not only in the diagnosis of inflammation but also to monitor the progression of healing. Thermography has important applications in research for the detection of illegal performance-enhancing procedures at athletic events.

Applications of thermography in non-destructive testing of structures

Abstract: Infrared thermography (thermal imaging) is an important and powerful technique for consideration when investigating any structural situation where a ready source of surface heating (or cooling) is available, or where the item under investigation itself supplies such conditions. The methods used are totally non-destructive and non-invasive, and can be highly cost-effective. This paper explores a wide range of applications; particularly relating to structural investigation situations. Some guidance is given on optimum timing, conditions and viewing locations for the various situations described as well as limitations of the technique.

Evaluation of defects in composite plates under convective environments using lock-in thermography

Abstract: Lock-in thermography is a technique which is increasingly being used for the evaluation of subsurface defects in composite materials such as carbon-fibre-reinforced polymers (CFRPs) in aircraft structures. Most CFRP structures have a finite thickness and non-destructive inspection is performed in a natural ambient environment. In this paper, a photothermal model is developed in order to investigate the behaviour of thermal waves in homogeneous plates and layered plates with finite thicknesses under convective conditions. The model is then utilized to predict the phase differences produced by multi-layer subsurface defects and optimum inspection parameters. The theoretical results are compared with the experimental results. The detectivity of lock-in thermography for CFRP is also presented in this paper.

Thermographic investigation of the fatigue behavior of reactor pressure vessel steels

Abstract: The fatigue behavior of reactor pressure vessel (RPV) steels during fatigue testing was monitored by an advanced, high-speed, high-sensitivity, nondestructive evaluation (NDE) technique called infrared (IR) thermography. Five stages of temperature profiles during fatigue were recorded: an initial increase of the mean specimen temperature followed by a temperature decrease, a constant (equilibrium) temperature region, an abrupt temperature increase, and a temperature drop after the specimen failure. Using the state-of-the-art IR camera, the temperature profiles were recorded cycle by cycle during 20 Hz fatigue testing. A theoretical model combining the thermoelastic, inelastic, and heat-conduction effects were used to explain and predict the temperature evolution during fatigue. Specifically, the temperature evolution was predicted, and the results were found to be in good agreement with the experimental data.

Lock-In IR-Thermography – A Novel Tool for Material and Device Characterization

Abstract: A novel non-destructive and non-contacting technique for the spatially resolved detection of small leakage currents in electronic devices and MOS materials is presented. Highly-sensitive lock-in infrared (IR-) thermography is used to localize leakage current induced temperature variations down to 10 μK at a lateral resolution down to 5 μm. Leakage currents of about 1 mA can be localized within seconds and some μA may be detected after less than 1 h measurement.

In-plane thermal diffusivity evaluation by infrared thermography

Abstract: A thermographic technique for measuring the in-plane thermal diffusivity of slabs is presented; it consists of heating the front surface of a platelike sample by a circular Gaussian source. The in-plane thermal diffusivity is obtained by monitoring the time evolution of the spatial distribution of the rear surface temperature by an infrared camera. Specifically, from the temperature distribution taken at different times along a line crossing the heating image of the circular spot center on the rear surface, it is possible to obtain the time evolution of the radius of the Gaussian. In order to get the thermal diffusivity value from the widening of this radius, a method for the reduction of the experimental data is presented; the resulting in-plane thermal diffusivity value is then compared with the value found in the literature and with values furnished by the laser flash and the thermal wave interferometry experiments carried out on the samples extracted by the plate. Satisfactory agreement between all the values was noted.

Thermography based diagnostics of power equipment

Abstract: Infrared analysis tools and an algorithm to assess the condition of power equipment are demonstrated. Thermographic analysis capabilities and limitations are highlighted, and then the dedicated software toolbox is presented with its features overview. Finally an approach to infrared measurements trending for use in condition monitoring applications is demonstrated. Feasibility of the proposed solution is verified with a case study of an HV disconnector inspection.

Thermal imaging of composites

Abstract: Active thermal imaging techniques and their applications to composite materials are reviewed. The techniques included are transient thermography, scanning thermal microscopy and scanning thermal probe microscopy. The factors that affect the images produced by both pulsed and periodic forms of active heating are considered. For pulsed heating, experimental and numerical modelling results for carbon fibre-reinforced plastic are used to show how the resolution of subsurface features depends on their size and depth and on the anisotropy in thermal materials properties common in such composites. For periodic heating, thermal wave characteristics are introduced to show how the resolution of subsurface features also depends on modulation frequency and focal spot radius. Examples are given of the applications of scanning thermal microscopy and scanning thermal probe microscopy that illustrate the potential of these techniques for the imaging of composite materials.

