摘要:

A theory is developed for the sound velocity and attenuation in a medium composed of closely packed solid particles immersed in a fluid. The absorption mechanism considered is that of viscous motion of fluid between the particles, and the macroscopic point of view is taken. For high enough frequencies the attenuation is proportional to the square root of the product of frequency and static flow resistance of the medium. Comparisons are made with data reported previously by others, and the agreement with the theoretical results is good for cases involving particles of nearly uniform size. Still another frequency effect, dependent on the size distribution, is evident for unsorted granular substance.

ISSN:0001-4966    

DOI:10.1121/1.1906958

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

A description of a tube method of determining the sound absorbing power of materials in which no exploring device is introduced in the path of the sound wave in the tube. The method is an extension of a research by Kennelly and Kurokawa on “Acoustic Impedance and Its Measurement,” and makes use of the motional impedance of a telephone receiver which serves as both the source of the sound wave in the tube and as the means for determining the fraction of sound absorbed by the material, a sample of which is attached to the piston which slides in the tube. Sample calculations for sound absorption are included.

ISSN:0001-4966    

DOI:10.1121/1.1906959

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Slowness in the rearrangement of ion configuration under acoustic perturbation should cause sound absorption in ionic solutions. This mechanism investigated from the standpoint of the Debye‐Ḧckel theory of strong electrolytes. The electrostatic part of the free energy of the solution is formulated in terms of temperature, volume, and an ion configuration function. The partial derivative of this expression with respect to volume gives the electrostatic component of pressure. A rate equation for change of ion concentration at a point enables us to find the variation in the ion configuration function with a small harmonic fluctuation in volume. Since the pressure is expressed in terms of the configuration function, this leads readily to the relaxational bulk modulus connected with rearrangement. The rate equation involves a parameter which in interionic theory has been identified as the relaxation time of the ionic atmospheres and can be evaluated from conductivity data. A calculation made forMgSO4solutions sets the relaxation frequencies for 0.001 and 0.01 molal concentrations at 21 and 143 mc, respectively, and shows the maxima in the wavelength absorption coefficients to be 20 and 660× 10−9respectively. The recently reported much higher excess absorptions forMgSO4at lower frequencies are thus due to processes other than ionic relaxation.

ISSN:0001-4966    

DOI:10.1121/1.1906960

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Incorporation ofCaTiO3orY2O3intoBaTiO3ceramics causes a downward shift of the second transition point, resulting substantial improvement of temperature stability in the normal operating range.Dielectric and electromechanical properties ofBaTiO3ceramics containingCaTiO3,Y2O3, andPbTiO3are shown from −40° to +120°C. The composition containing 5 weight percentCaTiO3combines high piezoelectric response with low temperature dependence of operating characteristics.

ISSN:0001-4966    

DOI:10.1121/1.1906961

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Expressions are given for the sound velocity and the absorption coefficient per unit wavelength for a van der Waals gas. Numerical calculations have been carried out for several triatomic gases. In general, the velocity corrections, under standard conditions, average about 0.5 percent, while the absorption corrections are two or three times larger.

ISSN:0001-4966    

DOI:10.1121/1.1906962

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

A comparison made between the results of experiment and theoretical predictions of translational dispersion in the monatomic gases argon and helium. Second‐order approximations to the dispersion are presented for the continuum theory, treating the Stokes‐Navier equations as exact, and for deductions from kinetic theory, assuming that the molecules behave as (1) elastic spheres, (2) Maxwellian molecules, and (3) molecules obeying a Lennard‐Jones type potential. Agreement between experiment and kinetic theory predictions is rather favorable in the range compared, which is at 0°C, approximately 970 kc, and down to about 2 mm Hg pressure. The increases velocity of propagation (at the lowest pressures) over that at standard conditions are 27 percent for argon and 0.6 percent for helium.

ISSN:0001-4966    

DOI:10.1121/1.1906963

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

An investigation of the behavior of Plexiglas and polystyrene lenses as focusing devices for ultrasonic radiation is described. A fixed frequency of 1 megacycle/second and intensities up to 6.6 W/cm2were employed. Using a thermocouple probe to obtain records of intensity of radiation in a water tank, it was found that above about 2 W/cm2the Plexiglas showed signs of physical breakdown. Up to the maximum intensities employed, polystyrene showed no indication of damage, while at 6.6 W/cm2the Plexiglas developed internal cavities near the outer edge of the lens, where the thickness was 4 mm.

ISSN:0001-4966    

DOI:10.1121/1.1906964

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

An analysis of the problem of a longitudinal wave normally incident upon the first of the four parallel boundaries separating five distinct media is presented. The filtering action which is characteristic of this physical situation is discussed, and it is found that this arrangement acts as a band pass filter with very narrow pass bands whose centers are separated by a frequency difference primarily dependent upon the thickness of the third medium. On the basis of this analysis, filters have been built which behave experimentally much as they are predicted to behave throughout the frequency region investigated (5000–20,000 cycles per second).

ISSN:0001-4966    

DOI:10.1121/1.1906965

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

The need for quantitative information on piping noise reduction obtainable by various devices such as flexible couplings, isolating hangers, or pipe‐wall damping treatments led to the development of a test setup for making the desired measurements. The setup consisted of a long, straight length of pipe in which the test device was installed. Broad‐band noise was introduced into the water or the pipe wall at one end of the system. Pipe‐wall vibrations were detected by accelerometers and were analyzed by means of an octave filter set. It was found that flexible couplings could be rated in terms of the difference in vibration levels at two points on opposite sides of the coupling. Differences of 20 to 45 db were found for some couplings at high frequencies and at atmospheric pressure. The effectiveness of damping treatments which extended along a considerable length of the pipe ranged from 0.2 to 0.5 db per foot. The isolation provided by resilient hangers was measured by comparing pipe‐wall and support structure vibrations, but test results must be used with caution since mounting conditions found in practical installations often vary widely from those provided by the test set‐up.

ISSN:0001-4966    

DOI:10.1121/1.1906966

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

An average of three measurements per month of upper atmosphere winds and temperatures was made during the period July 21, 1950 through May 31, 1951 by means of acoustical propagation studies. Field operations were centered in Wray, Colorado (40° N. lat, 102° W. long) and extended radially 200 km. A variation in azimuth and distance from sound source to recorder positions permitted the separation of wind and temperature components of the observed upper atmosphere sonic velocity gradients. It was found that upper winds were generally westerly and of large magnitude during the winter (autumnal to vernal equinox) and easterly and of small magnitude during the summer, with wide fluctuations during the equinoctial periods. Short‐term fluctuations in the wind vector were observed to be of the same order of magnitude as the vector itself. The short‐term fluctuation is now well established. A doubly‐periodic annual variation in temperature was observed above 25‐km altitude, with mean value in agreement with accepted NACA values.

ISSN:0001-4966    

DOI:10.1121/1.1906967

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP