Application Of Thermography Research Articles

Quantifying ageing effects in thermochromic liquid crystal thermography as applied to transient convective heat transfer experiments

Thermochromic liquid crystal (TLC) thermography is used in transient heat transfer experiments to determine distributions of convective heat transfer coefficient (HTC) inside models of internally cooled gas turbine engine components. As these components become more geometrically complex, the application of TLC thermography becomes increasingly challenging and additional sources of experimental uncertainty grow to be significant. The present work quantifies the uncertainties introduced by TLC ageing using a state-of-the-art imaging system and a new post-processing methodology that are optimised for the intensity-based method of analysing TLC data. A coating comprising multiple TLCs with different active temperature ranges is considered and subject to 33 repeated thermal cycles. These repeated cycles are shown to increase the random and systematic uncertainties in the TLC measurements, resulting in consequent increases in the uncertainties associated with calculated HTCs. Increases in systematic uncertainty are caused by reflectance in the measured wavelength band moving to different temperatures, while increases in random uncertainty are related to changes in individual crystals or crystal clusters with ageing. Approaches to calibrating out increases in systematic uncertainty are proposed and recommended, but increases in random uncertainty will always persist unless the TLC coating is removed and reapplied.

Application of thermography for cerebral perfusion imaging during aneurysm surgery

Abstract The success of aneurysm surgery depends on complete clipping of the aneurysmal sacculation without compromising quality of cerebral perfusion of vessels concerned. An established intraoperative method to visualize cerebral blood flow i n a pparent v essels i s fl uorescence vi deo angiography based on indocyanine green (ICG). However, major disadvantages of indocyanine green video angiography (ICG VA) are the need of a specialized imaging system, potential drug side effects as well as the limited number of repetitions due to long decay time of ICG in blood circulation. In particular the last drawback prevents brain parenchymal perfusion monitoring with ICG VA. The application of time-resolved thermography as a fast, contactless, noninvasive, marker-free and harmless imaging tool became a promising approach for perfusion imaging and thus offers several advantages compared to ICG. Measurements of deep structures in heat traps for identification of i nternal patterns, e ssential f or e .g. s uccess monitoring of aneurysm clipping, are still unsolved challenges of thermography. This work reveals as a proof of concept that the combination of thermography and an intravenous cold saline bolus injection as a contrast agent is capable to detect arterial and parenchymal perfusion located in the surgical cavity during aneurysm surgery in comparison to state-of-the-art ICG VA. The investigations provide evidence that thermography has the capability to perform intraoperative imaging of cerebral perfusion at an advanced stage in surgery for vessels and parenchyma located both cortically and in the surgical cavity.

Reducing Thermal Reflections for Infrared Thermography Applications on Tunnel Liners with Reflective Finishes

Infrared thermography (IRT) has been employed as a non-destructive evaluation (NDE) method to detect delaminations in bridge decks by ASTM standards since 2003. Compared with other NDE methods, IRT is fast for data acquisition and processing. In addition to applications on bridge decks, IRT can be employed to detect defects in other structures such as roadway pavements and tunnel liners. Recent IRT applications on tunnel liners with reflective finishes such as ceramic tiles show that the IRT results can be severely contaminated by infrared reflections of the vehicles and the illuminating systems in the tunnels. In this study, an algorithm is developed to mitigate the contamination caused by the thermal reflections in the IRT results. The reflection is reduced by combining thermal data from multiple thermographs. Perspective projection is employed to map thermal data to the same coordinates if the thermographs are taken with an infrared camera moving in the space. The algorithm is proven to be successful from the results from the lab experiments and field tests. The algorithm can work with IRT data collected by vehicle-mounted infrared cameras to achieve high-speed IRT for tunnel liners with reflective finishes.

Reducing Thermal Reflections for Infrared Thermography Applications on Tunnel Liners with Reflective Finishes

Infrared thermography (IRT) has been employed as a non-destructive evaluation (NDE) method to detect delaminations in bridge decks by ASTM standards since 2003. Compared to other NDE methods, IRT is fast in data acquisition and processing. In addition to applications on bridge decks, IRT can be employed to detect defects in other structures such as roadway pavements and tunnel liners. Recent IRT applications on tunnel liners with reflective finishes such as ceramic tiles show that the IRT results can be severely contaminated by infrared reflections of the vehicles and the illuminating systems in the tunnels. In this study, an algorithm is developed to mitigate the contamination caused by the thermal reflections in the IRT results. The reflection is reduced by combining thermal data from multiple thermographs. Perspective projection is employed to map thermal data to the same coordinates if the thermographs are taken with an infrared camera moving in the space. The algorithm is proved to be successful by the results from the lab experiments and field tests. The algorithm can work with IRT data collected by vehicle-mounted infrared cameras to achieve high-speed IRT for tunnel liners with reflective finishes.

