Digital Measurement of Ultrasonic Velocity

The ultrasonic material evaluation has been applied to composite materials and nonhomogeneous materials. In quantitative evaluation of these materials the ultrasonic velocity and attenuation are widely used. In addition acoustoelastic stress measurement requires high precision measurement of the ultrasonic velocity

Transient Lamb Wave Velocity Determination Using Holographic Mapping of Spatial Feautres of Propagating Waves

Measurement of surface displacements resulting from acoustic wave propagation in solids has been used extensively in determining elastic properties of materials [1],[2]. Additionally, examination of acoustic wave propagation in materials has been used as a nondestructive tool in testing the integrity of structures, evaluating the size and position of bulk material defects, determining material dimensions, and in general, characterizing a number of material or structural parameters [3]</p

Ultrasonic NDE of Adhesive Bonds: The Inverse Problem

Over the past quarter century, a wide variety of ultrasonic techniques have been developed to determine the phase velocity and thickness of elastic plates. Techniques to measure the phase velocity include toneburst [1–4], separable pulse methods [5–7], and spectroscopy [8–11]. These classical methods require that the specimen be thick enough such that two successive echoes from the front and the back faces of the specimen, respectively, be separable in the time domain. Kinra and Dayal [12], developed a through transmission technique which removes this particular limitation of the classical methods. This technique works satisfactorily for the measurement of the phase velocity for specimens whose thickness is greater than one-half of the wavelength; for thinner specimens, however, their numerical algorithm runs into convergence problems. Moreover, their numerical algorithm cannot be used to determine thickness at any wavelength. The reasons for their convergence problems are discussed in detail by Iyer, Hanneman and Kinra [13]. They demonstrated that a detailed sensitivity analysis is a necessary pre-requisite for the development of a robust inversion algorithm. Accordingly, a new inversion scheme based on the method of least squares was developed by Iyer and Kinra to determine thickness from the measurements of phase, magnitude and complex spectrum, respectively, [14–17]. In all of the above ultrasonic methods only one parameter can be determined i.e., an accurate knowledge of thickness is required to determine the wavespeed and vice versa. This defines the central objective of the present work: In this paper we present a technique for determining, simultaneously, the thickness and wavespeed of a thin layer

Theoretical study of the insulating oxides and nitrides: SiO2, GeO2, Al2O3, Si3N4, and Ge3N4

An extensive theoretical study is performed for wide bandgap crystalline oxides and nitrides, namely, SiO_{2}, GeO_{2}, Al_{2}O_{3}, Si_{3}N_{4}, and Ge_{3}N_{4}. Their important polymorphs are considered which are for SiO_{2}: $\alpha$-quartz, $\alpha$- and $\beta$-cristobalite and stishovite, for GeO_{2}: $\alpha$-quartz, and rutile, for Al_{2}O_{3}: $\alpha$-phase, for Si_{3}N_{4} and Ge_{3}N_{4}: $\alpha$- and $\beta$-phases. This work constitutes a comprehensive account of both electronic structure and the elastic properties of these important insulating oxides and nitrides obtained with high accuracy based on density functional theory within the local density approximation. Two different norm-conserving \textit{ab initio} pseudopotentials have been tested which agree in all respects with the only exception arising for the elastic properties of rutile GeO_{2}. The agreement with experimental values, when available, are seen to be highly satisfactory. The uniformity and the well convergence of this approach enables an unbiased assessment of important physical parameters within each material and among different insulating oxide and nitrides. The computed static electric susceptibilities are observed to display a strong correlation with their mass densities. There is a marked discrepancy between the considered oxides and nitrides with the latter having sudden increase of density of states away from the respective band edges. This is expected to give rise to excessive carrier scattering which can practically preclude bulk impact ionization process in Si_{3}N_{4} and Ge_{3}N_{4}.Comment: Published version, 10 pages, 8 figure

Tooth mobility and periodontal disease

IIW-type (International Institute of Welding) ultrasonic calibration blocks are used widely throughout the world in nondestructive testing of materials and structures. They are used to establish certain physical characteristics of ultrasonic search units (transducers and plastic wedges) and flaw detection systems. Figures la and lb illustrate the geometries of the two popular U.S. variations of the IIW-type block: IIW-Type 1 design referenced by ASTM (American Society for Testing and Materials), and IIW-Type 2 commonly known as the U.S. Air Force design. The blocks are nominally 300 mm (12 in.) long, 100 mm (4 in.) wide, and 25 mm (1 in.) thick. The geometry, physical characteristics, and uses of the ASTM design are specified in the ASTM standard E-164, while the Air Force design is described in the U.S. Air Force Technical Manual on Nondestructive Inspection Methods. A comprehensive summary of the different block designs and physical characteristics is given by Hotchkiss [1]