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Nov 1980

Volume 68, Issue S1, pp. S1-S116

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back to top Session CCC. Physical Acoustics IX: General
Contributed Papers
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The linear dynamic range of a simple optical nearfield diffraction technique for studying ultrasonic waves (A)

Ward A. Riley, Jr.

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S106-S107 (1980); (2 pages)

Online Publication Date: 11 Aug 2005

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An optical nearfield diffraction technique was recently described for studying ultrasonic waveforms in the low megahertz frequency range [W. A. Riley, J. Acoust. Soc. Am. 67, 1386–1388 (1980)]. The theoretical optical amplitude response of this technique is linear with acoustical pressure under only a limited range of experimental conditions. Higher harmonics of the fundamental ultrasonic frequency are also generated in the optical signal above this range. Application of this method to the calibration of transducers used in a variety of medical and industrial applications requires that careful consideration be given to the linear dynamic range of this approach. The objective of this work was to experimentally determine the practical linear dynamic range of an optical probe assembled from inexpensive components and used in conjunction with a good laboratory oscilloscope. Measurements were made on narrowband pulses transmitted by circular unfocussed transducers having fundamental frequencies of 2.5 MHz, 5.0 MHz, and 7.5 MHz. A linear dynamic range of approximately 20 dB was determined from these results. This corresponds to acoustical powers between approximately 0.1 and 10 mW in distilled water. The existence of random intensity fluctuations in the megahertz frequency range in the output of the helium‐neon laser source was the limiting factor at the lower end of this range. The nonlinearity of the optical nearfield diffraction pattern produced the upper limit. This 20‐dB window may be lowered approximately 10 dB by selecting a more efficient acousto‐optic medium than water. It may effectively be raised by at least 40 dB by examining normal reflections from the boundary of liquids having small acoustic impedance differences. Consequently, one can effectively observe acoustic pulses over a 70‐dB range with this approach. [Work supported by grant GM27755.]
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A vector‐potential approach to radiation from force‐like sources (A)

W. James Hadden, Jr.

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S107-S107 (1980); (1 page)

Online Publication Date: 11 Aug 2005

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This paper presents an extension of the previously reported analysis of sound radiated by a moving point force, in which the acoustic pressure is represented as the divergence of a vector potential function. A single relationship between the particle velocity and the potential is obtained from the continuity equation. This relationship is employed in the construction of the pressure field above a surface with finite acoustic impedance. Applications to predictions of helicopter rotor noise and to flow noise are discussed.
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Acoustic stop‐bands in solids with transverse property variations (A)

Thomas E. Burton

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S107-S107 (1980); (1 page)

Online Publication Date: 11 Aug 2005

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An acoustic medium whose properties are periodic in the propagation direction is known to have stop bands, frequency bands in which pressure waves are not propagated. A periodic fluid or continuous solid can have an infinite number of stop bands. An analogy has been found in solids with transverse variation that couples pressure waves into rotational waves. A simple analytical approximation for the propagator and effective impedance of the solid is presented for the case where the solid is very stiff in compression (has Poisson's ratio near one‐half), and where the pressure wavelength is much larger, the period of property variation. Results are presented for rubber‐like solids with piece‐wise constant stiffness and density. If the stiffnesses are complex (lossy), then the number of stop bands is finite, typically less than five.
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Differential sound absorption technique and unsymmetrical ion pairing in MgSO4 + NaCl solutions (A)

Cheng‐chih Hsu and Frederick H. Fisher

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S107-S107 (1980); (1 page)

Online Publication Date: 11 Aug 2005

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Sound absorption reduction in 0.02 M MgSO4 solutions with the addition of NaCl has been measured at 25°C and 1 atm, using a 100‐liter titanium spherical resonator. Using the equation Kurtze and Tamm [Acustica 3, 33 (1953)] developed, a/a0  =  [MgSO4]/(MgSO4] + F[NaCl]), our measured results for concentration ratios of [NaCl]/[MgSO4]  =  0, 1, 2, 4, and 6 yields F  =  0.146 ± 0.033, contrary to Kurtze and Tamm′s value, 0.21. Our value of F agrees well with the 0.134 value from theoretical calculations including effects of ionic strength and ion‐pairing of MgSO4, NaSO4−, and MgCl+, using dissociation constants of 0.0062, 0.1, and 0.178, respectively, for these salts. Theory also shows that F is not a constant, but a variable depending on [MgSO4] and [NaCl]/[MgSO4]. If the dissociation constants of the unsymmetrical salts are doubled, F = 0.093. F is 0.052 if only ionic strength effects are included, i.e., no unsymmetrical ion‐pairing. This technique therefore can be used to quantitatively study ion‐pairing of unsymmetrical salts. [Work supported by ONR and NSF.]
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Temperature and impurity dependence of the vibrational collision number for O2−H2, O2−He, and O2−CO2 systems between 300°–675°K (A)

I‐an Feng and M. C. Lee

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S107-S107 (1980); (1 page)

Online Publication Date: 11 Aug 2005

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The oxygen vibrational collision number for three binary systems (O2−H2, O2−He, and O2−CO2) has been measured between 300°–675°K at low impurity concentration using an acoustic resonant technique. For the pure oxygen case extrapolated from the O2−He system, for instance, the experimental vibrational collision numbers follow closely the curve derived from the Parker′s theory [J. G. Parker, J. Chem. Phys. 34, 1763 (1961)] and high temperature (> 1700°K) shock tube data [R. G. Millikan and D. R. White, J. Chem. Phys. 39, 3209 (1963)]. However, our experimental data disagree strongly with the shock tube data trend below 1700°K. The experimental vibrational collision numbers for the binary systems have been found in good agreement with Parker′s theoretical prediction. A new data analysis technique has been developed to sort out the ever‐elusive background loss in the resonant chamber resulting in a more reliable number for the molecular absorption at low impurity concentrations. [Work supported by NASA under Contract Number NAS7‐100.]
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Sound absorption in N2−H2O gas mixtures at elevated temperatures (A)

Allan J. Zuckerwar and Roger W. Meredith

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S107-S107 (1980); (1 page)

Online Publication Date: 11 Aug 2005

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Sound absorption measurements were conducted in N2−H2O gas mixtures at 297°, 343°, and 387°K to determine the location of the vibrational relaxation peak of N2 on the frequency/pressure (f/P) axis as a function of humidity and temperature. At low humidities, the best fit of the reported data to a linear relationship between (f/P)max and humidity h yields, within experimental error, the same slope (2.00 × 104 Hz/atm mole fraction) at all three temperatures. The slope is lower than the value of 2.6 × 104 reported by Chang, Shields, and Bass at higher humidities [J. Acoust. Soc. Am. 63, 577–581 (1977)], but the two sets of data are shown to be mutually consistent by means of a model in which V‐V transfer is assumed to provide the dominant relaxation path. The relationship between (f/P)max and h written into ANSI Standard S1.26/ASA23‐1978 contains an excessively large slope, does not account for the observed transition between the low‐humidity and high‐humidity slopes, and specifies an erroneous temperature dependence. [Work supported by NASA Grant NSG 1324.]
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Pulsed ultrasonic leaky waves on a titanium‐aluminum boundary (A)

Richard O. Claus and Ronald A. Kline

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S107-S107 (1980); (1 page)

Online Publication Date: 11 Aug 2005

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Pulsed 2.1‐MHz leaky waves on an adhesively bonded titanium‐aluminum interface have been generated and detected by aluminum Rayleigh wave mode conversion. Specimens were prepared by bonding 0.95‐cm × 1.27‐cm etched titanium alloy bars to large aluminum substrates and compressing so the thickness of the adhesive layer was much smaller than the acoustic wavelength. Total losses of less than 12 dB due to mode conversion and attenuation along the 1.27‐cm interface have been observed. The adhesive bond geometry is modeled as a liquid layer of thickness H separating two isotropic solid half‐spaces [A. R. Banghar, G. S. Murty, and I. V. V. Raghavacharyulu, J. Acoust. Soc. Am. 60, 1071–1078 (1976)]. Measured leaky wave velocity is approximately predicted by the case where H approaches zero and the viscosity of the liquid becomes large [D. A. Lee and D. M. Corbly, IEEE Trans. Sunics Ultrason. SU‐24, 206–212 (1977)]. Particle displacements near the boundary in both the titanium and the aluminum are derived for this case and changes in leaky wave attenuation due to small variations in H are predicted. [Work partially supported by NSF.]
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Surface fields on sound hard and sound soft obstacles with sharp and smooth boundaries (A)

V. V. Varadan, V. K. Varadan, and D. J. N. Wall

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S108-S108 (1980); (1 page)

Online Publication Date: 11 Aug 2005

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The computation of the surface fields generated on a sound hard or sound soft obstacle when irradiated by a plane harmonic wave is a challenging problem when the obstacle is of arbitrary shape and has corners. Not only is this computation the first step in determining scattered field, but it has other important practical applications such as the dynamic stress concentrations. The integral equation for the field on the surface of the obstacle is solved numerically using null field (T‐matrix approach). It will be shown that for scatterers with corners, a piecewise basis must be chosen to represent the surface fields. Results will be presented for cylindrical scatterers with square, elliptical, and intersecting circular cross sections.
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Measurement of spatial variation in absolute velocity distributed along an inhomogeneous, anisotropic, solid waveguide (A)

Harold M. Frost and James H. Prout

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S108-S108 (1980); (1 page)

