A Filled Silicone Rubber Materials System with Selectable Acoustic Properties for Molding and Coating Applications at Ultrasonic Frequencies
NAVAL RESEARCH LAB WASHINGTON DC
Pagination or Media Count:
This paper describes a convenient system of materials that can be used to prepare molded articles or spray-deposited thin coatings of materials with well-defined and continuously variable bulk acoustic properties. The system consists of four components. First, RTV-602 with catalyst is used as the rubber base it is convenient to work with, has a low longitudinal absorption, and does not readily support shear waves. Second, typically one of four microballoon types is added, usually in the quantity necessary to obtain the desired attenuation coefficient. Third, an appropriate amount of ferric oxide is added to achieve the required impedance match, sound speed, or density. Finally, toluene is used to dilute the mix to a usable viscosity we have found that toluene can be added in even large quantities and later removed, either before or after curing, without altering the final properties of the resulting rubber. Equations are presented which allow the reliable prediction of longitudinal wave speed, attenuation, impedance, and density over the useful range of composition variation. These equations were constructed using acoustical measurements at frequencies from 2.5 to 7 MHz, and from direct immersion density determinations. Echo-reduction measurements on flat plates have been used to verify that the spray deposition technique described here does not significantly alter the acoustical properties of these composite mixtures.
- Elastomers and Rubber