Improvement of building wall surface temperature measurements by infrared thermography

By using quantitative thermal scanning of building surface structures, it is possible to access the temperature field. For further calculation of the heat flux exchanged by these structures with the environment, one must quantify as finely as possible the temperature field on the bodies surfaces. For this purpose we have to take into account that real bodies are not black, which implies that a part of the ambient radiation received by the infrared camera detectors is reflected radiation. In this paper, we present a method to quantify the reflected flux by using an infrared mirror, which allows large surface temperature measurements by infrared thermography under near-ambient conditions with improved accuracy. In order to validate the method, an experimental study was carried out on a multi-layer wall, which simulated an insulation default. A good agreement was noticed between the thermocouple temperatures and the infrared corrected ones. Then, the method is applied to outdoor measurements.     

In situ assessment of structural timber elements of a historic building by infrared thermography and ultrasonic velocity

The infrared thermography (IRT) and the ultrasonic velocity measurements (UVM) promise to be particularly important to assess the state of deterioration and the adequacy of the boundary and microclimatic conditions for timber elements. These non-destructive methods supported by laboratory analyses of timber samples were conducted on a 13th century monument, Aslanhane Mosque in Ankara, Turkey. The combined interpretation of the results was done to assess the condition of structural timber elements in terms of their state of preservation, the dampness problems and the recent incompatible repairs affecting them. Results indicated that moist areas in the structure were associated with roof drainage problems and the repairs undertaken with cement-based mortars and plasters and oil-based paints. Juxtaposition of the IRT and UVM together with laboratory analyses was found to be useful to assess the soundness of timber, enhanced the accuracy and effectiveness of the survey and facilitated to build up the urgent and long-term conservation programs.     

A survey on infrared thermography for convective heat transfer measurements

During the past several years infrared thermography has evolved into a powerful investigative means of thermo-fluid-dynamic analysis to measure convective heat fluxes as well as to investigate the surface flow field behaviour over complicated body shapes. The basic concepts that govern this innovative measurement technique together with some particular aspects linked to its use are herein reviewed. Different operating methods together with their implementations are also discussed. Finally, the capability of infrared thermography to deal with several simple, or complex, fluid flow configurations is analysed.     

Vibration characteristics measurement of beam-like structures using infrared thermography

Infrared thermography (IRT) has matured and is now widely accepted as a condition monitoring tool where temperature is measured in a non-contact way. Since the late 1970s, it has been extensively used in vibrothermography (Sonic IR) non-destructive technique for the evaluation of surface cracks through the observation of thermal imaging of the vibration-induced crack heat generation. However, it has not received research attention on prediction of structural vibration behaviour, hence; the concept to date is not understood. Therefore, this paper explores its ability to fill the existing knowledge gap. To achieve this, two cantilever beam-like structures couple with a friction rod subjected to a forced excitations while infrared cameras capturing the thermal images on the friction interfaces. The analysed frictional temperature evolution using the Matlab Fast Fourier Transform (FFT) algorithm and the use of the heat conduction equation in conjunction with a finite difference approach successfully identifies the structural vibration characteristics; with maximum error of 0.28% and 20.71% for frequencies and displacements, respectively. These findings are particularly useful in overcoming many limitations inherent in some of the current vibration measuring techniques applied in structural integrity management such as strain gauge failures due to fatigue.     

Narrative review: Diabetic foot and infrared thermography

Diabetic foot is one of the major complications experienced by diabetic patients. An early identification and appropriate treatment of diabetic foot problems can prevent devastating consequences such as limb amputation. Several studies have demonstrated that temperature variations in the plantar region can be related to diabetic foot problems. Infrared thermography has been successfully used to detect complication related to diabetic foot, mainly because it is presented as a rapid, non-contact and non-invasive technique to visualize the temperature distribution of the feet. In this review, an overview of studies that relate foot temperature with diabetic foot problems through infrared thermography is presented. Through this research, it can be appreciated the potential of infrared thermography and the benefits that this technique present in this application. This paper also presents the different methods for thermogram analysis and the advantages and disadvantages of each one, being the asymmetric analysis the method most used so far.     

