Ultrasonic tomographic imaging of an encased, highly attenuating solid medium

Ultrasonic tomographic imaging has been performed on a highly attenuating, filled, hydroxyl-terminated polybutadiene, cast into a steel case. The dete ction of defects and the characterization of solid rocket propellant were t hus possible. Extremely low signal levels due to the attenuation and scatte ring properties of the polymer were present. In addition, a nonideal tomogr aphic reconstruction geometry was present, because of a cylindrical air-fil led cavity in the center of the polymer. Complications also arose from high -amplitude guided waves within the steel case, which tended to mask directl y transmitted signals through the propellant. These problems were solved us ing specially designed transducers and pulse-compression signal processing techniques. Modifications to the filtered back-projection reconstruction pr ocedure were made to account for the discontinuity caused by the hole. Imag es are presented showing the detection of an artificial defect to demonstra te the technique.