bluuebunny/crossref_metadata_2025 huggingface dataset:
High Power Operation of a Magnetostrictive Transducer
Authors: Hoover R. M.
Published: September 2005

As a result of the nonlinear properties of magnetostrictive transducers their impedance and efficiency is a function of the amplitude of the driving field. Earlier studies of high power operation of magnetostrictive transducers at the Harvard Underwater Sound Laboratory showed the need for further study of this subject. This earlier study has been extended by the use of a high power amplifier recently installed at the ORL Black Moshannon Calibration Station.

Impedance and efficiency data obtained on a nickel ring stack transducer operated with and without polarization are presented for a driving field range of 0.1 to 100 oersteds. The efficiency of the unpolarized transducer is shown to be comparable to that of the polarized transducer at high driving powers.

Input current wave form was also observed in this study, and data are presented to show the dependence of wave form on current level. With the unpolarized transducer it is shown that the wave form is a function of nonlinear coupling as well as nonlinear magnetic properties.

Both the experimental procedure used in this study, and the importance of the results to transducer operation at high power levels are discussed.
A Systematic Error in Underwater Acoustic Direction-Finding
Authors: Freeman J. J.
Published: September 2005

Postulating a uniform volume distribution of noise sources as a model of ambient ocean noise, the effect of the coherence between noise measured at different locations is examined. The systematic error introduced by this coherence in cross-correlator direction-finding systems is evaluated. Also, the relation of the maximum useful averaging time to the degree of coherence is derived.
Acoustic Measurements in Deep Water Using the Bathyscaph
Authors: Lomask Morton , Frassetto Roberto
Published: September 2005

The Bathyscaph Trieste made a series of dives for scientific purposes in the summer of 1957 in the Mediterranean Sea. Part of the work consisted of simple acoustic measurements in the 10- to 500-cps frequency range, and is herein described. Ambient noise levels were measured with some detail as a function of depth, sea state, and frequency; and pressure levels from a surface source were measured as a function of depth at different ranges, one range before the energy concentrated in the sound channel, and one range afterwards. Finally, the capabilities and limitations of the Bathyscaph as a vehicle for acoustic experiments are discussed.
Ultrasonic Absorption in Castor Oil: Deviations from Classical Behavior
Authors: Wuensch B. J. , Hueter T. F. , Cohen M. S.
Published: September 2005

An excess absorption has been observed in castor oil by pulse propagation measurements. It is most pronounced at the higher temperatures and the lower frequencies of the range investigated.
Theory of Temporal Auditory Summation
Authors: Zwislocki J.
Published: September 2005

A theory of temporal auditory summation is developed and applied to the threshold of audibility for various temporal patterns of pulses and sinusoidal vibrations. The theory is based on the assumption of an exponential decay of neural excitation and, for the threshold of audibility, it includes only one time constant. Various factors that may affect temporal auditory summation are discussed. It is shown that the same theory applies to muscle contractions.
New Method for Measuring Ultrasonic Velocity in Solids
Authors: Menon Sreekandath Gopala
Published: September 2005

A new method for finding ultrasonic velocity in solids is evolved based on Debye-Sears diffraction effects, when a plane wave front of light traverses in succession two ultrasonic fields of the same frequency. The method is applicable to homogeneous solids. transparent as well as opaque, only small specimens being required for the purpose.
An Experimental Pitch Indicator for Training Deaf Scholars
Authors: Anderson F.
Published: September 2005

An instrument is described which extracts from the complex speech wave, as produced by the deaf child or its teacher, information related to the subjective pitch of the sound. It then displays this information on the long-persistence screen of a revolving cathode-ray tube in such a manner that a continuous graph of pitch vs time is obtained. The deaf child is, therefore, enabled to compare visually the pitch patterns produced by its own voice with the standard as produced by the teacher and to correct defects in the pitch changes, rhythm, and phrasing of his speech.

An experimental model of this instrument is being used successfully, but some deficiencies exist which require further study before an improved design can be finalized.
Note on the Equalization and Cancellation Theory of Binaural Masking Level Differences
Authors: Durlach N. I.
Published: September 2005

This note provides a brief introduction to a quantitative theory of binaural masking level differences. A model is proposed for the operations performed by the brain on the received signals and this model is applied to some experimental data.
Does the Hypothesis of the Hydraulic Functioning of the Cochlea Bear on the Definition of Masking?
Authors: Meyer Max F.
Published: September 2005

Application of the theory of hydraulic functioning of the cochlea leads to a distinction between action of a tone upon another tone and action of a noise upon a tone, and confirms the demand for a redefinition of masking.
Air-Stiffness Controlled Condenser Microphone
Authors: Schultz T. J.
Published: September 2005

A very small condenser microphone has been developed which exploits materials and methods of construction only recently made available by the post-war developments in plastics. These techniques have made possible a microphone with extremely regular voltage amplitude and phase responses as functions of frequency and with a reasonably high sensitivity. An analysis is given for the resonance frequencies of a circular membrane stretched over a closed cavity with its center fixed over a small area.
American English Phonemes
Authors: Hamp Eric P.
Published: September 2005

In order to be useful as a basis for frequency tables for American English phonemes, retranscriptions of existing word lists must take account of recent advances in phonemic theory as applied to the study of American English structure, and must be based on freshly recorded utterances representing a significant number of important dialect varieties. Routine assignment of the traditional IPA symbols is inadequate.
Elastic, Piezoelectric, and Dielectric Constants of Polarized Barium Titanate Ceramics and Some Applications of the Piezoelectric Equations
Authors: Bechmann Rudolf
Published: September 2005

A complete set of the elastic, piezoelectric, and dielectric constants of polarized barium titanate ceramics is presented. The various electromechanical coupling factors, as derived from the piezoelectric equations, and their numerical values are also given. The determination of the elastic and piezoelectric constants using the resonant method applied to small bars, square plates, and disks is discussed.
Directional Circular Arrays of Point Sources
Authors: Welkowitz Walter
Published: September 2005

The Fourier series solution for the radiation field of a circular pressure ring is applied to the synthesis of a sound field expressed in the form of a Tchebyscheff polynomial. This leads to an exact solution in closed form for the amplitude and phase of excitation of point source elements on a circle when the main lobe width of the radiation pattern, the side lobe suppression, and the array circle diameter are specified. Calculations are carried out for two sample beam patterns to show the effects of different choices of array circle diameter and number of point source elements.
Response of a Nonlinear String to Random Excitation
Authors: Lyon Richard H.
Published: September 2005

The response of a perfectly flexible string with longitudinal deformation to random excitation is studied in some detail. The equations of motion are essentially those of Carrier [Quart. Appl. Math. 3, 157–165 (1945)]. The modified mean square response for the “elastic” string is discussed and it is shown that the mean square deflection is diminished from the linear case. From a study of the fourth moments, it also appears that the shape of probability distributions of the transverse displacement are altered, the response to gaussian noise being in general nongaussian.
Intelligibility of Diphasic Speech
Authors: Peterson Gordon E. , Sivertsen Eva , Subrahmanyam D. L.
Published: September 2005

This study concerns the intelligibility of speech under various periodic switching operations. In diphasic speech the signal is separated into successive segments which are reversed in phase. The intelligibility of this speech was found to be high for switching frequencies below about 100 cps; in the intermediate audio-frequency region the intelligibility fails to very low values. Throughout this intermediate frequency region, the intelligibility of diphasic speech is markedly less than that of interrupted speech. Some explanation for this difference is found in the Fourier expansion for the two cases. In interrupted speech the original spectrum is retained, but in diphasic speech terms for the spectrum in its normal form do not appear. It was experimentally observed that throughout the intermediate frequency region binaural diphasic speech, in which the signal is switched alternately from one ear to the other, is more intelligible than monaural diphasic speech or interrupted speech.
Periodic Shock Waves in Resonating Gas Columns
Authors: Saenger R. Alfred , Hudson George E.
Published: September 2005

When an oscillating piston forces the enclosed gas in a Kundt tube to vibrate with a finite amplitude near an acoustic resonance frequency of the gas column, shock waves are generated which travel periodically back and forth in the tube. There is also heating of the gas and a rise in its mean pressure. In this paper a theory of the steady state motion of the gas in its “fundamental” mode has been devised which includes the dissipative effects of wall friction and heat conduction to the tube walls. The dependence of shock strength, mean temperature, and mean pressure on piston amplitude, tube length, gas viscosity, and heat conductivity predicted by the theory are in good qualitative agreement with the small number of experimental data available at present.
Identification of Sound Level and “Matching from Sample”
Authors: Pollack Irwin
Published: September 2005

The “identification” and “discrimination” of components of elementary auditory displays are here differentiated in terms of the relative contiguity between the unknown signal and the set of possible signals that may be chosen. Listeners attempted to match arbitrary designations to sound levels of a tone under three conditions of relative contiguity between the unknown sound level and the set of possible sound levels. Significant improvements in matching are associated with increasing contiguity, especially under finely subdivided conditions encompassing a wide range of sound levels.
Contribution to the Theory of Radial Extensional Vibrations in Thin Disks
Authors: Moseley Donald S.
Published: September 2005

The theory of the radial mode of isotropic disks of vanishing thickness is extended to the case of small thickness-to-diameter ratio. Resembling the Rayleigh and Pochhammer-Chree correction to the longitudinal modes of a thin circular bar, the radial mode correction by Pochhammer-Chree method is shown to be {1−16[Rivh/(1 − v)2a]2}, where Ri are the roots of zero thickness disk theory, v is Poisson's ratio, and h/2a is the thickness-to-diameter ratio. Test of this and of a radial mode correction by Rayleigh's energy method has been made with the aid of frequency measurements on weakly prepolarized barium titanate ceramic disks whose h/2a ratios ranged from 0.0276 to 0.1171.
Noise Measurements around Some Jet Aircraft
Authors: Pietrasanta A. C.
Published: September 2005

