Polarimetric Microwave Inverse Scattering as Applied to Nondestructive Testing

The conventional procedures of nondestructive evaluation by means of ultrasonic techniques are limited by surface roughness and grain-boundary scattering of testmaterials. Especially ceramics must be coupled carefully with high-frequency ultrasonic transducers. Concerning these restrictions and in view of the possibility of contactless measurements of low-loss dielectric materials with microwaves, the application of electromagnetic waves in NDE appears to be a favourable alternative to conventional ultrasonic techniques [1]

Numerical Modeling and Imaging with ULIAS: Ultrasonic Inspection Applying Simulation

ULIAS is the short term for ULtrasonic Inspection Applying Simulation. ULIAS is a module based software package comprising modules for numerical modeling, imaging, data compression, signal processing, and visualization in 1-D/2-D/3-D

Reconstruction of Defect Geometries in Ultrasonic NDT

The international activities in developing new flaw characterization methods with special emphasis on acoustic imaging have been increased. To reduce the dependency upon amplitude information and due to the fact that flaw information is buried in the shape and fine structure of wave fronts, considerable attention has been given to the development of methods using time-of-flight information from different probe positions. For this reason, with mechanical scanners and specially build data acquisition and evaluation systems, a vareity of ways to produce images has been developed. These include echotomography, linear or two dimensional mono- or multi-frequency holography, tip echo interference methods, ALOK (amplitude-,time-of-flight-locus curves), Phased Array, SAFT or Rayleigh-Sommerfeld Holography. These methods use mathematical algorithms which seem to be independent or which have been derived heuristically. Based upon the concept of elastodynamic diffraction theory together with that of tomography a concept can be derived which reveals the inner connection of these algorithms. Differences in the reconstructions arise due to limitations like limited aperture, limited bandwidth, use of mode converted signals or due to complex surface shapes. An attempt is made to cover the theoretical background, to give an overview on existing data acquisition systems and to describe the strength, weaknesses, and difficulties in producing acoustic images

Electronic ground states of Fe2+_2^+ and Co2+_2^+ as determined by x-ray absorption and x-ray magnetic circular dichroism spectroscopy

The $^6\Pi$ electronic ground state of the Co$_2^+$ diatomic molecular cation has been assigned experimentally by x-ray absorption and x-ray magnetic circular dichroism spectroscopy in a cryogenic ion trap. Three candidates, $^6\Phi$, $^8\Phi$, and $^8\Gamma$, for the electronic ground state of Fe$_2^+$ have been identified. These states carry sizable orbital angular momenta that disagree with theoretical predictions from multireference configuration interaction and density functional theory. Our results show that the ground states of neutral and cationic diatomic molecules of $3d$ transition elements cannot generally be assumed to be connected by a one-electron process

Elastic Wave Propagation and Scattering in Austenitic Steel

Ultrasonic nondestructive testing of austenitic steel welds is very difficult, because fundamental wave propagation and scattering effects in such complicated anisotropic environments are only hardly understood [1, 2]. Therefore, a step-by-step evaluation of elastic wave propagation in transversely isotropic media has been initiated. Under the assumption of transverse isotropy the numerical EFIT code (Elastodynamic Finite Integration Technique) [3] - [7] was extended to anisotropic homogeneous media. It allows 3D computation of quasi pressure and quasi shear as well as surface waves in transverse isotropic media. Results for finite aperture transducer radiation and crack scattering in a single crystal austenitic weld are presented; measurements of amplitude dynamics, A-Scans and C-Scans confirm the EFIT simulations [8]

Analytical and Numerical Predictions of Short Pulsed Elastic Waves on a Half-Space

The numerical modeling of ultrasonic wave propagation in elastic solids is particularly attractive for NDT applications because of the relative ease with which the boundaries of realistic defect shapes and testing geometries can be handled. A two-dimensional explicit finite element code [1] has been developed for this purpose

Modelling survival and connectivity of Mnemiopsis leidyi in the south-western North Sea and Scheldt estuaries

Three different models were applied to study the reproduction, survival and dispersal of Mnemiopsis leidyi in the Scheldt estuaries and the southern North Sea: a high-resolution particle tracking model with passive particles, a low-resolution particle tracking model with a reproduction model coupled to a biogeochemical model, and a dynamic energy budget (DEB) model. The results of the models, each with its strengths and weaknesses, suggest the following conceptual situation: (i) the estuaries possess enough retention capability to keep an overwintering population, and enough exchange with coastal waters of the North Sea to seed offshore populations; (ii) M. leidyi can survive in the North Sea, and be transported over considerable distances, thus facilitating connectivity between coastal embayments; (iii) under current climatic conditions, M. leidyi may not be able to reproduce in large numbers in coastal and offshore waters of the North Sea, but this may change with global warming; however, this result is subject to substantial uncertainty. Further quantitative observational work is needed on the effects of temperature, salinity and food availability on reproduction and on mortality at different life stages to improve models such as used here

Experimental Evaluation of Ultrasonic Simulation Techniques in Anisotropic Material

The high performance of the available computer technology provides the possibility to simulate the real life for ultrasonic inspections in terms of primary ultrasonic data like rf-time signals. For isotropic material codes like Generalized Point Source Synthesis (GPSS) or Elastodynamic Finite Integration Technique (EFIT) and the theoretical predictions correlate well with experimental results. Recently, the codes mentioned above have been extended to operate also in anisotropic material. In a first step the codes GPSS and EFIT have been expanded to work in materials of parallel oriented columnar grain structure with transversely isotropic symmetry. In order to verify these codes a set of experiments was carried out on weld metal pads and on welds of defined grain structure. Radiation, propagation, reflexion on boundaries and interaction of the sound field with defects for the modes “through transmission” and “pulse echo” were simulated and compared with the experiment

Coordination-driven magnetic-to-nonmagnetic transition in manganese doped silicon clusters

The interaction of a single manganese impurity with silicon is analyzed in a combined experimental and theoretical study of the electronic, magnetic, and structural properties of manganese-doped silicon clusters. The structural transition from exohedral to endohedral doping coincides with a quenching of high-spin states. For all geometric structures investigated, we find a similar dependence of the magnetic moment on the manganese coordination number and nearest neighbor distance. This observation can be generalized to manganese point defects in bulk silicon, whose magnetic moments fall within the observed magnetic-to-nonmagnetic transition, and which therefore react very sensitively to changes in the local geometry. The results indicate that high spin states in manganese-doped silicon could be stabilized by an appropriate lattice expansion