Showing papers on "Thermography published in 1999"

Use of thermography for quantitative studies of spatial and temporal variation of stomatal conductance over leaf surfaces

Abstract: This paper describes a new approach to the calibration of thermal infrared measurements of leaf temperature for the estimation of stomatal conductance and illustrates its application to thermal imaging of plant leaves. The approach is based on a simple reformulation of the leaf energy balance equation that makes use of temperature measurements on reference surfaces of known conductance to water vapour. The use of reference surfaces is an alternative to the accurate measurement of all components of the leaf energy balance and is of potentially wide application in studies of stomatal behaviour. The resolution of the technique when applied to thermal images is evaluated and some results of using the approach in the laboratory for the study of stomatal behaviour in leaves of Phaseolus vulgaris L. are presented. Conductances calculated from infrared measurements were well correlated with estimates obtained using a diffusion porometer.

Process control by transient thermography

Abstract: A method and apparatus for detecting, locating, isolating and controlling variations in the manufacturing process by transient thermography. A heat source (200) imparts heat to a surface which is radiated in the infrared region. Infrared sensors (204, 206, 208, 210) are coupled to a processor which tracks the physical characteristics of the sample, and provides feedback to a central process controller to make adjustments to the manufacturing process. The sample can be a continuous product such as a green powder metal sheet or tobacco product.

Emissivity measurement and temperature correction accuracy considerations

Abstract: Extraction of temperatures or temperature differences with thermography is not possible without knowledge of the target emissivity. As the technology of thermography evolves, many applications from predictive maintenance through R&D projects have increasingly stringent requirements for quality temperature measurement. Today's IR cameras and software can correct for target emissivity variations on a point-by-point basis or over the entire image. One problem is how to measure emissivity, and how emissivity measurement uncertainties propagate to temperature uncertainties. This paper discusses emissivity measurement techniques, why table values are often not valid for a particular IR camera (why you must measure emissivity) and how emissivity measurement accuracy affects temperature measurement accuracy (error budget for opaque targets).

Surface Temperature Distribution of a Breast With and Without Tumour

Abstract: Breast cancer is a common and dreadful disease in women. Regular screening helps in its early detection. At present the most common methods of screening are by self examination and mammography. The surface temperature distribution of the breast can also provide some information on the presence of tumour. This distribution has a relation to the size and location of tumour and can be seen using thermography, where the infrared radiation emitted from the surface of the breast is recorded and a thermal pattern obtained. Thermography is a non-invasive and an inexpensive tool which could be used for early detection. In order to simulate the surface temperature distribution, a two-dimensional model of female breast with and without a carcinoma is considered. The breast is modelled with varying layer thickness close to the actual shape and numerically solved using finite element analysis. Temperature profiles are obtained for a normal breast and for a malignant one by varying the tumour size, location an...

Method and apparatus for quantitative nondestructive evaluation of metal airfoils using high resolution transient thermography

Abstract: An IR transient thermography imaging system includes high-power flash lamps fitted with spectrally tuned optical filters and a focal-plane array camera for IR image data acquisition. The image data processing control computer analyzes acquired IR image data frames and provides a color-keyed display of an imaged object that correlates to object thickness over the imaged surface area. Acquisition of IR data is initiated at a firing of flash lamps used to heat a surface of the object along with a reference standard. A predetermined number of IR image frames are acquired and recorded over a predetermined period of time after firing of the lamps to develop a temperature-time (T-t) history of the object surface and the reference standard. A contrast curve is calculated for each pixel in the image frame, each pixel corresponding to an elemental region on the object surface. Gaussian temporal smoothing of contrast curve data is performed to improve signal-to-noise characteristics and a derivative of the contrast curve is determined using data points mathematically related to image frame number. All local peaks in the derivative of the contrast curve are identified and given significance according to a predetermined weighting function. The frame number of the most significant peak is used to determine time of occurrence of an “inflection point” in the contrast curve which is then used in determining object thickness. Gain correction of pixel intensity data is employed to offset IR emissivity variations caused by surface curvatures and varying surface conditions on an object.

