Volume 103, Issue 5, May 1998
Index of content:
- GENERAL LINEAR ACOUSTICS 
103(1998); http://dx.doi.org/10.1121/1.422746View Description Hide Description
Classical Lamb waves in an homogeneous, isotropic linearly elastic plate are reconsidered. The displacement components are obtained in terms of thickness motions superimposed on a membrane carrier wave which defines the propagation along the plate. The carrier wave can be any solution of the reduced wave equation for a membrane. The analysis of the thickness motions results in the usual Rayleigh–Lamb frequency equation. A number of special cases for the carrier wave are considered.
103(1998); http://dx.doi.org/10.1121/1.422747View Description Hide Description
The feasibility of exciting a localized X-wave pulse from a finite aperture is addressed. Also, the possibility of using a finite-time excitation of a dynamic aperture to generate a finite-energy approximation to an X-wave pulse is explored. The analysis is carried out by using a Gaussian time window to time limit the infinite X-wave initial excitation. Huygens’ construction is used to calculate the amplitude of the radiated wave field away from the finite-time source. The decay rate of the peak of the X wave is compared to that of a quasi-monochromatic signal. It is shown that the finite-time X-wave propagates to much farther distances without significant decay. Furthermore, the decay pattern of the radiated X-wave pulse is derived for a source consisting of an array of concentric annular sections. The decay behavior of the radiated pulse is similar to that of an X-wave launched from a finite-time aperture. This confirms the fact that time windowing the infinite energy X-wave excitation is a viable scheme for constructing finite apertures. A discussion of the diffraction limit of the X-wave pulse is also provided.
103(1998); http://dx.doi.org/10.1121/1.422748View Description Hide Description
In this paper analytic formulas are developed for the ray path and travel time of a ray propagating in a wavy fiber–epoxy composite material and calculate them for rays initiating at various points with wave normals of differing directions. The arrival times observed by using various combinations of pointlike sources and pointlike detectors are found in good agreement with those predicted by the theory of geometrical acoustics.
103(1998); http://dx.doi.org/10.1121/1.422749View Description Hide Description
Acoustical data transmission through the wall of drill pipes is considered. Drill pipes are known to behave like bandpass filters; the position of the pass bands can be determined analytically. This work extends the frequency domain drill pipe models presented by Barnes and Kirkwood [J. Acoust. Soc. Am. 51, 1606–1608 (1972)], and more recently by Drumheller [J. Acoust. Soc. Am. 85, 1048–1064 (1989)]. The approach discussed in this paper has the advantage that it yields explicit expressions for the fine structure of the drill pipe’s frequency response in the pass bands. It furthermore allows the effect of energy dissipation and pipe segment length variations to be included in the model. The emphasis of the paper, however, lies on the time domain modeling of the drill pipe. The propagation of sound energy pulses through its wall, and the effect of multiple reflections and/or transmissions during this propagation, are described using a Markov chain. Explicit expressions result for the expected duration of an energy pulse’s trip from one end of the drill pipe to the other, depending upon the number of drill pipe segments and the transmission coefficient at the tool-joints connecting them. The results are applicable to any situation where sound or energy transmission through a cascade of acoustic components occurs.