Showing papers on "Acoustic source localization published in 1980"

On the simulation of sound localization.

Abstract: Sound localization both in the horizontal and the median planes was simulated by the aid of a digital computer through two loudspeakers located in the traverse plane. The simulation was performed by the use of the measured head-related transfer function (HRTF) for two ears. Results of localization tests of three subjects with different sized pinnae show that:(1) When the subject's own HRTF was used in the simulation, natural sound localization in both planes can be performed with the same accuracy as real sound sources.(2) The differences between individual HRTFs affect the accuracy of localization in the simulation. In particular, in the median plane, an HRTF with a high angle-dependency seems to be more advantageous than one with a low angle-dependency.

Sound velocity of supercooled water down to -33 °C using acoustic levitation

Abstract: The sound velocity in supercooled water has been measured at 54 kHz down to −33 °C by means of an acoustic levitation method. The accuracy of the results is estimated to be within ±1.3%. Comparison with published data obtained at 5 GHz and 925 MHz indicates an anomalous sound velocity dispersion.

Coupling of airborne sound into the earth: Frequency dependence

Abstract: Simultaneous measurements have been made of sound pressure above the ground and seismic velocity below the ground surface resulting from a source suspended in the air a variable distance from the surface. The ratio of seismic velocity to acoustic sound pressure has been determined; there are peaks in the ratio in the vicinity of 45 and 90 Hz depending on the height of the speaker. The source–receiver distance was 10, 30, and 60 m; the source height was varied between 1 and 10 m. The frequency of maximum acoustic coupling was found to agree well with theory; the first and third shear modes appear to be excited. Results for vertical, horizontal, and radial motion indicate the coupled seismic signal is greatest for vertical, next greatest for radial, and least for transverse, though the difference between radial and vertical displacement velocities was not great and depended on the speaker altitude.

Sound-emission locator and analyser for non-destructive testing - has test head containing acousto-electric transducers to determine direction of incident sound pulses

Abstract: The position of the sound sourceis determined from the arrival of sound pulses at different measurement points. The moment in time when a pulse or pulse-like feature arrives at each of three or more adjacent sections (1) within each measurement point is measured, The differences in the times of arrival at the three sections are formed and used to find the direction from which the sound is approaching the place of measurement. The position of the sound source is determined from this direction and from a knowledge of the positional coordinates of the measurement point. Frequency analysis or an analysis correlating directly with the direction of the sound is performed at each measurement point. The signals are filtered or analysed before then are digitised. The measurement point is defined by a test head. The sections consist of transducers within the head. Several such heads may be attached to the component under examination. The outputs of the transducers are amplified (2), digitised (3), the pulses counted (5), and the counts passed to a microprocessor (6). The system handles sound of unknown speed, rapid pulse repetition rate, high noise levels and long transit times.

Precise Measurement of SAW Propagation Velocity on LiNbO 3

Abstract: Minimum l w f u l AI film thickness for SAW interdigital transducers (IDT’s) is described. From the standpoints both of realizing high-performance SAW devices and of achieving precise design, i t is Manuscript received December 11, 1979;revised February 12, 1980. J. Temmyo is with Musashino Electrical Communication Laboratory, sashino-Shi, Tokyo 180, Japan. Nippon Telegraph and Telephone Public Corporation, Midoricho, Mutory, Nippon Telegraph and Telephone Public Corporation, Tokyo, Japan. He is now with the Electrical and Electronics Systems Engineering Course, The Technological University of Nagaoka, Kamitomiokacho, Nagaoka-Shi, Niigata 949-54, Japan. S Yoshikawa was with Musashino Electrical Communication Labora0018-9537/80/0400-0219$00.75 O 1980 IEEE

Use of generalised resolution methods to locate sources in random dispersive media

Abstract: Random dispersive media such as the shallow-water sound channel cause the far field of a point source to be random in time and space. Consequently, resolution methods such as d.f.t., `maximum-likelihood estimator? or`maximum-entropy method? are useful only to a limited extent for estimation of source parameters such as range, bearing or depth. This is because those methods are based on the assumption that the signal wavefront is coherent. The resolution methods can easily be generalised to the situation in which the desired signal is random. A shallow water sound propagation model is used to demonstrate the application of generalised power estimators to the problem of locating point acoustic sources in shallow water.

Sound conversion phenomena at the free surface of liquid helium. I. Calculation of the coefficients of reflection, transmission, and transformation of sound waves incident on the liquid-vapor interface of helium

Abstract: On the basis of a set of boundary conditions describing quite generally mass and energy transport processes across the free surface of helium II, the acoustic coefficients of reflection, transmission, and transformation of first sound, second sound, and the sound wave propagating in the vapor are calculated in the case of perpendicular incidence of sound waves against the liquid-vapor phase boundary. Considering rigorously the influences of the Onsager surface coefficients, the isobaric thermal expansion coefficients, and the thermal conductivities of the liquid and the vapor, we derive sets of equations from which the acoustic coefficients are determined numerically. For estimations, simple explicit formulas of the acoustic coefficients are given. It is shown that the evaporation and energy transport processes occurring at the free surface of helium II due to the incidence of sound waves may be connected with appreciable energy dissipation. The surface absorption coefficients of first, second, and gas sound waves are deduced.

Turning-point convergence-zones in underwater sound channel (i) a normal-mode theory

Abstract: In this paper, by use of the normal-mode method, the sound field of the turning-point convergence-zones in underwater sound channel is treated. Theoretical analysis shows that the sound field of the turning-point convergence-zone is the superposition of a great number of in-phase normal modes. Under certain conditions, the sound intensity at the turning-point convergence-zone is proportional to r-2, the convergence-gain is independent to the order of zone and the width of zone is proportional to the order of zone. These theoretical results are consistent with Hale's experiment. For a bilinear channel, the convergence-gain is where a1 is the relative velocity gradient, k0 is wave number and (ho-z) is distance from channel axis to source. By using the theory on the turning-point convergence-zone, the experimental results in model tank are analysed. Calculated positions of zones, convergence-gains and widths of zones in surface sound channel agree with experimental results.

A moments approach for analyzing geophysical reflection data

Abstract: : This publication presents a new approach developed for analyzing geophysical acoustic reflecting data. The forward problem of estimating source to receiver travel time, and the inverse problem of estimating a sound speed versus depth relationship are addressed using a moments approach. The moments approach provides a simple tool for estimating source to receiver reflection path travel time for a laterally homogeneous medium with an arbitrary sound speed versus depth relationship. The moments approach also provides a useful tool for inverting reflection data to obtain an estimate of the sound speed versus depth relationship. A nearly closed form technique for estimating a linear sound speed versus depth relationship is presented. Derivation of the moments approach and numerical examples are included. (Author)

Sound Propagation in a Shallow Water Region Overlying a Viscoelastic Halfspace

Abstract: Sound propagation in shallow water is investigated using the Green's function and normal mode expansion techniques. The ideal fluid is bounded above by a pressure-release condition and below by a viscoelastic solid. A depth-dependent sound velocity is considered in the fluid column. Numerical results are evaluated using a digital computer to perform the calculations determined by the theory. The input parameters are chosen from the conditions described at an experimental site in the Baltic Sea. The output is in the form of a plot of transmission loss versus horizontal source-receiver separation distance. The computer simulation agrees qualitatively with the experimental results and demonstrates the importance of the bottom boundary composition on the attenuation of the sound. The authors' approach to the bottom boundary condition incorporates the concept of impedance and hence is very general in application.

Beamforming when the sound velocity is not precisely known

Abstract: Beamforming is an integral part of most signal processing systems in active or passive sonars. The delays used to generate a beam are functions of the sound velocity, which depends on temperature, salinity, and pressure. There is a loss in array gain if the delays are incorrectly set. This will occur when the sound velocity in the water surrounding the hydrophones is different from the velocity that was used to set the delays. This paper makes two points: (1) fixed delay line sonars suffer a loss in gain when the true sound speed in the water is different from the velocity that is used to set the delays, and (2) there are signal processing techniques for two‐ or three‐dimensional arrays that yield source bearings that are independent of the true sound velocity. These techniques require variable time delays, which can be realized using digital processing.

Sound Diffraction And The Optimizing Of Acousto-Optic Modulator Efficiency

Abstract: The sound diffraction profile due to the rectangular electrode of an acousto-optic cell has been computer modeled, with specific attention to the sound profile in the direction orthogonal to light and sound propagation. The profile is uniform only immediately adjacent to the transducer, which is too close for effective light interaction. Effective interaction can occur only when the light beam is at least 1 or 2 millimeters away from the transducer, where the sound field exhibits Fresnel near field fluctuations in sound intensity, corresponding to regions of constructive and destructive interference. The light beam should fit within a region of constructive acoustic interference to optimize the acousto-optic coupling. A deflector requires changing acoustic carrier frequency and therefore changing near-field acoustic profile. The light beam must be located in a region of reasonably uniform sound intensity for all carrier frequencies. A simple experimental method has been developed to test these results, consisting of Schlieren imaging onto a CCD linear array.© (1980) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Sound propagation in a temporally varying waveguide

Abstract: The effects of temporal variations of the sound velocity on acoustic propagation from a time periodic point source in a layer of uniform depth h are studied. It is assumed that the sound speed is a slowly varying function of time, and that the upper and lower surfaces of the layer are free and rigid, respectively. An asymptotic expansion of the acoustic pressure field is obtained by using the methods of normal modes, two times and stationary phase evaluations of multiple integrals. The small parameter e that is used in the analysis is the ratio of the time scale of variation of the sound velocity to the frequency of the source. To lowest order in e, the acoustic pressure is given by the sum of a primary wave and a secondary wave. The primary wave consists of a finite modal sum of propagating waves and an infinite modal sum of evanescent waves. If the dimensionless sound speed oscillates about the value 1/am, where am is the propagation number of the mth mode, then the mth mode alternates between propagati...

Acoustic impedance measurement using constant volume velocity

Abstract: For determining acoustic impedances the direct methods are now often used, based on measuring the sound pressure excited on a measured object by the known volume velocity. With the sine sweep technique it is easily possible to maintain, with sufficient accuracy, the generated volume velocity constant. When using direct methods at higher frequencies gross errors can arise from the sound field inhomogenities in the coupling space among the sound source, the measuring microphone, and the measured object. For some coupling configurations it is, however, possible to find acceptable relations between the measured and the sought values.

A technique for measuring the sound velocity difference in two liquids

Abstract: A new technique for measuring the sound velocity difference in two liquids is presented by using interdigital transducers in contact with the liquids. The phase difference between two delayed signals obtained at the output transducers, corresponding to the sound velocity difference, is converted to a dc voltage via a circuit with a function of phase comparation. As an example, the difference between the sound velocity in solutions of NaCl and that in water is given as a function of concentration. Basic design considerations for the device and experimental performance are given.

Transmitted sound field due to an impulsive line acoustic source bounded by a rigid plate followed by a vortex sheet

Abstract: The propagation of sound due to a line acoustic source in the moving stream across a semiinfinite vortex sheet which trails from a rigid plate is examined in a linear theory for the subsonic case. A solution for the transmitted sound field is obtained with the aid of multiple integral transforms and the Wiener-Hopf technique for both the steady state (time harmonic) and initial value (impulsive source) situations. The contour of inverse transform and hence the decomposition of the functions are determined through causality and radiation conditions. The solution obtained satisfies causality and the full Kutta conditions. The transmitted sound field is composed of two waves in both the stady state and initial value problems. One is the wave scattered from the edge of the plate which is associated with the bow wave and the instability wave. These waves exist in the downstream sectors. The other is the wave transmitted through the vortex sheet which is also associated with the instability wave. Regional divisions of the transmitted sound field are identified.