摘要:

The absorption (α) and velocity (V) of sound in liquid mixtures were measured at four frequencies (ν) in the range 3.8 to 19.2 mc, using the Debye‐Sears‐Lucas‐Biquard optical technique improved by the addition of a differential photoelectric cell indicator. This improvement permitted the use of lower sound intensities together with a wider sound beam than in the visual extinction method, thus improving conditions with respect to cavitation and beam distortion. In the mixtures investigated, α/ν2was found to be independent of frequency within the accuracy of the method, and there was no measurable dispersion of acoustic velocity. An absorption peak at intermediate concentrations not shifting with frequency was found in mixtures of acetone and water, and of ethyl alcohol and water, but was not in evidence in mixtures of acetone and ethyl alcohol, and of glycerol and water. The absorption peaks await theoretical explanation.

ISSN:0001-4966    

DOI:10.1121/1.1916425

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP

摘要:

The maximum ultrasonic power density Υmaxwhich has been experimentally attained with a piezoelectric quartz crystal up to the present time is considerably less than the value computed from the electrical and mechanical characteristics of quartz. Failure of such systems is attributed to dielectric breakdown in the surrounding insulating fluid, and a simple theory is developed in which the maximum power density is predicted from the value of the dielectric strength. If the breakdown voltage gradient for the medium (V/d)maxis independent of thickness, the maximum power density does not change with frequency; but if (V/d)maxdecreases with thickness as is experimentally observed with many substances, Υmaxincreases with frequency approaching saturation value as ν approaches infinity. Experimentally, an output of 43 watts/cm2has been achieved at a frequency of 1000 kc. The determination of the power output by a calorimetric substitution method is described.

ISSN:0001-4966    

DOI:10.1121/1.1916426

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1916428

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1916429

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP

摘要:

The correlation and theoretical analysis of a large number of transmission measurements made in the Potomac River and Chesapeake Bay areas warrants the conclusions which follow. Given a source of audiofrequency sound in water, the sound pressure level which may be measured at appreciable distances will be influenced in a complicated way by the boundaries, especially by the bottom. The sea bottom may be classified by its behavior for sound as “soft,” “hard,” or intermediate in character. Specifically, the velocity of sound and the density of the bottom may be estimated from acoustic measurements (hydrophone soundings and range runs), by sampling, and from hydrographic data. The effect of the boundaries on sound propagation from a ship‐mounted source may be determined from an analysis of the normal modes of vibration of the acoustic system of the sea between surface and bottom. The analysis is particularly effective for frequencies at which the wave‐lengths are comparable to the physical dimensions of the system. For low frequencies and given bottom conditions, the most important factor governing the propagation is the ratio of the depth of the water to the free wave‐length of the sound. A detailed interpretation of the observed transmission phenomena may be given in terms of the initial stimulation, the relative attenuation, and the phase velocities of the modes. Damping and phase constants may be determined for each mode by means of special charts which give the propagation and distribution constants in terms of the acoustic properties of the system. The over‐all transmission is given as the sum of the effects produced by the individual modes. “Damped” transmission, which occurs over “soft” bottom, is always accompanied by considerable attenuation, the amount ranging in practice from about 12 db/1000 ft. as a lower limit to about 40 db/1000 ft. under conditions of strong bottom absorption. “Soft” bottoms are frequently encountered in land‐locked basins such as fiords, estuaries, and river channels. “Guided” transmission which occurs over “hard” bottom at all frequencies higher than a minimum critical frequency, is characterized by negligible damping due to bottom absorption and by an attenuation with distance caused primarily by cylindrical spreading from the source. The latter amounts to 3 db per distance double. “Hybrid” transmission, which occurs over hard bottom at frequencies below the lowest critical frequency, is associated with large and erratic damping from bottom absorption. The critical frequency depends upon the hardness of the bottom, and is slightly higher than the frequency for which the water depth is equal to a quarter wave‐length. The acoustic system of the sea between the surface and a hard bottom thus acts as if it were a high pass filter, analogous to an electromagnetic “wave guide.” This type of sound transmission is very commonly encountered, since hard bottom predominates along the sea coasts of all the continents.

ISSN:0001-4966    

DOI:10.1121/1.1902477

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP

摘要:

The modifications that have been developed in order to adapt the Sonigage to the quick inspection of Diesel cylinder liners are described. A method of introducing ultrasonic vibrations from a conventional flat‐crystal probe into a curve surface and an adaptor for determining thickness by interpreting the harmonic responses have proven to be valuable in expediting this type of work. In the hands of an experienced operator the technique can be made to yield much valuable information concerning the relative homogeneities of the castings.

ISSN:0001-4966    

DOI:10.1121/1.1902482

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP

摘要:

Boyle and Rawlinson's formula is applied to the design of low loss ultrasonic lenses of plastics, metals, and other solids. Plano‐spherical or plano‐cylindrical ultrasonic lenses are used in direct contact with the generating crystal as well and called “ultrasonic contact lenses” in analogy with the corresponding devices for the human eye. To reduce the loss of energy by reflection of ultrasonics at the boundary between two media of different acoustic resistivities plane parallel plates are employed, named “transmission plates.” They are analogs of the coatings used to extinguish reflection of light from glass. The high efficiency of the devices described above is recorded in various ways. The usual optical methods are simplified and improved by the application of the concentrated‐arc lamp. Eventually the possibilities of further developments are discussed and some problems awaiting solution.

ISSN:0001-4966    

DOI:10.1121/1.1902485

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP

摘要:

The phenomenon of ultrasonic intensity fluctuations has been studied experimentally outdoors under various kinds of weather conditions. There seem to be three types of fluctuations. Their causes are suggested by correlations of ultrasonic data with simultaneous micrometeorological observations. Two types of fluctuations are of the mean intensity. Those of the first are usually fairly slow with a period of several minutes and with a range of intensity variation of 10 to 30 db. Apparently they are observed only near boundaries of “shadow zones” and are caused by the motions of the “shadows” as the vertical gradients of the velocity of sound change. The second type is ordinarily faster, with a frequency of 2 or 3 per minute, and an intensity range of only 2 to 5 db. They are observed at a distance from shadow boundaries where the fluctuations of gradients can produce only changes in the convergence and divergence of rays with consequent variations in intensity. Third type fluctuations are usually extremely rapid, as frequent as several times per second, with an amplitude of variation of several db, and there is evidence that they are caused by the random motion, between source and receiver, of inhomogeneities or discrete bodies of air in the atmosphere. Typical diurnal cycles of ultrasonic fluctuations and of related weather conditions, as well as of micrometeorological phenomena, have been observed.

ISSN:0001-4966    

DOI:10.1121/1.1902492

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP

摘要:

Two types of whistles will be described which have been useful as high power sources for work in atmospheric ultrasonics. The first has an annular windway, an annular lip and cavity; weighs 2.5 oz.; is capable of delivering 0.1 watt at mouth blowing pressure and 10 watts when the pressure drop across the whistle is 8 lb./sq. in., and the air flow is 10 cu.ft./min. The second weighs 0.5 oz.; puts out 0.005 watt when mouth blown, and 0.5 watt when the airflow is 0.5 cu.ft./min., for a gauge pressure of 20 lb./sq. in. An experimental study of ultrasonic whistles has been carried out to discover how the intensity and frequency of their output depends upon their dimensions and upon the airflow. The relationships noted can be explained qualitatively by assuming that the whistle is a system of two oscillators, the first being the air in the cavity, and the second the “jet and edge,” which functions as driver and produces edge tones having properties similar to those observed by Brown in his studies of edge tones of lower frequencies and at lower air velocities.

ISSN:0001-4966    

DOI:10.1121/1.1902493

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP

摘要:

This paper presents a classification of distortions peculiar to sound recording on film. Sources of these distortions include imperfections of photographic reproductions, the optics of the system, the light modulator, and the photoelectric cell. The effects of these are considered on various types of variable density and variable area sound recording.

ISSN:0001-4966    

DOI:10.1121/1.1902506

出版商:Acoustical Society of America    

年代:1947

数据来源: AIP