Biomedical subjects

C Pecorari

Publications and source records attributed to C Pecorari.

4 recordsLinked to original sources

PubMed2000

Attenuation and dispersion of Rayleigh waves propagating on a cracked surface: an effective field approach

A new effective field approach describing the attenuation and dispersion of a Rayleigh wave propagating on a surface containing a distribution of one-dimensional, surface-breaking cracks is presented. Limited by the validity of the independent scattering approximation, the model utilizes the complex transmission coefficient of a single crack to build expressions for the phase velocity and attenuation coefficient of an effective Rayleigh wave. The model is shown to be able to accommodate the effect of compressive residual stresses that tend to close the distributed cracks at their mouth, and therefore substantially reduce the attenuation and the velocity change caused by an equivalent distribution of open cracks. Wherever possible, the predictions of the new model are compared with those of other approaches and critical remarks are offered which discuss the advantages of the effective field approach over the others. Finally, an extension of this approach to distributions of two-dimensional surface-breaking cracks is outlined.

Journal Article↗

PubMed2000

The quasistatic approximation for a cracked interface between a layer and a substrate

Heuristic in nature, the quasistatic approximation (QSA) describes the interaction of ultrasonic waves with imperfect interfaces by modeling the interfacial imperfection as distributions of springs and masses. The QSA does not provide any relationship between the interfacial stiffness constants and the micromechanics of the defects. The aims of this paper are threefold. First, a derivation from first principles of the QSA boundary conditions on a cracked interface is presented. Relationships linking the interfacial constants to the mechanical and geometrical properties of the distributed cracks are also obtained. Second, the stiffness dependence of a cracked interface between a layer and a substrate on the layer thickness is investigated. It is shown that the interfacial stiffnesses cannot be regarded as intrinsic properties of the interface, but they may also depend on the structural properties of the hosting system. Finally, the effect of the thickness dependence of the interfacial stiffnesses on the phase velocity of the lowest mode supported by the layered structure is investigated.

Journal Article↗

PubMed2000

Scattering-induced attenuation of an ultrasonic beam in austenitic steel

The scattering-induced attenuation coefficient of a beam of longitudinal waves propagating through an austenitic steel plate is measured as a function of the texture angle. The experimental data were obtained by mapping the incident and the transmitted ultrasonic field, and by evaluating the energy loss experienced by each plane wave component of the beam. Contrary to the behavior of data obtained by means of conventional techniques, that of the data reported in this work agrees qualitatively with the theoretical predictions. The reasons for the disagreement between theory and data obtained by means of conventional techniques are also discussed.

Journal Article↗

PubMed1993

On monitoring structural changes of anisotropic tissues by means of statistical analysis of ultrasonic images.

An investigation into statistical properties of ultrasonic image texture from three-dimensional clusters of anisotropic scatterers is carried out. The structural properties of the clusters are modeled after those of soft biological tissues, such as skeletal muscle tissues, both in their healthy condition and at the early stage of degenerative diseases. The average axial autocorrelation function of the intensity of the image texture is used to characterize and monitor changes of the geometrical properties of the tissue components. A distinct local increase of the autocorrelation is observed within a range of small time shifts, and it is explained in terms of the structure of the time-domain backscattered signal from each individual scatterer. It is shown that such an increase is sensitive to structural variations of the cluster similar to those occurring at the early stage of several muscular diseases.

Anisotropy↗