A Study On Fiber Magnetic Field Sensor And Its Characteristics Based On Silk Fibroin Magnetic Hydrogel

Magnetic field measurement is becoming increasingly important in many frontiers.With the increasing application of magnetic field measurement,performance requirements for magnetic field measurement technology are becoming more stringent.Traditional magnetic field sensors have problems such as susceptibility to electromagnetic interference and high cost.Making it difficult to meet the needs of modern magnetic field measurements.This leads to an in-depth study of fiber optic magnetic field sensors.Compared to other types of fiber optic magnetic field sensors,the high sensitivity,wide measurement range,and low cost of magnetic field sensors based on magnetic fluids have attracted the attention of a large number of researchers.Although this type of sensor has the advantages described above,magneto fluids have certain requirements for magnetic particle size,and the magnetic fluid encapsulation process is complex,which leads to rising manufacturing costs and problems that cannot be produced on a large scale in the industry.Hydrogel is a common soft material that can be coated on the surface of fiber structures for sensing,which can solve the above problems.This thesis introduces the magnetic hydrogel of silk fibroin and single-mode-non-core-single-mode（SNS）.A new type of fiber optic magnetic field sensor based on silk fibroin magnetic hydrogel is designed and proposed.The silk fibroin magnetic hydrogel is formed by mixing silk fibroin hydrogel with streptavidin-modified magnetic nanoparticles,which are coated on the surface of the SNS fiber structure as a magnetic-sensitive material and can be used for magnetic field detection.When the strength of the external magnetic field changes,The effective refractive index of silk fibroin magnetic hydrogel changes with the external magnetic field strength.The vanishing field on the no-core fiber can detect a change in its effective refractive index,resulting in a change in the optical path difference of the mode field involved in interference in the fiber structure.It eventually leads to a shift in the transmission spectrum.Hence,the sensor can measure the magnetic field strength of the outside world by detecting the shift of the interference dip in the transmission spectrum.In this thesis,the field distribution in optical fiber and the transmission characteristics of SNS fiber structure is explained,and the feasibility of the scheme is proved from the theoretical level through formula derivation.The effect of parameters on the sensor is studied by simulation and numerical calculation,and the relevant parameters of the sensor are optimized.The optimized parameters are used to prepare the sensor and its characteristics are analyzed.The participating mode interference in the sensor is mainly the three mode fields,which are LP₀₁mode,LP₀₂ mode,and LP₀₃ mode.The sensor exhibits a maximum sensitivity of up to 673.53pm/Oe and an average sensitivity of 263 pm/Oe.In addition,it exhibits a quick response of0.474s and other excellent features such as low hysteresis errors,good repeatability,and so on.The fiber magnetic field sensor based on silk fibroin magnetic hydrogel proposed in this thesis applies silk fibroin to the fiber magnetic field sensing field.The sensor consists of an SNS fiber structure and silkening magnetic hydrogel,using a coating structure,low cost,simple structure,easy to manufacture,opens up the fiber optic magnetic field sensor manufacturing process,for the large-scale production of fiber magnetic field sensors.In addition,the sensor uses biomaterials and has potential applications in biomedical,biosensory,and other fields.