Surface temperature measurement of the plasma facing components with the multi-spectral infrared thermography diagnostics in tokamaks

For the long-pulse high-confinement discharges in tokamaks, the equilibrium of plasma requires a contact with the first wall materials. The heat flux resulting from this interaction is of the order of 10 MW/m² for steady state conditions and up to 20 MW/m² for transient phases. The monitoring on surface temperatures of the plasma facing components (PFCs) is a major concern to ensure safe operation and to optimize performances of experimental operations on large fusion facilities. Furthermore, this measurement is also required to study the physics associated to the plasma material interactions and the heat flux deposition process. In tokamaks, infrared (IR) thermography systems are routinely used to monitor the surface temperature of the PFCs. This measurement requires an accurate knowledge of the surface emissivity. However, and particularly for metallic materials such as tungsten, this emissivity value can vary over a wide range with both the surface condition and the temperature itself, which makes instantaneous measurement challenging. In this context, the multi-spectral infrared method appears as a very promising alternative solution. Indeed, the system has the advantage to carry out a non-intrusive measurement on thermal radiation while evaluating surface temperature without requiring a mandatory surface emissivity measurement.In this paper, a conceptual design for the multi-spectral infrared thermography is proposed. The numerical study of the multi-channel system based on the Levenberg-Marquardt (LM) nonlinear curve fitting is applied. The numerical results presented in this paper demonstrate the design allows for measurements over a large temperature range with a relative error of less than 10%. Furthermore, laboratory experiments have been performed from 200 °C to 740 °C to confirm the feasibility for temperature measurements on stainless steel and tungsten. In these experiments, the unfolding results from the multi-channel detection provide good performance on temperature measurement, which supports our numerical evaluation and demonstrates the potential feasibility for metallic surface high temperature measurement with this method.     

Evaluation of topographical variation in ocular surface temperature by functional infrared thermography

The objective of this work is to evaluate topographical variation in the ocular surface temperature (OST) among the young, elderly and the subjects wearing contact lens using thermographic methodology. We recorded thermographic sequence lasting of 25 s for each eye. The ocular region in each of the thermal images in the sequence was identified and warped into a standard form. Then, the warped sequence was divided into a number of sub-sequences. A differential image which is an image matrix was obtained from each of these sub-sequences, by subtracting thermal images within the sub-sequence. And the histogram of the differential image was modelled by Gaussian mixture model to discriminate eyelashes from the ocular surface for every thermal image in the sub-sequence. Later, thermal data of eyelashes were eliminated in every thermal image and statistical analysis was performed on the sequences. Finally, topographical profile of each subject group was approximated by equations and illustrated using various temperature profiles. The ocular surface of the young subject was observed to be the warmest, and tear film was determined to play a major role in the topographical and temporal variations in OST. Significant topographical variation was observed among subject groups. Based on our compiled average OST profile (AOSTP), the maximum predictability of the bioheat simulation on ocular model can reach up to 90%.     

Measurement of annular air-gap using active infrared thermography

The paper discusses an infrared thermography (IRT) based procedure for quantification of annular air-gap in cylindrical geometries. Different annular air-gaps are simulated using aluminum hollow cylinders and solid stainless steel inserts of varying diameters. The specimens are externally heated using a hot air-gun and the temperature of the specimens are monitored during cooling using an infrared camera. The temperature decay during the cooling cycle follows an exponential profile in all the cases where the decay constant is air-gap dependent. The rate of temperature decay is fastest for the empty cases (without inserts) and lower for smaller air-gaps. The system is analyzed using a lumped system model by measuring the temperature over a time scale significantly higher than the transition time of the lumped system. It is observed that the Biot number of the system is less than unity, allowing analysis of the system in terms of a single time constant, neglecting internal temperature transients. It is observed that the time constant of temperature decay increases with decreasing annular air-gap. An empirical relation between the inverse of time constant of temperature decay and annular air-gaps is established. Using this calibration curve, unknown air-gaps up to 20 μm could be measured with good accuracy. Applications of this newly developed technique include detection of misalignment of concentric machineries and determination of fuel-to-clad gap of nuclear reactor fuels.     

Active infrared thermographic inspection technique for elevated concrete structures using remote heating system

Conventionally, the inspection of elevated concrete structures requires the use of scaffolding or an aerial truck. In this study, elevated railway structures constructed of reinforced concrete were inspected using active infrared thermography. The inspection area corresponded to half of the middle slab covering an area of 16.8 m²; one inspection was carried out that took about 15 min. A remote heating system consisting of a 6-kW air-cooled xenon arc lamp and a scanner system was developed to detect hidden defects in elevated concrete structures without the need for an aerial truck or scaffolding. The generation of a thermal image and irradiation are carried out simultaneously by the beam scanning. High-contrast infrared thermal images can be obtained by the simple image processing procedure that is proposed.     

Fault detection of antenna arrays using infrared thermography

A fast and easy method for fault detection in antenna arrays using infrared thermography is presented. A thin, minimally perturbing, microwave absorption screen made of carbon loaded polymer is kept close in front of the faulty array. Electromagnetic waves falling on the screen increase its temperature. This temperature profile on the screen is identical to electric field intensity profile at the screen location. There is no temperature rise observed on the screen corresponding to non-radiating (faulty) elements and hence can be easily detected by IR thermography. The array input power is modulated at a low frequency which permits thermography to detect even weak fields. It also improves the resolution of thermal images. The power fed to the array is only 30 dBm. In order to show the utility of this technique, an example of 14 GHz 4 × 4 patch antenna array is given. The simulations are carried in CST Microwave Studio 2013. A good agreement between simulation and experimental results is observed.     

基于红外热成像的微波热疗透热深度

 对临床上常用的2 450 MHz微波在均匀介质中的电透入深度进行了分析,基于生物组织的热波模型,研究了生物组织吸收微波能的热效应;实验采用红外热成像仪测温,以2 450 MHz的微波辐射器辐照均匀的分层仿生体模,根据实验数据对微波热疗中透热深度进行了研究,说明微波的透入深度和透热深度的区别,并给出微波辐射器的功率、辐照距离和辐照持续时间对透热深度的影响。结果表明:当采用增大功率、延长辐照时间和近距离辐照等手段,都可以提高微波在人体的透热深度,为体外微波热疗中的人体传输模型建立及热疗的无损测温与控温奠定实验基础。     

Thermal diffusivity of electrodeposited Ni and Co nanowires using infrared thermography

One-dimensional nanostructures such as Ni and Co nanowires (NWs) show anisotropic thermal properties in a direction parallel and perpendicular to the NW axis. Thermal diffusivity of Ni and Co NWs embedded in a 100-nm pore anodic alumina (AAO) template has been measured in a direction perpendicular to the NW axis, using an infrared thermography-based non-contact approach. The measured thermal diffusivity values in the radial direction are 0.728×10⁻⁶ and 0.732×10⁻⁶ m²s⁻¹, respectively, for the Ni and Co nanocomposites. The changes in the thermal diffusivity of the synthesized NWs alone were estimated using a first-order lower bound model (FOLBM). A nearly seven- and sixfold reduction, respectively, of thermal diffusivity in a direction perpendicular to the NW axis is estimated for the synthesized Ni and Co NWs.     

Real-time quantification of viable bacteria in liquid medium using infrared thermography

Quantifying viable bacteria in liquids is important in environmental, food processing, manufacturing, and medical applications. Since vegetative bacteria generate heat as a result of biochemical reactions associated with cellular functions, thermal sensing techniques, including infrared thermography (IRT), have been used to detect viable cells in biologic samples. We developed a novel method that extends the dynamic range and improves the sensitivity of bacterial quantification by IRT. The approach uses IRT video, thermodynamics laws, and heat transfer mechanisms to directly measure, in real-time, the amount of energy lost as heat from the surface of a liquid sample containing bacteria when the specimen cools to a lower temperature over 2 min. We show that the Energy Content (EC) of liquid media containing as few as 120 colony-forming units (CFU) of Escherichia coli per ml was significantly higher than that of sterile media (P < 0.0001), and that EC and viable counts were strongly positively correlated (r = 0.986) over a range of 120 to approximately 5 × 10⁸ CFU/ml. Our IRT approach is a unique non-contact method that provides real-time bacterial enumeration over a wide dynamic range without the need for sample concentration, modification, or destruction. The approach could be adapted to quantify other living cells in a liquid milieu and has the potential for automation and high throughput.     

Evaluation of paint coating thickness variations based on pulsed Infrared thermography laser technique

In this paper, a pulsed Infrared thermography technique using a homogeneous heat provided by a laser source is used for the non-destructive evaluation of paint coating thickness variations. Firstly, numerical simulations of the thermal response of a paint coated sample are performed. By analyzing the thermal responses as a function of thermal properties and thickness of both coating and substrate layers, optimal excitation parameters of the heating source are determined. Two characteristic parameters were studied with respect to the paint coating layer thickness variations. Results obtained using an experimental test bench based on the pulsed Infrared thermography laser technique are compared with those given by a classical Eddy current technique for paint coating variations from 5 to 130 μm. These results demonstrate the efficiency of this approach and suggest that the pulsed Infrared thermography technique presents good perspectives to characterize the heterogeneity of paint coating on large scale samples with other heating sources.     

基于红外热成像的微波热疗透热深度

对临床上常用的2 450 MHz微波在均匀介质中的电透入深度进行了分析,基于生物组织的热波模型,研究了生物组织吸收微波能的热效应;实验采用红外热成像仪测温,以2 450 MHz的微波辐射器辐照均匀的分层仿生体模,根据实验数据对微波热疗中透热深度进行了研究,说明微波的透入深度和透热深度的区别,并给出微波辐射器的功率、辐照距离和辐照持续时间对透热深度的影响。结果表明:当采用增大功率、延长辐照时间和近距离辐照等手段,都可以提高微波在人体的透热深度,为体外微波热疗中的人体传输模型建立及热疗的无损测温与控温奠定实验基础。     

Wavelet subspace decomposition of thermal infrared images for defect detection in artworks

Health of ancient artworks must be routinely monitored for their adequate preservation. Faults in these artworks may develop over time and must be identified as precisely as possible. The classical acoustic testing techniques, being invasive, risk causing permanent damage during periodic inspections. Infrared thermometry offers a promising solution to map faults in artworks. It involves heating the artwork and recording its thermal response using infrared camera. A novel strategy based on pseudo-random binary excitation principle is used in this work to suppress the risks associated with prolonged heating. The objective of this work is to develop an automatic scheme for detecting faults in the captured images. An efficient scheme based on wavelet based subspace decomposition is developed which favors identification of, the otherwise invisible, weaker faults. Two major problems addressed in this work are the selection of the optimal wavelet basis and the subspace level selection. A novel criterion based on regional mutual information is proposed for the latter. The approach is successfully tested on a laboratory based sample as well as real artworks. A new contrast enhancement metric is developed to demonstrate the quantitative efficiency of the algorithm. The algorithm is successfully deployed for both laboratory based and real artworks.     

Infrared thermography of masonry structures

The attention of the present paper was devoted to nondestructive evaluation of masonry structures with a Focal Plane Array infrared camera. Tests were carried out in laboratory on specimens, which simulated one- and two-layer structures, with defects of different geometry and nature and located at different depths. The defects detection was analysed through a cause/effect relationship between the characteristics of defects and hosting material and the observed defect thermal signature, or contrast, on the hosting material.     

Breakpoint detection of heating wire in wind blade moulds using infrared thermography

In order to manufacture the fibre glass wind blades, one kind of mould embedded with heating wire is used not only for making numerous ‘copies’ of the original sample, and also heating the mould to a certain temperature for curing. The heating wire is embedded in fibre glass as a sandwich structure, and it may break after a long time usage at high temperatures. In this study, a high voltage discharging (HVD) circuit is used to trigger HVD at the breakpoint, which generates heat and therefore causes temperature increase at the corresponding front surface, one infrared camera is used to monitor the temperature evolution. It successfully and quickly detects breakpoints in spar moulds.     

Suitable features selection for monitoring thermal condition of electrical equipment using infrared thermography

Monitoring the thermal condition of electrical equipment is necessary for maintaining the reliability of electrical system. The degradation of electrical equipment can cause excessive overheating, which can lead to the eventual failure of the equipment. Additionally, failure of equipment requires a lot of maintenance cost, manpower and can also be catastrophic- causing injuries or even deaths. Therefore, the recognition processof equipment conditions as normal and defective is an essential step towards maintaining reliability and stability of the system. The study introduces infrared thermography based condition monitoring of electrical equipment. Manual analysis of thermal image for detecting defects and classifying the status of equipment take a lot of time, efforts and can also lead to incorrect diagnosis results. An intelligent system that can separate the equipment automatically could help to overcome these problems. This paper discusses an intelligent classification system for the conditions of equipment using neural networks. Three sets of features namely first order histogram based statistical, grey level co-occurrence matrix and component based intensity features are extracted by image analysis, which are used as input data for the neural networks. The multilayered perceptron networks are trained using four different training algorithms namely Resilient back propagation, Bayesian Regulazation, Levenberg–Marquardt and Scale conjugate gradient. The experimental results show that the component based intensity features perform better compared to other two sets of features. Finally, after selecting the best features, multilayered perceptron network trained using Levenberg–Marquardt algorithm achieved the best results to classify the conditions of electrical equipment.