Smart Fibres FBG Temperature Sensors operates by one of two methods:
(i) Loose tube, whereby the FBG is isolated from external strain by a tubular housing, and wavelength variations due to the thermo-optic coefficient of the FBG are measured
(ii) Isolated coupon, whereby the FBG measures the expansion of a coupon of material, isolated from external strain, and wavelength variations due to the coupon thermal expansion plus the thermo-optic coefficient of the FBG are measured
The loose tube construction benefits from smaller sensor packaging and greater installation flexibility. The isolated coupon construction benefits from greated measurement sensitivity. For a truly, miniature temperature sensor, for example to embed within a composite, a terminal FBG can be housed within a polyimide capilliary of typ 400 μm diameter.