Giant magnetostrictive magnetic fields sensor based on dual fiber Bragg gratings

A giant magnetostrictive magnetic fields sensor based on dual fiber Bragg gratings is demonstrated. The sensor head consists of two fiber Bragg gratings of identical Bragg reflection wavelengths bonded on one giant magnetostrictive rod of Terfenol-D with one grating fixed on both ends and the other grating extensible freely. As the giant magnetostrictive rod lengthens according to an external magnetic field, only the fixed grating is stretched accordingly and the Bragg wavelength shifted to a larger value, while no strain is imposed on the other grating, which resulting in two reflectivity peaks in the dual gratings' reflected spectra. With the help of an optical spectrum analyzer, the difference between the Bragg wavelengths of the two gratings which relates to the applied external magnetic filed is readily measured. Temperature compensation is accommodated partly by the use of the dual fiber Bragg gratings configuration. Experimental results are presented and the properties such as measuring range, linearity, and sensitivity of the sensor design are discussed.