COMPOSITE COATINGS FOR ACOUSTIC PULSE ABSORPTION

ACOUSTIC LINERS CAN BE USED TO ATTENUATE PRESSURE OSCILLATIONS IN REGENERATIVE LIQUID PROPELLANT GUNS IN ORDER TO INCREASE THE LIFETIME OF THE GUN AND MINIMIZE THE IMPACT ON THE PROJECTILES BEING FIRED. THE DESIGN OF THIS TYPE OF ACOUSTIC ABSORBER IS MADE DIFFICULT BECAUSE OF BOTH THE EXTREME CONDITIONS THE LINER MUST WITHSTAND, AND THE BROAD-BANKED NATURE OF THE ACOUSTIC SIGNAL WHICH MUST BE ATTENUATED. IN ORDER TO EFFECTIVELY ATTENUATE THE PRESSURE OSCILLATIONS, THE LOADED COMPOSITE IS DESIGNED WITH A BINDER MATERIAL THAT HAS ITS IMPEDANCE MATCHED TO THE GUN CHAMBER TO ENSURE THAT THE ACOUSTIC TRANSMISSION INTO THE LINER IS MAXIMIZED (AND THEREFORE THE ACOUSTIC REFLECTION FROM THE LINERS IS MINIMIZED) WHILE THE PARTICLES IN THE BINDER ARE DISTRIBUTED SO THAT, DUE TO SCATTERING AND ABSORPTION, THE TRANSMITTED ACOUSTIC WAVE IS COMPLETELY ATTENUATED. THIS TYPE OF BROAD-BANDED, LOADED ABSORBER IS COMMONLY USED IN THE REDUCTION OF RADAR REFLECTIONS FOR STEALTH APPLICATIONS, WHERE A THIN COATING MUST ATTENUATE THE ELECTROMAGNETIC "OSCILLATIONS" OVER A LARGE FREQUENCY RANGE. IN THIS EFFORT WE PROPOSE TO INVESTIGATE THE REFLECTION OF ACOUSTIC PULSES FROM AN ABSORBING LINER USING THE RIGOROUS TECHNIQUES OF ELASTIC MULTIPLE SCATTERING. WE DRAW UPON OUR RECENT EXACT SOLUTION TO THE SCATTERING OF ELASTIC WAVES FROM ELASTIC SPHERES AND OUR EXPERIENCE IN THE DESIGN AND ANALYSIS OF ELECTROMAGNETIC ABSORBING COATINGS. OUR ANALYSIS WILL DETERMINE THE MATERIAL PROPERTIES AND LINER CONFIGURATION REQUIRED FOR THE ABSORPTION OF PRESSURE OSCILLATIONS IN THE HIGH TEMEPRATURE AND HIGH PRESSURE ENVIRONMENT OF REGENERATIVE GUNS.