Optical Fiber Magnetic Field Sensor Research Articles

Photonic crystal fiber sensors to excite surface plasmon resonance based on elliptical detection channels are used for highly sensitive magnetic sensing

To improve the detection performance of fiber optic magnetic field sensors a new photonic crystal fiber (PCF) based on surface plasmon resonance (SPR) was designed and investigated. The designed sensor uses an elliptical detection channel, and the modal transmission characteristics and magnetic field sensing characteristics of this fiber optic sensor are analyzed using the full vector finite element method (FVFEM). In addition, the effect of the detection channel on the detection accuracy at different curvatures was investigated. Compared with previous optical fiber magnetic field (MF) sensors, the designed sensor meets the requirements of both refractive index (RI) and MF measurements, and the MF sensitivity, RI sensitivity, and amplitude sensitivity (AS) of the sensor reach 0.739 nm/Oe, 12043.8 nm/RIU, and 754.88RIU−1, respectively. The designed sensor expands the application range of optical fiber sensors and reduces the cost. It has great potential for application in complex environments.

Distributed optical fiber magnetic field sensor based on polarization-sensitive OFDR.

A distributed optical fiber magnetic field sensor based on a polarization-sensitive optical frequency domain reflectometer (POFDR) is proposed. It extracts the accumulated Faraday rotation by combining the Stokes vectors and the backward Mueller matrices from the measured states of polarization (SOPs) and obtains the magnetic field component. This method avoids adjusting the input polarization during the magnetic field sensing process. It overcomes the drawback of the conventional POFDR scheme, which requires at least two sets of different input SOPs for each sensing. Finally, the aforementioned effectiveness has been experimentally verified by using a single-mode sensing fiber. The results show that the sensor has good repeatability and linearity. The measurement error of the magnetic field sensor is 19.4 mT. The measured magnetic field variations agree with the applied ones with similarities higher than 0.98.

Highly sensitive magnetic field sensor using magnetic fluid filled dual-core photonic crystal fiber

A high sensitivity fiber optic magnetic field sensor that utilizes a dual-core photonic crystal fiber (DC-PCF) filled with magnetic fluid (MF) has been proposed and validated to simultaneously detect magnetic field intensity and temperature. DC-PCF is a multimode fiber that supports various modes of light transmission and induces intermodal interference within fiber core. The numerical analysis of the mode characteristics of DC-PCF is conducted. The sensing structure relies on the use of a DC-PCF with air holes filled with a suitable material, such as MF substance. The analysis of the working principle of the DC-PCF for sensing and measurement is conducted by considering its structural characteristics and mode characteristics. The effective refractive index (ERI) of MF is affected by external magnetic field intensity and temperature. To extract the effective frequency points, the fast Fourier transform (FFT) method can be employed. Additionally, the inverse fast Fourier transform (IFFT) method can be utilized to determine the magnetic field sensitivity, which can reach up to 1.562 nm/mT. Furthermore, the temperature sensitivity can be as high as −1.043 nm/°C. The sensor demonstrates excellent repeatability and showcases low detection limits of 0.0128 mT and 0.0192 °C, respectively. Additionally, the proposed sensor exhibits substantial potential for further development in the field of high sensitivity magnetic field detection applications.

High-precision magnetic field sensor based on phase-shift fiber loop ring-down technique and FBG-magnetostrictive structure

A high-precision fiber-optic magnetic field sensor based on the phase-shift fiber-optic loop ring-down (PS-FLRD) technique and the structure of fiber Bragg grating (FBG) bonding to a magnetostrictive rod is proposed and experimentally demonstrated. A coarse wavelength division multiplexer (CWDM) is inserted into the fiber loop and serves as an optical edge filter (OEF) to provide wavelength-dependent transmittance. Due to the linear response of the CWDM, the wavelength shift of the FBG induced by the external magnetic field is linearly converted to a transmittance change of the fiber loop, which is reflected in the phase shift. Consequently, a relationship between the phase shift and the magnetic field applied to the FBG is established. The experimental results show a good linear relationship between the phase shift and the magnetic field. For magnetic field strengths ranging from 0 to 880 Gs, the measured sensitivity is 0.0056 deg/Gs with a resolution of approximately 18 Gs. Furthermore, the proposed scheme demonstrates excellent stability and repeatability, remaining unaffected by power fluctuations, which provides a promising solution for magnetic field sensing.

An Optical Fiber Magnetic Field Sensor Based on Mach–Zehnder Interferometer Composed of Two Peanut-Shaped Structures and Tapered No-Core Fiber

An Optical Fiber Magnetic Field Sensor Based on Mach–Zehnder Interferometer Composed of Two Peanut-Shaped Structures and Tapered No-Core Fiber

Characterization of Fiber-Optic Vector Magnetic Field Sensors Based on the Magneto-Strictive Effect.

Fiber-optic magnetic field sensors have garnered considerable attention in the field of marine monitoring due to their compact size, robust anti-electromagnetic interference capabilities, corrosion resistance, high sensitivity, ease of multiplexing and integration, and potential for large-scale sensing networks. To enable the detection of marine magnetic field vector information, we propose an optical fiber vector magnetic field sensor that integrates three single-axis sensors in an orthogonal configuration. Theoretical analysis and experimental verification are conducted to investigate its magnetic field and temperature sensing characteristics, and a sensitivity matrix is established to address the cross-sensitivity between the magnetic field and temperature; experimental tests were conducted to assess the vector response of the three-dimensional (3D) vector sensor across the three orthogonal axes; the obtained experimental results illustrate the commendable magnetic field vector response exhibited by the sensor in the orthogonal axes, enabling precise demodulation of vector magnetic field information. This sensor presents several advantages, including cost-effectiveness, easy integration, and reliability vectorially. Consequently, it holds immense potential for critical applications in marine magnetic field network detection.

