Researchers at Systems Planning and Analysis Inc., with funding from the Office of Naval Research in Arlington, Va., have produced a low-cost fiber optic network that will monitor the structural fitness of the US Navy's fleet. The system, which links sensor nodes in the hull of a ship, calculates and reports in real time the stress and strain that the vessel experiences at sea. The remote monitoring technology can be employed to schedule repairs and to update design, or can afford early warning of compromised integrity. Able to interrogate up to 120 discrete sensors, a fiber optic system could help engineers monitor a ship's structural health remotely, at a relatively low cost. Courtesy of Systems Planning and Analysis Inc. The system is based on commercial fiber Bragg grating and telecommunications technologies. Researchers are developing a sensor interrogation unit based on digital spatial wavelength domain multiplexing technology to enable cost-effective, massively multiplexed strain monitoring. The system interrogates up to 120 discrete fiber Bragg grating sensors at a sampling rate of up to 2 kHz. It can be reconfigured with a computer software-driven control system, which also provides online, real-time visualization tools that display structural response and deformations. Engineers have assembled and tested the prototype system, which meets the desired performance specifications. But they are refining it further to streamline and package it for field trials in early 2001. A commercial system is planned for release in 2002. Central to the expected success of the commercial monitoring system is the cost per sensor channel. "The per-channel cost is projected to be at least half of the cost of competing, conventional resistance strain-gauge technology," said Roshdy S. Barsoum, a program officer at the Office of Naval Research. Systems Planning and Analysis also is exploring the use of its monitoring technology in civil engineering, sponsored by the Turner-Fairbank Highway Research Institute of the Federal Highway Administration in McLean, Va. The company is adapting the system to enable Internet-based remote monitoring of the long-term structural soundness of bridges and highways. Research is under way to assess the optical and mechanical survivability and performance of the fiber Bragg grating sensors in composite filament-wound and pultruded carbon fiber bridge substructures and reinforced concrete.