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Mar 1972

Volume 51, Issue 3B, pp. 881-1112

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Interference Effect in a Multifrequency Ultrasonic Pulse Echo and Its Application to Flaw Characterization

Laszlo Adler and H. L. Whaley

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 881-887 (1972); (7 pages) | Cited 1 time

Online Publication Date: 11 Aug 2005

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The dependence of spectral variations within a reflected broad‐band ultrasonic pulse on the size and orientation of the reflector was determined experimentally. An analytical model is developed on the assumption that interference of the waves received from the edges of the reflecting surface is responsible for the variations of the received frequency spectra. It explains the experimental results very well. The feasibility of determining the size and orientation of hidden flaws in metals by this method is demonstrated.

Diffraction of a Gaussian Light Beam by Ultrasonic Cylindrical Standing Waves

L. E. Hargrove

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 888-893 (1972); (6 pages)

Online Publication Date: 11 Aug 2005

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A theory is developed for the farfield diffraction of a Gaussian light beam that passes axially through an ultrasonic cylindrical standing wave. The approach is applicable only in the range of parameters for which the ultrasonic perturbation may be characterized as an axially symmetric phase grating. Although the diffraction integral is not completely integrated in terms of known functions, some useful expressions for the average and time‐dependent light intensities are obtained. This acousto‐optic interaction geometry, with the light‐beam waist diameter equal to the first nodal diameter in the ultrasonic field, comprises an effective light modulator. Calculations of the on‐axis time‐dependent light intensity are presented and are confirmed by experimental results.

The Use of High‐Power Ultrasonics (Macrosonics) in Studying Fatigue in Metals

Warren P. Mason and Douglas E. MacDonald

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 894-899 (1972); (6 pages) | Cited 5 times

Online Publication Date: 11 Aug 2005

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High‐power ultrasonics has been a useful tool in studying fatigue in metals, since a large number of cycles can be obtained in a small time. In the case of brass and iron the mechanisms appear to differ with frequency, since at the high frequencies fatigue occurs in isolated regions whereas at the low frequencies the slip is generally spread over the grains. The same mechanism can be produced at high frequencies by going to higher temperatures. In iron the stress required for fatigue at higher frequencies is considerably less than for low frequencies. Recent measurements in titanium have shown that the required stress is about the same for high and low frequencies. The crack propagation velocity, however, is much faster at the ultrasonic frequencies. This was proved by striation measurements with a scanning electron microscope. Thus, the high‐frequency fracture is not only localized, it is virtually catastropic in the localized area.

17‐Moment Theory of Sound Propagation in Polyatomic Gases

Francis J. McCormack and Harold W. Creech

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 900-909 (1972); (10 pages) | Cited 2 times

Online Publication Date: 11 Aug 2005

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The problem of combined translational and internal relaxation of sound waves in polyatomic gases is studied using the 17‐moment approximation. When applied to the sound problem, the moment equations, which are valid for any number of internal degrees of freedom, yield a generalized complex matrix eigenvalue equation which is solved numerically for the absorption coefficient and propagation speed as a function of the rarefaction parameter (the approximate ratio of collision frequency to sound frequency). The physical parameters in the equations are the self‐diffusion coefficient (assumed the same for each internal mode), the internal relaxation times, and the internal specific heats. Our solutions for the combined absorption for the case of a single internal mode are compared to those obtained assuming the total absorption is the sum of that due to the translational and internal effects separately, and to that obtained by using the combination rule of Greenspan. Comparison is also made between the combined dispersion calculated by the 17‐moment method and the Greenspan rule. In addition, absorption curves are calculated for the case of two internal degrees of freedom for various combinations of internal collision numbers. When applied to rotational relaxation in N2 our theory yields, for a rotational collision number of 5.26, good agreement with experiment over the range of values of the rarefaction parameter for which a continuum theory is expected to be valid.

