Distributed grating sensors: an alternative to multiplexed grating arrays?

Abstract

Fibre Bragg gratings have been widely used for smart structures sensing applications. Until recently all sensor systems using gratings have only measured the average value of a physical field. The field has been averaged either over the length of a grating or over a length of fibre between gratings. To obtain a spatial image of the physical field, these sensors have been multiplexed to form a sensor array. Recently, fully distributed images of physical fields have been measured along the entire length of a grating. Distributed sensors show great promise for the detection and location of small physical features within structures, such as cracks and hot spots. As the fabrication length of gratings continues to increase, there appears great potential for distributed grating sensors. Distributed grating sensors may be classified as either narrowband or broadband, according to the spectral width of the interrogation source. Both types of sensor are discussed and briefly compared. The various forms of averaging gating sensors are also discussed and their performance is compared with that of distributed grating sensors using two specific smart structures applications.
The latest results of our broadband distributed sensor are presented. This distributed sensor may be viewed as an adaptive averaging sensor since the number of interrogation regions, their size, location and the spatial resolution may all be varied in response to the sensing information. Finally, a sensing network combining the advantages of both multiplexed and distributed sensors is demonstrated and discussed.

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