Fiber Grating Current Sensor Based On Giant Magnetostrictive Material

With the development of optical communication, several opticalcommunication technologies are gradually used in sensor application area.The development of fiber sensor in the world can be divided into two majorareas: principle research and application development. As the fibertechnology becomes more mature, the practical development of fiber sensorbecomes the hotspot and key point.As the electric power industry develops rapidly, the electric powertransmission capacity increases ceaselessly, the volt gets higher and higher,so does the current, the traditional current sensor can not meet this situationany more, the main points are: difficult to insulate, high cost, heavyequipment, vulnerable to electromagnetism interfere, short transmissiondistance, magnetism saturation due to CT, iron magnetism resonance, smalldynamic range, narrow frequency band, flammability, and easy to explode,etc. It is also difficult to achieve multipoint transmission and processingsignal at the same time. The fiber current sensor possesses advantagessuch as: little volume, easy to curve, resist electromagnetism, and resistacid or alkali environment, withstand high temperature and the sensor headcan be passive and so on. It can be better substitute of tradition currentsensor. Now it is the study focus.Fiber Bragg Grating is a new type passive apparatus, because it hassmall volume, is easy to couple with fiber, can be buried into equipment, hascertain centre wavelength, and can be modulated by stress and temperature;it can be wildly used in sensitive area.Giant magnetostrictive material is a new type magnetism-mechanismconversion material, compared to micro-displacement material such as:magnetostrictive material and piezoelectric ceramic, it has rapid responsespeed and big output power, and can act under low magnetic intensity. So itcan be the good stress tune organ of fiber grating.During my postgraduate area, under the direction of my tutor-GuoyubinProfessor, I do some research on fiber grating current sensor based on giantmagnetostrictive material. Few papers of this kind can be seen in thecountryAfter the introduce of status of current sensor, the basic principle of fibergrating and the characteristic of giant magnetostrictive material, thedeformation amplifying organ of giant magnetostrictive material was made,through this, the deformation of giant magnetostrictive material can bedelivered to the sensor grating. At the same time, heat insulation materialwas used in this organ, the influence of temperature can be reduced. Thedrive circuit of laser diode and ASE source was made. The drive circuit oflaser diode included automatic power-control, automatictemperature-control and protection circuits. After six months' use, itsstabilization gets proved, and it can also prevent the diode from over voltage,over current, and static's destroy. The output laser is stable;it can work inhigh-power for many hours. When the power is 50 mw (10 minutes), thestability is 0.01dBm, and under 120mw output power, it can continue workfor 12 hours and performance well .This experiment used fiber grating and giant magnetostrictive material,as the giant magnetostrictive material changes in the magnetic field, it candraught the fiber grating to test the current. The drive organ of giantmagnetostrictive material is made. It is the amplified deformation of giantmagnetostrictive material that was transferred to fiber grating, the tunerange of fiber grating was improved. Also the size of the giantmagnetostrictive material can be reduced and the sensitivity gets improvedtoo. Based on the foregoing work, studied the current sensor. Usehome-made ASE source as sensing light source, PIN circuit and gratingfilter as demodulator, a tunable current source as sensing signal, changethe current, then adjust grating filter, the maximum wavelength is thesensing grating wavelength. Through such method, get 6.8mA currentresolution.The designed current sensor in this paper adopts fiber grating assensing head, giant magnetostrictive material as current-deformationconversion, achieving passive sensing head, this is very suitable forflammability and easy to explode environment. Because several differentwavelengths fiber gratings can be made in one fiber, it is easy to achievearray sensing. This is important for multi-point current measure at the sametime. Due to the characteristic of fiber grating, this kind current sensor hasmany advantages such as: small volume, light weight, good insulation,resisting high-temperature, and high sensitivity. This current sensor will getgreatest development in the future.