High-powered parametric acoustic array in air

• Published in: The Journal of the Acoustical Society of America 2009-04, Vol.125 (4_Supplement), p.2688-2688
• Main Author: Haupt, Robert W.
• Format: Article
• Language: English
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.4784274

MIT Lincoln Laboratory has developed a prototype high-powered parametric acoustic array (HPPAA) for standoff acoustic excitation in several applications. Parametric arrays offer a highly directional, narrow beam mechanism to deliver sound in air to desired targets typically within a 100 m range. However, a difficult challenge arises in generating sufficient sound power at difference-frequencies below 1000 Hz at a range which can be critical for many target types. An important objective of the HPPAA design maximizes the difference-frequency pressure amplitude at range by maximizing the end-fire array length established by the PAA. The design optimizes the trade-offs between the three characteristic lengths that control the resultant end-fire array length including the pump or carrier wave attenuation, PAA aperture, and acoustic saturation of air. In field demonstrations, the HPPAA generated a carrier wave pressure power approximately 155 dB re-20-microPa one meter from the PAA face while generating a 300 Hz difference-frequency SPL of 90 dB re-20-microPa 8 meters from the PAA. These sound pressure levels at a few hundred hertz may enable safe standoff excitation and detection of buried landmines and may be useful in standoff nondestructive testing (NDT) damage detection and imaging of structures.