Fluorescence emission ratio imaging thermography for use in heat transfer analysis

Abstract: The present invention provides a fluorescent imaging thermographic method and system for use in surface temperature measurements, which are reproducible over time. The invention provides a temperature-sensitive fluorescent probe (23) comprising a rare earth compound in an ultraviolet and fluorescence transparent medium (25) in order for the intensity of the fluorescence to vary as the temperature varies. The probe comprises Eu (1,1,1,5,5,5-hexafluoroacetylacetone)3 for measuring temperatures greater than 24 °C, and Tb (1,1,1,5,5,5-hexafluoroacetylacetone)3 for measuring temperatures less than 24 °C. The probe is applied as a layer to a surface (22) and exposed to fluorescence-inducing energy (10), then the emitted fluorescence is measured (12) and a ratio-imaging algorithm determines the temperature at each location on the surface.

Thermography catheter with flexible circuit temperature sensors

Abstract: The present invention relates, to thermography catheters and, more particularly, to thermography catheters which use flex circuit technology to create the connections and thermocouples used to detect hot spots (areas with high metabolic activity) of the atherosclerotic plaque, vascular lesions, and aneurysms in human vessels.

A Study of Wood Inspection by Infrared Thermography, Part I: Wood Pole Inspection by Infrared Thermography

Abstract: Wood poles are among the main components of electrical distribution systems. They have to be replaced every 20–30 years due to wood decay. To reduce costs, utilities need an efficient nondestructive tool to determine the appropriate replacement time. Different techniques exist for this purpose, such as X- or gamma-ray tomography, indentation, and methods based on measurement of electrical conductivity, ultrasonic propagation, or simply bacterial culturing. Since none of these methods satisfy these utilities, it was decided to study in detail infrared thermography (NDT) in this particular context. The hypothesis is that in this particular context, wood decay corresponds to a different moisture content with respect to sound wood. In Part I of the paper the problem of wood pole NDT is analyzed using a dedicated thermal model and three different types of heating: internal through-hole, external, and by microwave. Experiments confirm modeling results: due to large defect depths, low wood thermal diffu...

Energy, Radiation and Temperature Regulation in Plants

Abstract: The temperature of any plant organ depends on the balance between incoming energy and energy loss. The energy exchanges involved include radiative transfer, sensible heat transfer by convection processes, latent heat transfer as a result of evaporation and transfer to and from storage (by conduction). The radiative transfer is frequently classified into either short-wave (or solar) radiation and long-wave (or thermal) radiation; these contribute differently to the overall energy balance. Various biophysical mechanisms are available to plants, through manipulation of the energy balance terms, for temperature regulation. For example, enhanced evaporation can help cool leaves in hot environments, whereas maximising absorption of sunlight can raise the temperature in cold environments. This article outlines the relative importance of these different processes in both leaf and canopy temperature regulation, highlighting differences between treatment of the energy balance at leaf and canopy scales. Examples of applications, such as the measurement of canopy temperature to determine plant water stress or to aid in the selection of drought tolerant varieties of plants, are also discussed. Key Concepts: A critical requirement of plants is that they maintain their leaf temperature as close as possible to the optimal temperature for growth; plants have a range of mechanisms that help them to optimise their temperature. Leaf and canopy temperature are dependent on the leaf energy balance, which itself is dominated by radiant exchanges. Radiation in natural environments relevant to leaf energy balance is conventionally separated into the ultraviolet (0.2–0.38 μm), the visible (0.38–0.7 μm) and the infra-red (0.7–100 μm). Radiation coming from the sun is often termed short-wave radiation, about half of which is in the visible region, a small amount in the ultraviolet, and the remainder in the near infra-red (0.7–3 μm). Long-wave, or thermal radiation is conventionally taken as the radiation between 3 (or sometimes 4) μm and 100 μm. The radiation emitted by natural surfaces as a function of their temperature is primarily in this wave-band. The thermal radiation emitted by any body increases according to the fourth power of the temperature (Stefan–Boltzmann's law). Leaf and canopy temperatures depend on the exchanges of energy between plants and the atmosphere both through radiation exchange and by means of sensible heat and latent heat fluxes. Leaf temperature therefore depends on the radiation climate (time of day, cloud cover and type, etc.), atmospheric conditions (wind speed, temperature, etc.), the soil conditions (soil type, water content, etc.) and the canopy properties (such as plant morphology, density, height, etc.) that together affect the size and ratios of the radiant, sensible and latent heat fluxes. Measurement of leaf temperature using infra-red thermometry or thermography can be used to detect plant water-deficit stress and to screen plants for their drought tolerance. Keywords: energy balance; solar radiation; temperature; thermal adaptations; thermal radiation; vegetation

Progress in ultrasound phase thermography

Abstract: Ultrasound Phase Thermography (UPT) is a non-destructive technique derived from Ultrasound Lock-In Thermography (ULT) which was established a few years ago. UPT provides defect selective imaging using thermal waves generated by elastic waves. The use of short ultrasound bursts instead of sinusoidal signals for excitation allows for faster measurements and better reproducibility as compared to ULT. However, the advantages of phase images are the same: recognition of defect depth and suppression of temperature gradients. Application of UPT to typical defects of aircraft materials and components provide specific information on their nature.

Medical applications of model-based dynamic thermography

Abstract: The proposal to use active thermography in medical diagnostics is promising in some applications concerning investigation of directly accessible parts of the human body. The combination of dynamic thermograms with thermal models of investigated structures gives attractive possibility to make internal structure reconstruction basing on different thermal properties of biological tissues. Measurements of temperature distribution synchronized with external light excitation allow registration of dynamic changes of local temperature dependent on heat exchange conditions. Preliminary results of active thermography applications in medicine are discussed. For skin and under- skin tissues an equivalent thermal model may be determined. For the assumed model its effective parameters may be reconstructed basing on the results of transient thermal processes. For known thermal diffusivity and conductivity of specific tissues the local thickness of a two or three layer structure may be calculated. Results of some medical cases as well as reference data of in vivo study on animals are presented. The method was also applied to evaluate the state of the human heart during the open chest cardio-surgical interventions. Reference studies of evoked heart infarct in pigs are referred, too. We see the proposed new in medical applications technique as a promising diagnostic tool. It is a fully non-invasive, clean, handy, fast and affordable method giving not only qualitative view of investigated surfaces but also an objective quantitative measurement result, accurate enough for many applications including fast screening of affected tissues.

Tracking of coherent thermal structures on a heated wall by means of infrared thermography

Abstract: This paper deals with measurements of convective velocity of large-scale thermal structures, using the thin foil technique and infrared thermography to visualize the thermal pattern on the wall. An image correlation method is proposed to track the displacement of the observed thermal pattern. The idea of the method is similar to that of particle image velocimetry, but the thermal patterns on the heated wall are used, rather than tracing particles. On this basis, the thermal patterns created by the coherent structures of turbulent channel flow are examined. Particular attention is paid to the determination of the optimal parameters of image acquisition, including spatial and temporal separation. An attempt is made to relate momentum and scalar transport analyses by considering the propagation velocity of large-scale temperature structures. The proposed technique appears to be an attractive alternative for non-intrusive analysis of turbulent flow, especially, where opaqueness of channel walls excludes the use of optical methods.

A Study of Wood Inspection by Infrared Thermography, Part II: Thermography for Wood Defects Detection

Abstract: Wood poles are among the main components of electrical distribution systems. They have to be replaced every 20—30 years due to wood decay. To reduce costs, utilities need an efficient nondestructive tool to determine the appropriate replacement time. Different techniques exist for this purpose, such as X- or gamma-ray tomography, indentation, and methods based on measurement of electrical conductivity, ultrasonic propagation, or simply bacterial culturing. Since none of these methods satisfy these utilities, it was decided to study in detail infrared thermography (NDT) in this particular context. The hypothesis is that in this particular context, wood decay corresponds to a different moisture content with respect to sound wood. In Part I of the paper the problem of wood pole NDT is analyzed using a dedicated thermal model and three different types of heating: internal through-hole, external, and by microwave. Experiments confirm modeling results: due to large defect depths, low wood thermal diffusivity, and the wood properties dependencies upon temperature, moisture, species, and fiber orientation, infrared thermography (IRT) is not appropriate for this inspection problem unless defects are close to the surface. Discussion of wood thermal properties is also included in Part I. In Part II of the paper, the wood decay inspection problem is revisited in a simpler manner: flat instead of circular geometry and shallower defects. Thermal modeling along with experimental results are presented, and the comparison is encouraging.

Performance evaluation of various antenna configurations for microwave thermography during superficial hyperthermia

Abstract: Microwave thermography is currently under investigation for its potential in non-invasive monitoring and control of tissue temperature during superficial microwave hyperthermia treatments. In this effort, six antennas were tested for their suitability as radiometric probes in terms of penetration depth, signal-to-noise ratio, and the sensitivity and accuracy of measured temperature signals over the frequency range from 1.2-3.5 GHz. Due to the intended integration of this radiometry technique with large area multi-aperture heat applicators such as Dual Concentric Conductor (DCC) arrays, the size of each receive antenna was limited to 4 cm. The performance of logarithmic and Archimedean spiral microstrip structures was compared to dielectric loaded waveguide antennas. Results showed adequate signal-to-noise ratio for all antennas at frequencies above 2.5 GHz and for all antennas except the electrically small waveguides over the entire frequency range. Overall, the signal sensitivity from 1 to 3 GHz was appr...

Medical Active Thermography - A New Image Reconstruction Method

Abstract: A new method of image reconstruction for active, pulse thermography is presented. Based on experimental results the thermal model of the observed object is proposed. Studies on thermal transients basing on the FEM object model are presented. Examples of reconstructed images are presented and described for phantoms and for in-vivo measurements. Possible applications are discussed.

Development of a New Crack Identification Technique Based on Near-Tip Singular Electrothermal Field Measured by Lock-in Infrared Thermography

Abstract: A new thermographic NDT technique was proposed, in which singular electrothermal field near crack tips under the application of periodically modulated electric current was measured using an infrared thermography combined with lock-in data processing technique. Experimental investigations were made on the resolution and the applicability in the identification of through-thickness artificial cracks and fatigue cracks embedded in steel and aluminum alloy plate samples. Modulated electric current was applied to the cracked sample by an induction coli. Lock-in thermal images synchronized to the reference current modulation signal were taken by the lock-in thermography. Significant singular electrothermal field was observed at the crack tip in the lock-in thermal image. The fatigue cracks as well as artificial cracks were found to be sensitively identified by the proposed technique in good resolution compared with the singular method using a conventional thermographic temperature measurement.

Thermography of human arterial system by means of new thermography catheters

Abstract: In this case report, we present the first clinical application of three thermography catheters for temperature measurements in the coronary arteries, the aorta, and the femoral arteries. The entire procedure was performed successfully without complications. Larger clinical studies are required in order to examine the feasibility for the application of the aortic and the peripheral artery thermography catheters and the clinical significance of temperature measurements in these arteries. Cathet Cardiovasc Intervent 2001;54:51-58.

Infrared thermography in the restoration of cultural properties

Abstract: Some of the work carried out at DETEC on the use of infrared thermography in the architectural restoration field is examined. Three different techniques, pulse thermography (PT), modulated thermography (MT) and pulse phase thermography (PPT) are analyzed through the control of some art treasures such as mosaics and frescoes. In particular, the following artifacts are considered: mosaics covering some external walls of the building of the Faculty of Engineering of Naples, frescoes in the Duomo of Sarno, frescoes in the Cripta SS. Stefani in Vaste (Le), mosaics and frescoes in the Archeological Museum of Naples coming from Pompeii and Ruvo. It is found that the choice of the technique depends on the specific surface to be tested: if only qualitative information about detachments and cracks are needed the pulse thermography is sufficient; if the surface is not very sensitive to temperature rising, the pulse phase thermography can be applied which gives information about the location of the defected zone. If instead, the analysis regards rare art treasures, lockin thermography is the only response.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Three-Dimensional Visualization and Measurement of Temperature Field Using Liquid Crystal Scanning Thermography

Abstract: A Liquid Crystal Scanning Thermography (LCST) technique is developed and implemented to visualize and measure three-dimensional temperature fields. Results are reported for natural convection in a differentially heated vertical cavity. Experiments are conducted under steady state conditions at Rayleigh numbers of about 10 4 with glycerin as the working fluid. The scanning arrangement is described in detail together with the calibration scheme, and image processing routines that enable the processing of the thermographs and extraction of quantitative temperature information from them, including local and global heat transfer rates. The resultant temperature fields and Nusselt number values are computed and validated against both standard empirical relations and numerical predictions. To date, LCT has not been used to determine Nusselt number for enclosed fluid systems. The ability of LCST to perform this task makes this novel experimental technique a useful tool

Emissivity-corrected infrared thermal pulse measurement on microscopic semiconductor targets

Abstract: The precision measurement and recording of high speed thermal transients on microscopic targets is critical to the manufacturing of semiconductors and other electronic devices as thermal budgets become over more demanding and devices become more compact and powerful. This paper describes the fully automated emissivity- corrected measurement of high speed thermal pulses at speeds up to 200 KHz representing the newest innovation in almost 25 years of thermal microimager evolution. Sample thermal images and time-based thermal scans are presented demonstrating the use of this transient measurement capability in the detection and identification of design and process defects. The documentation of a measurement spatial resolution of better than 3 micrometers is also reviewed.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.