Abstract : Fiber Bragg grating (FBG) sensing technology has unique advantages over other fiber sensing technologies, and therefore has greater research value. Based on the strain sensitivity of fiber Bragg grating and the magnetostriction effect of magnetic materials, this paper proposes a scheme to apply fiber Bragg grating to magnetic field sensing measurement and demonstrates its feasibility. Keywords : fiber Bragg grating; sensor; magnetostriction effect; magnetic field I. Introduction Fiber Bragg grating (FBG) refers to a grating with a certain period written inside the fiber core by using ultraviolet light irradiation to cause a permanent change in the refractive index of the fiber. Since the emergence of the lateral ultraviolet writing method [1] in 1989, the entire field of fiber communication and fiber sensing has been greatly affected. FBG has brought about a revolution in fiber devices, especially in fiber sensing, and has extremely broad application prospects. It greatly broadens the sensing mechanism of traditional fiber sensors and is a new type of sensor after intensity-type, interferometric and polarization-type fiber sensors. Compared with traditional sensors, FBG has the advantages of strong anti-interference ability, good stability and repeatability, and easy analysis and measurement. This paper proposes a scheme to use FBG to detect magnetic field. Based on the sensitivity of FBG to external stress, a magnetic field sensing head is formed by combining FBG with magnetostrictive material. The magnetic field detection purpose is achieved through magnetic force effect. Fiber grating technology is applied to the sensing and detection of magnetic field, providing a novel means for magnetic field measurement. II. FBG sensing system design scheme . In essence, FBG is a mode that couples light waves of a specific frequency transmitted in the optical fiber from the mode that was originally transmitted forward and confined in the fiber core to the mode that was transmitted forward or backward and confined in the cladding or fiber core through the interaction between waveguide and light wave, thereby obtaining specific transmission and reflection spectral characteristics. Its working principle is shown in Figure 1. The wavelength of the reflection or transmission peak of the fiber grating is related to the refractive index modulation period of the grating and the refractive index of the fiber core. The change of external temperature or strain will affect the refractive index modulation period of the fiber grating and the refractive index of the fiber core, thereby causing the change of the wavelength of the reflection or transmission peak of the fiber grating. This is the basic working principle of fiber grating sensor [2]. Temperature and strain (force) are the two most fundamental physical quantities that fiber optic gratings (FBGs) can directly sense and measure. They form the basis for sensing various other physical quantities, which are indirectly derived from the strain-temperature sensing capabilities of FBGs. For example, based on strain sensing capabilities and combined with auxiliary sensing elements such as elastic diaphragms, FBGs can be used to sense pressure, flow rate, and displacement. If FBGs are tightly bonded to magnetostrictive or anti-piezoelectric materials, they can be used to measure electrical quantities such as magnetic fields and electric fields. A typical FBG sensing system consists of four parts: a light source, a signal transmission line (optical cable), a sensor, a photoelectric converter, and a signal processor. Figure 2 shows a schematic diagram of the working principle of an FBG sensor. The light wave, as a carrier wave, is transmitted to the sensing head via the incident optical fiber. Some of its characteristic parameters are modulated by external physical parameters within the sensing head. The light wave containing the modulated information is transmitted to the photoelectric conversion section via the outgoing optical fiber. After demodulation, the magnitude and state of the measured physical quantity can be obtained. The FBG magnetic field sensing experimental device to be established in this paper is shown in Figure 3. In the diagram, the two ends of the FBG are clamped to a platform, with one end fixed and the other end able to slide freely. As the strength of the external magnetic field changes, the expansion and contraction of the magnetostrictive material also changes, thus converting the electromagnetic energy of the external magnetic field acting on the magnetostrictive material into mechanical energy. This mechanical energy then alters the stress within the FBG, causing a change in its Bragg wavelength. The change in Bragg wavelength can be directly read by a spectrometer. Therefore, the change in Bragg wavelength (ΔλB) can indirectly reflect the change in the magnetic field (H), thereby achieving the purpose of magnetic field detection. [b][align=center]For more details, please click: Research on FBG-based Magnetic Field Sensing Scheme[/align][/b]