Air-Gap Detection in Dielectric Materials by a Step-Frequency Microwave Technique

Most microwave NDE has been performed using continuous wave excitation and reception, due to the general availability of such equipment and the acceptable procedure of extracting information from the amplitude and phase of such signals. With the availability of sources that can be swept over a band of frequencies, the amplitude and phase information can be converted via the Fourier Transformation to the impulse response in the time domain. Instead of searching for changes in the amplitude and phase of microwave reflected from boundaries, interfaces, and defects, this time domain approach concentrates on the recognition of “echoes”. This approach is implicit in some of the more complex approaches in microwave imaging [1–3]. It is the purpose of this paper to demonstrate that this approach facilitates the detection of internal defects using microwave, in a manner similar to the practice of pulse-echo ultrasound. The time delay for a microwave “echo” is related to the location, and the Fourier transformed amplitude is related to some characteristics of the defect inside the material

Objective Ultrasonic Characterization of Welding Defects Using Physically Based Pattern Recognition Techniques

Computer-based methods for analysing ultrasonic data to distinguish between different defect types have been based on a variety of techniques such as adaptive learning [1], artificial intelligence [2] and statistical pattern recognition [3]. The uncertain classification reliability of these techniques when applied to a range of realistic defect types has, however, often been a significant practical limitation to their use

Ultrasonic Characterization of Porosity in Composite Materials by Time Delay Spectrometry

The presence of porosity in a wide range of materials, whether ceramics, steel or fiber reinforced composites, has a dramatic effect on the strength and mechanical properties of that material. Therefore, the presence of any porosity in a composite laminate during the manufacture of aerospace components is a basis for component rejection

Factor structure and psychometric properties of the connor-davidson resilience scale among chinese adolescents

Objectives: Resilience refers to psychological characteristics that promote effective coping and positive adaptation in adversity. This study investigated the factor structure and psychometric properties of the Chinese version of the Connor-Davidson Resilience Scale (CD-RISC) among adolescents. Methods: A total of 2914 Chinese adolescents living in Chengdu, Sichuan, completed the CD-RISC 1 month after the 2008 Sichuan earthquake. They also self-administered the Multidimensional Scale of Perceived Social Support, the Children's Depression Inventory, and the Screen for Child Anxiety Related Emotional Disorders. With confirmatory factor analysis, various factor structures of the CD-RISC reported in previous studies (eg, the 5- and 3-factor models) were examined at the first-order level; and a single factor of resilience was investigated at the second-order level in this sample. The internal consistency and concurrent validity were investigated. Sex and age differences were also examined. Results: Confirmatory factor analysis results showed that the 5-factor model originally derived among US community adults was replicated in our sample, and these 5 factors also loaded on a higher-order "resilience" factor. The Cronbach α coefficient was 0.89. The resilience scores demonstrated expected positive correlation with social support (r = 0.44) and negative correlations with depression (r = -0.38) and anxiety (r = -0.25) (Ps < .001). Male participants reported higher resilience scores than female participants, and younger participants also reported higher resilience scores than older participants. Conclusions: The Chinese version of the CD-RISC was demonstrated to be a reliable and valid measurement in assessing resilience among Chinese adolescents. © 2011 Elsevier Inc. All rights reserved.link_to_subscribed_fulltex

Surface Edge Explorer (see): Planning Next Best Views Directly from 3D Observations

Surveying 3D scenes is a common task in robotics. Systems can do so autonomously by iteratively obtaining measurements. This process of planning observations to improve the model of a scene is called Next Best View (NBV) planning. NBV planning approaches often use either volumetric (e.g., voxel grids) or surface (e.g., triangulated meshes) representations. Volumetric approaches generalise well between scenes as they do not depend on surface geometry but do not scale to high-resolution models of large scenes. Surface representations can obtain high-resolution models at any scale but often require tuning of unintuitive parameters or multiple survey stages. This paper presents a scene-model-free NBV planning approach with a density representation. The Surface Edge Explorer (SEE) uses the density of current measurements to detect and explore observed surface boundaries. This approach is shown experimentally to provide better surface coverage in lower computation time than the evaluated state-of-the-art volumetric approaches while moving equivalent distances

NDE of Thick Graphite/Epoxy Composites: Some Approaches and Problems

Composite materials are being used in many applications because they can be tailored to meet specific design requirements. Fiber and resin type, fiber orientation, layering, and thickness are deliberately used during prepreg layup or filament winding to give a composite structure specific, desirable properties. These quantities are useful design parameters, but produce attenuation of ultrasound and anisotropy in material properties, which cause difficulty in performing NDE. For example, thick, filament wound composites generally have more porosity than prepreg composites, which further increases attenuation of the ultrasonic signal. Geometric and/or viscoelastic effects cause dispersion of the wavespeed and attenuation coefficient i.e. they are frequency dependent. The general anisotropy of the composite causes the wave velocity to be a function of direction. However, some way to inspect structures made from these materials must be found if their usefulness is to be exploited