The noise fields around several jet aircraft have been measured for various engine operating conditions. Directivity patterns as a function of octave bands of frequency are presented. Acoustic power levels have been computed and found to agree with a previously published correlation of power level with engine operating conditions [O. K. Mawardi and I. Dyer, J. Acoust. Soc. Am. 25, 389 (1953)]. Analysis of these data has led to the development of a procedure for estimating the characteristics of the noise fields around non-afterburner jet aircraft operating at military power.
An Estimate of the Effect of Turbulence in the Ocean on the Propagation of Sound
Authors: Knauss John A.
Published: September 2005

A hydrophone monitoring a constant level sound source in the open ocean records a sound whose intensity fluctuates over short periods of time. Previously it has been demonstrated that much of this fluctuation can be accounted for by the temperature microstructure. It has been suggested that another cause of the observed fluctuation could be inhomogeneities the velocity field (turbulence). This paper is an attempt to estimate the magnitude of turbulence in the ocean. The conclusion is reached that turbulence contributes very little to the fluctuation observed in the intensity of underwater sound signals.
Noise Characteristics of Helicopter Rotors at Tip Speeds up to 900 Feet Per Second
Authors: Hubbard Harvey H. , Maglieri Domenic J.
Published: September 2005

Evidence is presented which suggests that the noise of full-scale helicopter rotors results mainly from conditions of unsteady flow. Measurements of the sound-pressure levels and spectra are presented for test conditions where gear train, engine, and other propulsion system noises are minimized. These data cover a range of tip speeds from 100 ft/sec to 900 ft/sec for various rotor disk loadings. Results indicate that both tip speed and disk loading have an important influence on the noise radiated from the rotor. During stall, the sound pressure levels increased at all frequencies, but particularly at the high end of the spectrum. As a matter of special interest, a highly-peaked wave form due to possible doppler effects was noted to be associated with high-tip speed operation.
Vibrational Relaxation in N2O - H2O and N2O - D2O Mixtures
Authors: Wight Howard M.
Published: September 2005

Ultrasonic absorption measurements were made to compare the relative effectiveness of H2O and D2O molecules in influencing thermal vibrational relaxation in N2O molecules. The displacement rates of the absorption per wavelength maxima induced by H2O and D2O were compared in N2O - H2O and N2O - D2O mixtures. Experimental apparatus was constructed for these measurements which utilized the “direct” absorption technique in conjunction with pulsed sound waves, having a frequency of approximately 113 kc. The parameter of frequency/pressure was varied by changing the gas pressure.

The data were taken at a temperature of 21°C in the frequency/pressure range of 100–700 kc/atmos. The maximum amplitude of the molecular absorption coefficient per wavelength in dry N2O was 0.153 and this occurred at 210 kc/atmos. Measurements were taken in N2O - H2O and N2O - D2O mixtures at H2O-vapor and D2O-vapor concentrations of 0.39%, 0.77%, and 1.14%.

The usual single relaxation time theoretical absorption curve could be fitted to the data for dried N2O. However, in the mixtures there was some evidence of two separate relaxation times, one possibly associated with N2O - N2O collisions and the other with N2O - H2O or N2O - D2O collisions. The maximum absorption coefficient in the mixtures was somewhat less than that observed in the dried N2O. The H2O molecules were 1.72 times more effective than the D2O molecules in shifting the frequency associated with the absorption maximum.
Absorption of Sound in Manganous Sulfate Solutions
Authors: Smithson J. R. , Litovitz T. A.
Published: September 2005

The absorption of sound in MnSO4 solutions was studied over the frequency range 1 to 55 Mc as a function of concentration, temperature, dielectric constant, and with D2O as solvent. The absorption maximum in the range 1 to 10 Mc was verified, and also a secondary relaxation peak, not previously reported, was observed near 30 Mc. The primary relaxation frequency was decreased when the dielectric constant was lowered, while the secondary relaxation frequency was increased. The absorption cross section was increased when the dielectric constant was decreased. The primary relaxation frequency increased with increasing temperature following Arrhenius' equation. The activation energy was determined for both isodielectric and isocomposition solutions. Substitution of D2O as a solvent had no effect on the primary relaxation frequency but increased the absorption cross section. The secondary relaxation was not observed in D2O solutions.