An Amplifier Gain Control for Ultrasonic Pulse‐Echo Measurements

Robert W. Reed, David E. Binnie, and F. G. Brickwedde

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 910-915 (1972); (6 pages)

Online Publication Date: 11 Aug 2005

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An automatic gain control (AGC) for maintaining constant gain of the i.f. amplifiers in an ultrasonic pulse‐echo system is described. The AGC stabilizes the receiver against long‐term drifts. It is applicable if the duty cycle of the sonic‐echo train is small (5% or less) and the rest of the cycle is available for introduction of a reference signal. The AGC samples the amplified reference signal and keeps its level constant, thereby maintaining constant gain in the i.f. amplifiers without the necessity for using an additional gated integrating amplifier. The AGC improved the reliability of measurements of sonic‐echo voltage from ±3% without the AGC to ±0.5% with the AGC over a long period of time. The total ultrasonic system for attenuation measurements in the range 20–500 MHz, including the AGC, is described.

Formulation of Wave Equation for Calculating Velocity of Sound in Suspensions

Avtar S. Ahuja

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 916-919 (1972); (4 pages) | Cited 3 times

Online Publication Date: 11 Aug 2005

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A wave equation for the propagation of sound in suspensions or emulsions has been formulated from the simple considerations of mass and momentum balances on a sufficiently small homogeneous and compressible volume element of the suspension in the sound field. The induced masses of the non‐neutrally buoyant oscillating particles and the adiabatic compressibilities of suspension components have been shown to modify the equations of continuity and momentum and thereby the wave equation, with respect to those equations for the single‐phase suspending fluid. A formula for the velocity of sound in suspensions has been deduced, which agrees with that derived from the scattering theory.

Schlieren Visualization of Radiation Caused by Illumination of Plates with Short Acoustical Pulses

Louis R. Dragonette

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 920-935 (1972); (16 pages) | Cited 2 times

Online Publication Date: 11 Aug 2005

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Schlieren visualization of the radiated field in water above and below aluminum plates, illuminated by short acoustic pulses, is presented. At certain angles of incidence of the incoming pulse, radiated wavefronts are seen to progress along the plates with specific angles of inclination and associated speeds of progression. In particular, strong effects are observed near the longitudinal and shear critical angles. The measured angles of incidence, at which these effects were generated, are in good agreement with predictions of Lamb theory for plates whose thicknesses are 0.58 wavelengths and larger. For thinner plates, the effects of water loading appear to become significant. A path trace analysis gives good agreement with the group velocity of observed effects when obvious trapped propagation paths are suggested by the reflection coefficient curves for a water‐aluminum boundary. Specific radiated wavefronts on plates are related to waves which were observed on cylindrical shells. Relationship of the shell results to Lamb modes is discussed. Plates with thicknesses from 0.002 to 0.241 cm, and frequencies of 5 and 7.2 MHz, are used.

Radiation Resistance of a Baffled Beam

C. E. Wallace

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 936-945 (1972); (10 pages) | Cited 3 times

Online Publication Date: 11 Aug 2005

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The radiation resistance of a beam is theoretically determined from the total acoustic power radiated into the farfield. The beam is supported in an infinite baffle, with both hinged and clamped supports considered. Asymptotic solutions are derived for frequencies well below the critical frequency. Curves, covering the entire frequency range between the low‐ and high‐frequency asymptotic solutions, are obtained through numerical integration for the first ten modes of beams with various width‐to‐length ratios. For frequencies well below the critical frequency, the ratio of the radiation resistance of a beam clamped at each end to that of a beam hinged at each end is 0.851 for the first mode, 0.711 for the second mode, and asymptotically approaches 2 as the mode number tends to infinity. For both hinged and clamped supports, the radiation resistance of all modes increases with the beam width‐to‐length ratio.

Radiation Resistance of a Rectangular Panel

C. E. Wallace

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 946-952 (1972); (7 pages) | Cited 21 times

Online Publication Date: 11 Aug 2005

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The radiation resistance corresponding to the natural modes of a finite rectangular panel is theoretically determined from the total energy radiated to the farfield. The panel is assumed to be simply supported in an infinite baffle. Asymptotic solutions for the low‐frequency region are derived, and curves covering the entire frequency range for various mode shapes and aspect ratios are obtained through numerical integration. When the ratio of the acoustic wavenumber to the panel wavenumber is a constant much less than unity, the radiation resistance for all modes is a minimum if the intranodal area (the area between adjacent node lines) is square, and increases with the aspect ratio of the intranodal area.

