Nondestructive testing of concrete with electromagnetic and elastic waves: Modeling and imaging

The theory of acoustic, electromagnetic and elastic wave fields in terms of governing equations, plane waves, spherical waves (Green functions) and scattered field representations is discussed under common aspects leading to a unified derivation of modeling and imaging algorithms. The latter require a linearization of the inverse scattering problem. Applications referring to the location and assessment of tendon ducts in concrete are presented utilizing synthetic as well as experimental data culminating in a real-life example for data taken from a bridge.     

Nondestructive evaluation of cork enclosures using terahertz/millimeter wave spectroscopy and imaging

Natural cork enclosures, due to their cell structure, composition, and low moisture are fairly transparent to terahertz (THz) and millimeter waves enabling nondestructive evaluation of the cork's surface and interior. It is shown that the attenuation coefficient of the defect-free cork can be modeled with a Mie scattering model in the weakly scattering limit. Contrast in the THz images is a result of enhanced scattering of THz radiation by defects or voids as well as variations in the cork cell structure. The presence of voids, defects, and changes in grain structure can be determined with roughly 100-300 microm resolution.     

Subharmonic gap structure and subharmonic Josephson steps

Subharmonic microwave-induced Josephson step structure is often observed in superconducting junctions that exhibit subharmonic gap structure. The two theories, multiparticle tunneling and self-coupling due to an electromagnetic field set up by the ac Josephson current, which have been suggested to explain the subharmonic gap structure are investigated with respect to the possible existence of subharmonic Josephson steps. Also treated is a Ginzburg-Landau calculation of the current-phase relation for Josephson junctions. All three theories give subharmonic Josephson steps with the same microwave-power dependence. The temperature dependence of the subharmonic step structure and the subharmonic gap structure is discussed. It seems the self-coupling is the main cause for both effects in tunnel junctions and for the subharmonic gap structure in Dayem bridges, while the subharmonic step structure in the Dayem bridge seems to be a geometrical effect related to “multiparticle” transfer processes.     

Nondestructive evaluation of large-area PZN-8%PT single crystal wafers for medical ultrasound imaging probe applications

A nondestructive quality evaluation and control procedure for large-area, (001)-cut PZN-8%PT wafers is described. The crystals were grown by the flux technique engineered to promote (001) layer growth of the crystals. The wafers were sliced parallel to the (001) layer growth plane. Curie temperature (Tc) variations, measured with matching arrays of dot electrodes (of 5.0 mm in center-to-center spacing), were found to be better than +/- 4.0 degrees C both within wafers and from wafer to wafer. After selective dicing to give final wafers of narrower Tc distributions (e.g., +/- 3.0 degrees C or better), the wafers were coated with complete electrodes and poled at room temperature at 0.7-0.9 kV/mm. Typical overall properties of the poled wafers were: K3T = 5,200 (+/- 10% from wafer to wafer), tan delta < 0.01 (all wafers), and kt = 0.55 (+/- 5%) (all percentage variations are in relative percentages). Then, the distributions of K3S, tan delta, and kt were measured by the array dot electrode technique. The variations in K3S (hence K3T) and kt within individual wafers were found to be within +/- 10% and +/- 5%, respectively. The dielectric loss values, measured at 1 kHz, were consistently low, being < 0.01 throughout the wafers. The kt values determined by the dot electrodes were found to be about 5% smaller than those obtained with the complete electrodes, which can be attributed to an increase in capacitance ratio due to the partial electroding. The k33 values, deduced using the relation K3S approximately (1 - k33(2))K3T, from the mean K3S and overall K3T values, average 0.94 (+/- 2%). The present work shows that the distribution of Tc within wafers can be used as a convenient check for the uniformity in composition and electromechanical properties of PZN-8%PT single crystal wafers. Our results show that, to control deltaK3T and deltakt within individual wafer to < or = 10% and 5%, respectively, the variation in Tc within the wafer should be kept within +/- 3.0 degrees C or better.     

Transient processes near the threshold of subharmonic resonance

Instability of a dynamical system near a subharmonic resonance is manifested in the prolongation of transient processes. It is shown for nonlinear pulsations of a gas bubble under the action of an acoustic carrier signal modulated by a pulse that the subharmonic radiation observed experimentally below the generation threshold can be explained by the contribution of characteristic oscillations which arise at the moment the pulse arrives and have a damping time comparable to the pulse duration, due to the parametric energy transfer. Pis’ma Zh. Tekh. Fiz. 25, 1–6 (September 12, 1999)     

LLRF systems for subharmonic buncher system of BEPCII Linac

The linear accelerator (Linac) completed in 2007 for the upgrading project of the Beijing Electron Positron Collider (BEPCII) provides 1.89 GeV electrons and positrons for the storage rings. BEPCII Linac decides to update the bunching system and adopts two-bunch operation to enhance beam quality and injection rate as its second update phase. Two subharmonic bunchers will be used in this project: one operates at 142.8 MHz and the other operates at 571.2 MHz. Each subharmonic buncher consists of the bunching cavity, power source, LLRF system and other related subsystems. This paper mainly describes the LLRF systems for the subharmonic buncher systems (SHB).     

Air-Coupled Nondestructive Evaluation Dissected

This work develops a two-dimensional theoretical model to simulate the behavior of a fully non-contact air-coupled nondestructive evaluation system for a thin isotropic plate. The model is divided into transmission, guided wave propagation and reception phase. The validation of the complete model was carried out by modeling the same system by means of finite element method using a Multiphysics software. In addition, the dependency of the generated Lamb waves on different transmitter’s parameters and incidence angle is thoroughly investigated. The results of the acoustic pressure excited by the transducer, the out-of-plane velocity amplitudes for the generated first antisymmetric Lamb wave mode, and the radiated pressure from the plate caused by the leaky Lamb wavefield were all compared between the two models and a reasonable degree of similarity was found.     

Nondestructive Eddy Current Testing

When a coil is placed in proximity to a conductor, the magnetic field in the vicinity of the coil is altered by eddy currents in the conductor. The conductivity of a sample material may be determined by measuring the field. Closed-form solutions are presented for the magnetic field at the surface of a semi-infinite conductor for two cases: a semi-infinite coil, the end of which is in contact with the conductor, and a loop of wire on the surface of the conductor.     

Stable and transient subharmonic emissions from isolated contrast agent microbubbles

Ultrasound contrast agents (UCAs) have been widely studied in recent years in order to improve and develop new, sophisticated imaging techniques for clinical applications. In order to improve the understanding of microbubble-ultrasound interactions, an acoustic dynamic characterization of UCA microbubble behavior was performed in this work using a high frame-rate acquiring and processing system. This equipment is connected to a commercial scanner that provides RF beam-formed data with a frame-rate of 30 Hz. Acquired RF sequences allows us to follow the dynamics of cavitation mechanisms in its temporal evolution during different insonifying conditions. The experimental setup allowed us to keep the bubbles free in a spatial region of the supporting medium, thus avoiding boundary effects that can alter the ultrasound field and the scattered echo from bubbles. The work focuses on the study of subharmonic emission from an isolated bubble of contrast agent. In particular, the acoustic pressure threshold for a subharmonic stable emission was evaluated for a subset of 50 microbubbles at 3.3 MHz and at 5 MHz of insonation frequencies. An unexpected second pressure threshold, which caused the stand still of the subharmonic emission, was detected at 3.3 MHz and 5 MHz excitation frequencies. A transient subharmonic emission, which is hypothesized as being related to the formation of new free gas bubbles, was detected during the ultrasound-induced destruction of microbubbles. An experimental procedure was devised in order to investigate these behaviors and several sequences of RF echo signals and the related spectra, acquired from an isolated bubble in different insonation conditions, are presented and discussed in this paper.     

Nondestructive testing of offshore structures

An overview of the major NDT requirements of the offshore industry is presented, and those areas where the development of new techniques is underway are highlighted. A review of the projects undertaken by Harwell's Offshore Inspection R&D Service Club is given and one of these, subsea node joint crack sizing using time-of-flight diffraction (TOFD), is described. Finally, a view is given on where the emphasis of future development should be placed.     

Optical Nondestructive Evaluation for Structures

This paper presents a new technique for evaluation of engineering structures, using optical measurement and probabilistic advancing cross-diagnosis. Its application is first computer-simulated, and then it is tested in the laboratory. With the cooperation of the U.S. Federal Highway Administration, a recently developed coherent laser radar system was used to measure structural deformation. The data are treated to reduce noise and used to derive multiple features for reliable diagnosis. Both the simulation and laboratory test results show consistent effectiveness of the proposed technique, indicating a promising direction of nondestructive evaluation combining optical and computer technology.     