On the NDT and E for the diagnosis of defects using infrared thermography

Abstract: The increasingly recognized applicability of infrared thermography has caused developments of remote-sensing diagnoses for various engineering applications. A significant advantage of this technique is that we can diagnose invisible defects nondestructively and safely. For maintaining and managing various structures satisfactorily, it is very important to detect many kinds of invisible defects such as separation, cavity, inclusion and so on. Although the infrared thermography for NDT and E has therefore been examined extensively, few fundamental investigations have addressed the numerical computation to evaluate the detection mechanism and the quantitative limit under various conditions. It is important to discuss them theoretically with the aid of the appropriate numerical computation. In this paper, therefore, we certify them using a series of fundamental numerical computation with the aid of the concerned experimental investigation using the infrared thermography. From the numerical and experimental investigations, the effects of defect's depth and size on the detection are elucidated. In addition to the fact, it is obvious that the applicability of the present NDT and E depends on a heating condition and a relative difference of thermophysical property between the defect and its surrounding.

Study on the Distribution Pattern of Skin Temperature in Normal Chinese and Detection of the Depth of Early Burn Wound by Infrared Thermography

Abstract: Objective Conduct basic research of the distribution pattern of skin temperature and estimate the wound depth in normal Chinese in the early stage of burn injury by using technical thermography. Methods (1) Two hundred twenty-three volunteers from the electrical power system were randomly chosen: 138 males and 85 females, mean age 42.5 ± 8.8, and mean weight 65.37 ± 9.7 kg. (2) Thermovisionr 470 Pro camera of AGEMA Corporation, Sweden, was used. (3) A total of 29,882 values of skin temperature from all over the body were classified, compared, and statistically analyzed. Results The difference in temperature on the y-axis of the body is relatively significant, from 0 to 9 °C. The difference in temperature on the x-axis of the body is relatively invariable. Conclusions The depth of early burn wound can be detected by using infrared thermography, which is an objective, fast, nontouching, and noninvasive method.

Pulse phase thermography for defect detection and visualization

Abstract: Pulse Phase Thermography (PPT) has been reported as a novel powerful technique of the thermal NDE. It employs application of the Discrete Fourier Transform (DFT) to thermal images obtained following flash heating of the front surface of a specimen. The computed phasegrams are excellent for defect visualization in a wide range of materials. This is in part due to their low sensitivity to uneven heating. This work is an attempt to analyze advantages and limitations of PPT. Results of application of the DFT to simulated temperature decays are presented. The temperature evolution on a surface has been simulated based on an analytical solution of the one-dimensional heat diffusion problem. A more sophisticated study has been done for different sizes of defects using numerical solution of the three-dimensional mathematical model. Capabilities of PPT for in-depth scanning and for monitoring of the material loss are discussed. The recommendations for the practical application of the PPT are presented. Experimental results obtained following these recommendations are reported.

Ultrasound lock-in thermography: feasibilities and limitations

Abstract: Conventional thermal wave imaging methods based on optical excitation are sensitive to all thermal boundaries and structures. However, if ultrasound is used for energy deposition, areas of enhanced mechanical loss angle are heated up selectively. As defects are usually correlated with an enhanced loss angle, ultrasound lockin thermography (ULT) is a defect-selective NDE method. Thermal wave emission from defects is monitored that are activated by absorption of ultrasound. In this paper we investigate the applicability of ULT for maintenance and inspection. Examples are presented showing the detection of defects in thick composite materials, of vertical cracks in several materials, and of hidden corrosion. Limitations given by the use of ultrasound are also discussed.

Development of a new crack identification method based on singular current field using differential thermography

Abstract: A new thermographic NDT technique was proposed, in which singularity of the temperature field near crack tips under application of the periodically modulated electric current was measured using differential thermography based on lock-in data processing technique. Experimental investigation was made on the resolution and the applicability in the detection of through-thickness cracks embedded in steel plate samples. Modulated electric current was applied to the cracked sample by an induction coil. Differential thermal images synchronized to the reference current modulation signal were taken by the differential thermography. Significant singular temperature field was observed at the crack tips in the differential thermal images. The cracks were found to be sensitively detected by the proposed technique in good resolution compared with the singular method using a conventional thermographic temperature measurement.

