摘要:

That very small gas bubbles can serve as nuclei for the formation of cavities in liquids is well established. That experimental observations on the rupture of liquids can be interpreted only on this basis is perhaps not so obvious but none the less true. In the present series of experiments on acoustic cavitation in water, two distinct types of bubble formation occur. One, the violent formation and collapse of vapor‐filled cavities, results from mechanical instability of gas nuclei. The other, relatively quiet gas bubble formation, occurs as a consequence of the slow growth of nuclei by “rectified” diffusion of dissolved gas from the surrounding liquid. Each process has a threshold of excitation by a sound field; which has the lower threshold in any given case depends largely upon the concentration of dissolved gas in the liquid. Measurements of the acoustic cavitation threshold in conventionally “deaerated” water, as a function of temperature and ambient hydrostatic pressure, reveal how the equilibrium size of gas nuclei depends upon these variables. Observations on sonically induced effervescence in saturated solutions provide at least a qualitative explanation for the pulse length and viscosity effects observed elsewhere. Cavitation at the surface of a sound projector apparently is profoundly affected by adsorbed gases. The conclusion that gaseous nuclei exist more or less in equilibrium with solutions not supersaturated with gas is contrary to the conventional theory of gaseous solutions. Stabilization of nuclei in the surface cracks of suspended solid particles is a very plausible but not entirely satisfactory explanation. Revision of the theory is a tempting subject for speculation.

ISSN:0001-4966    

DOI:10.1121/1.1917094

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

As our age becomes more industrialized, the problems of quieting machinery and appliances—whether they occur in industry, office or home—become more numerous and more difficult. The economy of using improved research methods and competent scientific personnel is emphasized. Determination of qualitative data (source of energy, source of radiation, relative spectral distribution, relative intensity of frequency peaks, etc.) is usually more important than spending excess time obtaining quantitative data (precise sound intensity, exact frequency spectrum, percent harmonic content, etc.). The importance of analysis of sound energy sources, sound radiation sources, and coupling factors between them will be emphasized. A system of analyzing noise problems, by schematic diagrams giving the energy flow between sound energy sources and the surrounding propagating medium, will be outlined and illustrated by actual data from typical research problems.

ISSN:0001-4966    

DOI:10.1121/1.1917100

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

The Applied Physics Laboratory of Johns Hopkins University, operating under contract with the Bureau of Ordnance of the U. S. Navy, set up during the war a testing laboratory for ram jet motors at Forest Grove, Maryland, a short distance outside of Washington, D. C., in a location surrounded by open country. Postwar building in the neighborhood made it necessary to quiet this installation if operation were to continue at the same location and the Kellex Corporation undertook design of the revisions. Since very large volumes of air and hot gases had to enter and leave the test cells, it was necessary to design a duct system which offered extremely low resistance to gas flow, but high attenuation to sound. This paper gives a brief description of the resulting construction which has allowed the laboratory to continue operation in the midst of a residential community.

ISSN:0001-4966    

DOI:10.1121/1.1917101

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

Some years ago Lamb determined the maximum power which can be scattered by small non‐rigid objects (e.g., resonators, microphones, etc.) located in a plane wave. Recently Foldy has found that an omni‐directional microphone located in a plane wave of wave‐length λ transmits maximum power equal to (λ2/4π) × the incident plane wave intensity. This result is identical with that for an antenna picking up electromagnetic waves. This paper presents results showing the relation between the sound scattered and absorbed by several types of microphones which are small in comparison with the wave‐length. Microphones located in plane waves near reflecting boundaries are included. The design of a microphone small in comparison with the wave‐length for transmitting maximum power will be discussed.

ISSN:0001-4966    

DOI:10.1121/1.1917108

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

The ability of a perfect crystal to reflect x‐rays is markedly enhanced by vibration, as has been reported by many writers. Measurements on statically bent quartz are given which establish a quantitative relationship between increased reflecting power and radius of bending. Several pictures show quartz plates in various modes of vibration, light nodal lines separating the dark zones of maximum bending. Other types of vibration are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1917115

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

A pulse method has been used to investigate the intensity distribution in the ultrasonic beam produced in water by vibrating quartz crystals having disk‐ and ring‐shaped electrodes. The plot of intensityvs.angular position was observed directly on an oscilloscope screen. Measurements were made at a frequency of about 1 mc sec.−1. The intensity distribution found for the disk agrees closely with theory and with results which have been obtained by other methods in this laboratory. Most of the energy is confined to a narrow cone with a small fraction of the energy appearing in side lobes which become practically negligible about 8 diameters from the source. For ring sources the intensity distribution is similar to that for a disk. However, the cone of the main beam becomes narrower as the ring is made thinner, as predicted by Williams, Heller and Hellens (J. Acous. Soc. Am.20, 583 (A) (1948)). In addition a larger fraction of the energy appears in the side lobes, which are discernible at greater distances from the source than in the case of the disk.

ISSN:0001-4966    

DOI:10.1121/1.1917122

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP