Index of content:
Volume 128, Issue 6, December 2010
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
Linearized forward and inverse problems of the resonant ultrasound spectroscopy for the evaluation of thin surface layers128(2010); http://dx.doi.org/10.1121/1.3500671View Description Hide Description
In this paper, linearized approximations of both the forward and the inverse problems of resonantultrasound spectroscopy for the determination of mechanical properties of thin surface layers are presented. The linear relations between the frequency shifts induced by the deposition of the layer and the in-plane elastic coefficients of the layer are derived and inverted, the applicability range of the obtained linear model is discussed by a comparison with nonlinear models and finite element method(FEM), and an algorithm for the estimation of experimental errors in the inversely determined elastic coefficients is described. In the final part of the paper, the linearized inverse procedure is applied to evaluate elastic coefficients of a 310 nm thick diamond-like carbon layer deposited on a silicon substrate.
128(2010); http://dx.doi.org/10.1121/1.3506348View Description Hide Description
A model of an idealized thermoacoustic engine is formulated, coupling nonlinear flow and heat exchange in the heat exchangers and stack with a simple linear acoustic model of the resonator and load. Correct coupling results in an asymptotically consistent global model, in the small Mach number approximation. A well-resolved numerical solution is obtained for two-dimensional heat exchangers and stack. The model assumes that the heat exchangers and stack are shorter than the overall length by a factor of the order of a representative Mach number. The model is well-suited for simulation of the entire startup process, whereby as a result of some excitation, an initially specified temperature profile in the stack evolves toward a near-steady profile, eventually reaching stationary operation. A validation analysis is presented, together with results showing the early amplitude growth and approach of a stationary regime. Two types of initial excitation are used: Random noise and a small periodic wave. The set of assumptions made leads to a heat-exchanger section that acts as a source of volume but is transparent to pressure and to a local heat-exchanger model characterized by a dynamically incompressible flow to which a locally spatially uniform acoustic pressure fluctuation is superimposed.
128(2010); http://dx.doi.org/10.1121/1.3500683View Description Hide Description
Diffuse ultrasonicbackscatter techniques are useful for probing heterogeneous materials to extract microstructural parameters and detect flaws which cannot be detected by conventional ultrasonic techniques. Such experiments, usually done using a modified pulse-echo technique, utilize the spatial variance of the signals as a primary measure of microstructure. Quantitative ultrasonicscattering models include components of both transducer beams as well as microstructural scattering information. Of particular interest for interpretation of many experiments is the propagation through a liquid–solid interface. Here, a recent single-scattering model is expanded to include components needed for comparison with experiments. In particular, the Wigner distribution of the displacement profile is derived to model the beam pattern of an ultrasonic transducer through a curved liquid-solid interface. A simple Gaussian beam is used to model the transducer beam pattern. This expression is then used in conjunction with an appropriate scattering operator to complete the derivation. The theory developed is then compared with experimental results for a fine-grained steel using both a planar and a cylindrical interface. These results are anticipated to impact ultrasonic nondestructive evaluation and characterization of heterogeneous media with arbitrary curvatures.