Showing papers in "Ultrasonics in 1988"

TL;DR: The results indicate that the threshold for transient cavitation produced in water by pulsed ultrasound is independent of pulse duration and acoustic frequency for pulses longer than approximately 10 acoustic cycles.

TL;DR: In this paper, a synthesis of various theoretical models representing the acoustic displacements generated by a point laser impact is given, and then validated by interferometer measurements of ultrasonic displacement generated both under ablation conditions and under thermoelastic conditions.

TL;DR: The results indicate that, unlike Doppler flow imaging systems, this technique defines the flow velocity vector in two dimensions and is not subject to aliasing.

TL;DR: In this paper, it was shown that cracks with normals aligned along the stress direction are closed preferentially in agreement with the theory of Walsh, however, for crack normals perpendicular to the applied stress there is some evidence of crack opening that is not predicted by the theory.

TL;DR: This review provides a comprehensive survey of the use of ultrasonic techniques with regard to foods and the difficulties inherent in using ultrasonics to provide useful information about foods.

TL;DR: In this article, a series expansion of the crack orientation distribution function in generalized spherical harmonics is proposed to estimate the probability of a crack having a given orientation with respect to a set of axes fixed in the rock and is used to calculate the variation of elastic wave velocity with propagation direction.

TL;DR: In this article, the effects of the rate of flow of argon gas through styrene during exposure to ultrasound on the polymerization rate and the molecular weight distribution of the polymer formed were investigated.

TL;DR: This Paper formalizes the determination of the fourth processing parameter namely, the frequency location of the bank of bandpass filters used for the spectral splitting, thereby removing the last remaining ambiguity of the split spectrum processing.

TL;DR: The signal transmission characteristics of underwater acoustic transducers are discussed and methods of tailoring those characteristics to meet required pass-band response targets are described, based on passive network theory.

TL;DR: In this article, a method has been devised for determining the density of a fluid by measuring the velocity and amplitude of an ultrasonic pulse passed through it, and the theory of the method is presented, together with the results of an experimental verification.

TL;DR: In this article, the texture of thin sheets of a commercial grade aluminium alloy was measured with both ultrasonics and neutron diffraction, using both piezoelectric and electromagnetic-acoustic transducers (EMATs).

TL;DR: In this article, it was shown that resonant moving bubbles introduce Doppler shifts on the sidebands generated at the sum and difference frequency of a pumping frequency field which is swept through the resonance frequency of the bubble, together with a higher frequency imaging field.

TL;DR: The preliminary conclusion that some samples of liver may exhibit low levels of wavefront disruption is consistent with recent evidence in the literature and requires the development of a reliable technique for determining the presence of gaseous microbubbles in tissue in vitro.

TL;DR: In this article, the analytical problem of transmission of an ultrasonic beam from a homogeneous, isotropic elastic half-space into a transversely-isotropic half space is addressed.

TL;DR: In this paper, a system of boundary integral equations for the crack-opening displacement has been obtained by using the elastodynamic representation integral for the scattered displacement field, and the results suggest the optimal choices of angles of incidence and observation for a maximum response in an ultrasonic test to detect and characterize surface breaking cracks.

TL;DR: This paper explains the various existing possibilities for clever physically based data collection, and the types of feature domains and features available for anomaly representation in materials, including a normal beam longitudinal wave high frequency area ratio feature mapping system.

TL;DR: A plastic-clad optical fibre system has been examined as a delivery system of pulsed laser energy for the generation of ultrasound, finding that laser power densities from the fibre were sufficient to produce ultrasonic waveforms corresponding to both the thermoelastic and plasma generation regimes.

TL;DR: In this paper, a ray tracing approach is used to study the expected pattern of defect reflection behavior for several weld types and several defect locations and orientations, and they find that when the ultrasonic beam is generated in the austenitic weld material without first passing through the base metal, then the strongly reflected specular signal travels in very unexpected directions.

TL;DR: Since the peak acoustic pressure within the pulse increased with decreasing pulse length and increasing acoustic pressure increases the probability of cavitation occurring, the mechanism responsible for this phenomenon is probably not cavitation.

TL;DR: In this article, the concept of generalized extinction cross-section was introduced in detail and exemplified by the problem of scattering by an elastic cylinder embedded in a viscoelastic matrix, and it was shown that under certain conditions the presence of inclusion may have a supporting effect on wave propagation.

TL;DR: In this paper, two methods were developed for the determination of three off-diagonal terms of the stiffness matrix of wood, i.e., compliance terms (Sij) and corresponding technical terms.

TL;DR: A phase-coded pulse compression system, which consists of a Barker code generator and a matched filter, has been implemented and applied to the ultrasonic non-destructive testing of materials as discussed by the authors.

TL;DR: The importance of multiple scattering processes for the propagation of ultrasound through dispersions is assessed in this paper, where the amplitude and complex wavenumber of multiply scattered plane wave collected by either the receiving or the emitting transducer are evaluated in terms of particle number density, wavelength of ultrasound and the forward and backward scattering amplitudes.

TL;DR: In this article, laser interferometry and laser-generated ultrasound have been applied to the calibration of contact transducers which are used to detect defects in solids by angled shear-waves.

TL;DR: Experimental results obtained with a 'button' transducer in direct contact with the myocardium are discussed and instrumentation and data analysis procedures for cardiac tissue characterization by a backscatter method are described.

TL;DR: Propagation of ultrasound in a number of thin solid elastic waveguides is described from the Pochhammer theory and the group velocities of the modes and the form of the particle amplitudes of the lowest longitudinal and flexural modes in each of the styles at a frequency of 3.5 MHz are presented.

TL;DR: The attenuation of ultrasound in homogenates of bovine skeletal muscle and suspensions of myofibrils was measured over the frequency range 1.5-7 MHz, and found to be proportional to protein concentration in both, and may be interpreted as the viscous component of the attenuation due to relative motion between the my ofibril and its surrounding saline.

TL;DR: In this paper, the directivity patterns of a wide range of electromagnetic acoustic transducers (EMATs) have been determined experimentally using a second, spiral coil EMAT as the detector around a cylindrical surface.

TL;DR: In this paper, the effects of variations in design parameters of ultrasonic transducers on performance characteristics, including center frequency, bandwidth and insertion loss, were investigated analytically, including acoustic impedance, resonant frequency, capacitance, electromechanical coupling constant of the piezoelectric element, acoustic impedance of the backing, thickness and acoustic imbalance of the matching layer, series inductance of the electrical tuning network, and thickness of the bonding layer.

TL;DR: A theoretical analysis of ultrasonic attenuation in aqueous suspensions of red blood cells verified the relative importance of several mechanisms: absorption accounts for 60% of the attenuation, viscous relative motion loss accounts for less than 30%, and the sound scattering contribution is negligible.