摘要:

Longitudinal recording has been achieved on plastic tape coated with ferroelectric material. Reproduced levels were constant with frequency at the low end, but in the system used there was an upper frequency limit at about 1800 cps with a tape speed of 147 ips. On one of the media tested, the recordings decayed about 9 dB in 150 sec, at a humidity of 20%. Improvement of the high‐frequency limitation probably depends on better design of the reproducing head. More‐permanent recordings might be obtained with stronger recording fields, resulting in deeper penetration of the recording medium, or perhaps with the use of a material with more‐suitable characteristics.

ISSN:0001-4966    

DOI:10.1121/1.1909996

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Logarithmic calibration of the range of audible frequencies serves both physical and musical acoustics. Logarithmic assessment of frequency intervals leaves open the choice for a log base, for divisive multipliers, and for some reference frequency serving tabulations of “acoustical logarithms.” Euler's binary‐log measure describes intervals in terms of fractions of an octave; the characteristic counts the octavesrethe frequency standard and the mantissas are invariant with the tonal species. Different forms of binary systems, their transforms (especially duodecimal), and other log systems (common, natural, commatic, etc.) are discussed. The angular transform of 2x, representable as an exponential spiral (helix), portrays the periodic properties of frequencies as perceived by the musical ear in the octave system. Huygens used common logs and antilogs to compute cycles of 12 and 31; Mercator proved the merits of the cycle of 53 by natural logs; Sauveur invented the first acoustical log step scale. Lambert, DeProny, and Drobisch elaborated binary measures, while Ellis, Hornbostel, Young, and Husmann constructed tabulations.

ISSN:0001-4966    

DOI:10.1121/1.1909997

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The ultrasonic pulse‐propagation characteristics of nonmetallic optical fibers were investigated the 10‐Mc/sec region. It was found that the lowest‐order longitudinalL(0,1) mode and the lowest torsional orT(0) mode could be propagated, using piezoelectric transducers. TheL(0,1) mode was propagated through single fibers as well as flexible bundles of fibers. TheT(0) mode was propagated through single fibers. The attenuation was of the order of 0.1 dB/μsec in fused silica fibers of 75 μ diam, and about three times greater in clad glass fibers of the same diameter. In very‐short‐fiber lines, many echoes were observed and the end‐face geometry was not critical. In flexible‐fiber bundles with epoxy fused ends, no echoes were seen owing to the high attenuation of the epoxy, which was greater than 10 dB/mm of coated length. Dispersion was negligible in the single‐fiber lines and flexible fiber bundles, but severe in rigid, fully fused fiber‐optic bundles that behaved essentially as solid rods. There was no significant difference in the ultrasonic behavior of optically coherent and noncoherent flexible‐fiber bundles of short length. Flexible fiber‐optic bundles with fused ends appear to retain the simple acoustic‐mode structure of the single fiber. Various multiple‐fiber arrays are considered in parallel and series grouping and with different input‐output configurations. A multiple‐delay generator using a combination of glass and fused silica fibers of different lengths is described. Further applications are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1909998

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The specimen under test is in the form of a rod with plane parallel ends. A thin annular groove is worked in the rod at about one‐third of its length. A transmitting‐receiving quartz crystal delivers ultrasonic pulses to the rod at its remote end. The pulse heights of the reflections from the constriction and the other end are measured on a cathode‐ray oscillograph. Assuming a plane‐wave propagation, a formula is derived to calculate the attenuation constant of the short portion of the rod in terms of the mentioned pulse heights. The obtained formula is independent of the length or attenuation of the long portion of the rod. This enables one to heat the short portion while the long portion is cooled, thus overcoming the difficulties of matching usually met with in high‐temperature measurements between a quartz transducer and specimen. The method is applied to measure the attenuation of longitudinal waves in pure aluminum at temperatures up to 700°K for frequencies of 3 and 5 Mc/sec, respectively. The results indicate a thermally activated internal friction whose value agrees with that previously obtained by Kâ at a frequency of 1 cps.

ISSN:0001-4966    

DOI:10.1121/1.1909999

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

An experiment was performed on the scattering of ultrasonic waves (25 65 kc/sec) from the turbulence produced by the flow through a grid in a 6×f‐in. nozzle. The transmitter and receiver were of the solid dielectric, condenser type. The scattered signal was separated from the direct and reflected signals by a pulse technique. The intensity of scattered sound was measured at angles from 21.5° to 165° to obtain the differential scattering cross section. The 1‐in. mesh grid was heated to obtain scattering from both the velocity and temperature fluctuations. The results were compared with the formulas derived by Lighthill, Kraichnan, and Batchelor. [Proc. Cambridge Phil. Soc.49531–551 (1953); J. Acoust. Soc. Am.25, 1096–1104(1953); inSymposium on Naval Hydrodynamics, F. S. Sherman, Ed. (National Academy of Science‐National Research Council, Washington, D.C., 1957), Publ. 515, pp. 409 430]. The general shapes of the curves predicted by the theory were obtained experimentally: the scattering was strongly in the forward angles, as was expected for high sound frequencies, with a minimum at 90°. The scattering from the velocity field displayed an additional minimum as 180° was approached, while the scalar field produced strong backscattering. Runs were taken at distances frown the grid to the center of the scattering volume of 5 and 22 in., and at Reynolds numbers of 4110–42 600, based on the grid mesh length.

ISSN:0001-4966    

DOI:10.1121/1.1910000

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The reflection of time‐harmonic plane dilatational or shear waves from the rigid or stressfree boundary of an “arbitrary” linearly viscoelastic half‐space is studied. Properties ofgeneral plane waves—i.e., plane waves whose amplitudes vary across their wavefronts—are used to determine the reflected dilatational and shear waves. In general, the reflected waves are general plane waves and there is a phase shift at the boundary. When certain specified conditions prevail, the reflected waves are attenuated only in their direction of propagation. Necessary and sufficient conditions on the material properties are derived for the existence of surface waves. It is shown that no surface waves can exist for certain viscoelastic materials. In general, surface waves are possible only for discrete incidence angles. However, for a special class of viscoelastic materials, which we callelasticlike, reflected surface waves may exist for a range of incidence angles greater than a specific critical angle. For the elasticlike materials, the phase shift at the boundary is the same as in the analogous elastic problem. In general, the phase velocities and reflected angles are functions of the incidence angle, the frequency, and material properties.

ISSN:0001-4966    

DOI:10.1121/1.1910001

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

The normal‐mode dispersion relation for guided propagation in a liquid layer lying above an infinitely deep liquid bottom appears as a transcendental equation relating the angular frequency ω and the horizontal wavenumberkin Perkeris' classic solution. It is shown in this paper that this transcendental equation may be solved exactly in a parametric form for any given normal mode. Equations are derived and discussed. They give frequency, phase velocity, and group velocity in terms of a single parameter μ and mode numbern.

ISSN:0001-4966    

DOI:10.1121/1.1910002

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

Equations developed by L. V. King [Can. J. Res.11, 135–155 (1934)] can lead to useful expressions for the velocity potential of a circular plane piston, in an infinite rigid baffle, radiating into a dissipationless fluid. An exact series is derived, in negative powers of distance from the center of the piston face to the field point, with specific formulas for all coefficients. The first term is the Fraunhofer approximation. It is then shown that a much simpler series, with the same first term and with explicit coefficients, closely approximates the exact one, provided that the piston radius is at least a few acoustic wavelengths in size and that the field point, as viewed from the source, is at only a small angle from the beam axis. This approximate series always converges, and rapidly so for distances from just outside the near field to the remote regions governed accurately by the Fraunhofer expression. At any distance outside the near field, the angular range of validity includes almost all of the power radiated in the beam.

ISSN:0001-4966    

DOI:10.1121/1.1910003

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

A hollow cylinder is encased in a thin elastic shell and subjected to a time harmonic pressure at the inner surface of the cylinder. Plane strain and axial symmetry are assumed. The material of the cylinder is incompressible in bulk and both elastic and viscoelastic behavior in shear are considered. The inner radius of the cylinder increases monotonically with time. The influence of loss of mass and stiffness on the forced motion of the system is considered. The oscillatory motion consists of the superposition of a maintained vibration and a transient term. The maintained vibration takes into account the loss of mass and stiffness in a quasistatic manner. For an encased viscoelastic cylinder, the transient term is damped rapidly. A bounded resonance effect occurs when the instantaneous frequency of the system passes through the value of the external forcing frequency.

ISSN:0001-4966    

DOI:10.1121/1.1910004

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP

摘要:

A randomly excited single‐degree‐of‐freedom oscillator in which an idealized form of plastic deformation can take place is studied. Through the use of an artificial process, statistics of this nonlinear, hysteretic system are deduced from linear system‐response statistics in two régimes of operation. The expected accumulated plastic deformation is found as a function of time and some other statistics derivable from the artificial process are indicated. A numerical example is given that illustrates the use of the method with low‐cycle fatigue data.

ISSN:0001-4966    

DOI:10.1121/1.1910005

出版商:Acoustical Society of America    

年代:1966

数据来源: AIP