Flexural Vibrating Free‐Edge Plates with Stepped Thicknesses for Generating High Directional Ultrasonic Radiation

Alfonso Barone and Juan A. Gallego Juarez

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 953-959 (1972); (7 pages) | Cited 3 times

Online Publication Date: 11 Aug 2005

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A transducer for the generation of high directional ultrasonic radiation in fluids is studied. It consists of a plate of particular shape set in oscillation by an adequate vibrator. Since the directional pattern depends substantially on the phase with which the single elements of the plate vibrate, the radiating surface is shaped into steps covering areas vibrating with the same phase, the height of the steps being equal to a half‐wavelength of the radiated sound, in order to obtain a coherent acoustic radiation. To facilitate the design of such plates, an approximate theory of their vibration is shown, and the experimental proofs, whose results confirm the full validity of the adopted method, are described.

Driven Nonlinear Oscillations of a String

Anthony I. Eller

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 960-966 (1972); (7 pages)

Online Publication Date: 11 Aug 2005

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Nonlinear vibrations of a string may become unstable when the string is driven with sufficient amplitude near resonance. This paper describes the experimental conditions under which transverse oscillations of a horizontal string, driven in the vertical plane, become unstable. It is found that the planar oscillations become unstable in two different ways. One instability involves a spontaneous growth or decrease in the amplitude of the driven vertical motion. The other instability involves the spontaneous appearance of a transverse horizontal component of vibration perpendicular to the driving force, thus leading to a whirling or nonplanar motion of the string. The paper also describes the response of the nonplanar mode of oscillation, and it is found, for example, that for certain conditions the driven vertical component of oscillation decreases in amplitude when the driving level is increased. The experimental results agree qualitatively with theoretical predictions based in part on the work of Anand [J. Acoust. Soc. Amer. 46, 667–677 (1969)].

Large Deflections of Impacted Helical Springs

James W. Phillips and George A. Costello

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 967-973 (1972); (7 pages) | Cited 2 times

Online Publication Date: 11 Aug 2005

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A theoretical formulation of the large deflections of helical springs is given, and coupled nonlinear equations of motion for a typical spring element are derived. Linearized forms of these equations are solved numerically and compared with experimentally obtained streak photographs of an impacted spring. The agreement between theory and experiment is good, as long as adjacent coils of the spring do not touch.

The Response of a Plate Bonded to a Randomly Vibrating Viscoelastic Half‐Space

Paul J. Remington

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 974-984 (1972); (11 pages)

Online Publication Date: 11 Aug 2005

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The response of an infinite Bernoulli‐Euler plate placed on the surface of a randomly vibrating viscoelastic half‐space is calculated, allowing for the presence of shear stresses between the plate and the half‐space. The shear stresses arise from the condition that the relative motion between the plate and the half‐space vanishes at the interface. The three components of displacement of the free surface of the half‐space before the plate is added are assumed to be stationary homogeneous random functions of position and time. From the wavenumber‐frequency spectra of these displacements the frequency spectra of the three components of displacement of the plate half‐space interface are calculated. As an example, the frequency spectrum of the vertical interface displacement is calculated for two assumed forms of the wavenumber spectra of the free‐surface displacements.

Damping Additions for Plates Using Constrained Viscoelastic Layers

Peter J. Torvik and Daniel Z. Strickland

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 985-991 (1972); (7 pages) | Cited 1 time

Online Publication Date: 11 Aug 2005

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An analysis is given for a damping addition employing several thin viscoelastic sheets and thin metallic layers. The damping layers are alternated with the constraining layers, which are segmented and are not anchored to the base plate. The effectiveness of such additions in increasing the damping of thin simply supported square plates is evaluated and methods for optimizing the design are considered. An experimental investigation of the effectiveness of such damping additions is also reported. Additions weighing a few percent of the weight of the base plate were found to produce substantial increases in the damping of the system. A nonoptimal design was found to produce less, but still substantial, damping.

