Showing papers in "Ultrasonics in 1997"

TL;DR: In this article, the development of flexible, cheap PVDF transducers for the generation and detection of Lamb waves in plates is described and experimental results showing a variety of modes on aluminium, steel, perspex and composite plates are presented.

TL;DR: In this paper, a femtosecond laser source was used to generate and detect high frequency elastic waves in submicron samples, and the authors measured the effective sound velocity of the bulk longitudinal modes propagating within the heterostructure as a function of the superlattice period.

TL;DR: In this article, an investigation is carried out to predict the most efficient leaky Lamb mode and associated frequency to detect defects in a specific layer of a multilayered composite plate.

TL;DR: In this article, the authors proposed a noncontact ultrasonic motor whose rotor is levitated ultrasonically and revolved at a very high speed, based on the theory of near-boundary acoustic streaming, a theoretical model for the calculation is developed.

TL;DR: The electromagnetic acoustic resonance (EMAR) is an emerging ultrasonic spectroscopy technique for nondestructive and noncontact materials characterization, relying on the use of electromagnetic-acoustic transducers (EMATs) and the superheterodyne circuitry for processing the received reverberation signals excited by long radio-frequency (RF) bursts.

TL;DR: In this paper, a high powered Q-switched Nd:YAG laser was used to initiate the Lamb wave spectrum in composite materials, and an optical fibre Michelson interferometer was employed to monitor the out-of-plane displacements associated with the propagating modes.

TL;DR: There are several designs of non-contact transducers that have been developed as mentioned in this paper, such as EMATs and LBU, which are typically of limited bandwidth and have lower sensitivity than conventional piezoelectric transducers, and are therefore typically useful in situations where there is sufficient signal strength, but where noncontact is necessary.

TL;DR: The clutter model is shown to refine some recently published models and is used to support the conjecture that clutter caused by relatively large grains often can be well approximated by a Gaussian stochastic process.

TL;DR: In this article, the authors derived the theory of subharmonic emission by parametrically excited distortion modes, which can explain the low level of the threshold, accounts for the observed oscillating ripples on bubble surface and demonstrates the coincidence between the frequency band where the emission of ω i ± ω p 2 signals were registered, and the one where parametric excitation of distortion modes are possible.

TL;DR: In this paper, the feasibility of using wideband air-coupled ultrasonic transducers for evaluating the integrity of bonded aluminum lap joints was investigated, and it was shown that defects in the bond-line can be detected and imaged by such a non-contract system.

TL;DR: In this paper, a method for collecting fine particles using a porous medium subjected to a standing ultrasonic wave field is described, which is readily accomplished by deactivating the acoustic field and flushing the particles from the porous medium through continued liquid flow.

TL;DR: In this article, two different techniques based on the processing of band-limited ultrasonic pulses reflected from the sample under investigation are presented for the detection of delaminations in thin multilayered composite plates.

TL;DR: The results showed that the correlation interpolation method is by far the most accurate for all time delays.

TL;DR: In this article, an ultrasonic Fresnel zone-plate has been micromachined from a thin stainless steel disk for the purpose of focussing highfrequency ultrasonic waves in air.

TL;DR: In this article, an experimental bubble collapse is designed such that a gas bubble expands slowly into a conical hollow through a reduction in the static pressure, and when this pressure is rapidly released, the resulting liquid shock causes the bubble to collapse into the cone.

TL;DR: In this paper, the flow front of molten aluminum inside the die has been probed by a two-channel acquisition system with a time resolution up to 1 ms using pulse-echo techniques.

TL;DR: In this article, the thermal diffusion equation with the consideration of thermal conductivity was used to obtain two terms contributing to the directivity patterns respectively for the longitudinal wave and the transverse wave.

TL;DR: In this paper, the authors present examples where apparently reasonable time domain results did not show the expected behaviour in the frequency domain, and the problem has been traced to subtle flaws in the design of the experiments.

TL;DR: In this article, a T-matrix and boundary element hybrid method was used to study the scattering of elastic waves by a crack in a plate and a fictitious surface was added to the crack to separate the infinite plate into two semi-infinite plates.

TL;DR: In this paper, the behavior of laser ultrasound sources in isotropic metals using ultra-short laser pulses in the thermoelastic regime was investigated, and numerical results showed that the thermal response rates of both steel and aluminum are much faster than their mechanical response rates.

TL;DR: In this article, a quasi-static model for ultrasonic guided waves interaction with imperfect interfaces is proposed, and the effect of this condition on the velocity is comprehensively discussed, with the objective of discriminating imperfect bonds.

TL;DR: In this paper, the authors investigated the source of ultrasonic scattering in clear turbulent water using a coherent Doppler sonar, from which the profiles of the turbulence parameters were determined.

TL;DR: In this article, the authors used micromachined air-coupled capacitance transducers to generate and detect ultrasonic longitudinal waves in a 5 mm-thick aluminum plate in a completely air coupled mode.

TL;DR: In this article, a method is described that can be extended to the use of surface acoustic waves to the control of film quality in an on-line process, exploiting the phenomenon that surface waves in coated materials show dispersion, giving rise to a characteristic deformation of wide-band surface wave impulses.

TL;DR: In this article, the effect of xanthene dyes on the acoustic cavitation threshold in an aqueous solution was investigated in a progressive wave field, and the ability of these dyes to reduce the threshold for sonochemically active cavitation was strongly correlated with their ability to stabilize foams.

TL;DR: In this paper, a new method for the determination of acoustic impedance of a material present in the form of a membrane is proposed based on the measurement of magnitudes at two different frequencies in the frequency spectra of double through-transmission signals with and without the membrane.

TL;DR: The signal processing combines wavelet decomposition and cross-correlation to measure time delays with a high degree of accuracy and considers optimal results is presented.

TL;DR: In this article, a simplified evaluation based on the Raman-Nath approach will give rise to considerable errors, depending on the light-sound interaction length and the ultrasound frequency, errors of the order of 50% are not rare.

TL;DR: In this paper, the experimental determination of the transfer function of a metal-coated ultrasonic fiber tip sensor for frequencies up to 40 MHz is presented, defined as transmission factor of acoustical displacement.

TL;DR: The design of wide-angle transducers for a real-time ultrasonic tomography system for objects in a liquid using reflection mode tomography is described and transducers with wide emission angles have been constructed.