Acoustic Wave Propagation Properties Research Articles

On-line Monitoring of Transformer Oil Degradation Based on Fiber Optic Sensors

In this paper, we present the preliminary results of our study on the use of a fiber optic sensor as a diagnostic and monitoring tool for evaluating the condition of transformer oil. An all-optical-fiber sensing system using a Mach-Zehnder interferometry technique was constructed to monitor acoustic wave propagation properties in differently aged transformer oil. It was found that the measured sound attenuation in the oil varies as it degrades, suggesting that the observation of sound attenuation with the fiber optic sensor can indicate the condition of service-aged transformer oil.

The autocorrelation function of stellar p-mode measurements and its diagnostic properties

The basic properties of acoustic wave propagation in stellar interiors can be analysed from the autocorrelation function (ACF) of intensity (or velocity) observations without measuring the resonant p-mode frequencies. We show how the strength of acoustic wave refraction in the stellar core, or forward acoustic amplitude, can be measured from a modulation in the ACF. This is the basic physical quantity which governs the so-called ‘small frequency separations’, and its measurement from the ACF can be used for determining the small frequency separations when the data is of insufficient quality for a reliable identification of the stellar p-mode frequencies.

Motion and size estimation of a free moving metallic particle in GIS based on propagation properties of acoustic waves

AbstractWe have investigated the propagation properties of Lamb waves and motion characteristic of free moving metallic particle in a gas‐insulated switchgear (GIS) tank to diagnose the insulation performance of GIS. We have proposed a new identification technique for defect location in GIS based on the time–frequency analysis of the Lamb waves using the Wavelet Transform. In this paper, we measured the acoustic signals excited by a metallic particle colliding with the tank sheath. Furthermore, we measured the moving particles under a high electric field in GIS using a high‐speed video camera. As a result, we examined the relationship between maximum lifting height and the flight time during subsequent impacts of a moving particle. Moreover, we estimated particle size based on the propagation properties of Lamb waves. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 26–33, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20023

Surface acoustic wave properties of freestanding diamond films

"Ideal" diamond has the highest acoustic velocity of any material known, and is of great interest as a substrate material for high frequency surface acoustic wave (SAW) device structures. However, little is known of the acoustic wave propagation properties of polycrystalline diamond grown by chemical vapour deposition (CVD) techniques, the commercially accessible form of this material. We report on propagation of laser-generated SAW on three forms of freestanding CVD diamond samples, "white" polycrystalline, "black" polycrystalline, and "highly oriented" diamond. Despite differing sample nature, SAW waves propagating along the smooth (nucleation) side of the diamond showed similar velocities in the range 10600-11900 ms(-1). These results are discussed in terms of the potential of each form of CVD diamond for SAW device fabrication.

Oscillations of vertically integrated relativistic tori - I. Axisymmetric modes in a Schwarzschild space-time

This is the first of a series of papers investigating the oscillation properties of relativistic, non-self-gravitating tori orbiting around a black hole. In this initial paper we consider the axisymmetric oscillation modes of a torus constructed in a Schwarzschild space-time. To simplify the treatment and make it as analytical as possible, we build our tori with vertically integrated and vertically averaged quantities, thus transforming the eigenvalue problem into a set of coupled ordinary differential equations. The tori are also modelled with a number of different non-Keplerian distributions of specific angular momentum, and we discuss how the oscillation properties change when different distributions of angular momentum are considered. Our investigation progresses by steps. We first consider a local analysis in Newtonian gravity and determine the properties of acoustic wave propagation within these objects, as well as the relations between acoustic and epicyclic oscillations. Next, we extend the local analysis to a general relativistic framework. Finally, we perform a global analysis and determine both the eigenfunctions and the eigenfrequencies of the axisymmetric oscillations corresponding to the p modes of relativistic tori. These behave as sound waves globally trapped in the torus and possess eigenfrequencies appearing in the simple sequence 2:3:4:..., independently of the distribution of angular momentum considered. The properties of the modes investigated here are in good agreement with those observed in recent numerical simulations, and could have a number of different applications. In X-ray binary systems containing a black hole candidate, for instance, p-mode oscillations could be used to explain the harmonic relations in the high-frequency quasi-periodic oscillations observed. In systems comprising a massive torus orbiting a black hole, on the other hand, p-mode oscillations could be used to explain the development or the suppression of the runaway instability.