The Past Twenty Years in Underwater Acoustics: Introductory Retrospection

F. V. Hunt

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 992-993 (1972); (2 pages)

Online Publication Date: 11 Aug 2005

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On the Medium from the Point of View of Underwater Acoustics

Alan Berman and Albert N. Guthrie

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 994-1009 (1972); (16 pages)

Online Publication Date: 11 Aug 2005

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This paper gives a brief survey of the state of knowledge in ocean acoustics circa 1948 and reviews the advances made during the past two decades. Twenty years ago the thermostructure of the ocean was known in moderate detail. while the character of the boundaries could be specified less precisely. A principal deficiency was in the ability to handle a mathematical model of the ocean which would give a prediction of the acoustic field in detail. While much remains unknown today, the past 20 years have seen a considerable accumulation of knowledge concerning the geographic and seasonal variations of the medium. Reasonably good specifications of the ocean boundaries are now available. The acoustic absorption coefficient in the ocean is known imperfectly, and the ability to specify the thermo microstructure is poor. Nonetheless, the intensive efforts of many investigators over the last 20 years have yielded a computational capability which now allows a general specification of propagation in relatively great detail.

Review of Underwater Acoustics Research: Noise

Gordon M. Wenz

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 1010-1024 (1972); (15 pages) | Cited 2 times

Online Publication Date: 11 Aug 2005

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The purposes, problems, and progress of radiated noise, self‐noise, and ambient noise research are reviewed. Purposes are related primarily to national defense, but applications to fishery and to the utilization of other natural resources are also noted. Basic problems, most of which were recognized 20 years or more ago, involve ascertainment of properties of the noise, identification of noise sources and mechanisms of noise generation, and the discovery and definition of noise dependencies on environmental factors. Many radiated and self‐noise sources and mechanisms have been identified. Major problems are those of noise measurement, noise reduction, and prevention. In the field of ambient noise, most measurements have been of sound‐pressure level. Some of the noise sources and environmental factors have been identified, and a capability for qualitative and gross prediction has been achieved. Recommended are further investigations of the variation of ambient noise with receiver depth, directionality of the noise field, statistics of both noise level and instantaneous noise values, additional work at frequencies below 10 Hz, and additional geographic coverage, making full use of current knowledge to fashion models for experimental guidance. Challenging problems exist in procedures and instrumentation for noise studies.

Twenty Years in Underwater Acoustics: Generation and Reception

T. F. Hueter

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 1025-1040 (1972); (16 pages) | Cited 2 times

Online Publication Date: 11 Aug 2005

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Development in the art of transducer design and array configuration has been spurred on mainly by two motivating forces: (1) Extensive research in underwater propagation has established the advantages of increasingly lower frequencies for long‐range detection and localization of targets and noise sources. (2) The advent of new piezoelectric and structural materials and of solid‐state electronic devices has led to substantial improvements in transducer performance with regard to sensitivity, power output, and depth of submersion. Theory has kept abreast with these developments, particularly in handling large arrays with their mutual impedance problems, in pointing to digital multibeamforming techniques, and in revealing the significance of waveform design to detection performance. A few new concepts were born and have won acceptance during this period. These include: the generation of sound by hydroacoustic means, the employment of compliant metal tubes for acoustic focusing and reflection, the exploitation of structural flexing modes for sound radiation, and the use of free‐flooded cavity structures as deep submergence sources. As we continue to adapt our sources and receivers to the ocean's transfer functions, noise patterns, and targets—false and true—there will be an increasing need for fundamental research into the acoustic properties of materials and for field test of experimental acoustic detection systems.

Propagation

A. O. Williams, Jr.

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 1041-1048 (1972); (8 pages)

Online Publication Date: 11 Aug 2005

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These 20 years have seen much progress in understanding of underwater sound propagation. Few new topics have appeared, but far more complex problems can now be handled—in considerable part, thanks to computers. Emphasis has shifted to lower frequencies, longer ranges, and wave‐theoretical methods. We are still limited by extreme variability of the medium and its boundaries, and by a gap of understanding between mechanical—chemical and acoustical properties. Efforts to narrow this gap should continue, as should the search for “invariants” of problems and for statistical theories to match averaged data.

A Review of Reverberation, Scattering, and Echo Structure

Claude W. Horton, Sr.

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 1049-1061 (1972); (13 pages) | Cited 4 times

Online Publication Date: 11 Aug 2005

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The last 20 years have seen a tremendous amount of work in the area of reverberation and scattering. An effort is made to summarize with graphs and charts the amount and nature of this work. Comparisons are made between the results of measurements at sea, measurements with models, and theoretical calculations. Since theoretical solutions of scattering from randomly rough surfaces involve numerous approximations, these different solutions are classified with the aid of tree diagrams so that one can chart a path through the various approximations. Most of the unclassified work on echo structure has been devoted to intensive analyses for targets of relatively simple geometric shape. For example, the sphere and the cylinder (with and without internal structure) still present interesting problems.

The First Twenty Years of Acoustic Signal Processing

Victor C. Anderson

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 1062-1065 (1972); (4 pages) | Cited 1 time

Online Publication Date: 11 Aug 2005

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The decade of the 1950s marks the beginning of acoustic signal processing as a subfield of underwater acoustics. The forerunner, signal recognition, gradually evolved into a unified class of spatial and temporal processing techniques and theory which came to stand on its own. The doctrines that emerged in that decade, such as spectrum analysis, correlation, and multiple beamforming, have continued to grow in sophistication, until we now find methods such as the fast Fourier transform, sequential detection, and adaptive beamforming handed down to us from the 1960s. The milestones of signal processing over the past 20 years present a striking record of progress in that field.

The Logarithmic Dependence of Surface‐Generated Ambient‐Sea‐Noise Spectrum Level on Wind Speed

Wayne W. Crouch and Peter J. Burt

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 1066-1072 (1972); (7 pages) | Cited 2 times

Online Publication Date: 11 Aug 2005

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A mathematical description of ambient sea noise is presented that takes into account the two dominant sources—surface agitation and distant shipping. The contribution from surface agitation is shown to be linearly dependent upon the logarithm of wind speed for depths between 400 and 2500 fathoms at several sites near Bermuda. When this is taken into account, the ambient‐noise data that include both sources can be analyzed to determine the individual levels of the sources. Also, the standard deviations of the two sources can be determined from the standard deviations of the measured levels.

Use of Side‐Scanning Sonar for Contouring Bottom Features

L. L. Greischar and C. S. Clay

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 1073-1075 (1972); (3 pages)

Online Publication Date: 11 Aug 2005

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A side‐looking sonar was used to study bottom features in Lake Mendota, Wisconsin. Interferences between direct and surface‐reflected signals gave a tiger‐striped pattern in the data. This pattern could be approximately interpreted as being the tracings of isoangle contours. However, this simple analysis was precluded by the strong gradients of sound‐velocity profile. Ray traces were used to construct a profile of the interference field. The profile was used to interpret the data. Features having lateral dimensions of 10 m and a few meters depth were contoured. The data was taken when the sonar was about 100 m from the features.

Characteristics of Line and Disk Underwater Sound Transducers in the Near‐ to Farfield Transition Region

C. M. McKinney, K. W. Harvel, and G. E. Ellis

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 1076-1082 (1972); (7 pages)

Online Publication Date: 11 Aug 2005

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The history of the study of radiation characteristics from certain simple apertures, which extends at least from Lommel (1884) to the recent work of Zemanek (1971), is summarized. Theoretical and experimental data concerning resolution, minor lobe behavior, and axial pressure level as a function of range in the near‐ to farfield transition region are presented and compared for a circular disk and a strip line transducer. The use of near‐ to farfield information in transducer calibration, range determination, and sonar design, is discussed.

Helmholtz‐Kirchhoff Theory for Sound Transmission through a Statistically Rough Plane Interface between Dissimilar Fluids

H. Medwin and J. D. Hagy, Jr.

J. Acoust. Soc. Am. Volume 51, Issue 3B, pp. 1083-1090 (1972); (8 pages) | Cited 2 times

Online Publication Date: 11 Aug 2005

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The dependence of sound transmission on the statistics of a randomly rough interface between two dissimilar fluids is studied by use of the Kirchhoff‐Helmholtz integral. Both plane waves and waves from a point source are considered. The analysis is very similar to that of scatter from a randomly rough surface; for example, for low roughness, the transmitted mean‐square pressure is coherent and e−R times the smooth surface value, whereas for large roughness the transmitted sound is incoherent and depends also on the surface correlation length. The critical roughness parameter for transmission is R  =  k22σ2[(c2/c1) cosθ1 − cosθ2]2 where k, c, and θ are the propagation constant, speed of propagation, and angle with the normal, respectively; subscript 1 refers to the incident medium; σ is the rms height of the surface.
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