Use of tile overlays to reduce the radiation efficiency of radiating surfaces

Abstract

An intriguing possibility for reducing the radiation efficiency of a structure is to overlay its radiating surfaces with a contiguous set of low mass tiles. Experimental results show that significant reductions in sound power are possible depending on number of tiles, their geometry, attachment methods, mass, stiffness, and the amount of shear damping used to connect their edges to one another. This paper presents results of a combined theoretical and experimental study performed on a clamped, flat plate driven at its center and with nearly infinite baffle boundary conditions. Tiles are overlayed on the surface of the plate and lightly attached with a polymer material. A scanning laser vibrometer is used to examine the vibration patterns of the plate and the corresponding tiles for several different tile configurations over a frequency range 20–1000 Hz. Results indicate that sound power reductions occur when the independent response of each tile combines to produce an overall volume velocity that is lower than that of the plate by itself over the frequency range of interest.