Ultrasonic embedding of nickel-coated fiber Bragg grating in aluminum and associated sensing characteristics

Fiber Bragg Gratings (FBGs) were embedded in metal foil using ultrasonic welding processes. Ultrasonic welding embedding processes, cross-sections of welded samples, the form change and wavelength shift of the Bragg peak during the processes, as well as the sensing characters of embedded FBGs were investigated. To understand the effects of metal foil properties on fiber embedding, optical fibers were embedded in similar and dissimilar metal foil samples. In order to study the effects of protective coating properties on the embedding processes, bare fibers, chemical nickel-plated fibers and chemical-electro nickel-plated fibers were compared in the ultrasonic welding process. Results indicate that only chemical-electro plated fibers and FBGs were successfully embedded in aluminum foils due to good protection and an appropriate matrix metal. Examination of the form change and wavelength shift shows that the FBGs are preserved well after the plating and ultrasonic welding processes. Thermal sensing results show that temperature sensitivity of the FBG was enhanced after chemical-electroplating and further enhanced after embedding in aluminum, which resulted from different thermal expansion coefficients of the SiO2, aluminum and the nickel layer. Strain sensing results show (i) the embedded FBG remains in good condition when a cyclic tensile load (0–40 N) is applied; (ii) the relationship between wavelength and the applied load shows a linear trend.

► FBG was embedded in the aluminum foil by using of ultrasonic welding method.
► The form change and wavelength shift shows that the FBGs are preserved well.
► Thermal sensitivity of the FBG was enhanced after plating and embedding.
► The embedded FBGs remained in good condition under a cyclic tensile load (0–40 N).
► FBG wavelength shift and applied load shows a linear relation during loading cycle.