Near-field microwave non-destructive evaluation and inspection of structures and materials is widely used in various applications. Single-frequency measurements were found to be effective in detecting defects and abru...
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Near-field microwave non-destructive evaluation and inspection of structures and materials is widely used in various applications. Single-frequency measurements were found to be effective in detecting defects and abrupt changes, such as cracks and air voids, within homogeneous structures. However, in some complex structures with many variables, multiple-frequency measurements were utilised to solve problems associated with more unknown parameters. Those problems involved layered structures with more diversity in terms of number of factors that define the structure, namely, the thicknesses and relative complex permittivities (epsilon(r)) of the layers. Later on, more systematic broadband techniques, such as frequency-modulated continuous wave, proved to be effective in measuring thicknesses of layers in a multilayered structure. However, obtaining permittivity information was still a big challenge. This study presents a novel analytical near-field model that relates the radiation of a rectangular waveguide with the reflection when applied to a dielectric multilayered structure. The input-output relation is characterised by the frequency response of the structure which was analytically derived. As a side result the distribution of the reflection coefficient over the aperture was also analysed and the expression was derived. The main goal is to define the relationship between the structure layers, in terms of thicknesses and relative permittivities and the aperture's complex reflection coefficient (Gamma) for all frequencies of operation. This model can be used in developing new microwave non-destructive evaluation techniques for inspecting the integrity of layered structures with potentially high resolution.
The development in materials technology has produced stronger, lighter, stiffer, and more durable electrically insulating composites which are replacing metals in many applications. These composites require alternativ...
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The development in materials technology has produced stronger, lighter, stiffer, and more durable electrically insulating composites which are replacing metals in many applications. These composites require alternative inspection techniques because the conventional nondestructive testing (NDT) techniques such as thermography, eddy currents, ultrasonic, X-ray and magnetic particles have limitations of inspecting them. Microwave NDT technique employing open-ended rectangular waveguides (OERW) has emerged as a promising approach to detect the defects in both metal and composite materials. Despite its promising results over conventional NDT techniques, OERW microwave NDT technique has shown numerous limitations in terms of poor spatial resolution due to the stand-off distance variations, inspection area irregularities and quantitative estimation in imaging the size of defects. Microwave NDT employing OERW in conjunction with robust artificial intelligence approaches have tremendous potential and viability for evaluating composite structures for the purpose mentioned here. Artificial intelligence techniques with signal processing techniques are highly possible to enhance the efficiency and resolution of microwave NDT technique because the impact of artificial intelligence approaches is proven in various conventional NDT techniques. This paper provides a comprehensive review of NDT techniques as well as the prospect of using artificial intelligence approaches in microwave NDT technique with regards to other conventional NDT techniques.
This paper presents a near-field microwave nondestructive testing technique for disbond/crack detection and evaluation in a concrete structure backed by an infinite half space of any material. A model describing the i...
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This paper presents a near-field microwave nondestructive testing technique for disbond/crack detection and evaluation in a concrete structure backed by an infinite half space of any material. A model describing the interaction of waves radiated out from an open-endedrectangular waveguide, in the near-field, with any layered medium will be utilized. The theoretical model calculates the effective reflection coefficient of the structure, at the aperture of the waveguide, as a function of the frequency of operation, the thickness and dielectric properties of the layers of the structures, including the standoff distance. The frequency of operation and standoff distance (the measurement parameters) can be optimized to achieve maximum sensitivity to the presence of the disbond. The presence of a disbond in a structure is viewed as an additional layer and will change the properties of the effective reflection coefficient (phase and magnitude). This change will depend on the thickness and location of the disbond. This fact will be used to investigate the potential of utilizing multiple frequency measurements to obtain disbond location and thickness information. A fuzzy logic model relating the phase of reflection coefficient, frequency of operation, and standoff distance to the disbond thickness and depth was generated and utilized. (C) 2003 Elsevier Ltd. All rights reserved.
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