Optical Nondestructive Evaluation for Structures

Abstract

This paper presents a new technique for evaluation of engineering structures, using optical measurement and probabilistic advancing cross-diagnosis. Its application is first computersimulated, and then it is tested in the laboratory. With the cooperation of the U.S. Federal Highway Administration, a recently developed coherent laser radar system was used to measure structural deformation. The data are treated to reduce noise and used to derive multiple features for reliable diagnosis. Both the simulation and laboratory test results show consistent effectiveness of the proposed technique, indicating a promising direction of nondestructive evaluation combining optical and computer technology.     

陶瓷涂层的无损检测

无损检测可避免有损检测带来的使用安全隐患,这是一种值得推广应用的技术.为此,介绍了陶瓷涂层常见缺陷种类及产生原因,阐述了陶瓷涂层无损检测的几种重要方法的基本原理以及目前国内外在这方面的研究现状.     

基于激光热激励红外热成像纤维增强聚合物复合材料加固混凝土结构界面损伤无损检测

红外热成像（IRT）检测技术常被用于纤维增强聚合物复合材料（FRP）加固混凝土板的剥离损伤无损检测。但传统热源激励IRT法受加热距离短、热灵敏度低、功耗大等因素影响较大。本文提出了基于光学激发线激光热源的IRT法对FRP加固混凝土的剥离检测方法,该方法通过控制线热束在FRP加固混凝土结构的表面形成移动扫描热激励,通过红外热像仪测量结构中的界面剥离引起的表面局部热分布异常。基于模拟和实验研究结果,证明该方法对FRP加固混凝土结构中界面剥离检测具有如下优势:利用激光扫描热成像技术检测FRP改造混凝土结构中剥离损伤的可行性;实现了FRP加固混凝土结构的远距离、高热灵敏度及低功耗的损伤检测。      

Nondestructive permittivity measurement of substrates

The complex permittivity, κ'[1-j(tan δ)], of a thin, flat dielectric is calculated from the characteristics of the H₀₁₁ resonance in a cylindrical cavity, with the specimen inserted on the central transverse plane. Dielectric constants from 1 to 300 have been measured with errors less than 1%. The resolution of the loss tangent measurement is approximately 10 ppm at 12 GHz. No irreversible specimen preparation is required, and its shape and size, if larger than the cavity diameter, are arbitrary     

Laser Based Nondestructive Inspection Techniques

The most familiar laser based optical nondestructive methods are based on the interference of the wave fronts of monochromatic light reflected from a test surface. We explore the origins, applications, advantages and limitations of these techniques with a journey through the realm of Holographic Interferometry, Electronic Speckle Pattern Interferometry and Shearography. These methods are applied to the widest range of materials from metals to composites attempting to determine the conditions of the material that contribute to failure, in for example critical parts of a structure. These techniques are inherently of fairly high sensitivity, are non-contacting, they are able to inspect a whole field in a single procedure and results are obtained at almost real time. The inspection procedure on a test piece is identical for all three techniques. An image of the object??s surface is recorded and stored in a suitable medium; subsequently the object is perturbed mildly by mechanical or thermal means which results in its surface being deformed. At this stage a second image is captured and is made to interfere with the first image resulting in an image of the surface with zebra like stripes superimposed on it. This is known as a fringe pattern and abrupt changes in direction or spacing of these fringes may indicate a subsurface condition that affects the surface deformation. Thus porosity, voids, de-bonds, cracks, de-laminations etc. are detected. These techniques have also limitations particularly with the stability of the test piece and the inspecting instrument in relation to each other. Particular attention is paid in avoiding excessive test piece motion or environmental vibration both which will exceed the stringent requirements for fringe formation. It is well established that these laser based NDT techniques have found innumerable applications in the laboratory/field/factory environment and particularly Shearography but surprisingly it does not yet have a standard, like for example an ISO International Standard, hence we are calling for the involvement in this respect by the technical committee TC?135 of the ISO.     

Design of low-cost 183 GHz subharmonic mixers for commercial applications

Techniques are presented for designing fixed-tuned millimetre-wave components with the least number of parts to minimise the cost and maximise the potential for volume manufacture. Design techniques for millimeter-wave mixer components targeted at potentially high volume applications, such as medical and security screening and nondestructive testing, require certain compromises in the use of CAD tools. The compromise techniques are demonstrated using commercially available foundry diodes in the design of a 183 GHz subharmonic mixer for earth observation applications. The resulting mixer exhibits 6.85 dB double sideband conversion loss and a mixer temperature of 988 K using 5 mW of local oscillator power at 92 GHz