Showing papers on "Acoustic wave published in 1987"

Nonlinear two-dimensional elastic inversion of multioffset seismic data

Abstract: The treatment of multioffset seismic data as an acoustic wave field is becoming increasingly disturbing to many geophysicists who see a multitude of wave phenomena, such as amplitude-offset variations and shear-wave events, which can only be explained by using the more correct elastic wave equation. Not only are such phenomena ignored by acoustic theory, but they are also treated as undesirable noise when they should be used to provide extra information, such as S-wave velocity, about the subsurface. The problems of using the conventional acoustic wave equation approach can be eliminated via an elastic approach. In this paper, equations have been derived to perform an inversion for P-wave velocity, S-wave velocity, and density as well as the P-wave impedance, S-wave impedance, and density. These are better resolved than the Lame parameters. The inversion is based on nonlinear least squares and proceeds by iteratively updating the earth parameters until a good fit is achieved between the observed data and the modeled data corresponding to these earth parameters. The iterations are based on the preconditioned conjugate gradient algorithm. The fundamental requirement of such a least-squares algorithm is the gradient direction which tells how to update the model parameters. The gradient direction can be derived directly from the wave equation and it may be computed by several wave propagations. Although in principle any scheme could be chosen to perform the wave propagations, the elastic finite-difference method is used because it directly simulates the elastic wave equation and can handle complex, and thus realistic, distributions of elastic parameters. This method of inversion is costly since it is similar to an iterative prestack shot-profile migration. However, it has greater power than any migration since it solves for the P-wave velocity, S-wave velocity, and density and can handle very general situations including transmission problems. Three main weaknesses of this technique are that it requires fairly accurate a priori knowledge of the low-wavenumber velocity model, it assumes Gaussian model statistics, and it is very computer-intensive. All these problems seem surmountable. The low-wavenumber information can be obtained either by a prior tomographic step, by the conventional normal-moveout method, by a priori knowledge and empirical relationships, or by adding an additional inversion step for low wavenumbers to each iteration. The Gaussian statistics can be altered by preconditioning the gradient direction, perhaps to make the solution blocky in appearance like well logs, or by using large model variances in the inversion to reduce the effect of the Gaussian model constraints. Moreover, with some improvements to the algorithm and more parallel computers, it is hoped the technique will soon become routinely feasible.

Theory of reflection

Abstract: This book deals with the reflection of electromagnetic and particle waves by interfaces. The interfaces can be sharp or diffuse. The topics of the book contain absorption, inverse problems, anisotropy, pulses and finite beams, rough surfaces, matrix methods, numerical methods, reflection of particle waves and neutron reflection. Exact general results are presented, followed by long wave reflection, variational theory, reflection amplitude equations of the Riccati type, and reflection of short waves. The Second Edition of the Theory of Reflection is an updated and much enlarged revision of the 1987 monograph. There are new chapters on periodically stratified media, ellipsometry, chiral media, neutron reflection and reflection of acoustic waves. The chapter on anisotropy is much extended, with a complete treatment of the reflection and transmission properties of arbitrarily oriented uniaxial crystals. The book gives a systematic and unified treatment reflection and transmission of electromagnetic and particle waves at interfaces. It is intended for physicists, chemists, applied mathematicians and engineers, and is written in a simple direct style, with all necessary mathematics explained in the text

System for temperature profile measurement in large furnances and kilns and method therefor

Abstract: Measurements of the times of flight of sound waves can be used to determine temperature in a gas contained in a long tube which confines sound waves Sound pulses are transmitted and received by a suitable loud speaker attached to one end of the long tube A number of stubs or other discontinuities produce the sound reflections whose times of arrival are measured The time intervals yield average sound speeds in each interval between any two stubs from which temperatures are calculated Corrections for thermal expansion of the tube are easily made

Acoustic Absorption by Sunspots

Abstract: The paper presents the initial results of a series of observations designed to probe the nature of sunspots by detecting their influence on high-degree p-mode oscillations in the surrounding photosphere. The analysis decomposes the observed oscillations into radially propagating waves described by Hankel functions in a cylindrical coordinate system centered on the sunspot. From measurements of the differences in power between waves traveling outward and inward, it is demonstrated that sunspots appear to absorb as much as 50 percent of the incoming acoustic waves. It is found that for all three sunspots observed, the amount of absorption increases linearly with horizontal wavenumber. The effect is present in p-mode oscillations with wavelengths both significantly larger and smaller than the diameter of the sunspot umbrae. Actual absorption of acoustic energy of the magnitude observed may produce measurable decreases in the power and lifetimes of high-degree p-mode oscillations during periods of high solar activity.

Acoustic wave viscosity sensor

Abstract: An acoustic wave device utilizing plate modes having components of displacement parallel to a crystal surface has been demonstrated to be an effective sensor of liquid shear viscosity (η) over a wide viscosity range. When a liquid is present on the sensor surface, the propagation loss of the acoustic wave depends upon η in a calculable fashion. Because the device functions at 159 MHz, liquid relaxation effects occur with high viscosity liquids, causing the propagation loss to saturate. Viscosity is sampled in the 50‐nm‐thick liquid layer which couples to the acoustic wave, so that only a single drop of liquid is required for measurement.

Method and system for measuring azimuthal anisotropy effects using acoustic multipole transducers

Abstract: An acoustic borehole well logging method and apparatus for measuring azimuthal anisotropy of a formation traversed by a borehole using at least one multipole transducer. In a preferred embodiment, a dipole wave transmitter and at least one detector sensitive to dipole waves are employed. In an alternative preferred embodiment, a monopole transmitter and at least one multipole detector are employed. In the inventive method, two acoustic wave arrivals are detected, each associated with a different azimuthal orientation relative to the longitudinal axis of the borehole (i.e. each is transmitted by a multipole transmitter oriented at such angle, or is detected by a multipole detector oriented at such angle, or both). The inventive apparatus preferably includes at least one transducer unit including two or more multipole transmitters (or two or more multipole detectors) oriented at different azimuthal angles relative to the tool's longitudinal axis.

Ultrasound Doppler Probing of Flows Transverse with Respect to Beam Axis

Abstract: It is an accepted fact that transverse Doppler effects of the first order in v/c are nonexistent for all physical wave phenomena, including acoustics, i.e., the Doppler effect is zero for radiation normal to the direction of motion. However, this statement assumes that the incident field is a plane wave, which is not true in general for finite aperture sources. Consequently, the probing of flows transverse to the axis of finite diameter beams, particularly focused beams, is feasible. This geometry will be advantageous in many applications where the classical orientation of the sound beam, oblique to the flow, is not possible. With this motivation in mind, the theory and experimental feasibility of measuring Doppler spectra in transverse geometries is presently investigated.

The effect of the ion temperature on the ion acoustic solitary waves in a collisionless relativistic plasma

Abstract: The effect of the ion temperature on ion acoustic solitary waves in a collisionless relativistic plasma is discussed using the Korteweg–de Vries equation. The phase velocity of the ion acoustic waves decreases as the relativistic effect increases, and increases as the ion temperature increases. Only a compressional soliton of the ion acoustic wave is formed in this system. Since its amplitude increases for the lower ion temperature as the relativistic effect increases, we deduce the formation of a precursor by the presence of the streaming ions. In contrast, for the higher ion temperature, the amplitude decreases slowly. Furthermore, it is shown that the oscillatory solution of the Korteweg–de Vries equation smoothly links with the nonlinear Schrodinger equation in a relativistic plasma.

Analysis of intermodal coupling in a two-mode fiber with periodic microbends.

Abstract: Simple expressions for the coupling between the LP01 and LP11 modes of a two-mode optical fiber with a periodic microbending structure are developed. Implementation of the microbend structure using a flexural acoustic wave is described. The dependences of the acoustic frequency and power requirements on the pertinent fiber parameters are presented.

The numerical solution of the three-dimensional inverse scattering problem for time harmonic acoustic waves

Abstract: The inverse scattering problem under consideration is to determine the shape of an acoustically soft obstacle in $\mathbb{R}^3 $ from a knowledge of the time harmonic incident wave and the far field pattern of the scattered wave. It is assumed that the frequency is in the resonance region, i.e. high frequency asymptotic methods are not available. A method for solving this problem is presented which is based on the theory of Herglotz wave functions and avoids the use of integral equations. Numerical examples are given showing the practicality of this approach.

Nozzleless liquid droplet ejectors

Abstract: A nozzleless print head for ink jet printing and the like comprises one or more essentially planar surface acoustic wave transducers which are submerged at a predetermined depth in a liquid filled reservoir, so that each of the transducers launches a converging cone of coherent acoustic waves into the reservoir, thereby producing an acoustic beam which comes to a focus at or near the surface of the reservoir (i.e., the liquid/air interface). The acoustic beam may be intensity modulated to control the ejection timing, or an external source may be used to extract droplets from the acoustically excited liquid on the surface of the reservoir on demand. Regardless of the timing mechanism employed, the size of the ejected droplets is determined by the waist diameter of the focused acoustic beam. To control, the direction in which the droplets are ejected, provision may be made for producing a controllable acoustical asymmetry for steering the focused acoustic beam in a direction generally parallel to the surface of the reservoir.

On waves in gases. Part II: Interaction of sound with magnetic and internal modes

Abstract: This work completes a two-part review on waves in gases, of which the first part [Rev. Mod. Phys. 58, 117 (1986)] dealt with the modern aspects of acoustics of jets, turbulence, and ducts; this second part extends the range of topics from sound to magnetic, internal, and (to a lesser extent) inertial waves, thus considering all four restoring forces (pressure, gravity, and Lorentz and Coriolis forces). The motivations for the study of these waves were outlined in the introduction to Part I. Part II reviews the coupling of acoustic, magnetic, and internal waves, in four stages: in Sec. I dispersion relations are used to study the propagation and radiation of magneto-acoustic-gravity-inertial waves in media for which the wave speeds and scattering scales are constant; in Sec. II the case of linear waves in stratified media, with nonuniform propagation velocity, is then discussed by means of special functions, appearing as exact solutions of second-order problems; in Sec. III the study of linear waves with variable propagation speeds is extended to certain classes of higher-order problems including a discussion of cutoff frequencies, critical levels, partition of energy, mode coupling and conversion, etc; in Sec. IV the preceding studies are extended to damped and nonlinear waves, to include dissipation with variable damping scales and large disturbances in media under nonuniform external forces, such as magnetic flux tubes. The conclusion (Sec. V) sums up both parts of the review, in the sense that it deals with all types of waves in fluids; it mentions a few currently controversial topics, points out some directions for future research, and indicates methods available to address these issues.

Acoustic wave propagation through porous media with arbitrary pore‐size distributions

Abstract: In the Biot theory, the effect of frequency on the oscillatory viscous forces within a porous medium is treated by replacing the kinematic viscosity ν by an oscillatory viscosity νF. Here, F is a function of angular frequency ω, the kinematic viscosity ν, and the single pore size a. In this paper, a mathematical expression of F is presented for arbitrary distribution of pore sizes that can be used in the Biot theory without modification. It is shown that porous media with a given permeability and porosity may be represented by an infinite number of pore‐size distributions. The dispersion and attenuation of acoustic waves through such porous media are independent of the pore‐size distribution at the low‐ and high‐frequency limits, while they are strongly dependent on the pore‐size distribution in the intermediate frequency range. For porous media with φ‐normal pore size distributions having a given value of permeability, the maximum specific attenuation decreases and the bandwith of dispersion increases wi...

Energy separation in a vortex street

Abstract: When a bluff body is placed in a crossflow, the total temperature in its wake can become substantially less than the incoming one, as manifested by the fact that the recovery factor R on its rearmost surface takes negative values at high subsonic flow: this is the phenomenon referred to here as the Eckert-Weise effect. Although a vortex street has been a suspected cause, the issue of whether this is so, and what the mechanism is, has remained unsettled. In this experimental and theoretical investigation, we first examine the cause of the Eckert-Weise effect by enhancing the vortex shedding through acoustic synchronization: resonance between the vortex shedding and transversely standing acoustic waves in a wind tunnel. At the lowest synchronization, where a ringing sound emanates from the wind tunnel, R at the rearmost section of the cylinder is found to become negative even at a Mach number of 0.2; the base pressure (Cpb) takes dips correspondingly, indicative of the intensification of the vortex street. At this lowest acoustic resonance, the decrease of R and Cpb, uniform along the span, agrees with the expectation based on the spanwise uniformity of the lowest standing wave. At the next acoustic resonance where the standing wave now varies along the span, the corresponding dips in R and Cpb, non-uniform along the span, reveals an interesting ‘strip-theory’-like behaviour of the vortex intensities in the vortex street. These results correlating the change in R with Cpb confirm that the Eckert-Weise effect is indeed caused by the vortex shedding, the mechanism of which is examined theoretically in the latter half of the paper.A simple theoretical argument, bolstered by a full numerical simulation, shows that the time-varying static pressure field due to the vortex movement separates the instantaneous total temperature into hot and cold spots located around vortices; once time-averaged, however, the total temperature distribution conceals the presence of hot spots and takes the guise of a colder wake, the Eckert-Weise effect. Therefore the correct explanation of the Eckert-Weise effect, a time-averaged phenomenon, emerges only out of, and only as a superposition of, instantaneous total temperature separation around vortices. Such a separation is not confined to the outside of vortex cores; every vortex in its entirety becomes thermally separated. Nor is it limited to the far downstream equilibrium configuration of the Karman vortex street but applies to the important near-wake vortices, and to any three-dimensional vortical structure as well. For low subsonic flows in particular, this dynamical explanation also leads to a similar separation of total pressure; these features may thus be potentially exploited as a general marker to identify and quantify vortices.

The Potential of the Bulk Acoustic Wave Device as a Liquid-Phase Immunosensor

Abstract: A summary of previous experiments is presented, which is concerned with partial immersion of bulk and surface acoustic wave devices in liquid media in order to produce chemical sensors. The the- ory of kinetics of antibody-antigen complexation at a planar surface is described together with a qualitative treatmen't of the propagation of acoustic shear waves through the interface between the solid device and the bulk liquid. Surface treatment of a bulk wave crystal by Lang- muir-Blodgett film technology and by silanization is employed to dem- onstrate that the structure of the interface is important in determining the time-dependent frequency of the device. Immobilization of antisera to the crystal-electrode surface by two different methods is used to examine experimentally the response of the device to interfacial reac- tion with an antibody. The future potential of liquid-phase acoustic wave sensors is evaluated.

The electron/electron acoustic instability

Abstract: The electron acoustic wave becomes a normal mode of an unmagnetized collisionless plasma in the presence of two electron components with similar densities, but strongly disparate temperatures. The characteristic frequency of this mode is the plasma frequency of the cooler electron component. If these two electron components have a relative drift speed several times the thermal speed of the cooler component, the electron/electron acoustic instability may arise. This paper describes the parametric dependences of the threshold drift speed and maximum growth rate of this instability, and compares these with the same properties of the electron/ion acoustic instability. Under the condition of zero current, the electron/ion acoustic instability typically has the lower threshold drift speed, so that observation of the electron/electron acoustic instability is a strong indication of the presence of an electrical current in the plasma.

