Structural-acoustic coupling in a partially opened plate-cavity system: Experimental observation by using nearfield acoustic holography

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 ol bad radiator are found to be around the natural frequencies of the plate. (C) 2001 Acoustical Society of America. [DOI: 10.1121/1.1320476].