摘要:

The spectral distribution of scattered light is calculated for the model of a liquid in which the bulk and shear relaxation processes are each characterized by a multiplicity, or a continuous set, of relaxation times. The treatment is a generalization of that given by the authors previously [Phys. Rev.173, 231 (1968)] in which bulk relaxation was ascribed to the relaxation of a thermodynamic order parameter relaxing with a single relaxation time. It is found that, in general, one has to introduce two independent distribution functions associated with the bulk relaxation times. Only when all the bulk relaxation processes are of the same type (pressure induced, temperature induced, etc.), does the expression for the spectral function contain just one distribution for bulk relaxations. This is in contrast to the results obtained by previous workers and may have significance in relation to a reported discrepancy in interpreting (in terms of a single distribution function for bulk relaxation) experimental data on Brillouin scattering and ultrasonic absorption in glycerine.

ISSN:0001-4966    

DOI:10.1121/1.1912516

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The temperature dependence of the piezo‐optic coefficient and the elasto‐optic coefficient has been measured for water, ethyl alcohol, methyl alcohol, carbon tetrachloride, benzene, toluene, acetone, hexane, and cyclohexane. Only for the unassociated liquids, benzene and carbon tetrachloride, are the measurements in agreement with simple theory.

ISSN:0001-4966    

DOI:10.1121/1.1912517

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

A thin‐film resonance technique is described for measuring the dispersion and absorption of acoustic waves in lossy liquids from 0.5 to 2.2 GHz. The method uses Bragg scattering of laser light to measure the incident and reflected acoustic power from a 4.2‐μ liquid film formed between two sapphire rods. It is shown how the velocity and absorption are calculated from the measured acoustic reflection coefficient. The technique is used to study the two Dow Corning resins 276‐V2 and 276‐V9, both of which are found dispersionless within experimental error. The absorption per wavelength initially decreases with frequency for both resins; for resin V9, however, the absorption shows an increase at the higher frequencies. The results obtained are interpreted in terms of relaxational processes.

ISSN:0001-4966    

DOI:10.1121/1.1912518

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The character of surface and pseudosurface waves in a discrete lattice is discussed. Results are given for the particular example of a model fcc crystal with (100) surfaces and anisotropy ratio η>1. The lattice results extend and complement the elastic continuum results of Lim and Farnell. General arguments allow qualitative extension of the present results to encompass the cases of cubic crystals having different surfaces [viz., (110) or (111)] or having anisotropy ratio η<1.

ISSN:0001-4966    

DOI:10.1121/1.1912519

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

A series of field tests was conducted to determine the enhancement in reception of infrasonic signals in the atmosphere made possible by the use of a multiplicity of sensors. Firings of a 5‐in. cannon were used as the source. The effect of the pattern and spacing of the sensors on signal‐to‐noise ratio was investigated until useful criteria were established. Multiplicities up to 224 active sensor elements were employed. The signal‐to‐noise enhancement was shown to be approximately equal to the square root of the number of sensors. Sensor multiplicity enabled the reception of signals at distances up to 47 miles upwind from the source.

ISSN:0001-4966    

DOI:10.1121/1.1912520

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Measurements of the backscatter of sound waves from three types of rough surfaces and a 6‐in. stepdown were performed. Linearly frequency‐modulated pulses were used in an effort to reduce fluctuations in the returned pulses caused by turbulence in the air. The use of FM pulses displayed the extreme frequency sensitivity of the backscatter from a very rough surface; however, the FM pulses allowed the returned signal to be averaged over a frequency interval determined by the degree of frequency modulation. Using this type of averaging, it was found that the mean‐square backscatter from all surface types was only weakly dependent upon frequency; similarly, a relatively weak dependence on angle of incidence was found in the range of 0°–60°. The frequency range of the measurements was from 40 to 200 kHz; in this range the transmitted signal was linearly frequency modulated by 10, 20, and 40 kHz from initial frequencies of 40, 80, 120, and 160 kHz.

ISSN:0001-4966    

DOI:10.1121/1.1912521

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

A theoretical study has been made on the free‐field correction of laboratory standard microphones mounted on a semiinfinite rod. In the analysis, we have discussed the diffraction phenomena of plane sound waves by the actual microphone system, taking into consideration the effect of a recess as well as the interaction between microphone diaphragm and medium. A new method of solving wave equations met with these boundary conditions, called the infinite‐matrix method, is presented in this paper. Our whole problem is divided into three parts. The first is concerned with the external free field, which can be solved rigorously by Wiener‐Hopf technique; the others refer to the solution of the sound field inside a recess and, finally, to motions of a diaphragm. After putting these solutions into the form of matrix equations with unknown variables, we obtain a system of simultaneous matrix equations by connecting solutions with each other. Numerical results are given for the free‐field correction of the Western Electric Company type 640AA microphone. Comparison with the experiment, made at the National Bureau of Standards, indicates that sufficient agreement is obtained.

ISSN:0001-4966    

DOI:10.1121/1.1912522

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The effect of a rough moving surface upon transmission between an omnidirectional source and receiver in an isovelocity medium is described for the case of a “slightly rough” surface using the method of physical optics. This is done by relating the spectral density of the received pressure to the spectral density of the source and the wave spectrum of the surface and also the geometry. The dependence of the received spectrum upon the interference between the direct and reradiated waves and the characteristics of the “frequency smearing” caused by scattering are described. A favorable comparison of the theory with the results of an experiment performed under nearly ideal conditions in a model tank is made.

ISSN:0001-4966    

DOI:10.1121/1.1912523

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The velocity dispersion of the Young's modulus mode in a number of finite cylindrical fused silica, aluminum, steel, and brass rods was determined. Their velocity dispersion is shown to agree extremely well with that calculated from the Pochhammer‐Chree theory for infinite rods of the same materials over the range of Ω values from 0 to 2.6, whereΩ=ωa/cs,ais the bar radius, andcsis the shear‐wave velocity. Small differences between the experimental and theoretical velocity dispersion occur when Ω exceeds 2.6; this is attributed to the occurrence of a phase shift when theL(0,1) mode is reflected from the endfaces of a rod. For every rod a few harmonics have been found to occur that do not lie on a smooth graph of frequency versus harmonic number. They may be displaced in frequency, or replaced by several resonances lying close together in frequency. This phenomenon occurs at specific values of Ω, which are associated with an end resonance and the higher‐order symmetric modes.

ISSN:0001-4966    

DOI:10.1121/1.1912524

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The normal‐mode solution for the response of a point‐excited cylindrical shell converges poorly for high frequencies. Converting the normal‐mode series to an integral representation using a Watson transformation, we obtain a new alternate representation of the solution which converges with only very few terms in the high‐frequency regime. Furthermore, this new representation, when compared to the response of a point‐excited plate, can be interpreted as a superposition of propagating disturbances that circumnavigate the cylinder in helical paths from the drive path to the field point, with the phase velocity characteristic of flexural waves in a flat plate.

ISSN:0001-4966    

DOI:10.1121/1.1912525

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP