Temperature compensated magnetostriction based fiber Bragg grating current sensor
A compact and inexpensive optical fiber sensor for the measurement of DC and AC currents is developed. The sensor consists of a fiber Bragg grating (FBG) bonded on two end-to-end joined pieces of metal alloys, one metal alloy being Terfenol-D and the other MONEL 400. Terfenol D has huge magnetostriction, so when a magnetic field is applied stress is created in it and it expands. This property of Terfenol is used as a transducer to convert electrical measurand to mechanical.
A magnetic field applied along the two alloy bars will make the reflection spectrum of the Bragg grating split into two. The distance between the peaks of the reflection spectrum and the total intensity of light reflected back from the grating is directly proportional to the magnetic field applied along the alloys. The resultant split in the spectra can be measured with a simple technique using a single photo-detector. On the other hand, as Terfenol D and MONEL 400 have almost identical thermal expansion coefficients, a change in temperature does not cause the reflected spectra of the grating to move apart and, therefore, does not affect the magnetic field measurement. So the measurements are not affected by temperature.