Optical Fiber Magnetic Field Sensor Research Articles

High sensitivity magnetic field sensor based on a Mach-Zehnder interferometer and magnetic fluid

An intensity modulation optical fiber magnetic field sensor based on MZI and magnetic fluid is proposed and demonstrated. The MZI is composed of a no core fiber-thin core fiber-no core fiber (NTN) structure and the cladding of thin core fiber is etched by hydrofluoric acid. The fiber structure is immersed in magnetic fluid. The sensitivity of the etched device is 5.3 times that of the non-etched device. The maximum sensitivity of magnetic field intensity achieved in our experiment as high as 0.563 dB/Oe. Meanwhile, the fringe visibility achieved 30.78 dB. This device has the advantages of convenient manufacture, small volume and high sensitivity. It has application potential in the field of magnetic field sensing.

Magnetic field and temperature two-parameter sensor based on optical microfiber coupler interference (OMCI) wrapped with magnetic fluid and PDMS.

In this paper, an optical fiber magnetic field and temperature sensor based on an optical microfiber coupler (OMC), Polydimethylsiloxane (PDMS), and magnetic fluid (MF) is proposed, and its magnetic field and temperature sensing characteristics are analyzed theoretically and verified experimentally. Based on the OMC and using MF as the sensing medium, the sensor can respond to the magnetic field and temperature respectively after encapsulated by PDMS. The experimental results show that the maximum magnetic field sensitivity is 96.8 pm/Oe, and the maximum temperature sensitivity is 919.1 pm/°C. To overcome the cross-sensitivity of the magnetic field and temperature of the sensor, the sensitivity matrix is established and demodulated. In addition, we discuss the optimization of the sensitivity demodulation matrix by the size design of the PDMS package and the OMC structure. The proposed two-parameter sensor in this article has the advantages of high sensitivity, low cost, small volume and high integration, which is of great significance for the multi-parameter sensing of basic physical parameters such as magnetic field and temperature.

Applications of magneto-strictive, magneto-optical, magnetic fluid materials in optical fiber current sensors and optical fiber magnetic field sensors: A review

Currently, electromagnetic current and magnetic field sensors are suffering from disadvantages of a complex insulating structure, high cost, easily explosive and difficult to digitized. Optical fiber current sensors and optical fiber magnetic field sensors are promising methods to overcome these risks due to these features of the optical fiber itself insulating, light weight, digitizable. Moreover, it is more potential to transform them from lab to application. This review focus on the optical fiber current sensors and optical fiber magnetic field sensors based on magnetically sensitive materials. According to the different magnetically sensitive materials to be coated, the optical fiber current sensors and optical fiber magnetic field sensors based on magneto-strictive materials, magneto-optical (MO) materials and magnetic fluid (MF) materials are discussed in detail. The sensing mechanism of three magnetically sensitive materials are studied. And the optical fiber current sensors and optical fiber magnetic field sensors are researched about the sensing principle, characterization, structure, and performance of the sensors. The future development direction is prospected about optical fiber current sensors and optical fiber magnetic field sensors based on magnetically sensitive materials, and then the future development prospects and challenges of three magnetically sensitive materials are analyzed in detail.

Magnetic field sensor based on helical long-period fiber grating with a three-core optical fiber.

A high sensitivity optical fiber magnetic field sensor is proposed and implemented by using a helical long-period fiber grating (HLPFG) based on a three-core fiber (TCF) bonded to a U-shaped aluminum (Al) wire. An electrical current flowing through the Al wire in a perpendicular magnetic field can generate Ampere force, which changes the distance between the two arms of the U-shaped Al wire. Thus, when the intensity and direction of the magnetic field change, the bending curvature of TCF-HLPFG bonded to the U-shaped Al wire varies with the change of Ampere force, which is represented as the shift of resonant wavelength in the spectrum. The as-fabricated sensor can respond to the magnetic field direction and the intensity with a range from -15 mT to 15 mT, and the measured sensitivity is 456.5 pm/mT with Al wire electrical current 1A. The proposed sensor has the advantages of low cost, nondestructive measurement method and ease manufacture, and is expected to be applied to weak magnetic field measurements.

Reflective fiber-optic magnetic field sensor based on a magnetic-fluid-filled capillary probe structure

A novel reflective magnetic field sensor is presented and experimentally demonstrated. The sensing probe is fabricated by splicing a section of uncoated four-core fiber (FCF) between two sections of no-core fibers (NCFs), and the end face of the last NCF is coated by silver. The sensor structure is sealed in a magnetic fluid (MF)-filled capillary, so that the NCF–FCF–NCF magnetic field sensing probe structure is obtained. The NCF is used to excite the high-order modes of the FCF’s cladding. Combined with the adjustable refractive index of MF, the sensor is sensitive to the magnetic field and temperature. Experimental results indicate that the presented sensor can measure the low magnetic field and high magnetic field. In the low magnetic field ranges of 0–10 mT and 10–18 mT, the wavelength near 1548 nm varies linearly with the magnetic field intensity, and the sensitivities are −7.43 pm mT−1 and −60 pm mT−1, respectively. The sensitivity of the interference intensity is −0.30782 dB mT−1 in the low magnetic field intensity range of 0–18 mT. The sensor under low magnetic field is also affected by temperature. In the temperature range of 20 °C–70 °C, the temperature sensitivity of the wavelength shift around 1548 nm is 62.33 pm °C−1, and the corresponding sensitivities of the interference intensity are −0.03888 dB °C−1 and −0.02076 dB °C−1 in the range of 30 °C–50 °C and 50 °C–70 °C, respectively. However, the effect of temperature on the sensor in the high magnetic field (18–36 mT) can be ignored. Within the high magnetic field intensity range of 26–36 mT, the sensitivity of the interference intensity near 1598 nm is −1.20993 dB mT−1. The dual-parameter matrix is used to eliminate the cross-sensitivity of temperature in the low magnetic field. This sensor, with the advantages of easy fabrication, high sensitivity and low cost, has the potential application in the magnetic field monitoring.

High-sensitivity fiber optic magnetic field sensor based on lossy mode resonance and hollow core-offset structure

An optical fiber magnetic field sensor based on lossy mode resonance (LMR) was designed. Furthermore, a hollow core-offset structure was designed to enhance the performance. Due to the destruction of the circular symmetry structure, the sensor has strong birefringence, resulting in x-polarization and y-polarization with two independent resonance valleys. The refractive index changes from 1.358 to 1.390 and a high sensitivity of 11,483.12 nm/RIU was obtained. In addition, the influence of structural parameters on the sensor was investigated. Magnetic field sensitivities of 893 pm/Gs and 754 pm/Gs were obtained theoretically. The feasibility of LMR is demonstrated for magnetic field measurements and a reference is provided for an optical fiber magnetic field.

Computational Modeling of Optical Fiber-Based Magnetic Field Sensors Using the Faraday and Kerr Magnetooptic Effects

Fiber-optic magnetic field sensors are attracting interest for applications in navigation, magnetic resonance, geophysics, space systems, power transformers, and generators, especially for harsh environments, at long distances, and for multiple monitoring points. This article presents a computational modeling for optical fiber-based magnetic field sensors using the magnetooptical Faraday and Kerr effects on the polar configuration. We propose two sensor profiles: one using a thin film of Fe and the other using a Ce:YIG layer. A simplified analytical model based on Fresnel equations is used to guide the numerical modeling built on COMSOL Multiphysics. The sensors’ design methodology is also presented, which optimizes the sensor operating range and sensitivity. The proposed sensor sensitivity, resolution, and operating range are presented and compared to others found in the literature. The results indicate the possibility of building high-resolution sensors for a restricted range of magnetic field intensities or a wide-operating range sensor.

Miniature Fiber-Optic Magnetic Field Sensor Based on Ampere Force and Fiber Laser

A compact fiber-optic magnetic field sensor is proposed by packaging an orthogonal dual-frequency fiber grating laser and a copper wire with alternating electrical current together inside epoxy resin. The alternating current generates Ampere force in a magnetic field, which changes the birefringence of the fiber laser and hence tunes the frequency of the beat signal after photodetection. The magnetic field magnitude can then be detected by measuring the frequency change of the beat signal. The sensitivity of the sensor can be tuned with a maximum response of 35.21 kHz/kGs demonstrated. Moreover, the sensor shows good immunity to environment interference.

Magnetic sensor based on serial-tilted-tapered optical fiber for weak-magnetic-field measurement.

An optical fiber magnetic field sensor based on serial-tilted-tapered fiber (STTF) integrated with magnetic fluid is proposed. The compact STTF structure consists of two closely tilted-tapered fibers with a length of approximately 836 µm, which results in stronger mode coupling. The transmission characteristics of the proposed sensor under different magnetic field intensities (MFIs) have been studied. The results show that the proposed structure has an outstanding response to MFI and that the highest sensitivity is 32.67 pm/Oe in wavelength and 0.0336 dB/Oe in transmission in the range of 0-75 Oe. The minimum resolution of the proposed sensor is up to 0.6734 Oe. These types of sensors have great potential application in weak magnetic field measurements due to their compact structure and good sensing performance.

Temperature compensated three-dimension fiber optic vector magnetic field sensor based on an elliptical core micro fiber Bragg grating.

In this paper, a temperature-compensated three-dimension vector fiber optic magnetic field sensor based on an elliptical core micro fiber Bragg grating (FBG) has been proposed and experimentally demonstrated. The elliptical core fiber was tapered to form a microfiber, in which a FBG was inscribed. Due to the magnetism-manipulation of the anisotropic aggregation of ferromagnetism nanoparticles around the fiber surface, the effective refractive index of the evanescent field for two orthogonal polarization modes was modulated, and the magnetic field orientation can be detected by interrogating the wavelength interval between two reflection peaks. However, two reflection peaks show the identical response to ambient temperature. Hence the proposed sensor can achieve the measurements of the magnetic field intensity and the orientation simultaneously without the temperature cross-sensitivity. The experimental results show that the magnetic field orientation sensitivity of 15 pm/deg and intensity sensitivity of 81 pm/mT can be achieved, and the maximum standard variation of the temperature cross-sensitivity is only 0.02 nm. The proposed elliptical core micro FBG appears to have potential applications in navigation, vehicle detection, and current sensing.

Fiber-Optic Vector Magnetic Field Sensor Based on Mode Interference and Magnetic Fluid in a Two-Channel Tapered Structure

An innovative approach to high-sensitivity simultaneous intensity and direction measurement in a two-channel tapered sensor is proposed and demonstrated. The sensor is comprised of magnetic fluid (MF)- filled micro-capillary and two accompanying micro-fiber, thus enabling evanescent interaction to take place between the optical mode in the capillary and MF. Given the magnetic nanoparticles (MNPs) of MF manifest anisotropic magnetic field. Experimental and numerical simulations were performed simultaneously, which provided a better understanding of the interaction between light and MF in addition to clarifying the dynamic process of MNPs within MF with the assistance of varying magnetic field. The experimental results are well consistent with the numerical simulation results and show that the sensitivity of this sensor reaches up to 244 pm/mT, with the direction error being merely ±1.4°. Therefore, the proposed sensor exhibits a unique sensitivity for the measurement of magnetic field intensity and direction in 3D space, which makes it best suitable for applications in transportation, medicine, and smart device.

Micro-structured optical fiber magnetic field sensor based on magnetic fluid filling

A novel micro-structured fiber magnetic field sensor based on magnetic fluid (MF) filling is proposed. The air hole radius in the cladding of fiber is reduced from inner layer to outer layer, and the numerical analysis is performed by the finite element method (FEM). For the [Formula: see text]-pol mode, the proposed sensor has an average sensitivity of 960.61 pm/Oe, and for the [Formula: see text]-pol mode, the average sensitivity can reach 884.85 pm/Oe. The sensor has the advantages of small size and high sensitivity and is competitive in magnetic field sensors.

Variations of magnetic field measurement with an extrinsic Fabry-Perot interferometer by double-beam technique

The magnetic field variations were measured by a designed optical fiber magnetic field sensor based on the extrinsic Fabry-Perot interferometric sensor with both single and double beam techniques. Behavior of a giant magnetostrictive material Terfenol-D rod was examined at room temperature, under magnetic field variations and varying applied force. In both techniques, as the force increased, the full width half maximum of the peaks decreased; therefore, a larger number of bright and dark fringes occurred with the magnetic field. The displacements increase from 9.24 ± 0.03 to 13.20 ± 0.03 μm for the single beam for 8.65, 9.75, 11.47 and 13.35 N. For the double beam, the displacements are found to be 3.69 ± 0.02, 3.69 ± 0.02, and 4.51 ± 0.02 μm for 8.65, 9.75, and 11.47, respectively. While Terfenol-D is under different forces, the orientations of magnetic domains are investigated. In summary, the magnetic field could be measured precisely at both short and long ranges by these techniques.

Structural, morphological, optical, dielectric and magnetic field sensing characteristics of Bi1-xKxMnO3 and BiMn1-yCoyO3 nanopowders: A comparative study

Composites of BiMnO3 such as Bi1-xKxMnO3 and BiMn1-yCoyO3 (x = y = 0.05, 1.0, 1.5) based fiber optic magnetic field sensors were fabricated and sensitivity analysis was performed at room temperature. The properties of nanosized particles synthesized using hydrothermal method were studied using X-ray diffraction, scanning electron microscope, ultraviolet–visible spectrometer and Dielectric measurement. The results reveal the formation of nanocrystallite of size ∼ 50 nm with rice like morphology in the bandgap range between 1.2 eV and 1.5 eV. The 5% K doped BMO has better magnetic field sensitivity at a source wavelength of 693 nm and pristine BMO has better sensitivity at 772 nm.

Intensity-interrogated magnetic field sensor with resolved temperature cross sensitivity based on down-fusion taper and S-taper integrated with magnetic fluids

An intensity-interrogated fiber-optic magnetic field sensor functionalized with magnetic fluids is proposed and experimentally demonstrated by encapsulating an S-taper concatenated with down-fusion taper in a silica capillary. The down-fusion taper serves as a higher order mode exciter, whereas the S-taper is employed to couple the cladding modes back into the fiber core, and so an interferometric spectrum could be acquired for sensing interrogation. Spectral characteristics of the proposed sensor dependent on magnetic field intensity and environmental temperature are investigated in detail. Experiment results show that the maximum magnetic field sensitivity reaches −0.02336 dB / Oe within a specific range of 25 to 200 Oe, and the temperature sensitivity reaches 0.07116 dB / ° C within a temperature range of 26°C to 46°C. By exploiting the distinction between magnetic field intensity and temperature sensitivities of peak 1 and dip 1 that are selected for intensity interrogation, temperature cross-sensitivity issue can be resolved.

Magneto-elastic-optical coupling of Terfenol-D based optical fiber magnetic field sensors

A magneto-elastic-optical coupling model for Terfenol-D based single-mode optical fibers is proposed, in which the nonlinear magneto-elastic coupling characteristics of Terfenol-D is taken into consideration. The field-dependent material constants for magnetic coating is predicted and in good agreement with experimental results. The coupling effects of external stimuli (e.g. magnetic field and stress) on magneto-optic (MO) coupling coefficient of optical fibers are investigated for the first time. The results show that the relative phase change is enhanced by changing the thickness or Poisson’s ratio of constituent materials. More importantly, appropriate applied tensile/compressive stress can control the value of optimal bias field as well as enhance MO coupling coefficient of optical fibers under different magnetic fields. This research provides a method to evaluate and improve magnetic performance of the optical fiber magnetic field sensors consisting of giant magnetostrictive materials.

Vector optical fiber magnetometer based on capillaries filled with magnetic fluid.

A novel and practical magnetic field sensor based on optical fiber optics is proposed in our work. We first demonstrate magnetic sensing with the structure that single-mode optical fibers are fused with capillaries in parallel in an experiment. We clearly show the aggregation and arrangement variation with the magnetic field of magnetic nanoparticles in capillaries. Based on the tunable effective refractive index of optical modes in a waveguide structure of a sensor, the optical properties and sensing mechanism in the sensing structure were simulated and further analyzed. We achieved the detection of a space magnetic field, including intensity and its direction. We obtained that the sensitivity of a sensor is 112 pm/mT, presenting good performance in the same kind of optical fiber magnetic field sensor.

Highly Sensitivity Fiber-Optic Vector Magnetometer Based on Two-Mode Fiber and Magnetic Fluid

A compact fiber-optic vector magnetic field sensor combining a tapered two-mode fiber (TMF) and magnetic fluid is proposed and experimentally demonstrated. The modal interference effect is mainly caused by LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> and LP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> modes, and an additional refractive-index-modulation (RIM) on TMF taper lateral is introduced by femtosecond laser for enhancing the interference intensity. Moreover, the RIM provides the sensor a significant direction-dependence due to its asymmetric position relatively to fiber axis. The spectral response to magnetic field intensity and direction of the proposed sensors has been investigated. And, the results show that the wavelength-referenced magnetic field sensitivity reaches up to 71.98 pm/Oe in the range of 40-120 Oe and the intensity-referenced sensitivity reaches up to 0.11 dB/Oe. Meanwhile, the sensor presents great directional resolution with intensity-reference (0.11 dB/deg).

Optical fiber magnetic field sensor based on birefringence in liquid core optical waveguide

An optical fiber magnetic field sensor based on the birefringence of magnetic fluid is proposed by filling the magnetic fluid into a hollow-core waveguide. The birefringence characteristics of magnetic fluids with different concentrations tuned by magnetic field were investigated under different magnetic fields when the filled hollow-core waveguide is placed in a Sagnac loop. As the magnetic field increases, the internal chain-like structure of the magnetic fluid increases, resulting in changes in birefringence. The experimental results show that the device has a highly linear response to the variation of magnetic field intensity in the range of 0–300 Oe with the maximum sensitivity of 29.2 pm/Oe and resolution of 0.68 Oe. The proposed magnetic field sensor has such advantages as ease of fabrication, simple structure, low cost and it is expected to find potential applications in the magnetic field measurement with high accuracy, optical fiber gyroscopes, magneto-optic modulators and so on. Due to the external field tunability, the device also provides a promising technology for microfluidics research.

Magnetic Field Sensing Based on SPR Optical Fiber Sensor Interacting With Magnetic Fluid

A novel magnetic field sensing system based on surface plasma resonance (SPR) optical fiber sensor and filled with magnetic fluid (MF) is proposed and demonstrated for the first time. In the magnetic field SPR optical fiber sensor, SPR is excited by Ag as metallic material and MF is filled into the capillary sealed with epoxy glue, which utilizes the tunable refractive index (RI) of MF, and the transmission spectrum will change with different magnetic field intensities. The magnetic-optic effect of MF and the high RI sensitivity of optical fiber SPR sensor are utilized to enhance the sensitivity of the novel magnetic field sensor significantly. In the experiment, the performances of the magnetic field sensing system are tested by applying different measured magnetic fields. The final results indicated that a sensitivity of 303 pm/Gs is achieved. Compared with other optical fiber magnetic field sensors, the advantages of the proposed sensor in this paper are simple structure, small in size, easy to make, low cost, high sensitivity, and anti-interference.