Index of content:
Volume 128, Issue 5, November 2010
- GENERAL LINEAR ACOUSTICS 
128(2010); http://dx.doi.org/10.1121/1.3490855View Description Hide Description
A technique for the rapid, smooth turn-on of a transducer is described. The method is based on a previously described technique [J. C. Piquette, J. Acoust. Soc. Am.92, 1203–1213 (1992)]. In the previous method, transducer output amplitude is severely reduced compared to that obtained when driving the transducer using a standard gated sine due to the presence of a ramp component in the transient-suppressing voltage waveform. In the present work, approximate methods that eliminate the ramp component are described. Eliminating the ramp component results in significantly greater output amplitude, although the level of transient suppression that is achieved is not as good as that seen when using the exact transient-suppressing drive. Nonetheless, the smoothness (i.e., lack of spikes) in the transducer response is not compromised by the approximations.
128(2010); http://dx.doi.org/10.1121/1.3493433View Description Hide Description
A model is developed for studying the acoustic behavior of a cMUT array. This model is based on separate calculations of the terms describing the behavior of a single cMUT on one hand, and those corresponding to acoustic mutual coupling on the other hand. The terms are combined into an equivalent circuit with matrix terms which displays only one degree of freedom per cell. This approach allows the simulation of several dozen cMUTs considered individually with a very short computer time. A Finite Difference model is used for the simulation of an isolated cell radiating acoustic energy and the determination of its equivalent electromechanical circuit. It is shown for various mutual coupling situations that the coupling between cells can be correctly approximated using a very simple mutual impedance term. The model is compared with experimental results, using a set of different cMUT configurations. Experimental results were obtained with electrical impedancemetry and laser interferometry techniques performed in fluid immersion.
Implementation of a constrained Ritz series modeling technique for acoustic cavity-structural systems128(2010); http://dx.doi.org/10.1121/1.3488306View Description Hide Description
A prior study [Ginsberg, J. H. (2010b). J. Acoust. Soc. Am.127, 2749–2758] used Ritz series in conjunction with Hamilton’s principle to derive general equations describing the time domain response of an acoustic cavity bounded by an elastic structure. The equations of motion are supplemented by constraint equations that explicitly enforce velocity continuity at the cavity’s surface. These constraints are imposed by the surface traction, which is represented by unknown coefficients of Ritz-type series. The resulting set of equations are differential-algebraic type. Three methods are presented to convert the governing equations to forms that are familiar to structural acoustics, including one that transforms them from differential-algebraic type to the standard ordinary differential equations associated with linear multi-degree-of-freedom vibratory systems. In cases where only the structure is excited, the formulation offers options as to how displacement/velocity boundary conditions on the nonstructural boundary are enforced, as well as whether zero pressure boundary conditions are enforced at all. An example of a one-dimensional waveguide that is closed at one end by an oscillator is used to explore the quality of solutions obtained from each of these options. Results for natural frequencies and mode functions are examined for accuracy and convergence.