The Application of Medical Thermography to Discriminate Neuroischemic Toe Ulceration in the Diabetic Foot

This study aimed to determine whether thermal imaging can detect temperature differences between healthy feet, nonulcerated neuroischemic feet, and neuroischemic feet with toe ulcers in patients with type 2 diabetes mellitus (T2DM). Participants were prospectively divided into 3 groups: T2DM without foot problems; a healthy, nonulcerated neuroischemic group, and an ulcerated neuroischemic group. Thermal images of the feet were obtained with automated segmentation of regions of interest. Thermographic images from 43 neuroischemic feet, 21 healthy feet, and 12 neuroischemic feet with active ulcer in one of the toes were analyzed. There was a significant difference in toe temperatures between the 3 groups ( P = .001), that is, nonulcerated neuroischemic (n = 181; mean temperature = 27.7°C [±2.16 SD]) versus neuroischemic ulcerated (n = 12; mean temperature = 28.7°C [±3.23 SD]), and healthy T2DM group (n = 104; mean temperature = 24.9°C [±5.04 SD]). A post hoc analysis showed a significant difference in toe temperatures between neuroischemic nonulcerated and healthy T2DM groups ( P = .001), neuroischemic ulcerated and healthy groups ( P = .001). However, no significant differences in toe temperatures were identified between the ulcerated neuroischemic and nonulcerated neuroischemic groups ( P = .626). There were no significant differences between the ulcerated toes (n = 12) and the nonulcerated toes (n = 57) of the same foot in the ulcerated neuroischemic group ( P = .331). Toe temperatures were significantly higher in neuroischemic feet with or without ulceration compared with healthy feet in patients with T2DM. There were no significant differences in temperatures of ulcerated toes and the nonulcerated toes of the same foot, implying that all the toes of the same foot could potentially be at risk of developing complications, which can be potentially detected by infrared thermography.

Application of thermography for thermoplastic waveguide fabrication

AbstractThe production of short polymer optical fibers from small material batches is valuable for materials research, especially in the investigation of copolymers. A two‐step fiber drawing process is usually used for this purpose. The drawing temperature of the individual materials is an important parameter in the process. Temperature measurements using contactless methods are preferred because they enable online monitoring and do not affect the drawing process. Such measurements can be carried out with a pyrometer, which allows the measurement of a wide range of temperatures but requires a precise adjustment of the spot to the core of the preform. To circumvent this limitation, a thermographic camera with a resolution of 134 µm per pixel in the heating zone is used. The measurement range 0–250 °C is suitable for the usual drawing conditions. The device is installed outside the resistive heating furnace. The absolute temperature is obtained by calibrating the sensor to the beam path and the material emission properties. Different materials, shapes and thicknesses lead to variations in these parameters. In this work, an analysis of the temperature calibration for poly(methyl methacrylate), poly(styrene) and the copolymers poly[styrene‐co‐(isobornyl methacrylate)] and poly[(methyl methacrylate)‐co‐(isobornyl methacrylate)] is presented. These are all thermoplastic polymers and may be used for the fabrication of polymer optical fibers. © 2018 Society of Chemical Industry

Investigation of Multiple Heat Source Effects in Lock-In Thermography Applications in Semiconductor Packages

Three-dimensional (3-D) packages have become a technology integrator for multiple functional devices into one component as a cost-effective way to enable Moore’s law for continuous scale-down. There are new challenges arising from the 3-D packages for fault isolation because of continued miniaturization and added complexity in the $z$ -direction of advanced IC devices, which require the development of more capable fault isolation tools and techniques for better accuracy, resolution, and sensitivity. Lock-in thermography is a powerful noncontact and nondestructive investigating technique that has recently become widely adopted in the semiconductor industry because of its sensitivity and quick time to data. As more components are integrated into 3-D packages, there are more active devices and routing becomes very complex. It is very common that multiple defects or heat sources can exist at the same time in a single package. These multiple heat sources interact with each other and affect defect depth accuracy to a very large extent. This paper presents a fundamental analysis to understand the interaction between multiple defects and its effect on the accuracy of defect depth estimation. Furthermore, this paper also presents real test cases to further the understanding and confidence in the proposed correlations. The learnings and techniques discussed in this paper can lead to industry-wide tool and technical developments, and benefit the failure analysis and 3-D package development community.

Medical thermography: capabilities and perspectives

Medical thermography is a modern diagnostic method that is currently gaining popularity due to high informative value and non-invasiveness. The aim of the study was to review the capabilities and prospects of medical thermography in modern medicine. The analysis of domestic and foreign literature on the application of medical thermography methods for the period of 2012-2017 was performed. The article presents the capabilities of imaging in various fields of medicine, evaluates the prospects of further development of the method, advances and disadvantages of thermography were identified. It also provides the review of the application of medical infrared thermography in clinical medicine. The experience of thermography application in various medical fields was investigated: angiology, otolaryngology, surgery, neurology, obstetrics and gyenecology, etc. Apart from medical aspects of this topic, the article discusses the history of medical thermography as well as provides the physical principles of this method. At present, thermal imaging can solve a wide range of problems: determining the presence of changes in the human body, and, as a result, the probability of pathology development, monitoring the effectiveness of treatment and rehabilitation. Every year more and more studies are carried out, confirming the high efficiency, reliability and safety of thermography, thermographic screenings are suggested, that can be assumed as prediction of future method's popularity.

Applicability of active infrared thermography for screening of human breast: a numerical study.

Active infrared thermography is a fast, painless, noncontact, and noninvasive imaging method, complementary to mammography, ultrasound, and magnetic resonance imaging methods for early diagnosis of breast cancer. This technique plays an important role in early detection of breast cancer to women of all ages, including pregnant or nursing women, with different sizes of breast, irrespective of either fatty or dense breast. This proposed complementary technique makes use of infrared emission emanating from the breast. Emanating radiations from the surface of the breast under test are detected with an infrared camera to map the thermal gradients over it, in order to reveal hidden tumors inside it. One of the reliable active infrared thermographic technique, linear frequency modulated thermal wave imaging is adopted to detect tumors present inside the breast. Further, phase and amplitude images are constructed using frequency and time-domain data analysis schemes. Obtained results show the potential of the proposed technique for early diagnosis of breast cancer in fatty as well as dense breasts.

IR thermography-based monitoring of respiration phase without image segmentation

BackgroundRespiratory rate is an essential parameter in biomedical research and clinical applications. Most respiration measurement techniques in preclinical animal models require surgical implantation of sensors. Current clinical measurement modalities typically involve attachment of sensors to the patient, causing discomfort. We have previously developed a non-contact approach to measuring respiration phase in head-restrained rodents using infrared (IR) thermography. While the non-invasive nature of IR thermography offers many advantages, it also bears the complexity of extracting respiration signals from videos. Previously reported algorithms involve image segmentation to identify the nose in IR videos and extract breathing-relevant pixels which is particularly challenging if the videos have low contrast or suffer from suboptimal focusing. New methodTo address this challenge, we developed a novel algorithm, which extracts respiration signals based on pixel time series, removing the need for nose-tracking and image segmentation. Results & comparison with existing methodsWe validated the algorithm by performing respiration measurements in head-restrained mice and in humans with IR thermography in parallel with established standard techniques. We find the algorithm reliably detects inhalation onsets with high temporal precision. ConclusionsThe new algorithm facilitates the application of IR thermography for measuring respiration in biomedical research and in clinical settings.

Defect Detection in Solid-State Battery Electrolytes Using Lock-In Thermal Imaging

Defective regions in battery materials often generate excess or non-uniform heat profiles during operation. Here, we discuss lock-in thermography as a high-sensitivity, spatially-resolved, and non-destructive technique to characterize defects and guide the targeted optimization of new battery materials and cell designs. As an example, we thermally image all-solid-state cells with β-Li3PS4 electrolyte, showing point-like heat signatures that correlate with cell breakdown. Based on the current/voltage cycling characteristics and electrochemical impedance spectroscopy, we attribute heating at the breakdown sites primarily to resistive current flow through dendrites. To assist in enabling wider application of lock-in thermography to emerging battery materials, we discuss several parameters necessary to optimize this technique, including the influences of surface thermal emissivity, thermal diffusivity, and lock-in modulation frequency.

NDT thermographic techniques on CFRP structural components for aeronautical application

This paper describes the application of active pulsed Thermography (PT) as a Non-Destructive Test (NDT) method for the investigation of CFRP aeronautical components. The analyzed specimens include T-shaped stringers, previously monitored by ultrasonic analysis, and laminated flat plates with internal production defects. Several set-up tests allowed to identify optimal configurations for the defect detection, according to specimen geometry and defect location. A custom post-processing algorithm has been developed to improve thermographic data for more precise defect characterization, whilst a successive full-field contrast mapping allows to achieve a reliable defect distribution map and a better definition on larger areas. Detection of defects was studied with a specific thermal contrast evaluation, with a suitable choice of undamaged reference area during the transient cooling phase. The influence of heating time and experimental set-up on the thermal contrast results has also been studied; moreover, the ability of thermographic technique to detect real small production defects with accuracy and reliability is verified for CFRP aeronautical components.

An advanced radiometric calibration approach for uncooled thermal cameras

AbstractUncooled thermal cameras are increasingly used in thermography applications due to their lower cost and size. However, there are two significant limiting constraints which must be taken into consideration in a radiometric calibration before the actual application: (i) temporal non‐uniformity (a temperature‐dependent drift problem); and (ii) spatial non‐uniformity (fixed‐pattern noise – FPN). Conventional temporal non‐uniformity corrections (NUC) take advantage of an internal reference source but such methods are not valid for sequential images when the focal‐plane array (FPA) temperature is changing rapidly. A novel shutterless correction method is proposed to stabilise the camera's response. Moreover, instead of implementing the spatial NUC first, multi‐point correction is leveraged to remove FPN after the temporal NUC. Finally, a Planck curve is applied to convert thermal image values into object temperatures. Experimental results show that the proposed method is more effective for images with rapidly changing FPA temperatures than conventional shutterless methods and traditional shutter‐based methods.

Nondestructive Testing of Ceramic Hip Joint Implants with Laser Spot Thermography

AbstractThe paper presents an application of laser spot thermography for damage detection in ceramic samples with surface breaking cracks. The measurement technique is an active thermographic approach based on an external heat delivery to a test sample, by means of a laser pulse, and signal acquisition by an infrared camera. Damage detection is based on the analysis of surface temperature distribution near the exciting laser spot. The technique is nondestructive, non-contact and allows for full-field measurements. Surface breaking cracks are a very common type of damage in ceramic materials that are introduced in the manufacturing process or during the service period. This paper briefly discusses theoretical background of laser spot thermography, describes the experimental test rig and signal processing methods involved. Damage detection results obtained with laser spot thermography are compared with reference measurements obtained with vibrothermography. This is a different modality of active thermography, that has been previously proven effective for this type of damage. We demonstrate that both measurement techniques can be effectively used for damage detection and quality control applications of ceramic materials.

Thermography Applied to the Study of Fatigue Crack Propagation in Polycarbonate

Thermography was used to study the propagation of fatigue cracks during cyclic loading of pre-cracked SAE keyhole polycarbonate specimens. A micro-bolometer infrared camera (FLIR A655sc) and a commercially available software program (DeltaTherm2) were employed. The stress intensity factors were determined using a hybrid thermoelastic stress analysis (TSA) technique. The crack growth rate was determined via thermography using two different approaches. The first approach used the output of the crack-tip position from the developed TSA algorithm and the number of cycles between data sets. The second approach used temperature measurement as a new way to determine da/dN (crack growth rate) directly. As a result, da/dN vs ΔK (stress intensity factor range) graphs were plotted and fitted using Paris’ law. A comparison between the resultant da/dN vs ΔK curves and results found in the literature, as well as curves from the finite element method (FEM) simulations showed good agreement. The conclusion was that thermography is a very powerful tool that can detect, measure and monitor fatigue cracks in polycarbonate.

Pulsed Thermography Applied to the Study of Cultural Heritage

In this paper, an overview of the recent applications of pulsed infrared thermography is presented. Pulsed infrared thermography, which provides stratigraphic information by analyzing the heat diffusion process within the sample after a thermal perturbation, is applied to the investigation of different kinds of cultural heritage artefacts. In particular, it is used to analyze repairs, decorative elements, and casting faults on bronzes, to detect texts hidden or damaged in ancient books/documents, and to characterize paint decorations. Moreover, the integration of pulsed infrared thermography and three-dimensional shape recording methods is proposed in order to provide a three-dimensional representation of the thermographic results. Finally, it is shown how the obtained thermographic results may be crucial from the historical and artistic points of view for understanding the modus operandi of a specific artist and/or of a workshop and for reconstructing the manufacturing process of the analyzed artefacts.

Heat transfer modeling using analytical solutions for infrared thermography applications in multilayered buildings systems

There is growing interest in implementing predictive maintenance techniques to buildings and structures and consequently there is a pressing need for research in effective non-destructive testing (NDT) tools. Infrared thermography (IRT) is a popular NDT tool that has been used in various areas. However, since most known IRT testing techniques have been developed for evaluating materials such as metals, its use in buildings has been limited. In this study, we seek to further IRT applications in buildings by conducting experimental active IRT tests and comparing the results with heat transfer simulations. A simulation model based on analytical expressions is used to compute heat transfer by diffusion in multilayered media and active IRT tests are carried out in a controlled environment using a test specimen that imitates a defective building element. The test duration and frequency of acquisition are varied, asare the specimen characteristics (defect depth, thickness and thermal properties). A phase contrast approach is used to access features which could be useful in evaluating and characterizing defect depth, thickness and thermal properties. Additionally, the influence of noise on phase contrast results is analyzed by introducing random temperature variations in the time domain results that are generated by the simulation model.

Application of IR thermography and thermal inverse modelling to evaluate power losses in ferromagnetic strips

The authors deal with the problem of determining the local properties and power loss in ferromagnetic material subjected to mechanical cutting. They use an IR camera to record local temperature rise on the surface of ferromagnetic strips including in the punched region. Next, the temperature measured is used in the numerical models that allow estimation of the power loss density distribution. A simple inverse thermal model for a ferromagnetic strip with non-uniform power loss is presented. The correctness of the results obtained from the simple inverse model is verified using the 3D thermal Finite Element Model (FEM) and compared with the results from the literature.

Application of thermography for monitoring stomatal conductance of Coffea arabica under different shading systems

Stomatal regulation is a key process in the physiology of Coffea arabica (C. arabica). Intrinsically linked to photosynthesis and water relations, it provides insights into the plant's adaptive capacity, survival and growth. The ability to rapidly quantify this parameter for C. arabica under different agroecological systems would be an indispensable tool. Using a Flir E6 MIR Camera, an index that is equivalent to stomatal conductance (Ig) was compared with stomatal conductance measurements (gs) in a mature coffee plantation. In order to account for varying meteorological conditions between days, the methods were also compared under stable meteorological conditions in a laboratory and Ig was also converted to absolute stomatal conductance values (g1). In contrast to typical plant-thermography methods which measure indices once per day over an extended time period, we used high resolution hourly measurements over daily time series with 9 sun and 9 shade replicates. Eight daily time series showed a strong correlation between methods, while the remaining 10 were not significant. Including several other meteorological parameters in the calculation of g1 did not contribute to any stronger correlation between methods. Total pooled data (combined daily series) resulted in a correlation of ρ=0.66 (P≤2.2e−16), indicating that our approach is particularly useful for situations where absolute values of stomatal conductance are not required, such as for comparative purposes, screening or trend analysis. We use the findings to advance the protocol for a more accurate methodology which may assist in quantifying advantageous microenvironment designs for coffee, considering the current and future climates of coffee growing regions.

The Use of Thermography Images in the Description of the Humidification Bulb in Soilless Culture

ABSTRACTThermography is a tool used in many scientific disciplines, including agriculture. Determining the behavior of a nutritive solution in soilless culture containers using substrates is very important in order to establish the position of drippers, drainage holes, the use of humidification agents, and fertigation management in culture units. This paper describes the application of thermography to determine the humidification bulb in horticulture crops to rapidly diagnose the best way to advance fertigation in different horticultural substrates in soilless culture. Thermography was seen to be an excellent tool for evaluating the movement and distribution of the nutritive solution within the soilless culture container with different substrates.