Showing papers on "Acoustic wave published in 1985"

Surface-wave devices for signal processing

Abstract: 1. Introductory Survey. 2. Acoustic Waves in Elastic Solids. 3. Electrical Excitation at a Plane Surface. 4. Analysis of Interdigital Transducers. 5. The Multi-Strip Coupler and its Applications. 6. Propagation Effects and Materials. 7. Delay Lines and Multi-Phase Transducers. 8. Bandpass Filters. 9. Chirp Filters and Their Applications. 10. Devices for Spread-Spectrum Communications. Appendices. References. Index.

Guided acoustic-wave Brillouin scattering.

Abstract: Forward light scattering by the thermally excited guided acoustic modes of an optical fiber produce numerous narrow lines not predicted by the usual theory of Brillouin scattering. Optical heterodyne detection has been used to resolve the scattering spectrum which begins at about 20 MHz and extends to the detection limit. A simple theory quantitatively accounts for the frequencies, polarizations, and intensities of the components. The light scattering from these modes constitutes a thermal-noise source in optical fibers that may prove significant in other experiments.

Scattering of acoustic waves into Tollmien-Schlichting waves by small streamwise variations in surface geometry

Abstract: By using the triple-deck scaling of Stewartson (1969) and Messiter (1970) it is shown that small but relatively sudden surface geometry variations that produce only very weak static pressure variations can nevertheless produce strong, i.e. O(1), coupling between an externally imposed acoustic disturbance and a spatially growing Tollmien-Schlichting wave. The analysis provides a qualitative explanation of the Leehey and Shapiro (1979) boundary-layer receptivity measurements and is in good quantitative agreement with the Aizin and Poliakov (1979) experiment. It may also explain why small 'trip wires' can promote early transition.

An advanced computational method for radiation and scattering of acoustic waves in three dimensions

Abstract: The method proposed in this paper provides a computational method for implementing the Helmholtz integral formula for acoustic radiation and scattering problems associated with arbitrary shaped three‐dimensional bodies. In particular an isoparametric element formulation is used in which both the surface geometry and the acoustic variables on the surface of the body are represented by second‐order shape functions within the local coordinate system. A general formula for the surface velocity potential and the exterior field is derived. This result is applicable to nonsmooth bodies, i.e., it includes the case where the surface may have a nonunique normal (e.g., at the edge of a cube). Test cases are shown involving spherical, cylindrical, and cubical geometry.

Analysis of Metal-Strip SAW Gratings and Transducers

Abstract: Reflexion d'ondes acoustiques de surface et changements de vitesse causes par des reseaux de rubans metalliques court-circuites

Speed of sound in the solar interior

Abstract: The sound speed of the solar interior is directly determinable on the basis of the frequencies of solar 5-min oscillations, irrespective of solar model, and relying only on a simple asymptotic description of the oscillations in terms of trapped acoustic waves. It is plausible that, by using this asymptotic determination as an initial trial in a more accurate inversion, and imposing constraints of smoothness on the solution resulting from the iteration, a good model representing the large scale structure of the sun which satisfies the observed frequencies may be determined.

Localization of acoustic waves

Abstract: The localization of sound waves moving in a random array of hard scatterers is studied for both two- and three-dimensional systems using a diagrammatic technique. For d=2 acoustic waves are found to be localized for all frequencies with the localization length growing exponentially for both high and low frequencies. For d=3 there are mobility edges at an intermediate frequency and at a high frequency. Between these mobility edges the sound waves are localized. The connection between this problem and quantum-mechanical electron localization is discussed.

Surface acoustic wave touch panel system

Abstract: A system for recognizing and locating a touch induced perturbation of a surface acoustic wave propagating along one of a multiplicity of paths disposed transverse to a predetermined coordinate axis on a surface of a touch panel and for utilizing the magnitude of the perturbation to produce a control effect. The system comprises a substrate having a surface capable of propagating surface acoustic waves and is so characterized that a touch on that surface causes amplitude damping of a surface wave passing through the region of touch which damping is related to touch pressure. A transducer, responsive to touch-perturbated surface waves develops an output signal having a first characteristic indicative of the position of the touch on the substrate surface and having a second characteristic indicative of touch pressure. A control system, which includes a memory and a computer, upon receipt of the output signal, responds to the first characteristic to develop a first control signal reflecting the location of the touch and responds to the second characteristic to develop a second control signal reflecting touch pressure.

Active sound attenuation system with on-line adaptive feedback cancellation

Abstract: An active acoustic attenuation system (2) is provided for attenuating an undesirable output acoustic wave by introducing a cancelling acoustic wave from an omnidirectional speaker (14) at the output (8), and for adaptively compensating for feedback from the speaker (14) to the input (6) for both broad band and narrow band acoustic waves, without pre-training. The feedback path (20) is modeled with a single filter model (40) adaptively modeling the acoustic system (4) on-line without dedicated off-line pre-training, and also adaptively modeling the feedback path (20) from the speaker (14) to the input microphone (10) on-line for both broad band and narrow band acoustic waves without dedicated off-line pre-training, and outputting a correction signal to the speaker (14) to introduce a cancelling acoustic wave.

Time-resolved studies of Nd:YAG laser-induced breakdown. Plasma formation, acoustic wave generation, and cavitation.

Abstract: The use of high intensity ultrashort pulsed laser radiation to produce optical breakdown is an important approach for the surgical treatment of intraocular structures. We have investigated the transient properties of Nd:YAG laser induced breakdown in a saline model using time-resolved spectroscopic techniques. Spatially resolved pump and probe techniques are applied to study the dynamic behavior of the plasma formation, acoustic wave generation, and cavitation processes which accompany the optical breakdown. Measurements of plasma shielding and luminescence indicate that the laser induced plasma forms on a subnanosecond time scale and has a lifetime of several nanoseconds. An acoustic transient is generated at the breakdown site and propagates spherically outward with an initial hypersonic velocity, then loses energy and propagates at sound velocity. Transient heating following the plasma formation produces a liquid-gas phase change and gives rise to cavitation or gas bubble formation. This gas bubble expands rapidly for several microseconds, then slows to reach its maximum size and finally collapses.

Self-focusing of nonlinear ion-acoustic waves and solitons in magnetized plasmas

Abstract: The Zakharov-Kuznetsov equation describing Korteweg–de Vries waves and solitons in a strong, uniform magnetic field is rederived taking space stretching to be isotropic. This equation is then used to investigate nonlinear waves and solitons for long-wave instabilities. A solid angle of instability develops around the plane perpendicular to the magnetic field. For weakly nonlinear waves this angle is very narrow: widening as the amplitude of the nonlinear wave is increased. The soliton wave is unstable for all directions other than parallel to the field. Previous results of other authors, limited to solitons and perpendicular propagation are recovered. Calculations are illustrated by polar diagrams for the perturbations. Some broader implications are pointed out.

Surface Acoustic Waves

Abstract: In 1887 Lord Rayleigh(1) showed that a semi-infinite, isotropic, elastic medium, bounded by a single, stress-free, planar surface, can support surface vibration modes that are wavelike in directions parallel to the surface of the solid, but whose amplitudes decay exponentially with increasing distance into the solid from the surface, with a decay length that is of the order of the wavelength of the wave along the surface. The displacement vector of these waves lies in the sagittal plane, i.e. in the plane defined by the direction of propagation of the wave and the normal to the surface. These waves are acoustic waves in that their frequencies are linear in the magnitude of the two-dimensional wave vector characterizing their propagation along the surface. They are consequently non dispersive, i.e. their speed of propagation is independent of their wavelength parallel to the surface, which is due to the absence of a characteristic length in the system under consideration. Their frequencies also lie below the continuum of frequencies allowed the normal vibration modes of an infinite elastic medium for the same value of the two-dimensional wave vector. Such surface acoustic waves are now known as Rayleigh Waves.

Touch control system for controllable apparatus

Abstract: A system for recognizing touch positions along an axis on a surface associated with a touch control apparatus comprises a substrate having a surface capable of propagating surface acoustic waves and so characterized that a touch on that surface causes a perturbation of a surface wave passing through the region of touch. An input surface wave transducer coupled to the substrate surface launches a burst of surface waves on the surface. An output surface wave transducer coupled to the substrate detects received surface waves. Wave redirecting gratings derive wave components from the launched wave and redirect them across the substrate surface to the output transducer. The wave components are caused to traverse the axis along a progression of paths associated with different touch positions along the axis. Circuitry coupled to the input and output transducers initiates surface wave bursts across the substrate surface and detects touch-induced perturbations of the received waves indicative of the location of a touch along the axis.

Dynamics of an expanding fluid-filled crack

Abstract: The dike intrusion mechanism proposed recently by B. R. Julian and his colleagues for several large earthquakes at Long Valley caldera has stimulated new interest in the mechanics of fluid injection. This study is an attempt to resolve some of the questions raised by this interpretation by numerically simulating the dynamics of a propagating fluid-filled crack. The computations are based on the two-dimensional finite difference method applied by Aki and coworkers to a similar problem of a fluid-driven crack. We extend this earlier study by improving the boundary conditions applied in the plane of the crack and by analyzing a crack containing a viscous fluid that supports acoustic wave propagation. The problem has two time scales: the duration of the rupture, which is proportional to the distance the crack propagates, and the period of the acoustic resonance of the fluid, which is a function of the length of the crack and the acoustic velocity in the fluid. For a small extension of a long crack containing a fluid of low bulk modulus, these time scales are markedly different. The initial motion of the walls near the propagating crack tip is directed outward, so the radiated first motion is compressive everywhere. The increase of the crack tip volume, however, induces a pressure drop in the fluid which propagates over the length of the crack with the velocity of the acoustic wave, causing a partial collapse of the wall radiated as a long-period dilatation. The dilatation following the short compressional first arrival is well marked in the vicinity of the crack plane, and for a buried vertical crack it is a conspicuous feature of the near-field vertical ground motion close to the crack trace. These properties of the signal suggest that first motion studies of this frequency-dependent source may be delicate without broadband instruments. Inhomogeneous waves propagating at the liquid-solid interface produce high-frequency vibrations which are observed only in the immediate vicinity of the crack. The source duration depends strongly on the fluid viscosity and associated viscous damping at the crack wall; damping of the motion by the radiation of elastic waves is a comparatively small effect.

Touch control arrangement for graphics display apparatus

Abstract: A system for recognizing touch positions along a coordinate axis on a surface associated with a touch control apparatus comprises a substrate having a surface capable of propagating surface acoustic waves and is so characterized that a touch on that surface causes a partial absorption of energy of a surface wave passing through the region of touch. An input surface wave transducer coupled to the surface launches a burst of surface waves on the surface in a first direction parallel to the axis. An output surface wave transducer coupled to the surface receives the burst of surface waves. A first surface wave reflecting arrangement derives wave components from the launched wave and reflects them across the surface to a second wave reflecting arrangement that redirects the reflected components in a direction opposited the first direction. The reflecting arrangements collectively cause wave components to traverse the surface orthogonally to the coordinate axis along a progression of paths associated with different positions along that axis. Circuitry coupled to the input and output trnasducers initiate surface wave bursts across the substrate surface as well as dsetect touch-induced damping of the received waves. A detector serves to develop an electrical signal representative of the time occurrence of the damping and thus an indication of which of the plurality of paths was traversed by the touch-damped wave and thereby the location of the touch on the substrate surface.

Diffuse elastic waves at a free surface

Abstract: For a diffusely vibrating elastic body, the participation of the surface in the general disturbance is evaluated. It is shown that in the vicinity of a free surface a diffuse acoustic field may legitimately be regarded as a sum of incoherent isotropic and homogeneous independent plane waves incident upon the surface together with their respective outgoing reflected consequences. The work contributes to a conceptual basis for the study of acoustic emission signals on time scales large compared to acoustic travel times across the structure.

On Tollmien-Schlichting Wave Generation by Sound

Abstract: It is well known that acoustic disturbances incident upon the boundary layer may cause Tollmien-Schlichting waves. An intense generation of these waves is observed in local inhomogeneities of the flow [1]. To investigate this phenomenon we shall consider a two-dimensional gas flow about a flat plate directed along a free-stream flow (fig.1). The free-stream velocity U∞ is taken to be subsonic with M < 1. Introduce cartesian coordinates x′, y′ aligning their origin with the plate leading edge and orienting x′ along the plate surface. Denote velocity vector components in this coordinate system by u′ and v′, density by p′, and viscosity coefficient by μ′ . Let the gas under consideration have an adiabatic constant r and its thermodynamic state be described by the Clapeyron equation.

Waveform synthesis of surface waves in a laterally heterogeneous Earth by the Gaussian Beam Method

Abstract: The present investigation is concerned with an application of the Gaussian beam method to surface waves in the laterally heterogeneous earth. The employed method has been developed for ray tracing and synthesizing seismograms of surface waves in cases involving the laterally heterogeneous earth. The procedure is based on formulations derived by Yomogida (1985). Vertical structure of the wave field is represented by the eigenfunctions of normal mode theory, while lateral variation is expressed by the parabolic equation as in two-dimensional acoustic waves or elastic body waves. It is demonstrated that a large-amplitude change can result from a slight perturbation in the phase velocity model.

Temperature Compensated Piezoelectric Lithium Tetraborate Crystal for High Frequency Surface Acoustic Wave and Bulk Wave Device Applications

Abstract: All dielectric, elastic and piezoelectric constants, and their first and second order temperature coefficients have been newly determined. Based upon these data set, Rayleigh SAW, leaky SAW and bulk wave properties have been studied for the various orientation and propagation from theoretical and experimental points of view. Both theoretical and experimental results have shown that Rayleigh SAW possesses a particularly useful cut with the zero temperature coefficient of delay (ZTCD) at (oO,~~O,~OO). A new temperature-compensated leaky SAW orientation has been located around (Oo,750,750) with vs of 4120m/s and k = 1.6%. Further it has been conf irmedj, theoretically

The measurement of acoustic noise generated by moving artificial sediments

Abstract: Laboratory measurements relating to the acoustic detection of marine sediment transport are reported. A series of underwater measurements have been conducted on agitated artificial sediments, and the acoustic noise generated by interparticle collisions monitored. Measurements of the total acoustic pressure and spectral pressure levels were made on a wide range of particle diameters for different values of the mass of agitated material, the collision velocities, and the swept bandwidth of the spectrum analyzer. The objective was to relate the total pressure level to the mass of mobile material and ascertain if there was an acoustic spectral signature unique to particle size. This information could then be used to guide the interpretation of acoustic measurements of bedload transport taken in the marine environment and provide specifications for the development of an acoustic system to monitor remotely the material moving along the seabed.

Far UV pulsed laser melting of silicon

Abstract: Calorimetric, acoustic, and morphological studies of silicon irradiated with intense 14‐ns, 193‐nm excimer laser pulses are reported. To within the experimental uncertainty, the entire radiation absorbed is converted to heat at all fluences. The volume changes on melting leads to enhanced acoustic wave generation. The morphology of the surface damage is consistent with the existence of both standing surface acoustic waves and of capillary waves.

Apparatus for locating passive intermodulation interference sources

Abstract: An apparatus for locating passive interference sources by using a pair of different RF signals in conjunction with an acoustic signal to generate intermodulation products in metal-to-metal junctions. The acoustic tagging technique utilizes a focused, high power beam of acoustic energy to mechanically vibrate the suspected offending junction. This mechanical vibration causes the level of intermodulation products that are generated in the junction to become amplitude modulated at the frequency of the acoustic illumination. The detection of the AM sidebands with a low noise RF receiver that is tuned to a particular intermodulated component, permits the offending junction to be located.

Cathode ray tube for use in a touch panel display system

Abstract: A cathode ray tube for use in a touch panel system that is capable of recognizing touch positions along a coordinate axis of a touch display surface of the system has a flat glass faceplate capable of propegating surface acoustic waves. An input surface wave transducer, acoustically coupled to the touch display surface, serves to launch a burst of surface waves on that surface. At least one array of wave reflective elements are disposed in or on the touch display surface for directing the surface waves derived from the input trasnducer across the touch display surface.

Receiver for a spread spectrum communication system having a time-multiplexed convolver

Abstract: A convolver having at least a first interdigital transducer for generating a first surface acoustic wave in response to an input signal and a second interdigital transducer for generating a second surface acoustic wave counter to the first surface acoustic wave in response to a time reversed-time multiplexed reference signal. A segmented summing bus having a plurality of fingers extending into the interaction region of the first and second surface acoustic waves generates a plurality of samples indicative of the convolution of the first and second surface acoustic waves. The convolver also includes a pair of acoustic horns, one disposed between the segmented summing bus and each of the interdigital transducers and a ground bus having a plurality of filler segments extending intermediate the fingers of the segmented summing bus.

Path-Integral Treatment of Acoustic Mutual Coherence Functions for Rays in a Sound Channel,

Abstract: The mutual coherence function (MCF) of the acoustic wavefunction from a point source is derived by the path‐integral technique for transmission in the presence of a sound channel. Separations in time, transverse horizontal position, vertical position, and acoustic frequency are treated. Approximate coherence times, lengths, and bandwidths due to internal‐wave fluctuations are derived. The MCF of frequency is explicitly evaluated for fluctuations due to internal waves. The shape of an ensemble‐averaged pulse is derived from the MCF of frequency.

Ocean acoustic tomography: Travel time biases

Abstract: The travel times of acoustic rays traced through a climatological sound-speed profile are compared with travel times computed through the same profile containing an eddy field. The accuracy of linearizing the relations between the travel time difference and the sound-speed deviation at long ranges is assessed using calculations made for two different eddy fields measured in the eastern Atlantic. Significant nonlinearities are found in some cases, and the relationships of the values of these nonlinearities to the range between source and receiver, to the anomaly size associated with the eddies, and to the positions of the eddies are studied. An analytical model of the nonlinearities is discussed.