Acoustic wave supressor for Coriolis flow meter

Abstract: A Coriolis-type mass flowmeter in which the flow tube is vibrated at a resonance frequency approximately equal to the frequency for forced or natural vibration in a higher anti-symmetric mode, such as the second mode. In the preferred embodiment the flowmeter is symmetrical and has sections of oval cross-section that provide low bending resistance to the vibration at the points where the amplitude of vibration is the largest. The preferred embodiment uses electronic signal detection/processing means that generates two signals proportional to flow tube velocity in the direction of vibration of equal distance but on opposite sides of the plane of symmetry of the tube, generates a sum and a difference of the two signals, integrates the sum, demodulates the integrated signal and the difference of the two signals to produce peak amplitude signals, and divides the peak amplitude signals to produce an output that is proportional to mass flow rate. The preferred embodiment is further equipped with a novel acoustic wave suppressor, including a bypass conduit and a flexible diaphragm mounted within the flow tube, which suppresses acoustic waves by transmitting them across the diaphragm, thus isolating the flowmeter from the acoustic waves.

Finite-Element Solution of Periodic Waveguides for Acoustic Waves

Abstract: Rights © 1987 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.” IEEE, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 1987, Volume: 34, Issue: 4, page(s): 472477 Type article File Information ITUFFC34-4.pdf

System for marine seismic exploration

Abstract: System for seismic profiling of structures (2) beneath the sea bottom, comprising an acoustic transducer array (12) which synchronously and coherently generates an acoustic wave adapted to be reflected from said structures (2). When the reflected acoustic waves propagate towards the water surface (1), there is caused a perturbation of the electromagnetic reflection coefficient thereof. Receiver means for detection and characterization of the received acoustic field at the surface (1), comprises a radar system (10) illuminating the region concerned of the surface (1) and imposes thereat a number of interferograms each corresponding to the acoustic field from a scattering point given by the position thereof and the frequency of the field. By recording the degree of coincidence between the interferograms and the acoustic perturbation pattern on the water surface (1), the seismic properties of said structures (2) are surveyed.

The inverse scattering problem for time-harmonic acoustic waves in a penetrable medium

Abstract: Probleme de diffusion inverse pour la determination de la forme d'un obstacle diffusant a partir de la connaissance du champ lointain

Combustion-Acoustic Interaction of a Flat Flame Burner System Enclosed Within an Open Tube

Abstract: Previous theories of flame/acoustic interaction have successfully modelled the coupling of acoustic oscillations with combustion zone fluctuations of a flat flame. These theories are now extended to include the effect of (a) finite tube length both upstream and downstream of the burner and (b) the impedance of the burner itself. The inclusion of these effects has led to realistic modelling of some experiments conducted in recent years. In particular it is found that all important is the impedance of the acoustic wave just downstream of the flame. Due to the interaction of the acoustic disturbance with diffusive effects within the combustion zone (which effects are now on the same time scale as an acoustic time period), the phase difference between the pressure and velocity fluctuations can change sign. It is this phenomenon which will precipitate acoustic resonance for flames with upstream and/or downstream ports. A particular mode, determined by the geometry of the system, will induce a positive...

Acoustic waves in alternating fluid/solid layers

Abstract: This article describes the results of ultrasonic experiments made to investigate several features of wave propagation in parallel fluid/solid layer systems and compares the results to theory. Immersion experiments were made at frequencies from 0.2–2 MHz on systems composed of water/Plexiglas and water/aluminum parallel layers. The one wave normal to the layering, and the two waves that can propagate parallel to the layering were both observed. Key experimental results demonstrating anisotropy, wavenumber and frequency stop bands, and phase velocity dispersion are shown that are in agreement with theory. The exact analytical theory based on first principles and the corresponding model experiments have implications leading to a better understanding of Biot’s theory of long wavelength propagation in a fluid saturated porous elastic medium.

Observation of large-amplitude ion acoustic solitary waves in a plasma

Abstract: Propagation of nonlinear ion acoustic waves in a multi-component plasma with negative ions is investigated in a double-plasma device When the density of negative ions is larger than a critical value, a broad negative pulse evolves to rarefactive solitons, and a positive pulse whose amplitude is less than a certain threshold value becomes a subsonic wave train In the same plasma, a positive pulse whose amplitude is larger than the threshold develops into a solitary wave The critical amplitude is measured as a function of the density of negative ions and compared with predictions of the pseudo-potential method The energy distribution of electrons in the solitary wave is also measured

Acoustic well logging method and apparatus

Abstract: An acoustic well logging method and apparatus utilizes a rare earth acoustic transducer to provide low frequency acoustic energy within the borehole, and characteristics of a subsurface geological formation may be obtained, such as the formation permeability by measuring values of the attenuation of the Stoneley waves produced by the rare earth acoustic transducer.

Propagation of Compressive Waves through Fibril Magnetic Fields

Abstract: The surface effects of interactions between the solar 5-min p-modes and the large-scale fibril magnetic field are discussed using a multiple scattering approach. Attention is given to the propagation of linear disturbances in a two-dimensional, highly conducting magnetized plasma with many parallel flux tubes in pressure equilibrium with a surrounding stationary field-free plasma. Multiple scattering in the fibril half-space is shown to generate acoustic waves that cascade to ever-smaller length scales. The scale reduction, proportional to the depth into the fibril magnetic field, is responsible for the damping of p-mode oscillations observed in plages. 39 references.

Estimation of hydraulic fracture geometry from pumping pressure measurements

Abstract: A pump is coupled through a discharge line to a wellbore, which in turn intersects a fracture, the wellbore and fracture being filled with fluid to form a fluid system. Sensors are located in position at the top and, under certain circumstances, at the bottom of the wellbore. The dimensions of the fracture are calculated from data generated by the sensors by analyzing the incident and reflected waves within the fluid system the acoustic waves being generated by pressure pulses from a pump and travel from the pump through the fluid into the fracture. In preferred embodiments of this invention, transfer functions are developed by analysis of the data, so that the data recorded by sensors at the top of the wellbore accurately represent pressure fluctuations at the bottom of the wellbore. Transfer functions relating pressure fluctuations at the top of the wellbore to pressure fluctuations at the bottom of the wellbore, i.e., at the mouth of the fracture, exhibit resonant phenomena in the fracture from which fracture length can be determined. A Fourier transform is generated of transfer fucntions relating the impulse at the top of the annulus to the impulse response at the fracture entrance and through the fracture, to provide a time domain analysis of the waves in the fracture. This way, travel times of waves in the fracture can be determined, and this data used to estimate the length and height of the fracture, given that the wave speed in the fracture is known.

Surface Transverse Wave Mode Analysis and Coupling to Interdigital Transducers

Abstract: The acoustic modes propagating under a surface grating of metal strips are computed for arbitrary cuts, propagation directions, and choices of piezoelectric material. Surface Skimming Bulk Waves (SSBW) which exist in the absence of the metal grating are shown to be trapped at the surface when the grating is present, giving the Surface Transverse Wave (STW) solutions. The relevant physical quantities such as acoustic displacement, scalar potential, electric field, and power density are also computed for these modes. Excellent agreement with experimental results for STW resonators fabricated on rotated Y-cuts of Quartz is shown. Next, the coupling of an unapodized Interdigital Transducer (IDT) to STW’s is analyzed using normal mode theory. The real part of the IDT radiation impedance is calculated directly, and the imaginary part of the impedance is obtained from the real part through a Hilbert transform. Good agreement with experimental results for devices fabricated on rotated Y-cuts of Quartz is demonstrated.

Active suppression of acoustic resonance

Abstract: The minimization of acoustic potential energy has been proposed as a method of actively controlling a harmonic reverberant sound field. In this paper an analysis of plane waves in a finite length duct provides insight into the physical mechanisms of this method and allows comparison with two other methods, the acoustical virtual earth and the absorbing termination. A practical technique of achieving the reduction of acoustic potential energy is presented and discussed.