| Fiberoptic magnetostrictive sensors are devices capable of magnetic field measurements in the sub-nanoTesla range. There are several critical aspects affecting the performance of these sensors such as: the preparation of the device itself and the sensor interrogation scheme used. In this work we have studied the effect of several of these parameters on the sensor performance. We also have tested several fiber interferometric interrogation techniques which are different from the widely used Mach-Zehnder option. Among the parameters affecting the sensor performance we include annealing conditions for the magnetostrictive material and sensor design parameters such as the coupling between the fiber and the magnetostrictive material, magnetostrictive material shape demagnetization and operating frequency. For the fiber interferometer options we implemented: an end-coupled Michelson, a passively demodulated 3 x 3 Michelson and an in-line low visibility Fabry-Perot. The magnetostrictive materials used were samples of metglas ribbon and metglas wire.; We have found the annealing conditions to be a critical factor in getting an optimal sensor response. The annealing temperature is responsible for an increase in the sensitivity (a factor of 5 or higher), and the strength of the annealing field causes an improvement in the quality of the response (higher linearity and lower hysteresis), as compared with the response from a raw sample. We have also found that the axial or end-coupling of fiber to magnetostrictive material offers an improvement over the standard parallel coupling. The interferometer arrangements tested worked as satisfactorily as the Mach-Zehnder set-up, but they offer better characteristics for practical applications such as single-endness and localized measurement. |
