Application of Waterman-Truell and the Dynamic Generalized Self-consistent Models on Concrete

AbstractAcoustic wave propagation in heterogeneous and dispersive media is a very complex phenomenon, where the phase velocity and attenuation are function of the material microstructure, and becomes frequency-dependent parameters. In this paper, the interaction between ultrasound waves and cement-paste specimens have been analyzed by two multiple scattering models, based on homogenization approach, and experimental data. The experimental phase velocity, attenuation and the dispersion results show good agreement with the theoretical models; the experimental phase velocity and attenuation decrease for higher w/c ratio, as predicted by the theoretical models

Crack assessment in cement-based materials using Ultrasound and T

The elastic properties and durability of concrete based structures, directlydepend on the microstructure of the hydrated cement paste. The microstructurevaries with time due to several chemical reactions and mechanical loads,leading to micro fractures, among other effects. For this reason, it is necessaryto develop techniques to locate and measure fractures. Ultrasound hasproven to be a reliable diagnostic tool, so the primary objective of this paperis to propose a composite nondestructive methodology based on NMR relaxometryand through-transmission ultrasound for crack assessment in cementpaste specimens. While the Hilbert-Huang transform of ultrasonic signals areable to locate the defects, the T2 transverse relaxation time gives the watercontent in the crack. The results show, that the Hilbert-Huang transformenhanced the ultrasonic echoes coming from the fracture allowing to detectand locate fractures with an error of 15%, and the crack size is given by thedecay parameter of the relaxation time T2, based by exponential fitted theFID signal

Numerical Analysis of a Flexible Dual Loop Coil and its Experimental Validation for pre-Clinical Magnetic Resonance Imaging of Rodents at 7 T

A surface radio frequency coil was developed for small animal image acquisition in a pre-clinical magnetic resonance imaging system at 7 T. A flexible coil composed of two circular loops was developed to closely cover the object to be imaged. Electromagnetic numerical simulations were performed to evaluate its performance before the coil construction. An analytical expression of the mutual inductance for the two circular loops as a function of the separation between them was derived and used to validate the simulations. The RF coil is composed of two circular loops with a 5 cm external diameter and was tuned to 300 MHz and 50 Ohms matched. The angle between the loops was varied and the Q factor was obtained from the S11 simulations for each angle. B1 homogeneity was also evaluated using the electromagnetic simulations. The coil prototype was designed and built considering the numerical simulation results. To show the feasibility of the coil and its performance, saline-solution phantom images were acquired. A correlation of the simulations and imaging experimental results was conducted showing a concordance of 0.88 for the B1 field. The best coil performance was obtained at the 90° aperture angle. A more realistic phantom was also built using a formaldehyde-fixed rat phantom for ex vivo imaging experiments. All images showed a good image quality revealing clearly defined anatomical details of an ex vivo rat