N21A-T010 TITLE: Novel Acoustic Source Concepts for Target Identification and Classification

RT&L FOCUS AREA(S): General Warfighting Requirements

TECHNOLOGY AREA(S): Sensors

OBJECTIVE: Develop a concept, design, and prototype of an acoustic source capable of directly exciting resonances in a wide variety of targets on or suspended from the seafloor.

DESCRIPTION: Manmade objects such as mines and unexploded ordnance (UXO) are subject to resonances when excited by the right forces. These resonances can provide classification and identification information, even in the presence of clutter. Acoustic Radiation Force (ARF) methods have been developed and adopted in the medical ultrasound community for clinical use. Using ultrasonic transducers, ARF methods have been demonstrated in the laboratory to induce target resonances for classification and identification purposes. Research under this topic seeks to develop the necessary hardware and operational concepts for demonstrating the potential for ARF methods to incite resonances in full-scale targets in real-world conditions. Demonstrating achievable acoustic intensity values given the frequency dependent absorption of the medium is a risk.

PHASE I: Develop a concept for an acoustic source capable of directly exciting resonances in some canonical target shapes such as plates or cylinders. Produce a technical report detailing the mathematics and physics supporting the concept, including the conditions under which the concept is expected to work. The technical report shall include requirements or specifications for an acoustic transducer capable of demonstrating the concept. It is preferred that the concept be demonstrated by small-scale laboratory experiments verified by numerical modeling, however results from numerical modeling only results would be acceptable. Develop a Phase II plan, including, if applicable, analysis and considerations for exciting resonances in full-size targets based on results from small-scale experiments.

PHASE II: Demonstrate the concept developed in Phase I in controlled conditions on more realistic target shapes and sizes. This phase will require the procurement, or the design and construction, of an acoustic source capable of exciting target shapes and sizes that might be expected in operations. For example, shapes might include 2' x 1' cylinders and or unexploded ordnance (UXO) sitting proud on the sea bottom. The contractor shall also demonstrate the concept�s ability to reject clutter in controlled conditions. The expected deliverable is a report on the demonstration and requirements for a prototype system for demonstrating the concept in realistic conditions. For the Phase II option, if exercised, design, build, and demonstrate a prototype transducer capable of exciting target shapes representative of mines and/or UXO in a realistic ocean environment against targets both proud on the bottom and partially buried (< 50%). The demonstration shall include an assessment of performance for targets in environments with sandy bottoms, muddy bottoms, and high clutter areas (mine countermeasures doctrinal bottom type clutter category 4). The prototype transducer can be demonstrated from any type of platform, fixed or moving (up to 5 knots), such as a rail or a ship.

PHASE III DUAL USE APPLICATIONS: The expected transition will be a novel acoustic transducer design capable of exciting target resonances for identification purposes in cluttered underwater environments. The transducer shall be capable of exciting resonances from heights of up to 3 yards above the target. The design should be applicable across a range of applications for detecting and classifying objects on the seabed including remediation of UXO dumping sites, naval mine hunting, and underwater archaeology. Across these applications target sizes may range from less than 1 inch diameter for UXO to 20 inches or more in diameter for mines that may be over 4 feet in length. The design characteristics of the transducer may specify a range of target sizes, but shall be flexible enough to mount on a variety of different platforms including unmanned underwater vehicles. The final design/build specifications, to include size, weight, and power requirements along with design of mounting configurations shall be tailored to a mission specific platform with requirements provided by the transition sponsor.

REFERENCES:

1. Huber T.M., Algren M., and Raisbeck C. "Spatial Distribution of Acoustic Radiation Force for Non-Contact Modal Excitation." Mains M. (eds.) Topics in Modal Analysis and Testing, Volume 10: Proceedings of the 34th IMAC, A Conference and Exposition on Structural Dynamics 2016. . https://asa.scitation.org/doi/10.1121/1.4987606
2. Huber T.M., Beaver N.M., and Helps J.R. "Non-contact Modal Excitation of a Classical Guitar using Ultrasound Radiation Force." Journal of Experimental Techniques, 37(4), July 2013, pp. 38-46. http://physics.gac.edu/~huber/guitars/ultrasound_cordoba/
3. Lingsch, S.C. - "Using a Mine-Hunting Sonar for Real-Time Environmental Characterization." Oceans �99 MTS/IEEE Riding the Crest into the 21st Century: Conference and Exhibition. Conference Proceedings, vol. 3, pp. 1181-1187. http://ieeexplore.ieee.org/document/800159/

KEYWORDS: Acoustics; Vibrations; Modal Analysis; Transduction; Radiation Forces; Target Classification

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