Index of content:
Volume 125, Issue 5, May 2009
- STRUCTURAL ACOUSTICS AND VIBRATION 
125(2009); http://dx.doi.org/10.1121/1.3086267View Description Hide Description
Systematically derived equations for fluid-loaded thin poroelastic layers are presented for time-harmonic conditions. The layer is modeled according to Biot theory for both open and closed pores. Series expansion techniques in the thickness variable are used, resulting in separate symmetric and antisymmetric plate equations. These equations, which are believed to be asymptotically correct, are expressed in terms of approximate boundary conditions and can be truncated to arbitrary order. Analytical and numerical results are presented and compared to the exact three dimensional theory and a flexural plate theory. Numerical comparisons are made for two material configurations and two thicknesses. The results show that the presented theory predicts the plate behavior accurately.
Optimal simulations of ultrasonic fields produced by large thermal therapy arrays using the angular spectrum approach125(2009); http://dx.doi.org/10.1121/1.3097499View Description Hide Description
The angular spectrum approach is evaluated for the simulation of focused ultrasound fields produced by large thermal therapy arrays. For an input pressure or normal particle velocity distribution in a plane, the angular spectrum approach rapidly computes the output pressure field in a three dimensional volume. To determine the optimal combination of simulation parameters for angular spectrum calculations, the effect of the size, location, and the numerical accuracy of the input plane on the computed output pressure is evaluated. Simulation results demonstrate that angular spectrum calculations performed with an input pressure plane are more accurate than calculations with an input velocity plane. Results also indicate that when the input pressure plane is slightly larger than the array aperture and is located approximately one wavelength from the array, angular spectrum simulations have very small numerical errors for two dimensional planar arrays. Furthermore, the root mean squared error from angular spectrum simulations asymptotically approaches a nonzero lower limit as the error in the input plane decreases. Overall, the angular spectrum approach is an accurate and robust method for thermal therapy simulations of large ultrasoundphased arrays when the input pressure plane is computed with the fast nearfield method and an optimal combination of input parameters.
Decentralized harmonic control of sound radiation and transmission by a plate using a virtual impedance approach125(2009); http://dx.doi.org/10.1121/1.3106124View Description Hide Description
The problem under study in this article is the active control of sound transmission and radiation of a panel under a periodic excitation. The control strategy investigated uses independent control loops between an individual polyvinylidene fluoride (PVDF) sensor and an individual lead zirconate titanate(PZT) actuator. The specific approach employed here uses the concept of virtual impedance. The aim is to determine for each frequency the optimal impedance between each PVDF sensor and the corresponding PZT actuator in order to reduce the sound power radiated by the plate. Theoretical predictions are compared to measurements of the sound radiated and transmission loss of a panel mounted with eight PZT-PVDF units. Reductions of up to 20 dB of the acoustic power can be achieved around mechanical resonances of the system, while the control strategy has little effect for off-resonance excitations.