Acoustic Sensors - Applications

• Ultrasound imaging of humans through closed windows, doors, and walls could be a critical capability in hostage and drug enforcement scenarios. Drug enforcement agents routinely break down doors without knowing what's on the other side. San Diego County just paid several million dollars to a resident shot by drug enforcement agents who mistakenly broke into his home. For this application, direct injection of the high-frequency acoustical vibrations at a window, door, or wall avoids two acoustical impedance mismatches between air and solids. The acoustical generator should be pulsed for a few ms at 20 to 30 pps in synch with the receiver frame time. A frequency of 50 to 100 kHz is probably best.

• Ultrasound imaging should be able to find hidden compartments in cargo containers, trucks, motor vehicles, and luggage, and identify the contents of the compartments nonintrusively. For finding hidden compartments in trucks, and probably also "seeing" what is inside them, acoustic wavelengths of ~1 cm (35 kHz, few degree resolution) should be adequate. Current technology is to use laser rangefinders to compare inside and outside dimensions of a truck body. Advantages of acoustic imaging include a quicker inspection in several directions and imaging of the contents of a compartment. An acoustic imaging device may even be able to inspect car trunks for human cargo quickly without popping the lid.
  

• Civilian applications of contact ultrasound imaging include weld inspection (perhaps robotically) during manufacture of car bodies and finding subsurface flaws in aircraft structures and oil pipelines. Certain economies might be achieved by remote imaging, and these applications would avoid the use of x rays for inspection. Subsurface flaws in aircraft structures and oil pipelines are big and expensive problems. For detecting and imaging these flaws, direct injection of acoustic vibrations into the aircraft structure or oil pipelines seems preferable. For oil pipelines that are mostly cylindrically symmetric, one might look for point scattering (kd «1) from flaws at a resonant acoustical wavelength of the pipeline. For imaging flaws in aircraft structures, high-power contact sonography might be more effective than remote acoustical imaging.

• Remote imaging of drug factories or military assets through jungle or forest canopy or through camouflage can be performed acoustically by aircraft using advanced imaging techniques, such as synthetic aperture imaging. For example, if the acoustical beam is broad enough to cover the entire target, the Doppler return from the front and rear of the target will differ, providing a characteristic signature.

Acoustic Sensors | Technical Specifications

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