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Journal of the Acoustical Society of America

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May 2004

Volume 115, Issue 5, pp. 1851-2634

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The calculation of radiated acoustic pressure fields from irregular multi-sided polygons

Adrian Neild and David A. Hutchins

J. Acoust. Soc. Am. Volume 115, Issue 5, pp. 2021-2031 (2004); (11 pages)

Online Publication Date: 16 Apr 2004

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This paper presents a method of calculating the pressure at any point emerging from a plane piston of polygonal shape in an infinite baffle. This is achieved by calculation of the impulse response as a time-stepped function, and considering the effect of each edge of the polygon in turn. The pressure is found from the convolution of this function with the time derivative of the piston velocity multiplied by the density of the propagation medium. Calculated pressure fields are shown for both a series of sources shaped as regular polygons, and for a source with an irregular shape. It is shown that the approach could be useful for the calculation of radiated fields from sources of arbitrary shape. © 2004 Acoustical Society of America.
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43.35.Ae Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in gases
43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
43.20.El Reflection, refraction, diffraction of acoustic waves

Ultrasonic delineation of aortic microstructure: The relative contribution of elastin and collagen to aortic elasticity

Jon N. Marsh, Shin Takiuchi, Shiow Jiuan Lin, Gregory M. Lanza, and Samuel A. Wickline

J. Acoust. Soc. Am. Volume 115, Issue 5, pp. 2032-2040 (2004); (9 pages)

Online Publication Date: 16 Apr 2004

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Aortic elasticity is an important factor in hemodynamic health, and compromised aortic compliance affects not only arterial dynamics but also myocardial function. A variety of pathologic processes (e.g., diabetes, Marfan’s syndrome, hypertension) can affect aortic elasticity by altering the microstructure and composition of the elastin and collagen fiber networks within the tunica media. Ultrasound tissue characterization techniques can be used to obtain direct measurements of the stiffness coefficients of aorta by measurement of the speed of sound in specific directions. In this study we sought to define the contributions of elastin and collagen to the mechanical properties of aortic media by measuring the magnitude and directional dependence of the speed of sound before and after selective isolation of either the collagen or elastin fiber matrix. Formalin-fixed porcine aortas were sectioned for insonification in the circumferential, longitudinal, or radial direction and examined using high-frequency (50 MHz) ultrasound microscopy. Isolation of the collagen or elastin fiber matrices was accomplished through treatment with NaOH or formic acid, respectively. The results suggest that elastin is the primary contributor to aortic medial stiffness in the unloaded state, and that there is relatively little anisotropy in the speed of sound or stiffness in the aortic wall. © 2004 Acoustical Society of America.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.58.Dj Sound velocity
43.80.Ev Acoustical measurement methods in biological systems and media

Lamb wave propagation in elastic plates coated with viscoelastic materials

F. Simonetti

J. Acoust. Soc. Am. Volume 115, Issue 5, pp. 2041-2053 (2004); (13 pages) | Cited 11 times

Online Publication Date: 16 Apr 2004

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This paper addresses the effects of attenuative coatings on the dispersion characteristics of Lamb wave propagation in elastic plates. The topology of phase velocity and guided wave attenuation spectra is analyzed as a function of the coating internal damping (longitudinal and shear bulk attenuations) and it is proved that in contrast to elastic plates, all modes are propagating albeit with large attenuation in some cases. An energy-based correspondence between the dispersion of the attenuative bilayer and that of a related elastic bilayer is derived in order to investigate separately the effects of the longitudinal and shear bulk attenuations on the attenuation of the guided modes. It is shown that at low frequency the guided wave attenuation is only slightly affected by the longitudinal bulk attenuation, while the contribution of the shear bulk attenuation is substantial. The attenuation characteristics of shear horizontal modes are compared with those of Lamb modes in order to identify the mode and the frequencies which result in minimum guided wave attenuation. © 2004 Acoustical Society of America.
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43.35.Mr Acoustics of viscoelastic materials
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products

Laser-generated thermoelastic acoustic sources in anisotropic materials

David H. Hurley

J. Acoust. Soc. Am. Volume 115, Issue 5, pp. 2054-2058 (2004); (5 pages) | Cited 2 times

Online Publication Date: 16 Apr 2004

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An analytical model appropriate for thermoelastic generation of acoustic waves in anisotropic materials is presented for both plane and line sources. The interaction of acoustic waves produced by subsurface sources with the bounding surface is accounted for using a method of images. For the plane source case, analytical solutions are found that form an appropriate basis for an angular spectrum of plane waves. For the line source case and for specific crystal symmetries and source orientations, it is shown in the limit of strong optical absorption, a buried line source is equivalent to applying a shear stress dipole at the bounding surface. However, contrary to the isotropic case, the character and strength of the equivalent surface stress is a function of propagation direction. © 2004 Acoustical Society of America.
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43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography

Thermoacoustic enrichment of the isotopes of neon

D. A. Geller and G. W. Swift

J. Acoust. Soc. Am. Volume 115, Issue 5, pp. 2059-2070 (2004); (12 pages) | Cited 2 times

Online Publication Date: 16 Apr 2004

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The enrichment of the neon isotopes in a thermoacoustic device is demonstrated. Because the thermal diffusion ratio of neon is small, an apparatus longer than a wavelength was necessary in order to easily observe the separation. The device was modular and extensible, so that arbitrarily large separations could in principle be obtained. The acoustic duct was a series of multiple, identical quarter-wavelength modules with side-branch drivers. In this way, waveforms close to that of a traveling wave were maintained in the duct, despite the high acoustic attenuation caused by the duct’s small diameter and large length. The concentrations of the isotopes were measured at one end of the duct using a quadrupole mass spectrometer. For the operating frequency of 227 Hz, the maximum separation gradient obtained was 0.43%/m, and mole fluxes at zero gradient as high as 3 nmol/s were observed. Effects of turbulence, though not observed, are also discussed, and the scaling properties of this method are compared with those of traditional mixture-separation methods. © 2004 Acoustical Society of America.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.35.Ty Other physical effects of sound

Measurements of the resistance of parallel-plate heat exchangers to oscillating flow at high amplitudes

Ray Scott Wakeland and Robert M. Keolian

J. Acoust. Soc. Am. Volume 115, Issue 5, pp. 2071-2074 (2004); (4 pages) | Cited 3 times

Online Publication Date: 16 Apr 2004

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Measurements of the acoustic resistance of parallel-plate heat exchangers are reported. The resistance is measured for two identical exchangers separated by a small gap, and also by a large gap. High amplitude deviations from linear theory are analyzed in terms of a minor loss coefficient. Results are compared to theoretical predictions made in a previous article. © 2004 Acoustical Society of America.
Show PACS
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
43.25.Ed Effect of nonlinearity on velocity and attenuation
47.60.-i Flow phenomena in quasi-one-dimensional systems
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