Research Of Magnetic Field Sensor Based On Photothermal Effect Of Magnetic Fluid

The rapid development of smart cities,resource exploration,national defense technology,and space exploration cannot be separated from the stable supply of power systems.With the widespread application of Ultra High Voltage(UHV)power transmission,the hidden danger of overload has increased sharply,and the requirements for electromagnetic detection technology are also getting higher and higher.Researchers are constantly investigating magnetic field detection method that enabled achieve high stability,sensitivity,and anti-interference to monitor the safety and security of power systems in real time,and provide key technologies for smart grid.The magnetic fluid is a novel optical material,and its refractive index will change with the external magnetic field due to the fluidity of liquid.Therefore,we combine magnetic fluid and optical fiber sensing to achieve magnetic field detection,which can provide new solutions for the development of new magnetic field sensors.In addition,the magnetic fluid exhibits a strong photothermal effect,thus it has great potential in improving the accuracy of magnetic field detection.In this paper,the photothermal effect of the magnetic fluid is combined with the optical fiber.Three different optical fiber structures were constructed and analyze their light transmission characteristics respectively,and the magnetic field intensity measurement based on the photothermal effect of the magnetic fluid is realized.The main content of this paper includes:1.A fiber-optic magnetic field sensor based on compact cascaded tilted tapered fiber(STTF)integrated with magnetic fluid is proposed.A fusion splicer was used to fabricate the STTF structure through arc discharge,and the transmission characteristics of the sensor under different magnetic field intensities were studied.The results show that the structure has an obvious spectral response to the change of magnetic field intensity.In the range of 0?75 Oe,the highest sensitivity of the sensor is 32.67 pm/Oe and 0.0336 dB/Oe.The minimum resolution of the sensor can reach 0.6734 Oe.It exhibits the advantages of compact structure,ease of fabrication and low cost,and has great application potential in the field of magnetic field measurement in power system maintenance.2.A fiber-optic magnetic field sensor of Sagnac interferometer based on photothermal effect of magnetic fluid is proposed.The experiment studied the spectral transmission characteristics of the sensing unit before and after the pump light irradiation under different magnetic field strengths.The results show that this structure has a spectral response to the magnetic field strength by combining the photothermal effect of magnetic fluid and the mode mismatch during welding,with a sensitivity of 12.1 pm/Oe and a minimum resolution of 1.818 Oe.Therefore,the photothermal effect of the magnetic fluid can effectively improve the performance of the sensor.3.Combining the photothermal effect of the magnetic fluid,a magnetic field sensor with a coreless-polarization maintaining fiber composite fiber structure is proposed.Multi-mode interference occurs in the coreless fiber,making the structure sensitive to changes in the external environment.The spectral transmission characteristics with different magnetic field strengths are studied,and analyze the output spectrum under the irradiation of pump light.The results show that the sensitivity can be improved effectively by combining the photothermal effect of the magnetic fluid,are 11.17 pm/Oe and 0.033 dB/Oe respectively,and the minimum resolution is 1.970 Oe.This solution is expected to provide new ideas for magnetic field detection,and it will represent a promising candidate for the smart grid maintenance and development.