Abdelhakim Bendada

Comparative Study of Active Thermography Techniques for the Nondestructive Evaluation of Honeycomb Structures

In this article, the theoretical and experimental aspects of three active thermography approaches: pulsed thermography (PT), lock-in thermography (LT), and vibrothermography (VT), are discussed in relation to the nondestructive evaluation (NDE) of honeycomb sandwich structures. For this purpose, two standard specimens with simulated defects (delaminations, core unbonds, excessive adhesive, and crushed core) were tested, and results were processed, examined, and compared. As will be pointed out, the similarities and differences between these active approaches allow conclusions to be made about the most suitable approach for a particular application. In addition, results from NDE inspection by X-rays and c-scan ultrasounds are provided and discussed for reference.

Infrared face recognition: A comprehensive review of methodologies and databases

Abstract Automatic face recognition is an area with immense practical potential which includes a wide range of commercial and law enforcement applications. Hence it is unsurprising that it continues to be one of the most active research areas of computer vision. Even after over three decades of intense research, the state-of-the-art in face recognition continues to improve, benefitting from advances in a range of different research fields such as image processing, pattern recognition, computer graphics, and physiology. Systems based on visible spectrum images, the most researched face recognition modality, have reached a significant level of maturity with some practical success. However, they continue to face challenges in the presence of illumination, pose and expression changes, as well as facial disguises, all of which can significantly decrease recognition accuracy. Amongst various approaches which have been proposed in an attempt to overcome these limitations, the use of infrared (IR) imaging has emerged as a particularly promising research direction. This paper presents a comprehensive and timely review of the literature on this subject. Our key contributions are (i) a summary of the inherent properties of infrared imaging which makes this modality promising in the context of face recognition; (ii) a systematic review of the most influential approaches, with a focus on emerging common trends as well as key differences between alternative methodologies; (iii) a description of the main databases of infrared facial images available to the researcher; and lastly (iv) a discussion of the most promising avenues for future research.

Locally adaptive texture features for multispectral face recognition

This work introduces a new locally adaptive texture features for efficient multispectral face recognition. This new descriptor called Local Adaptive Ternary Pattern (LATP) is based on the Local Ternary Pattern (LTP). Unlike the previous techniques, this new descriptor determines the local pattern threshold automatically using local statistics. It shares with LTP the property of being less sensitive to noise, illumination change and facial expressions. These characteristics make it a good candidate for multispectral face recognition. Linear and non linear subspace learning and recognition techniques are introduced and used for performance evaluation of face recognition in the new texture space: PCA, LDA, Kernel-PCA (KPCA), Kernel-LDA (KDA), Linear Graph Embedding (LGE), Kernel-LGE (KLGE), Locality Preserving Projection (LPP) and Kernel-LPP (KLPP). The obtained results show an increase in recognition performance when texture features are used. LTP and LATP are the best performing techniques. The overall best performance is obtained in the short wave infrared spectrum (SWIR) using the new proposed technique combined with a non linear subspace learning technique.

Active infrared thermography techniques for the nondestructive testing of materials

Active infrared thermography refers to the group of methods employed to inspect the integrity of materials or systems through the use of an external energy source and an infrared detector. The external stimulus can be of many forms such as warm or cold air, heat pulses, periodic thermal waves, or mechanical oscillations, e.g. ultrasounds. The way data is captured and processed, as well as the typical applications differ according to the excitation source. This chapter presents a review of three of the most common active techniques in the field of thermography: pulsed thermography, lock-in thermography and vibrothermography.

Delamination detection and impact damage assessment of GLARE by active thermography

GLAss REinforced (GLARE) is a fibre metal laminate (FML) consisting of alternating layers of thin aluminium and glass fibre reinforced prepregs, whose improved physical properties confer it an interesting advantage over aluminium and composite materials for a number of aerospace applications. On the other hand, contrary to monolithic structures, GLARE can suffer from internal damage either during fabrication or in-serve stages. Non-destructive testing and evaluation (NDT&E) of GLARE is still a challenge, especially considering that large structures are typically sought (e.g., aircraft fuselage). In this paper, we investigated the use of infrared thermography for the inspection of GLARE. The experimental results presented herein demonstrate that it is possible to detect delamination-type defects and to assess the impact severity on GLARE through active thermography techniques, specifically pulsed thermography and vibrothermography. C-scan ultrasonic testing was performed as well with the intention of providing supplementary results.

Thermal Faceprint: A New Thermal Face Signature Extraction for Infrared Face Recognition

In this work we present an efficient approach for physiological features extraction from infrared face images. The physiological features represent the network of blood vessels under the face skin. These networks are unique to each individual. The proposed technique permits the construction of Faceprints (similar to fingerprints) from thermal infrared images of faces. The extracted faceprint is unique and can be used in infrared face recognition.

Qualitative and quantitative assessment of aerospace structures by pulsed thermography

Pulsed thermography (PT) is an NDT&E technique allowing the remote examination of materials and systems. PT is particularly interesting for the inspection of aerospace structures since it can be used to perform safe inspection of large structures in a fast manner and without having to remove the components from the aircraft. Pulsed thermographic data however, is contaminated by noise of many forms. Fortunately, numerous signal processing techniques are available to perform qualitative and quantitative data analysis of data. In this paper, we present three processing techniques that have shown very promising results. We provide the theoretical background and experimental details as well as some representative results that highlight the pros and cons of each technique. As it will be pointed out, an interesting approach is the combination of existing processing techniques in order to use the most attractive features from each technique while reducing the non-desirable characteristics.

Diagnostics of panel paintings using holographic interferometry and pulsed thermography

Holographic and thermographic techniques have been recently applied in artwork diagnostics for the quantitative evaluation of defect size and depth in laboratory samples of artworks. The aim of this study is a comparison between holographic interferometry (both double exposure and real time), and pulsed thermography (PT) processing techniques such as differential absolute contrast (DAC) and pulsed phase thermography (PPT) for the detection of the subsurface flaws on wooden panel paintings. The performance of holographic techniques can be reserved for investigation of particular defects (cracks, detachments) at incipient stages, where high resolution/sensitivity is required, while PT can provide interesting quantitative results in situ.

A hollow waveguide infrared thermometer for polymer temperature measurement during injection moulding

We describe a novel on-line infrared method for remote sensing of the surface and the bulk temperatures of a polymer film during injection moulding. The method may also be applied to other polymer forming processes such as extrusion and blow moulding. The key feature of the new method is the use of a hollow waveguide that is incorporated into the injection mould to transmit the thermal radiation from the target to the sensor. The main characteristic of the hollow waveguide is that it exhibits low transmission loss of the thermal energy in the mid-and far-infrared, and no end reflection. This allows measurement of quite low temperatures, as low as near room temperature. Conventional optical fibre thermometers can neither measure such low temperature ranges nor measure the polymer surface temperature. In this paper, we present the first on-line results of critical tests of the new device. A Husky injection moulding press was used for the experiments. Good correlation was found between the radiometric results and those obtained with a thermal sensor inserted near the polymer mould interface, and with infrared imaging after the polymer part was ejected from the injection mould.

Inspection of aerospace materials by pulsed thermography, lock-in thermography, and vibrothermography: a comparative study

Inspection of aerospace components has always been a challenge. Infrared thermography has demonstrated to be a useful tool for this matter. In this paper, we offer a comparative study involving three active techniques: pulsed thermography, lock-in thermography and vibrothermography. Some of these techniques have proven to be more effective than others for a specific type of system. We compare the experimental results from these three techniques as applied to two typical aerospace parts: honeycomb structures and Glare. The later is perhaps the most challenging of all as will be pointed out. Some insights are provided regarding the most suitable technique for a number of typical situations.