The safety of diver exposure to ultrasonic imaging sonars / Ronald Kessel, Craig Hamm, Vincent Myers, DRDC - Atlantic Research Centre. : D68-11/10-2018E-PDF

"To achieve image-quality resolution, imaging sonars operate in the ultrasonic regime at frequencies on the order of 300 kHz up to 1.5 MHz. Although there are no known instances of harm or adverse effects caused by imaging sonars to divers, it is known from diagnostic ultrasound that human exposure to ultrasonic energy can be harmful. The risks identified in diagnostic ultrasound have apparently never been examined for imaging sonars. The risks posed by a diver hand-held imaging sonar are examined here in light of the metrics used in diagnostic ultrasound, especially the thermal and mechanical indices (TI and MI respectively). One imaging sonar in particular is assessed. Its ultrasonic field was characterized by direct measurement under anechoic conditions at the Defence R&D Canada Acoustic Calibration Facility and MI and TI were conservatively applied to assess the risk of harm to divers who may be exposed to the ultrasonic beam of the sonar during dive operations. This report reviews the exposure characteristics of ultrasonic fields and their connection to metrics commonly used by sonar engineers, the indices of diagnostic ultrasound, the experimental setup and results, and the implications for safe standoff and exposure time. The methodology can be applied to other ultrasonic sonar makes, models and technologies for imaging sonars and diver detection sonars"--Abstract, p. 847.

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