Online Publication Date: 11 Aug 2005

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Man‐made composites such as graphite‐fiber reinforced epoxy or aluminum pose an apparent dilemma. The very structural complexity needed for useful traits, like high strength/weight ratio, hinders the structure‐to‐properties correlation process needed for rational material design and use. Also, traditional bulk‐acoustic‐wave non‐destructive tests involving velocity and attenuation data are often not suited for characterizing inhomogeneous materials. Viz., spatial variations in properties within the “thicknesses” between accessible transducer mounting surfaces are masked and even property averages are distorted by multiple scattering. Combined use of guided acoustic waves and scannable ultrasound transducers, however, can sometimes overcome these problems. We illustrate this with measurements of absolute velocities in wire via the noncontacting, torsional wave transducers we described at the 99th AAA meeting (paper XII). With a three‐transducer setup featuring two receivers of calibrated separation x ≪ L  ≃  30 cm (L: wire length), we revealed significant velocity inhomogeneities in graphite/aluminum metal matrix composite wire over section lengths Δ x < 1 cm. Data imprecision was less than ± ½%. Velocity could be correlated meaningfully with the percent volume fraction of graphite. [Supported by Naval Sea Systems Command.]
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Broadband optical interferometer for monitoring Rayleigh waves (A)

Richard O. Claus and John H. Cantrell, Jr.

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S108-S108 (1980); (1 page)

Online Publication Date: 11 Aug 2005

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A wideband differential interferometer has been developed to detect ultrasonic surface wave pulses. The interferometer combines the advantages of wideband Michelson techniques with those of similar narrowband differential methods used to measure cw ultrasonic waves [C. H. Palmer, J. Acoust. Soc. Am. 53, 948 (1973); D. P. Jablonowski, Appl, Opt. 17, 2064 (1978)]. In our system, two coherent light beams are focused on the surface supporting the pulsed waves. The reflected beams are combined interferometrically, filtered, and detected using a broadband optical receiver. Receiver output is proportional to the difference between the normal components of surface particle displacement at the location of the two beams. If an acoustic pulse arrives at one beam focus at time t1 and at the other at t2  =  t1 + Δt, output signal bandwidth during Δt is limited only by detector response. For t > t2, bandwidth is determined by the differential acoustic sensitivity which may be adjusted by altering beam separation. Sensitivity calibration for a nominal 1‐MHz bandwidth and measurements of pulses on a 0.3 cm thick 7070 Pyrex plate are presented.
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A unified picture of plane wave reflectivity from a liquid‐solid interface and a solid plate in a liquid (A)

T. D. K. Ngoc, W. G. Mayer, J. M. Claeys, and O. J. Leroy

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S108-S108 (1980); (1 page)

Online Publication Date: 11 Aug 2005

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The ultrasonic plane wave reflection coefficient for a solid plate immersed in a liquid must be reducible to that for a liquid‐solid interface as the solid plate thickness becomes very large. This can be achieved when absorption is taken into account. The calculated results describe the reflectivity characteristics of a thick solid plate and provide practical criteria to determine the lower limit of the solid sample thickness that can be considered as a half‐space. [This work was supported by the Office of Naval Research, U.S. Navy, and the Scientific Affairs Division, NATO.]
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High‐frequency sound propagation in a moving medium (A)

Y. C. Cho and E. J. Rice

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S108-S108 (1980); (1 page)

Online Publication Date: 11 Aug 2005

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An equation determining the sound ray path in a spatially varying mean flow [L. D. Landau and E. M. Lifshitz, Fluid Mechanics (Addison‐Wesley, Cambridge, MA, 1959) is examined and expanded to study a high‐frequency sound propagation in both potential and rotational mean flows. The study includes the high‐frequency sound refraction through a shear layer of finite thickness.
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Sound attenuation in a liquid‐filled rectangular duct lined with a viscoelastic material in the presence of a uniform flow (A)

Sung‐Hwan Ko Cho and Louis T. Ho

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S108-S108 (1980); (1 page)

Online Publication Date: 11 Aug 2005

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A two‐dimensional theoretical study has been made of the sound attenuation in a liquid‐filled rectangular duct internally lined with a viscoelastic material. In the theoretical analysis, it is assumed that the rectangular duct is rigid, and the viscoelastic liner is an isotropic elastic medium. The viscoelastic liner is a rubber‐like material that has a loss factor associated with the shear modulus. The liner is in perfect contact with the duct wall. The fluid in the lined duct is characterized by the medium density and the speed of sound in the medium. The viscoelastic liner is characterized by Lamé constants which can be expressed in terms of any two of the following quantities; Young's modulus, bulk modulus, and Poisson's ratio. The deviation of the eigenvalue equation was based on the theory of elasticity, the acoustic wave equation in the presence of a uniform flow, and the standard boundary conditions. The eigenvalue equation has been solved numerically, and the sound attenuation was obtained using the calculated eigenvalues.
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