Thermal Wave Imaging Technique Research Articles

Automatic defect detection in a steel sample using frequency-modulated thermal wave imaging

Non-stationary thermal wave imaging (NSTWI) techniques are primarily used to assess material properties and structural integrity without damaging a structure. Frequency-modulated thermal wave imaging (FMTWI) is a well-known NSTWI approach that uses a low-peak power heat source to examine structures in a reasonable experimentation time. Recently, various methods, such as pulse compression, Fourier transform, principal component analysis (PCA) and independent component analysis (ICA), have been introduced to handle the non-linearity of transient thermal signatures. However, handling non-linearity and developing a fully automatic defect detection system remains very challenging due to certain limitations of the aforementioned methods. To overcome these problems, this paper proposes an artificial neural network (ANN) for the identification of subsurface flaws in a mild steel sample investigated using the FMTWI approach. The accuracy and the performance of the proposed neural network (NN) are evaluated through a confusion matrix and region of convergence (ROC) analysis for the classification of defective and healthy pixels in an infrared image sequence. The developed NN model has achieved 99.7% accuracy in classifying the pixels correctly.

An Analytical Approach for Pulse Compression Favorable Digitized Frequency Modulated Thermal Wave Imaging Technique for the Quantitative Estimation of Breast Cancer

An Analytical Approach for Pulse Compression Favorable Digitized Frequency Modulated Thermal Wave Imaging Technique for the Quantitative Estimation of Breast Cancer

Micro-crack defects detection of semiconductor Si-wafers based on Barker code laser infrared thermography

Micro-crack defects are easy to form in the semiconductor Si-wafer surface during the production process, which finally effect the quality of silicon based microelectronic products. In order to ensure the quality and performance of products, it is important and necessary to carry out nondestructive testing (NDT) for Si-wafers. This paper experimentally investigates the performance of the Barker code laser infrared thermography (BCLIT) technique for the semiconductor Si-wafer defect detection, using an optical infrared thermography set-up in transmission method. The thermal wave signal response of the laser to the Barker code modulation waveform is collected by an infrared camera, which was stored as image sequences. Then the detectability was studied according to processed results via the Total Harmonic Distortion (THD) algorithm from obtained image sequence. In addition, linear frequency modulation thermal wave imaging (LFMTWI) technique was used to compare and analyze the performance of BCLIT. Experiments performed on the Si-wafer under the low power density condition indicate that the higher of the excitation power and the wider of the crack width, the better the detection effect. Furthermore, the performance of BCLIT is better than the traditional LFMTWI with all cases in evaluation index result of signal-to-noise ratio (SNR). The research results show that the BCLIT technique significantly improve SNR and defect detectability, and it can be used for the semiconductor Si-wafers micro-crack defects detection even under low power density excitation.

Novel pulse compression favorable excitation schemes for infrared non-destructive testing and evaluation of glass fibre reinforced polymer materials

Infrared thermography (IRT) has been extensively used in the field of non-destructive testing and evaluation (NDT&E) as a condition monitoring tool in commercial as well as industrial applications. It is a fast, non-contact, whole field and quantitative technique for NDT&E applications by mapping the thermal profile over the test sample. This paper presents a novel three-dimensional analytical model for characterization of glass fibre reinforced polymer (GFRP) sample having flat bottom hole defects. The capability of the proposed method is highlighted with recently introduced pulse compression favorable thermal wave imaging modalities. Further, the analytical results have been validated with simulated and experimental studies on the proposed frequency modulated thermal wave imaging (FMTWI), Barker coded thermal wave imaging (BCTWI) and digitized frequency modulated thermal wave imaging (DFMTWI) techniques to analyze the performance of the defect detectability by taking normalized correlation coefficient as a figure of merit. Obtained results clearly shows the capabilities of the DFMTWI over the FMTWI and BCTWI using correlation based matched filter post-processing approach.

Pulse Compression Favorable Thermal Wave Imaging Techniques for Non-Destructive Testing and Evaluation of Materials

This article highlights the application of pulse compression favorable Frequency Modulated Thermal Wave Imaging (FMTWI) technique for testing and evaluation of Carbon Fibre Reinforced Plastics (CFRP). The concept of InfraRed Image Correlation (IRIC) has been introduced to reconstruct the correlation fringes for the pulse compressed data obtained from the matched filter approach to detect the flat bottom hole defects in a CFRP specimen. Further, comparison has been made with the acquired phasegrams using frequency and time domain based data processing approaches. Obtained results clearly demonstrate the strengths of the proposed IRIC based post-processing scheme in providing the spatio-temporal correlation fringes for thermal Non-Destructive Testing & Evaluation (NDT&E) of CFRP materials.

Probability of Detecting the Deep Defects in Steel Sample Using Frequency Modulated Independent Component Thermography

Active thermography is a widely used non-destructive testing and evaluation technique (NDT&E) for evaluating the properties of materials without impairing its future usefulness. In this work, a mild steel sample made of artificial flat-bottom holes at varied depths, was examined with the emerging non-stationary thermal wave imaging (NSTWI) technique, i.e. frequency modulated thermal wave imaging (FMTWI). The pulse compression favorable of NSTWI technique is eminent for compressing the applied thermal energy into a narrow-compressed pulseto enhance the depth resolution and sensitivity. In this work, pulse compressed thermographic data generated from FMTWI experimentation is analyzed with the unsupervised learning approach independent component analysis (ICA) to test their mutual return in the detection of the deep defects in a mild steel sample and this proposed technique was referred to as frequency modulated independent component thermography (FMICT). In comparison, the effect of FMICT was contrasted with othermethodsi.e. pulse compression of time domain and ICA of feature space by considering the signal-to-noise ratio (SNR) as a figure of merit. Furthermore, a probability of detection (POD) analysis framework based on the minimum threshold SNR criteria for apparent visibility of the defects has been presented to assess the probability of identifying defects at various depths using such approaches. The influence of the SNR threshold value for the above strategies on the POD curves has also been presented.

Detection of slags in structural steel sample using InfraRed thermal wave imaging

The estimation of defects in any material is a critical problem in the domain of InfraRed thermography (IRT). The paper presents simulation aspects of three-dimensional heat transfer model for a finite thickness structural steel sample having six different slag inclusions using a low peak power frequency modulated thermal wave imaging (FMTWI) and its digital counterpart digitized frequency modulated thermal wave imaging (DFMTWI) technique. The sample surface is subjected to proposed thermal heat flux and defect analysis was carried out by studying the thermal gradient over the test sample surface. Further, time domain pulse compression approach allowing better defect depth analysis has been discussed to evaluate the correlation coefficients and time delays for the proposed approaches. Results show better performance of the DFMTWI approach with high correlation coefficient values for all the defects with low time delays than the FMTWI approach.

Probability of defect detection in pulse compression favourable thermal excitation schemes for infra‐red non‐destructive testing

InfraRed non-destructive testing and evaluation (IRNDT&E) has emerged as a promising approach for non-destructive testing and evaluation (NDT&E) of various materials because of its inherent merits such as remote, non-invasive, qualitative as well as quantitative inspection capabilities. Among the various IRNDT&E techniques, recently proposed modulated pulse compression favourable thermal wave imaging (PCTWI) techniques, especially frequency modulated thermal wave imaging (FMTWI) and its digitised version digitised FMTWI (DFMTWI) have gained popularity over the conventional sinusoidal modulated [lock-in thermography (LT)] and pulse-based thermographic techniques [pulse thermography (PT) and pulse phase thermography (PPT)] by providing better depth resolution, in less experimentation time, using low peak power excitation heat sources. The present work highlights a comparative study on highly depth resolved continuous depth scanning PCTWI techniques, with single frequency thermal excited LT, on the basis of defect detection probability. The proposed study has been carried out on a glass fibre reinforced polymer test sample with Teflon inserts as defects by considering peak side lobe ratio as a figure of merit. The experimental results clearly show that the probability of detection of defects for DFMTWI is far superior as compared to FMTWI and LT.

Guest Editorial: Non‐Destructive Testing

Guest Editorial: Non‐Destructive Testing

Novel Analytical Approach for Estimation of Thermal Diffusivity and Effusivity for Detection of Osteoporosis

Infrared thermography is a full field, non-contact inexpensive, patient friendly and safe imaging modality for estimation of thermo-physical properties of various bio-materials. Among the widely used thermal wave imaging modalities, recently proposed frequency modulated thermal wave imaging technique gained importance due to its quantitative characterization capabilities along with its deeper subsurface visualization abilities. This work highlights a novel analytical analysis for three dimensional Fourier heat diffusion equation by considering internal heat generation. An aperiodic pulse compression favorable thermal wave imaging method is proposed for estimation of thermo-physical properties of bone for identification of severity of osteoporosis. Effect of osteoporosis on thermo-physical properties such as thermal effusivity and diffusivity has been studied. Further proposed analytical approach has been validated by results obtained from the commercially available finite element based COMSOL software.

Theoretical study on infrared thermal wave imaging detection of semiconductor silicon wafers with micro-crack defects

The semiconductor silicon wafer with micro-crack defects was detected using infrared thermal wave imaging technique. The 3-D thermal conduction model in semiconductor silicon wafer excited by linear frequency modulated continuous laser was established, and it was solved by finite element method. The results show the effectiveness of the proposed method for detecting micro-crack defects in semi?conductor silicon wafers.

Defect detection capabilities of independent component analysis for Barker coded thermal wave imaging

Active pulse compression favourable infrared imaging techniques are promising evaluation techniques among other thermal non-destructive testing and evaluation modalities for identification of subsurface defects in the test samples. This is due to their merits such as high defect detection sensitivity and resolution by using relatively low peak power heat sources and in a moderate experimentation time in comparison with widely used pulse and modulated conventional thermal wave imaging modalities. Various data processing methods have been developed to extract the thermal features of defects from the captured thermographic data. The cross-correlation based pulse compression method is recommended for Barker coded thermal wave imaging technique as it enhances the concentration of applied thermal energy into mainlobe and distributes the significantly less energy into the sidelobes of cross correlation data. In this paper, the stated property of Barker coded thermal wave imaging along with the independent component analysis approach has been utilised. The study in this paper is focused on the application of independent component analysis approach on captured thermal response data, entire cross correlation data and only the mainlobe of CC data. The results obtained clearly indicate that the application of independent component analysis on cross correlation data has improved the detectability, visibility, and contrast (interms of signal-to-noise values) of the defects. Further, the results obtained with the different methods have been compared by taking Signal to noise ratio as the figure of merit.

Comparative study of different infrared thermal wave imaging techniques for defect detection of composite materials

Comparative study of different infrared thermal wave imaging techniques for defect detection of composite materials

Coded thermal wave imaging technique for infrared non-destructive testing and evaluation

ABSTRACTActive InfraRed Thermography (IRT) is one of the promising Non-Destructive Testing (NDT) and evaluation method for inspection of various solid materials. Its inherent inspection capabilities such as remote, wide area monitoring, fast, quantitative and safe deployment in field test makes active IRT as a vital testing technique in NDT community. The present work introduces a novel application based on recently proposed Golay Coded Thermal Wave Imaging (GCTWI) to examine mild steel and carbon fibre reinforced polymer (CFRP) test samples having sub-surface defects. Further defect detection capability of the proposed approach is compared with the conventional frequency domain phase approach on each sequence by considering the signal-to-noise ratio as a figure of merit.

Barker-Coded Thermal Wave Imaging for Non-Destructive Testing and Evaluation of Steel Material

Thermal non-destructive testing (TNDT) is one of the emerging inspection and evaluation techniques mostly used for subsurface defect detection in various industrial components. Besides the conventional thermography techniques (such as lock-in and pulse), recently introduced non-stationary thermal wave imaging (NSTWI) techniques gained its applicability in TNDT community due to their inherent testing capabilities such as improved sensitivity and enhanced resolution in inspecting and evaluating various solid materials for detecting subsurface defects. Barker-coded thermal wave imaging (BCTWI) is a one of the widely used NSTWI techniques, which facilitates the use of low peak power heat sources in moderate experimentation time in contrast to conventional TNDT techniques. In this paper, the pulse compression favorable NSTWI (BCTWI), the reconstructed pulsed (main lobe) data have been considered and processed using independent component analysis and named Barker-coded independent component thermography (BCICT). This proposed BCICT is implemented on a mild-steel sample to detect the artificially simulated flat bottom circular holes located at different depths inside it. The proposed technique extracts the sub-surface details such as flaws/defects hidden inside the sample by an unsupervised learning process, which helps in eliminating the manual interpretation of subsurface defects. The applicability of the proposed algorithm has been evaluated and validated experimentally with two different excitations schemes by considering the contrast and signal-to-noise ratio (SNR) as figure of merit. The results indicate that the BCICT technique offers higher contrast and SNR in comparison to conventional pulse-based TNDT technique.

