摘要:

Continuing development has increased the capabilities of the spectral‐analysis instrumentation reported earlier [D. E. Wood and T. L. Hewitt, J. Acoust. Soc. Am.35, 1274–1278 (1963)]. This analyzer operates in real time by very rapid scanning of the outputs of a bank of bandpass filters. A unique process of true interpolation generates continuous spectral cross sections that preserve accurate frequency relations of signal components. The cross sections are recorded on strip film by photographing their display on a CR tube. Spectrographic‐picture formats previously described include complete cross‐section records and spectrograms showing amplitude by intensity‐modulation. A new display technique clarifies frequency patterns by marking just at the amplitude maxima or “peaks” in spectral cross sections. The simplified picture of the spectral “hilltops” pinpoints the frequencies and frequency modulations of features such as speech formants. This binary type of picture requires no grey scale and improves the resolution of small features. The “peak” display may be combined with other formats by means of a selector‐combiner device. A novel analog integrator now provides flexible time‐averaging by adding spectral cross sections in numbers variable from 2 to over 1000. The periods of averaging can be overlapped and the integrator could be equipped to provide simultaneous multiple outputs representing different averaging periods. The analyzer system is organized to take full advantage of the various kinds of flexibility with a minimum of operational steps. The combination of simple control, real‐time operation, and strip‐film recording provide the capabilities for large‐scale investigations, while flexibility of analysis and display increase the information to be seen in the spectrographic pictures.

ISSN:0001-4966    

DOI:10.1121/1.1919029

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Ultrasonic attenuation and velocity measurements have been made in pure germanium and silicon (doping<1014impurity atoms per cc) and in dopedn‐type germanium andp‐type silicon. The attenuation in pure materials shows a continuous decrease as the temperature is decreased and a very low attenuation below 20°K. These results indicate that the energy losses are accounted for entirely by phonon‐phonon interactions. A calculation has been made of these losses, using a model based on the Akheiser effect and incorporating the recently measured third‐order elastic moduli of silicon and germanium. For both materials, the calculated values predict correctly the large difference between longitudinal and shear waves and agree quantitatively within 50% with the measured values over the whole temperature range.

ISSN:0001-4966    

DOI:10.1121/1.1919031

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The Mindlin‐McNiven equations for axially symmetric waves are used to determine the radial strains in a circular, semiinfinite, isotropic, elastic rod for both pure and mixed end conditions when a constant pressure is suddenly applied to its end. Using double‐integral transforms, the solution is obtained in terms of three Fourier integrals, each one representing one mode of propagation. These integrals are too complex to be evaluated exactly and, therefore, an asymptotic solution, valid for large distance of travel, is obtained for the head of the pulse by using the method of steepest descent. The results predict the existence of edge resonance and further demonstrate its influence on the strain field.

ISSN:0001-4966    

DOI:10.1121/1.1919033

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Starting with two Boltzmann‐like equations, a kinetic theory is made of the long‐wavelength disturbances that propagate in a two‐component neutral fluid. A transition is observed from separate adiabatic sound speeds for each gas in the case of weak coupling to the single adiabatic sound speed of the gas mixture plus strongly damped relative motion in the opposite extreme of strong coupling between the gases.

ISSN:0001-4966    

DOI:10.1121/1.1919035

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The first part of this paper treats the axisymmetric transverse vibrations of membrane shells. The stress differential equations of motion with longitudinal inertia neglected are solved for a class of shells that includes the ogive, cone, cylinder, and sphere. The emphasis is placed on predicting the lowest natural frequency of vibration for shells with a free boundary. These frequencies are compared with the previously known results of the bending solutions for the shallow spherical‐shell segment and for the hemispherical shell. In the second part, attention is turned to the shell whose mode of deformation is primarily flexural by applying hypotheses associated with edge effects. The deformation is specified by a pair of differential equations that are solved for a class of shells of revolution. The frequency equation is obtained and particularized to specific geometries.

ISSN:0001-4966    

DOI:10.1121/1.1919037

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The theoretical steady‐state response of an axially excited bar having solid damping is determined. The effect of adding one or two dynamic absorbers is considered, as well as the effect of adding concentrated mass only. Tuning of the absorbers and optimization of damping are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1919039

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

An acoustic or electromagnetic wave propagating in a material medium experiences fluctuations in amplitude and phase that can be attributed in part to scattering from inhomogeneities due to variations in the refractive index of the transmission medium. Since such “patches of inhomogeneity” are often regarded as lenticular in shape, it is the purpose of this paper to extend, for both plane and spherical sound waves, contemporary wave‐fluctuation theory (based on a Gaussian correlation function for refractive index) to include the circumstance of spheroidal inhomogeneities. Mean‐square amplitude and phase fluctuations are considered for acoustic waves propagating in a statistically isotropic medium in which random deviations of the refractive index are small. Large‐scale inhomogeneities of arbitrary spheroidal shape are treated, and the influence of transmitter‐to‐receiver range, acoustic wavelength, and “patch” dimensions on variations in wave amplitude and phase is derived for this general case. Particular attention is given the high‐frequency ray limit (Bergmann region) and the low‐frequency (Fraunhofer diffraction) region. The significant effects on wave fluctuations of both spherical and nonspherical inhomogeneities are compared for plane and spherical acoustic waves.

ISSN:0001-4966    

DOI:10.1121/1.1919041

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The eikonal equation of ray acoustics is discussed for the general case, with the index of refraction a function of the three space coordinates. Two examples illustrating the influences of a two‐dimensional heat source and a thermal‐mixing zone on the acoustic‐ray paths are presented. Numerical results show that, for long‐range acoustical ray tracing, inhomogeneities of the ocean in the horizontal plane can cause refraction effects, which are not negligible in comparison with effects due to vertical inhomogeneities. Rays, which travel in the vicinity of a heat source, can be refracted as much as 6°. Thermal‐mixing zones can increase the range of shadow zones near the ocean surface up to 50%. Even new shadow zones can be formed.

ISSN:0001-4966    

DOI:10.1121/1.1919043

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

A theoretical expression is developed for the sensitivity of liquid‐filled, cylindrical, ceramic hydrophones having rigid and semirigid end caps. The theory gives good agreement with experimental measurements on a lead zirconate‐titanate hydrophone with two end‐cap conditions and three different enclosed fluids.

ISSN:0001-4966    

DOI:10.1121/1.1919045

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

This paper investigates requirements for neutral acoustic stability in cavities with a transpiring wall where there is a mean flow in the absence of acoustic disturbances. The growth rates of the acoustic fields are also considered. The method of calculation utilizes time averages of the mass, momentum, and energy‐conservation equations to second order in the acoustic‐field quantities. It is found that growth rate and neutral stability may be expressed in terms of only first‐order quantities. The results are shown to be in agreement with those calculated from first‐order admittance considerations, but differ, in general, from those of Dyer, who uses a method of calculation similar to the present paper. The resolution of this conflict is discussed. The effect of mean flow is often of considerable importance, and the extent to which flow tends to excite or damp the acoustic field is related to mode configuration and flow‐field geometry. Application to the problem of determining the acoustic response of burning rocket propellants is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1919047

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP