Showing papers in "Ultrasonics in 1991"

TL;DR: The behaviour of gas bubbles and gas encapsulated spheres as echographic contrast agents is reviewed and the analysis of their velocity of sound, back-scatter intensity, second harmonic emission and resonant frequency opens up new perspectives in the development of contrast agents for echocardiographic research with potential clinical applications.

TL;DR: The higher experimental speeds observed here emphasize the value of acoustically concentrating particles into relatively large clumps prior to initiating transport, which predicts an upper limit, which increases with particle size, for the speed of an entrained body.

TL;DR: In this paper, an ultrasonic device is described which can be used to measure the ultrasonic velocity, attenuation coefficient and characteristic impedance of liquid materials, such as temperature, density and the particle size and concentration of dispersed phases.

TL;DR: In this article, a method utilizing leaky Lamb wave (LLW) spectra for the nondestructive evaluation of fiber reinforced composite laminates is discussed. Butler et al. used a signal coding scheme, incorporating a frequency modulated tone burst, to analyse the ultrasonic reflection signals from the plate.

TL;DR: In this paper, a combined finite element and Lamb wave modal expansion method is presented for analysing scattering of time harmonic Lamb waves by material and geometric irregularities in an isotropic linearly elastic infinite plate.

TL;DR: In this paper, the authors used a point-like transducer to detect plate-wave acoustic emission in cross-ply laminate graphite/epoxy coupons by tensile loading.

TL;DR: In this article, the ability of these signals to accurately size and resolve bubbles, both singly and in arrays, has been studied, both in arrays and in a single bubble.

TL;DR: In this article, the authors found that the enhanced decomposition was proportional to both the acoustic pressure and the square root of the acoustic intensity, and that the analysis was also applicable to the solvolysis of 2-chloro methylpropane, a volatile substrate.

TL;DR: In this article, a convenient method for optically exciting and monitoring Lamb waves in thin plates is described, where the interference pattern of two high power laser beams on a sample surface produces periodic heating and thus coherent antisymmetric Lamb waves are excited.

TL;DR: Frequency dependences of main parameters of the interferometer are obtained and the possibility of high precision measurements of velocity and absorption of ultrasound in liquids under the high pressures by means of fixed path interferometers with liquid-backed transducers is shown.

TL;DR: In this article, the authors introduced the bulk heterogeneous wave concept into the well known Thomson-Haskell method for computing transmission/reflection coefficients through stratified media and tested the new expression for the matrix transfer between interfaces given in this paper without showing instability.

TL;DR: In this article, the authors used the finite element code ATILA to compute the stress field, which is then compared to the mechanical limit of the material using classical criteria, and found that very good agreement was found when the computed results were compared to strain gauge measurements.

TL;DR: A hardware two-dimensional real-time filter is described which consists of a hybrid digital/analogues system in which the video signal from any scanner is sampled to 256 points per line and passed sequentially through a series of shift registers, in order to derive a 5 x 5 window of values which surrounds the image point currently being processed.

TL;DR: In this paper, the authors used short-pulse transducers and laser-generated ultrasound to study diffraction by machined defects and fatigue cracks and found good agreement between experiment and theory for an open fatigue crack.

TL;DR: In this paper, the use of high intensity ultrasound as an initiator of polymerization in methyl methacrylate has been investigated and the results confirm that pure, dry, vinyl monomers can be polymerized by this method but that there are simultaneous polymerization and degradation processes occurring so that the molecular weight is a complex function of sonication time.

TL;DR: In this article, a model for the scattering of ultrasonic waves from smooth and randomly rough defects is presented, which uses Kirchhoff theory and is elastic, such that mode-conversion between compressional and shear waves is included in the formulation.

TL;DR: To predict attenuations to within, say, 20% for mixtures such as these is a major achievement and theoretical predictions based on a novel hydrodynamic model are in excellent agreement with the measured values.

TL;DR: In this article, one-dimensional frequency and time domain solutions for the pressure for Beer's law absorption of radiation in a fluid in contact with a second transparent medium are given for short pulses of 532 nm radiation from a Nd:YAG laser are used to generate exponential waves in solutions containing various concentrations of a dye.

TL;DR: In this article, the authors present the possibilities of applying ultrasonic methods in asphalt concrete testing and present the results of testing cylinder-shaped samples, which are then used in testing a model of the surface layer of flexible pavement.

TL;DR: In this paper, experimental and theoretical data are presented on the ultrasonic properties of polydisperse oil-in-water dispersions, both emulsions and suspensions (containing crystallized oil particles) have been studied.

TL;DR: In this paper, the impulse response method is used to study the transient pressure field radiated by focussed transducers under different types of excitation, and it is shown that the perceived shape of the ultrasonic beam depends on whether the positive or negative cycle of the pulse was detected.

TL;DR: In this paper, the authors considered the problem of the reflection/refraction of a plane wave at a solid layer in a geometrical Debye's series and proposed several methods of expansion into the series: matrix sum (one summation), taking into account all double reflections/refractions on both interfaces (three summations), and analysing the elementary reflection and refraction on each interface separately (seven summations).

TL;DR: In this paper, finite element methods and modal analysis techniques have been used to predict the transient mechanical displacement over the surface of piezoelectric discs when they are excited by voltage pulses across electrodes on their top and bottom surfaces.

TL;DR: In this article, it was shown that acoustic layering and reorientation are dominant effects for long and short fibres, respectively, for paper-making fibres and that light scattering behavior during ultrasonic excitation is required.

TL;DR: It is concluded that quantification of pulsed Doppler spectra may be feasible if the sample volume is positioned within the central 25% of the vessel.

TL;DR: The HOC method is relatively simple to apply, has remarkable data and information compression capabilities, preserves the spectral parameters of the signals and has good feature discrimination abilities, which make it attractive for application to non-destructive evaluation (NDE) analyses whenever the inspection techniques involve the accumulation and processing of time domain signals.

TL;DR: In this article, a line focus acoustic microscope and a specimen containing a subsurface crack is used to calculate V(z) and V(x, z) curves for various locations and orientations of the crack.

TL;DR: In this paper, pure iron has been eroded in various aqueous solutions at 50°C using a 20 kHz vibratory facility and the erosion kinetics determined, the corrosion component during erosion determined electrochemically, the size distribution of the erosion products determined and the eroded surface examined metallographically.

TL;DR: The relationship between the ultrasound beam and the observed signal spectrum has been investigated by employing a computer-based model of the ultrasound field which enabled the calculation of the Doppler signal from a scatterer moving through the field and the spectrum of this signal.