These results indicate that the hydrogen ion is not involved in the rate-determining reaction causing the observed relaxation effects. Furthermore, the results seem to rule out the reaction between two ions of unlike sign as the rate determining step in the primary relaxation process and to make the reaction between ions of like sign improbable. All observed data can be explained on the assumption that the reaction is between two dipole molecules.
Sound Source near a Velocity Discontinuity
Authors: Gottlieb Peter
Published: September 2005

The far-field solution for a line and a point source near a tangential velocity discontinuity has been calculated by summing (integrating) the plane waves that make up the source. The exact field integrals were evaluated approximately by the stationary phase method, and this approximation gives the far field. It was found that the sound was strongly peaked in some directions, and considerably reduced in others. This angular dependence is shown graphically for certain cases. The physical significance of these results is discussed for both subsonic and supersonic motions, and the relationship to the jet-noise problem is suggested.
Temperature Coefficient of the Speed of Sound in Water near the Turning Point
Authors: Greenspan Martin , Tschiegg Carroll E. , Breckenridge Franklin
Published: September 2005

A sing-around ultrasonic velocimeter was used to locate the temperature for which the velocity of sound in water is a maximum at 73.95°C. It is suggested that water held near this temperature is a suitable standard for intercomparison and calibration of instruments.
Equivalent Linearization of the Hard Spring Oscillator
Authors: Lyon Richard H.
Published: September 2005

The technique of “equivalent linearization” is applied to the problem of random vibration of a hard spring oscillator. Since an exact solution of this problem is available, it is possible to deduce the efficiency with which the approximate technique estimates such parameters as frequency of zero crossings and moments. It is found that second and fourth moments are estimated rather well but the average frequency may be substantially in error.
Pulse Superposition Method for Measuring Ultrasonic Wave Velocities in Solids
Authors: McSkimin H. J.
Published: September 2005

The frequently used pulse method of measuring ultrasonic wave velocities in solids involves a high-frequency quartz crystal transducer cemented to one end of a specimen having parallel end faces. The phase shift for waves reflected from the transducer must be considered for highest accuracy. It is shown that combining several measurements of phase delay (at two frequencies differing by approximately 10%) with a theoretical analysis of the reflection phase angle makes possible a determination of velocity to within one part in 5000 for round trip delays greater than 5 μsec. Indirectly, the approximate thickness of the cement bond between transducer and specimen can be determined. The advantages of the method for making measurements as a function of temperature or pressure are discussed.
Extensional Waves in a Semi-Infinite Elastic Rod
Authors: McNiven H. D.
Published: September 2005

In conducting experiments on waves in an elastic rod, J. Oliver discovered a new mode of symmetric vibration in which the motion was predominantly at the end of the rod. It is shown that this “end mode” arises when pure extensional waves are coupled with waves with complex wave numbers. Approximate equations are used to study the reflection of pure extensional waves at the end of a semi-infinite rod. The properties of the resulting end mode are studied in detail and are compared with the phenomena reported by Oliver.
Underwater Communication
Authors: Isaak R. D.
Published: September 2005

To test several types of voice and code signals, communication was carried on over the conventional submarine underwater telephone between two submerged submarines. The signals included normal speech, differentiated and clipped speech, quarter-speed speech, and multiple-tone Morse code. It was found that normal speech was received at least as reliably as any of the more elaborate signals tried.
Vibration of, and Bending-Wave Propagation in Plates
Authors: Skudrzyk E. J. , Kautz Barbara R. , Greene D. C.
Published: September 2005

The theory of electrical lines and filters is based on the concept of a characteristic impedance. Similar concepts are permissible for mechanical systems. It thus becomes possible to derive a generalized theory of vibrating systems that is free from insignificant characteristics of the vibrator. The conclusions are illustrated by computations and by measurements for flat plates. The results are used to develop a theory of the propagation of bending waves in plates and shells on lines similar to the theory of reverberation in room acoustics.
Two Schemes of Speech Compression System
Authors: Chang Sze-Hou
Published: September 2005

Since the wave form of speech is apparently continuous and the phonemic entity is discrete, it is reasonable to expect that during the developmental stages of speech compression systems the process will gradually evolve from continuous to mixed discrete-continuous and finally to a completely discrete type. Two plans for such systems are discussed. Plan I is an attempt to use two discrete features of speech together with continuous extractions of the formants, moments, and pitch of speech. Plan II is an attempt to identify phoneme-like elements through a scheme of successive selection.
Some Systems for Speech-Band Compression
Authors: Vilbig Friederich , Haase Kurt H.
Published: September 2005

Speech-band compression aims to reduce the frequency band width without impairing the desired informational content. Physical compression systems are of two types: spectrum-alteration systems and vocoder (voice coding) systems. Spectrum alteration is not restricted to speech, is relatively simple to perform, but achieves only a compression factor of 3 to 5. Considerably higher ratios (10 to 20) are obtainable by vocoder-type systems. Here, by a spectrum analysis on the transmitter side, a “pitch” frequency is extracted and a system function is derived. Both are then transmitted to a receiver where speech is synthesized. At the A. F. Cambridge Research Center, the following vocoder-type systems are being developed and investigated: the scan vocoder with envelope scanning, the pulse vocoder in which the envelope is coded, and the formant vocoder in which the envelope is represented by three formant frequencies. By means of alterations and additions, the scan vocoder can be transformed into a pulse or a formant vocoder.
Free Extensional Torsional Vibrations of a Prolate Spheroidal Shell
Authors: DiMaggio F. L. , Silbiger A.
Published: September 2005

The axisymmetric extensional modes of free vibrations of a thin prolate spheroidal shell separate into two classes, one class with displacements perpendicular to the meridional planes and one class with displacements in the meridional planes. This paper concerns itself with the former, the torsional modes. The differential equation for the mode shapes, obtained by application of Hamilton's principle, is found to be satisfied by single prolate spheroidal angle functions of the first kind, and the transcendental frequency equation is readily solved with the aid of tabulated eigenvalues. Numerical and graphical nondimensional results are presented for the first eight modes.
Sonar Transducer Pulse Calibration System
Authors: Wallace John D. , McMorrow E. W.
Published: September 2005

The development of equipments and techniques for making measurements on underwater transducers is described. The Naval Air Development Center used a circular tank with no special linings, and directed its effort to develop a suitable electronic pulse test equipment. It is concluded that the accuracy and reliability of the calibration facilities, measurement techniques, and the use of the round wooden tank are satisfactory for most underwater transducer evaluations.
Band Width and Channel Capacity Necessary to Transmit the Formant Information of Speech
Authors: Flanagan James L.
Published: September 2005

Computations of the band widths and signal-to-noise ratios necessary for the transmission of continuous data on the first three formants of speech are presented. The results indicate that, on the average, band widths of 7.1, 6.7, and 5.3 cps and signal-to-noise ratios of 33, 24, and 20 db are sufficient for the transmission of signals specifying the frequencies of the first, second, and third formants, respectively. The band-width and signal-to-noise figures are computed on the basis that the error incurred in each formant signal is less than the just discriminable difference in formant frequency at least 65% of the time. The channel capacity necessary for the transmission of the three formant signals is, therefore, of the order of 200 bits per second.
Detection of Complex Signals as a Function of Signal Bandwidth and Duration
Authors: Creelman C. Douglas
Published: September 2005

A study is reported which examined the efficiency of human observers in the detection of a stimulus waveform which is a train of damped sinusoids. The signal duration and degree of damping (or spectral bandwidth) were varied, with the energy of the signal held constant. Increased bandwidth is shown to decrease detection of relatively long duration signals. A negligible effect of bandwidth was found for short durations. Detection of an amplitude difference, in contrast to detection of the presence of weak signal in noise, is shown to be relatively unaffected either by signal duration or bandwidth over the range of values studied.
Detection of Signals in Noise: A Comparison between the Human Detector and an Electronic Detector
Authors: Sherwin Chalmers W. , Kodman Frank , Kovaly John J. , Prothe Wilbert C. , Melrose Jay
Published: September 2005

The observer's responses to aural signals in noise are compared to the output of an electronic detection system whose constants are intended to be close to those of the human auditory detection system.

Of the four variations of an electronic detector tested, the best correlation between the detector and the observer occurred for signals of duration 0. 3 second, band pass 60 cps (single tuned RLC circuit), square law detector, output filter time constant, 0.15 second.

The incomplete correlation between the signal responses of the observer and the detector can be explained by assuming that the observer's threshold fluctuates randomly about a mean value with a dispersion of about 20% of the mean, or alternatively that there is internal noise with this dispersion generated inside the observer's detection system.

The observer's false alarms appear to be caused by noise fluctuations (as measured by the electronic detector) of the same average magnitude and dispersion as those calculated for a detector with the same threshold fluctuation. However, the observer's false alarm rate is about an order of magnitude lower than that calculated for the fluctuating threshold detector so it is clear that the model is deficient in some important respects.
Masking of Tones by Bands of Noise
Authors: Bilger R. C. , Hirsh I. J.
Published: September 2005

Measurements were made of the masking of pure tones by bands of noise, each band width corresponding to a pitch interval of 250 mels, with band level varied from 40 to 120 db (above 0.0002 microbar). A modified Békésy audiometer permitted recording as a function of frequency, so that masked audiograms could be compared with the noise spectra to ascertain how well the ear followed the frequency characteristics of the noise bands at different levels. It was found that values for the critical band according to Fletcher and to Hawkins and Stevens predict quite precisely the masking for tones whose frequencies lie within the band. More masking than would be predicted is found for frequencies above the band, the discrepancy increasing as the noise level increases. Below the band, the masked threshold is again predicted precisely by the critical-band hypothesis, but only to a point, beyond which, for high noise levels, a “remote” masking is observed that is constant with frequency for any particular level and is much more than can be predicted from the effective levels (from either system noise or imperfect band rejection) obtaining at those low frequencies where this masking is observed. Whereas masking for tones within the band increases linearly with level, this “remote” masking rises in an accelerated manner, as a function of level, and then shows deceleration at the highest levels. Some speculative interpretation is attempted.
Observations of the Stability of a Normal Mode Sound Field in an Intermediate Scale Model
Authors: Scrimger Joseph A.
Published: September 2005

Spectra of sound-pressure amplitude versus frequency in the range 1.1 to 2.4 kc have been obtained at regular intervals in shallow (10 ft) water during two periods of extended observation. The acoustical data have been presented in the form of contour diagrams of sound-pressure amplitude versus frequency and time as coordinates and compared with water conditions.

The form of the contour diagrams permits differentiation between field-structure variation and variation in attenuation although differentiation between the associated processes has not been possible. Temporal variation in the vertical sound-velocity profile produced only small changes in the gross features of the field structure, as inferred from the contour diagram, for up to the first three modes of propagation. For frequencies above 1.6 kc (i.e., when three or four modes were stimulated) the variations in field structure were prominent. Attempts have been made, with little success, to explain periods when the received signal was strongly attenuated in terms of vertical sound-velocity structure.
Propagation of Sound in Five Monatomic Gases
Authors: Greenspan Martin
Published: September 2005

The speed and attenuation of sound at 11 Mc were measured in He, Ne, A, Kr, and Xe at various pressures between atmospheric and a few mm Hg, and the results were compared with existing theories.
Anomalous Sound Dispersion in the Fatty Acids
Authors: Mayer W. G. , Hiedemann E. A.
Published: September 2005

An ultrasonic pulse method is used to measure the velocity dispersion due to changes in sound intensity in three fatty acids. With constant frequency the velocity increases with increasing sound amplitude in the ranges from the melting points to approximately 15°C above.
Effects of High Static Stress on the Piezoelectric Properties of Transducer Materials
Authors: Krueger H. H. A. , Berlincourt Don
Published: September 2005

Piezoelectric ceramic elements in high-power acoustic transducers are subjected to high static as well as dynamic stress. This is particularly true of well-matched transducers operating in deep water, since the static stress in the piezoelectric element may be several times the water pressure. The present study was undertaken in an effort to determine the effects of static compressive stress on the piezoelectric properties of two commercial lead titanate zirconate compositions, PZT-4 and PZT-5, and of two barium-titanate compositions, commercial Ceramic B (a barium calcium titanate), and the composition 88 wt% barium titanate, 12 wt% lead titanate (BaPb12Ti). The permanent effects of stress exposure, determined at zero stress after exposure to a given stress, were found to be more severe with stress parallel to the polar axis than with perpendicular stress, as expected. Under maintained stress, however, the effects of perpendicular stress are more severe. PZT-4 and BaPb12Ti, generally better suited for use as radiating transducers, show effects dependent upon exposure time but independent of the number of stress cycles. Ceramic B and PZT-5 show effects dependent upon the number of stress cycles and less dependent upon the total period of stress exposure. Of the compositions tested, PZT-4 and BaPb12Ti were least affected by high static stress, suffering relatively little from exposure to stress as high as 15 000 psi. Of these two compositions. PZT-4 has markedly higher coupling (k33∼0.64 compared to 0.365) and therefore offers higher transducer bandwidth.
Sensitive Electrodynamic Balance for Measurement of Absorption of Ultrasonic Waves in Liquids
Authors: Mokhtar M. , Youssef H.
Published: September 2005

In this paper a new method for measurement of absorption of ultrasonic waves in liquids is developed. Its main feature is a low frequency (L.F.) modulated ultrasonic transducer actuating a thin circular disk which is placed at some distance above it within the ultrasonic cell. The disk is suspended by a glass rod from a metallic reed which forms one plate of a small air condenser. The vibrations of the suspended system, which are resonant with the L.F. modulating component, are detected by a crystal controlled oscillator, working at the steep portion of its crevasse. The output of the oscillator is applied to a wave analyzer whose output gives directly a measure of the ultrasonic pressure on the disk.

In a further development in the detecting end, a null method is used in which the reed is brought to rest by a L.F. balancing voltage supplied by the same modulator and the zero reading is adjusted by the aid of a cathode-ray oscillograph.

Two liquids are chosen for testing the apparatus, namely, benzene and water representing both high and low absorptive liquids, respectively. The values obtained are, 2α/v2 = 16.2×10−16 sec2 cm−1 for benzene, and 2α/v2 = 52×10−17 sec2 cm−1 for water, which compare favorably with the values obtained by the more elaborate pulse method. Moreover, the high sensitivity of the method eliminates all the complications which usually accompany high-power ultrasonic beams.
Reflection of Plane Sound Waves from an Irregular Surface
Authors: Parker J. G.
Published: September 2005

A plane sound wave is assumed to be incident upon an irregular pressure release surface z=ζ (x,y). The solution for the reflected field is regarded as a superposition of plane waves having an amplitude spectrum A (k1,k2). Next, the Fourier transform G(x,y) of A (k1,k2) is introduced and subjected to the boundary condition on ζ This leads to an integral equation for G(x,y) that cannot be readily solved. However, if one causes G(x,y) to depend exponentially on a function u(x,y), then a differential equation may be derived from this integral equation, the solution of which gives an approximate form of u(x,y); the degree of approximation involved depends on the smallness of ζ.

This method is applied to the problem of sound scattering from a one-dimensional sinusoidally corrugated surface and the results compared with experimental measurements of LaCasce and Tamarkin and also with the results of a theory due to Rayleigh. This comparison shows the predictions of the theory presented here to be as good as the Rayleigh theory in all cases and closer in the majority of cases.
Measurements on Sound Absorbers for Jet-Engine Test Cells
Authors: Waterhouse Richard V. , Cook Richard K. , Berendt Raymond D.
Published: September 2005

The space absorbers were long cylindrical shells of perforated metal, containing glass fiber. The absorbers were to be used in an aero-engine test cell, and these conditions were simulated in the measurements by mounting a few absorbers in a long concrete pipe, so that the cross-sectional ratio (absorber/enclosure) was the same in each case. The direction of propagation of sound was parallel to the axis of the cylinders so that absorption occurred at grazing incidence. The concrete pipe was terminated by a rigid reflector, and the attenuation figures were deduced from the resulting interference pattern using impedance tube theory. The theory was extended to the case of octave bands of noise, when the interference pattern for the mean squared pressure is (p2) = [cosh2ax sinh(2ax/3)]/(2ax/3) + [cos(2kx) sin(2kx/3)]/(2kx/3), where a is the sound attenuation constant, k is the wave number at the center frequency of the band, and x the distance along the pipe measured from the reflecting end. Experimental results were obtained which followed this pattern, and the required sound attenuation constant was obtained by a graphical method. Measurements were made at low frequencies only, 300 cps and below.
Piezoelectric Generation of an Electrical Impulse
Authors: Redwood M.
Published: September 2005

The following problem is examined theoretically: A pressure is applied to an open-circuited bar of piezoelectric ceramic; after steady-state conditions have been achieved, an electrical resistance R is connected between the electrodes and simultaneously the pressure is removed. General equations describing the subsequent current and energy dissipation in the resistor are developed, and examined in detail for a specific transducer of lead zirconate-titanate ceramic. The general equation for current consists of a series of time-delayed functions, signifying physically that a mechanical wave propagates through the transducer with successive reflections at the end faces, releasing strain energy originally stored in the material; this energy is then dissipated in electrical form in the resistance. The initial current h*s two components, an exponential function representing the discharge of energy stored in electrical form in the transducer capacitance C0 (about 10% of the total stored energy), and a step function representing the release of energy stored in mechanical form (remaining 90%). If R is small the exponential function predominates, and has a time constant which is approximately RC0; the stored electrical energy is released very rapidly, while the mechanical energy is released much more slowly. If R is large (of the order of 104 ohms), exponential function and step function are of comparable magnitudes, and the time constant of the exponential is modified by the mechanical impedance of the transducer.
Variable Resonant Transducer
Authors: Robey Donald H.
Published: September 2005

The application of lateral forces by a relatively stiff structure such as a small iron vise to one end of a longitudinally vibrating crystal or composite bar, e.g., a crystal and backing plate, has been used to control and vary the resonant frequency of the system. A change in resonant frequency of over an octave for a composite system has been measured. It is believed that the phenomenon depends upon the (dynamic) elastic range of friction as first noted for the static case by J. S. Stevens in 1899, in addition to the elastic parameters. It is noted that for a given crystal (material and dimensions) and backing plate (material) there are optimum backing plate lengths to obtain both maximum and minimum changes in resonant frequency. For example a one inch 45° Y-cut Rochelle salt crystal with a one-half inch steel backing plate can undergo a continuous change in resonant frequency from 26.5 to 66.7 kc. The same crystal with a three inch backing plate will only change from 22.2 to 24.4 kc. It was found that the type of clamping herein described results in an additional mode of vibration which may be very low in frequency depending on the lateral force.
On the Vibration Statistics of a Randomly Excited Hard-Spring Oscillator. II
Authors: Lyon Richard H.
Published: September 2005

Previous calculations of the statistical behavior of a hard spring oscillator excited by purely random and Gaussian noise are extended. The moments of the displacement and its extrema are found in an analytic form and their interrelations are exploited. Recurrence relations, asymptotic expressions, and computations of the moments are presented. Envelope autocorrelations for three narrow-band linear filters are found, and the mean size of clumps of cycles exceeding predetermined levels is obtained. For the hard-spring oscillator we find that the relative envelope fluctuation is less than that of a linear oscillator and that the mean clump size is also smaller in general.
Hydrophone for Measuring Particle Velocity
Authors: Leslie C. B. , Kendall J. M. , Jones J. L.
Published: September 2005

