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A recent paper [M. Stojanovic J. Acoust. Soc. Am. 117, 1173-1185 (2005)] presented theoretical performance bounds of time reversal communications. In this letter, the performance of time reversal communications is evaluated using at-sea experimental data and compared to the theory for two different approaches; (1) time reversal alone and (2) time reversal combined with channel equalization. It is found that approach (1) shows a good agreement between theory and data. On the other hand, approach (2) indicates that the data is about 3-5 dB below the theory which assumes perfect knowledge of the channel, an infinite number of taps to remove the intersymbol interference, and no need for phase tracking. Taking these into consideration, the theoretical performance can provide a useful upper bound for predicting performance of time reversal communications.

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In order to understand the cause and effect relation between a structure and a fluid, many studies on structural-acoustic coupling have been done. However, the studies were restricted to the interaction between only a structure and a fluid located on one or the other side of the structure. It is our aim to understand the coupling mechanism of a generally coupled system that has direct interaction between a finite interior fluid and a semi-infinite exterior one. We believe that this configuration allows the structure to interact with the fluid of the finite volume and that of the infinite one, thus providing a more general structure-fluid coupling (or structural-acoustic coupling) mechanism. For this purpose, we selected a partially opened plate-cavity system which has two different modally reacting boundary conditions: a plate and a hole. In order to understand the physical coupling phenomena of the selected system, visualization of the sound fields was performed experimentally. We used near field acoustic holography to estimate sound field variables, such as pressures and intensities. Examining the acoustic variables, we found that there are two types of coupling mechanisms depending on frequency and associated wavelength. One is where the plate and the cavity are so strongly coupled that the plate can be considered as a source. In this case, the system radiates acoustic energy effectively through the plate. The other is where the coupling interaction behavior decreases the radiation efficiency. The frequencies that determine whether the plate is a good or bad radiator are found to be around the natural frequencies of the plate.

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