Visualization of subsurface defects in composites using a focal plane array infrared camera

Abstract: A technique for enhanced defect visualization in composites via transient thermography is presented in this paper. The effort targets automated defect map construction for multiple defects located in the observed area. Experimental data were collected on composite panels of different thickness with square inclusions and flat bottom holes of different depth and orientation. The time evolution of the thermal response and spatial thermal profiles are analyzed. The pattern generated by carbon fibers and the vignetting effect of the focal plane array camera make defect visualization difficult. An improvement of the defect visibility is made by the pulse phase technique and the spatial background treatment. The relationship between a size of a defect and its reconstructed image is analyzed as well. The image processing technique for noise reduction is discussed.

Optimal thermographic procedures for moisture analysis in building materials

Abstract: The presence of moisture in building materials causes damage second only to structural one. NDT are successfully applied to map moisture distribution, to localize the source of water and to determine microclimatic conditions. IR Thermography has the advantage of non-destructive testing while it allows to investigate large surfaces. The measures can be repeated in time to monitor the phenomenon of raising water. Nevertheless the investigation of moisture in walls is one of the less reliable application of Thermography IR applied to cultural heritage preservation. The temperature of the damp areas can be colder than dry ones, because of surface evaporation, or can be warmer, because of the higher thermal inertia of water content versus building materials. The apparent discrepancies between the two results are due to the different microclimatic conditions of the scanning. Aim of the paper is to describe optimal procedures to obtain reliable maps of moisture in building materials, at different environmental and microclimatic conditions. Another goal is the description of the related energetic phenomena, which cause temperature discontinuities, and that are detected by thermography. Active and passive procedures are presented and compared. Case studies show some examples of procedures application.

Advanced Image Processing for Defect Visualization in Infrared Thermography

Abstract: Results of a defect visualization process based on pulse infrared thermography are presented. Algorithms have been developed to reduce the amount of operator participation required in the process of interpreting thermographic images. The algorithms determine the defect''s depth and size from the temporal and spatial thermal distributions that exist on the surface of the investigated object following thermal excitation. A comparison of the results from thermal contrast, time derivative, and phase analysis methods for defect visualization are presented. These comparisons are based on three dimensional simulations of a test case representing a plate with multiple delaminations. Comparisons are also based on experimental data obtained from a specimen with flat bottom holes and a composite panel with delaminations.

Thermography, a tool for reliability and safety

Abstract: A thermography survey program, using appropriate equipment and properly trained personnel, can be an extremely effective cool to prevent equipment failures potentially resulting in lost production, equipment damage and personnel exposure to hazards. Basically, there are no limits to the application of infrared thermography in the hands of a certified, qualified inspector. Any equipment or object where temperature patterns or levels indicate equipment condition is a good application for infrared thermography. However, training and experience are essential in being able to safely collect useful data and to accurately interpret the data gathered. Without proper equipment operated by, and acquired data interpretation done by, well trained personnel with proper certification a thermography program can easily result in misinterpretation and lead to more harm than good.

Transient thermography using evanescent microwave microscope

Abstract: Very high spatial resolution thermography is of great importance in electronics, biology, and in many other situations where local variations in temperature are needed to study heat dissipation or to monitor metabolism rate which can be directly related to the heat production. Infrared imaging techniques probably are the best way of obtaining thermal maps of large structures. However, the spatial resolution of infrared imaging techniques is limited to a few 100 μm and their temperature resolution is usually around 0.1 K. Here we report on a new evanescent microwave method that is capable of mapping temperature distributions with ≈1 μm spatial resolution. The temperature sensitivity of this probe was better than 0.1 V/K with a minimum detectable signal of 0.01 K with a response time faster than 1 μs.

Infrared thermography: applications in heart surgery

Abstract: Infrared thermography has become a way to monitor thermal abnormalities present in number of diseases and physical injuries. It is used as an aid to diagnosis, prognosis and therapy. Results obtained using the last generation of equipment (computer assisted thermographic systems, detectors without liquid nitrogen cooling system) and new techniques as dynamic thermography with independent source of driving radiation shows that it is a reliable tool for medical assessment and diagnosis. Most important--the Infrared Thermography is a non-invasive measurement technique, with non-stress for patients. This paper describes Intraoperative Thermoangiography during coronary bypass surgery.© (1999) 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.

Automated thermographic defect recognition and measurement

Abstract: Although pulsed thermography has been demonstrated as a means of detecting subsurface defects in a wide range of materials, quantification of defect size and depth has only been possible using high performance IR cameras, often operating at high frame rates. Quantitative methods have also required that the operator identify an umblemished, defect-free region to serve as a basis for comparison to the rest of the sample. The expense and complexity imposed by these requirements have limited implementation of quantitative methods to relatively high end aerospace applications. We have developed a method for acquiring and analyzing pulsed thermographic data that requires no a priori knowledge of the sample and does not require subjective decision making by the operator. Size and depth measurements have been demonstrated on metal and composite materials, with computation times on the order of 5 seconds for a sequence of 300 320x240 frames. The method can be applied to either digital or analog signals from any IR camera.

Measurement of temperature on Scindapsus leaves subjected to ultraviolet radiation using infrared thermography techniques

Abstract: The temperatures on the surfaces of intact Scindapsus (pothos lime) leaves subjected to ultraviolet radiation (UV-A, UV-B) as a function of time were investigated. The thermal images of leaves were taken at intervals of 1 min for 2 to approximately 11 h using a thermal video system, by which thermal information in the 3 to 5.4 micrometer infrared band were recorded. After the tests, the difference between the mean temperature of the leaf and the atmospheric temperature at each time point under each condition was determined. The results showed that the temperature differences for UV-A and UV-B irradiation were different from those for visible light supplied by a green house lamp. Therefore, the temperature on the leaf surface suggested the possibility of applications in the prediction of the level of UV-A and UV-B radiation.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Image processing procedures for the thermal measurements

Abstract: Image processing procedures used in improving the understandability of thermal maps obtained from measurements are discussed in the paper. Visibility enhancing methods and image composition methods are presented in connection with LC thermal mapping and infrared (IR) thermography.

Pulsed thermographic inspection and application in commercial aircraft repair

Abstract: Pulsed infrared thermographic inspection has proven to be a fast, accurate, reliable and cost effective NDE alternative to traditional ultrasonic NDE of commercial aircraft structures. Accurate damage assessment and verification of proper repair is of utmost importance to the commercial aircraft operator today. Pulsed infrared thermographic inspection can be utilized on a wide variety of aircraft structures with a high degree of accuracy. Acoustical structures that previously could not be scanned with traditional ultrasonic methods can be evaluated using pulsed infrared thermographic inspection.

Low-cost low-power uncooled a-Si-based micro infrared camera

Abstract: An amorphous silicon (a-Si) microbolometer-based uncooled infrared camera technology, offering a low- cost, low-power solution to infrared surveillance for both civilian and military application is presented. A- Si exhibits a temperature dependent resistance with a 3000K temperature coefficient of resistance (TCR) of 2.7 percent/K. The uncooled a-Si microbolometer detector structure employs a low thermal mass a-Si membrane structure with high thermal isolation legs monolithically integrated on a CMOS readout integrated circuit (ROIC) chip. A refractive resonant cavity design results in approximately 90 percent infrared absorptance over the 8-13 um spectral band. A-Si also exhibits a UV/visible photoconductive response for multispectral applications. The ROIC involves an integrating amplifier per pixel and a column multiplexed output. A 15 x 31 micro infrared camera (MIRC) has been developed, which exhibits f/l noise equivalent temperature difference, thereby significantly reducing the power requirements. The 15 x 31 camera demonstrated exhibits a 35 mm camera form factor employing a low cost f/l singlet optic and LED display, as well as low cost vacuum packaging. A larger 120 x 160 version of the MIRC is also in development and will be discussed.