High-Frequency Sound Absorption Characterization of Mock Energetic Materials

Energetic materials, namely explosives, propellants, and pyrotechnics, are commonly used in a number of distinct applications in which they are exposed to high-frequency acoustic and ultrasonic stimulation. Given this, it is desirable to measure their frequency-dependent acoustic properties, such as absorption and acoustic impedance. Conventional methods of measuring these acoustic properties are limited to a maximum frequency of approximately 6 kHz due to the requirement of maintaining plane wave propagation when using the standing wave tube method (a limitation which is controlled by the cross-sectional dimension of the tube). Since that frequency range is insufficient to characterize emerging energetic materials use-cases, a low-cost standing wave tube system capable of measuring the response of a small (approximately 1 cm^3) sample up to 12 kHz was developed. This system was used to characterize the sound absorption of several mock polymer-bonded explosive sample sets with varying compositions, as well as a neat (binder-only) sample set. These results were compared with results obtained from a commercially available standing wave tube system up to 6.4 kHz. Overall, the sound absorption of the materials tested was very low, but they may still be able to absorb substantial amounts of energy in harsh acoustical environments. The experimental techniques reported in this work can be utilized to further understand energetic material systems and improve their safety in practical applications.