Digitised Frequency Modulated Thermal Wave Imaging for Non-destructive Testing and Evaluation of Glass Fibre Reinforced Polymers

ABSTRACTThe active thermal non-destructive testing and evaluation techniques have gained wide acceptance in health monitoring of various solids materials such as metals, composites and semiconductors. The most popular active infrared thermographic methods for non-destructive testing and evaluation applications are pulse based thermography and lock-in thermography techniques. But the usage of these techniques is limited due to their inherent limitations. To overcome the limitations of the existing approaches, the present work demonstrates the effectiveness of digitized frequency modulated thermal wave imaging technique for detection of different shaped defects in a glass fibre reinforced polymer specimen. Further, the usage of post-processing scheme facilitates defect detection with high resolution and also preserves the shape of defects.

Evaluation of coating thickness by thermal wave imaging: A comparative study of pulsed and lock-in infrared thermography – Part II: Experimental investigation

In this work, we focused on the experimental arrangement of thermal wave imaging (TWI) methods for the quantitative evaluation of non-uniform topcoat thickness of thermal barrier coatings (TBCs). Two TWI techniques, pulsed thermography (PT) and lock-in thermography (LIT) were implemented on plasma sprayed TBCs with varied topcoat ranging from 0.1 mm to 0.6 mm. In PT, a short and high energy light pulse was applied on a sample surface whereas, in LIT, the sample surface was excited by a sinusoidal heat flux at several modulation frequencies ranging from 2 Hz down to 0.01 Hz. Furthermore, an infrared camera was used to capture the surface temperature of a thermal wave that propagated into the sample and the effect of the applied heat flux in both techniques was analyzed by Fourier transform. The results of PT and LIT techniques were compared based on the evaluated accuracy of each technique. Finally, it was concluded that both the techniques could be applied to the fast and accurate evaluation of TBCs thickness.

Infrared thermography for detection and evaluation of bone density variations by non-stationary thermal wave imaging

Osteoporosis has been characterized as a skeletal disorder of reduced bone strength that leads to an increased risk of fracture. As the age of the person grows, early diagnosis of the disease is necessary to maintain good bone strength and to avoid unbearable fractures. While the disease cannot be reversed, it can be effectively managed by detecting bone density variations. Recently introduced non-stationary thermal wave imaging techniques have gained wide acceptance in the thermal non-destructive testing research community due to their merits over the conventional methods. This paper attempts to test the capabilities of one of the widely used non-stationary thermal imaging techniques to characterize the severity of osteoporosis in the modeled human bone. A 3D finite element analysis has been carried out to model a multilayered bone having different density variations, with tissue, skin and muscle over layers. Obtained results from frequency domain analysis scheme has been studied in order to detect the density variations with improved test sensitivity.

Infrared Thermal Wave Imaging for Nondestructive Testing of Fibre Reinforced Polymers

Among various widely used InfraRed Thermal Non-Destructive Testing (IRTNDT) modalities, Non-Stationary Thermal Wave Imaging (NSTWI) techniques have proved to be an indispensable approach for the inspection and evaluation of various materials. Growing concern for the development of surface and subsurface defect detection techniques with moderate peak power heat sources (than the widely used conventional pulse based thermographic methods) and in a reasonably less testing time (compared to sinusoidal modulated lock-in thermography), makes these NSTWI techniques invaluable for this field. The present work highlights a comparative study on various NSTWI techniques, further experimental results are presented to find their defect detection capabilities by taking signal to noise ratio (SNR) into consideration.

Suitability of frequency modulated thermal wave imaging for skin cancer detection—A theoretical prediction

A theoretical study on the quantification of surface thermal response of cancerous human skin using the frequency modulated thermal wave imaging (FMTWI) technique has been presented in this article. For the first time, the use of the FMTWI technique for the detection and the differentiation of skin cancer has been demonstrated in this article. A three dimensional multilayered skin has been considered with the counter-current blood vessels in individual skin layers along with different stages of cancerous lesions based on geometrical, thermal and physical parameters available in the literature. Transient surface thermal responses of melanoma during FMTWI of skin cancer have been obtained by integrating the heat transfer model for biological tissue along with the flow model for blood vessels. It has been observed from the numerical results that, flow of blood in the subsurface region leads to a substantial alteration on the surface thermal response of the human skin. The alteration due to blood flow further causes a reduction in the performance of the thermal imaging technique during the thermal evaluation of earliest melanoma stages (small volume) compared to relatively large volume. Based on theoretical study, it has been predicted that the method is suitable for detection and differentiation of melanoma with comparatively large volume than the earliest development stages (small volume). The study has also performed phase based image analysis of the raw thermograms to resolve the different stages of melanoma volume. The phase images have been found to be clearly individuate the different development stages of melanoma compared to raw thermograms.