Experimental and theoretical characterization of the surface acoustic wave propagation properties of GaN epitaxial layers on c-plane sapphire

Surface acoustic wave (SAW) propagation properties of gallium nitride (GaN) epitaxial layers on sapphire were theoretically and experimentally characterized. GaN thin films were grown on a c-plane sapphire substrate using a metalorganic chemical vapor deposition system. The experimental characterization of SAW propagation properties was performed with a linear array of interdigital transducer structures, while SAW velocities were calculated by matrix methods. Experimentally, we found pseudo-SAW and high-velocity pseudo-SAW modes in the GaN/sapphire structure, which had a good agreement with calculated velocities.

Motion and Size Estimation of a Free Moving Metallic Particle in GIS based on Propagation Properties of Acoustic Waves

We have investigated propagation properties of Lamb waves and motion characteristic of free moving metallic particle in gas insulated switchgear (GIS) tank to diagnose insulation performance of GIS. We have proposed a new identification technique of the defect location in GIS based on the time-frequency analysis of the Lamb waves using the Wavelet Transform. In this paper, we measured the acoustic signals excited by a metallic particle colliding with the tank sheath. Furthermore, we measured the moving particle under the high electric field in GIS using a high speed video camera. As a result, it was examined that the relationship between maximum lifting height and the flight time during subsequent impacts of a moving particle. Moreover, we estimated particle size based on propagation properties of Lamb waves.

GIS中の超音波伝搬特性とそれに基づく新しい部分放電発生位置標定

GIS中の超音波伝搬特性とそれに基づく新しい部分放電発生位置標定

Surface acoustic wave propagation properties of nitrogenated diamond-like carbon films

Nitrogenated diamond-like carbon (a-C:N) thin films on Si(100) were deposited by radio frequency magnetron reactive sputtering. Using ZnO piezoelectric thin films, the surface acoustic wave (SAW) propagation properties of a-C:N thin films on Si(100) have been experimentally investigated using bidirectional interdigital transducers between ZnO and a-C:N/Si(100). A generalized SAW mode with velocities between 5000 and 7000 m/s were observed. A high velocity pseudo-SAW mode was also observed and identified with simulated data, of which the velocity was 13 850 m/s. We calculated the film elastic constants from the phase velocities in the layered structure. The calculated constants for a-C:N thin films on Si were c11=392.1 and c44=185.7 GPa.

Scanning acoustic microscopy and its applications to material characterization

The scanning acoustic microscope is a powerful new tool for the study of the physical properties of materials and has been successfully used for imaging interior structures and for nondestructive evaluation in materials science and biology. Its principles of operation, resolution, penetration ability, and contrast mechanisms are simply described in this paper. Recent progress in the application of acoustic microscopy to material characterization in solid materials is summarized. The experimental elastic microanalysis of bulk materials is carried out by measuring $V(z)$, which includes examining the reflectance function of solid material, measuring the phase velocity and attenuation of leaky surface acoustic waves at the liquid-specimen boundary, and determining the elastic constants of the material. The layer thickness and mechanical properties of layered solids are studied by examining the dispersion properties of surface acoustic waves. A knowledge of the propagation properties of acoustic waves on the surface of materials is essential for understanding the contrast mechanisms and quantitative measurements in acoustic microscopy; these propagation properties are thus also briefly described in this paper. Finally, further developments of the scanning acoustic microscope aimed at improving its performance for quantitative evaluation are presented. These could expand the scope of the acoustic microscope as a diagnostic tool in many areas of science and technology.

An analysis of thin-rod flexural acoustic wave gravimetric sensors immersed in liquid

A perturbation analysis of acoustic wave propagation properties for a stiff thin rod surrounded by a liquid is presented. A study is made of the velocity sensitivity of the lowest flexural acoustic mode, F(11), along a thin rod due to mass changes in the rod and variations in the surrounding liquid density. It is shown that the presence of the liquid decreases the velocity of the F(11 ) mode and also the mass sensitivity.

Dynamic approach for finding effective elastic and piezoelectric constants of superlattices

A dynamic approach is presented for determining a set of equivalent elastic, piezoelectric, and permittivity constants for a superlattice consisting of a periodic multilayer of anisotropic materials. The objective is to predict the acoustic properties of such a periodic structure in the long-wavelength (low-frequency) limit. It is shown that the acoustic wave propagation properties for propagation in any plane defined by an arbitrary direction and the superlattice axis are contained in a 6×6 system matrix requiring only a subset of at most 29 material constants (from a total of 46) for its construction. The computation of an equivalent system matrix for a superlattice is demonstrated and the manner of obtaining the equivalent density, six permittivities, 21 stiffness, and 18 piezoelectric constants is given.