SBIR-STTR Award

A submarine periscope is modeled as a cylindrical metal reflector poking out of a rough sea. The time variant component of its radar cross section (RCS) behaves as a Swerling Type I target whose magnitude can be reduced by application of RAM. Various options exist for incorporation of RAM into an outer periscope head which can be retrofitted to equipment already at sea. These options include encapsulating or compound molding RAM into a finished part. Injection molding the head from a resistive plastic matrix is another possibility. The research herein looks at detailed mechanical and electrical requirements, and methodology for incorporating RAM into a plastic periscope outer head. As part of this research, flat panel samples of material are fabricated and electrically tested. Consideration is given to cost, producibility, and combat survivability of the finished parts.

The radar reflectivity of a submarine periscope head is large and renders a submarine vulnerable to detection by aircraft surveillance and /or ship radars in a combat situation. During the Phase I research, it was determined that an outer plastic periscope head which incorporates a radar absorbing material (RAM) within the costing is a viable solution to provide a nominal -15 dB broadband radar cross section (RCS) reduction relative to an all metal periscope head of the same geometry. A number of RAM particulates is were investigated and stainless steel microfibers were found to be effective. In the current research, increased absorption bandwidth will be investigated via a mix of fiber lengths. In addition, alternate fiber types (carbon, etc.) will be investigated from the viewpoint of manufacturing ease and cost. A method of RF surface matching is necessary to attain high absorption over a very wide electrical bandwidth. During the Phase I research geometrical methods, such as surface grooves, were investigated. A better solution to be explored in current research is a multilayer outer skin designed to enhance electrical performance. This imposes consideration of the manufacturing technique: rotational and/or centrifugal casting will be researched, as well as other approaches. Several full scale RAM loaded plastic periscope heads will be fabricated and tested as part of this research. This research will produce a low cost, high performance waterproof RAM which will improve the survivability of submarines in a combat situation. The material will find other low observable naval applications of both submarines and ships.