Volume 115, Issue 6, June 2004
Index of content:
- STRUCTURAL ACOUSTICS AND VIBRATION 
On the natural frequencies of short cylinders and the universal point. Direct determination of the shear modulus115(2004); http://dx.doi.org/10.1121/1.1739485View Description Hide Description
This work presents a study of the relation between the lowest nondimensional natural frequencies of a short, free cylinder vibrating in axisymmetric modes, its slenderness ratio, and its Poisson’s ratio. Ritz’s method applied to the study of the symmetric vibration of cylinders confirms that all curves, which show the dependence of frequency versus slenderness, pass through a point, called universal, independently of Poisson’s ratio. The lowest universal frequency is 2.6036 and corresponds to a cylinder whose quotient of its length and its diameter is 0.853 22. The rules leading to the identification of the first symmetric mode are inferred from the numerical results. A cylinder with universal slenderness ratio is set into free vibration by applying an axial impact. The lowest axisymmetric natural frequencies are obtained from measurement of the axial displacement by speckle interferometry. A simple arithmetical operation permits calculation of the shear modulus from the value of the first symmetric frequency, the diameter of the cylinder, and its density. The quotient of frequencies of two similar cylinders is studied as a function of their elastic properties and diameters.
115(2004); http://dx.doi.org/10.1121/1.1715111View Description Hide Description
The scattering of acoustic ultra-wideband X-wave pulses by a nonrigid sphere is simulated for purposes of material identification and characterization. Using the backscattered spectrum of the X-wave pulses, a procedure is described for estimating the radius, speed of sound, and density of the sphere. The effectiveness of the suggested technique is verified in the case that the peak of the X wave is incident on the centers of the sphere, as well as for the off-center incidence case.
A finite-element/boundary-element method for the modeling of piezotransducer radiation in fluids using a polynomial development of the Green’s function115(2004); http://dx.doi.org/10.1121/1.1694998View Description Hide Description
Ultrasound transducers are widely used in acoustic imaging applications to launch and receive pressurewaves radiated and diffracted in fluids or solids. The design and optimization of these devices require the development of accurate models taking into account their actual working conditions. Particularly, much of work has been devoted to simulate ultrasound transducers radiating in semi-infinite fluids. Such developments are devoted to accurately predict the frequency bandwidth of ultrasound transducers (optimization of their axial resolution) but also their sensitivity. In the proposed work, a mixed formulation combining finite element and boundary element methods has been developed to simulate acoustic radiation of piezotransducers in fluids, using a rigorous analytical development of the 2D Green’s function of the fluid. Results of the proposed calculation are compared to those provided using a more classical approach previously developed based on a numerical integration using Gauss points and weights. It is shown that the proposed approach yields efficient analysis of 2D problems with a very low sensitivity to the number of boundary elements used to simulate radiation phenomena.