Mathematical expressions are derived for the motion of a rigid, uniform sphere in an underwater sound field. The results show that at low frequencies a neutrally buoyant sphere of this type has a velocity equal to the particle velocity of the water at the same location when the sphere is removed. A velocity pickup may be mounted inside such a sphere to form a hydrophone sensitive to particle velocity. Two practical design applications are presented. A low-frequency hydrophone with a diameter of five inches was constructed having an essentially flat response between 15 and 700 cps with a sensitivity of 0.18 volt/cm/sec working into a 500-ohm load. A higher frequency design with a 2.5-inch diameter operated from 70 to 7000 cps with somewhat lower sensitivity and impedance level. Velocity hydrophones of this type are easy to build, easily calibrated, stable, and possess good directionality.
Effect of Alcohol Impurity on Ultrasonic Vibrational Relaxation in Liquid CS2
Authors: Slie W. M. , Litovitz T. A.
Published: September 2005

Ultrasonic attenuation measurements were made in liquid carbon disulfide-alcohol mixtures over a frequency range from 5 to 155 Mc at a temperature of −63°C. From these measurements the vibrational relaxation frequency for the liquid was calculated. Methyl, propyl, and butyl alcohol were added in various concentrations up to 0.6 mole percent. In every case the relaxation frequency increased with the addition of the impurity. This increase was found to be a linear function of the impurity concentration which is consistent with the assumption that the vibrational-translational energy transfer is a binary collision process. The shifts in relaxation frequency per mol % of impurity were found to be a linear function of the molecular weight of the impurity molecules for both the gas and liquid data.

A comparison was made of the ratio of collision efficiency of like to unlike molecules in both the gas and liquid state. It was found that within experimental error this ratio is the same in both states. This was interpreted as meaning that the vibrational relaxation process for unlike collisions was the same in both liquids and gases. Further, it appears that the efficiency of an AB-type collision is more strongly temperature dependent than for the AA-type collisions.
Acoustic Propagation in a Two-Layered Model Transverse Waves in Bottom
Authors: Eby R. K. , Williams A. O.
Published: September 2005

The complex shear modulus of Hycar rubber has been determined from acoustical measurements, over a wide range of frequencies and temperatures. From these data and the density of the rubber, the speed of transverse waves has been computed. Results are compared with values inferred in a previous paper, when the rubber was used as the bottom material in a model-scale test of shallow-water propagation. Discrepancies are about 15%.
Calibration of Vibration Pickups at Large Amplitudes
Authors: Jones E. , Edelman S. , Sizemore K. S.
Published: September 2005

Axial resonances of long rods and tubes were used to generate motion for accurate calibration of vibration pickups over the frequency range from below 1 to above 20 kc at acceleration levels up to 12 000g. The resonators were driven by an electromagnetic shaker at low frequencies and by a piezoelectric ceramic stack shaker at high frequencies. Vibration amplitude was measured optically by means of a microscope using stroboscopic light and by means of the interference fringe disappearance technique. Adequate overlap between the two methods was achieved by going up to the 60th disappearance of the fringes. A simple, direct measurement of the phase angle between the pickup signal and the motion is described. Construction details of a small, light pickup which is unaffected by the high acceleration levels are given.
Reduction of the Response to Vibration of Structures Possessing Finite Mechanical Impedance
Authors: Snowdon J. C.
Published: September 2005

Expressions have been derived from which the isolation provided by a simple mounting system when supported by any nonrigid foundation may be determined, if the mechanical impedance of the foundation is known. As an example, the mechanical impedance of a damped beam at its midpoint has been employed to simulate the behavior of such a foundation. Knowledge of the dynamic mechanical properties of natural rubber and a high-damping synthetic rubber has enabled the behavior of antivibration mountings to be described realistically.

If the ratio of the mass of the mounted item to the mass of the foundation is large, the isolation afforded by a mounting is found to be much less than that predicted by its transmissibility curve, which relates to an ideally rigid foundation. It is shown, however, that the isolation provided by a mounting can be increased significantly at high frequencies if an additional mass is employed to load the foundation, the greatest isolation then being provided by a low-damping rubber such as natural rubber. Damping of the foundation is found to have little influence upon the over all level of the isolation afforded by the mounting system.
Dynamic Tensile Strength of a Ferroelectric Ceramic
Authors: Gerson Robert , Burlage S. R. , Berlincourt Don
Published: September 2005

The dynamic tensile strength of a piezoelectric lead titanate zirconate ceramic used for power transducers was tested by driving small bars of ceramic electrically at their longitudinal resonance until they fractured. The measured dynamic tensile strength of small specimens of ceramic of good quality was found to be about 13 000 psi. This value was very drastically reduced for ceramic which was not of optimum quality.
Vibrations of Cross-Stiffened and Sandwich Plates with Application to Underwater Sound Radiators
Authors: Greenspon Joshua E.
Published: September 2005

A simplified theory is presented for obtaining the frequencies, deflections, and stresses in cross stiffened and sandwich plates under dynamic loading. Formulas are derived giving the effect of the water on the natural frequency and the approximate Q of the plate. The application of resonant plates as underwater sound radiators is discussed, and procedures for designing such radiators are given.