A phase sensitive fiber optic strain gauge that is both spatially local and unidirectional is described. The design consists of a path balanced lead -in /out Michelson interferometer using a single -mode directional coupler. It is tested as a surface adhered device in both uniaxial and rosette configurations. The device is integrated between plies of graphite/PEEK thermoplastic to provide lamina strain measurements. Performance parameters -gauge factor, transverse sensitivity, and failure strain -are evaluated. The utility of such a strain gauge is discussed in the general context of smart structures and skins.

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A proprietary fibre optic sensing technology has been developed and is capable of simultaneously utilising an existing fibre optic communication cable as an integrity-testing sensing cable, thus providing continuous, real-time monitoring of the fibre cable and any structure near the cable (ie., ground, tunnels, ducts, pipes, buildings, equipment, vessels, etc.). With this system, simultaneous fibre optic communications and real-time vibration monitoring was demonstrated using a wavelength multiplexed fibre system for a channel bandwidth of 500 MHz over 18 km of standard singlemode fibre. Real-time vibration monitoring was also demonstrated using standard singlemode and multimode fibre over lengths of 28 km and 53 km, respectively. Trials of the system are currently underway in Australia and the first commercial field installation with this capability is to be completed in mid-1998 in Indonesia. This paper highlights the benefits and potential of this dual-capacity system and details results obtained to-date.