Magnetic Field and Temperature Two-Parameter Sensor Based on Mach–Zehnder Interferometer and Faraday Rotation Effect

A novel combination of structural design and sensing theory is proposed for an optical fiber magnetic field and temperature two-parameter sensor based on the Mach-Zehnder interferometer (MZI) and Faraday rotation effect. The sensor structure includes a polydimethylsiloxane (PDMS) microcavity and a small section of offset spliced fiber. Numerical analysis shows that the sensor exhibits high temperature sensitivity, which has been experimentally verified. The sensor has a temperature sensitivity of -846 pm/°C in the 20 to 35°C and a magnetic field intensity sensitivity of 190 pm/Gs in the range of 0 to 150 Gs. The temperature and magnetic field intensity responses of the sensor are linear and have been optimized for sensitivity demodulation. The sensor is well-suited for standardized monitoring of temperature and magnetic field in applications requiring accurate measurements.

High Sensitivity Surface Plasmon Resonance Magnetic Field Sensor Based on Au/Gold Nanoparticles/Magnetic Fluid in the Hollow Core Fiber

A type of surface plasmon resonance (SPR) magnetic field sensor based on Au/gold nanoparticles/magnetic fluid (MF)-processed hollow core fiber is proposed in this work, which fully utilizes SPR’s high sensitivity to RI and the magnetron refractive index characteristic of MF. The metal material Au excites SPR and gold nanoparticles excite the localized surface plasmon resonance (LSPR). The coupling of surface plasmon polariton (SPP) with localized surface plasmon (LSP) increases the local electric field strength, thus improving the sensor’s sensitivity. Both the theoretical analysis on the sensing mechanism and the experimental findings demonstrate that this novel SPR magnetic field sensor has a wide measurement range and high sensitivity. In the range of magnetic field strength from 0 to 603 Gs, the sensitivity can reach up to 156 pm/Gs, and the linearity is good (the coefficient of determination is 0.996). Compared with other optical fiber magnetic field sensors, the sensor proposed in this paper has the benefits of easy fabrication, excellent sensitivity, simple structure, strong anti-interference ability, and wide measurement range, exhibiting significant application potentials in the fields of military drills, aerospace, etc.

Ampere force fiber optic magnetic field sensor using a Fabry-Perot interferometer.

The paper presents a novel fiber-optic vector magnetic field sensor using a Fabry-Perot interferometer, which consists of an optical fiber end face and a graphene/Au membrane suspended on the ceramic ferrule end face. A pair of gold electrodes are fabricated on the ceramic ferrule by femtosecond laser to transmit electrical current to the membrane. Ampere force is generated when an electrical current flows through the membrane in a perpendicular magnetic field. The change in Ampere force causes a shift in the resonance wavelength in the spectrum. In the magnetic field intensity range of 0 ∼ 180 mT and 0 ∼ -180 mT, the as-fabricated sensor exhibits magnetic field sensitivity of 5.71 pm/mT and 8.07 pm/mT. The proposed sensor has great potential application in weak magnetic field measurements due to its compact structure, cost-effectiveness, ease to manufacture, and good sensing performance.

Ultrasensitive magnetic field sensor based on cladding-etched long-period grating.

We demonstrate a high-sensitivity fiber-optic magnetic field sensor, which consists of a cladding-etched long-period fiber grating (LPFG) near the dispersion turning point (DTP) integrated with a magnetic fluid (MF). By reducing the cladding diameter of the LPFG, the fundamental mode is coupled to the lowest order cladding mode (LP0,2) near the DTP, which has a much higher surrounding refractive index sensitivity. Thanks to the excellent magneto-optical characteristics of the MF, the proposed sensor can achieve a magnetic field intensity sensitivity of 44.69 nm/mT in the range of 3-7.4 mT. The minimum magnetic field intensity that can be detected is 0.45 µT due to the 0.02-nm wavelength resolution of the optical spectrum analyzer. The proposed etched DTP-LPFG-based sensor with ultrahigh magnetic field sensitivity could have potential applications in magnetic fields and electrical systems.

A high-sensitivity magnetic field sensor using spindly optical fiber taper

In this paper, a high-sensitivity magnetic field sensor is proposed. The sensor consists of a spindly optical fiber taper (SOFT) coated with magnetic fluid. The SOFT structure is made through fusing taper method and connected to a fiber loop for magnetic field sensing. The experiment results show that the sensor is barely dependent on laser wavelength within the range of 1520 nm to 1575 nm. When the magnetic field of 180 Oe is applied, the transmission change reaches up to 3.324 dB at 1550 nm. Additionally, the magnetic field sensitivity of the sensor is −23.4μs/Oe in the linear region of 10 Oe−80 Oe. Compared with the traditional fiber optic magnetic field sensor with the fiber loop ring-down (FLRD), the proposed SOFT sensor could achieve higher magnetic field sensitivity.

Magnetic flux leakage detection based on a sensitivity-enhanced fiber Bragg grating magnetic field sensor.

We propose a sensitivity-enhanced fiber Bragg grating (FBG) magnetic field sensor for magnetic flux leakage (MFL) detection. The testing system consists of the FBG, suspended strain concentration structure, and two ceramic tubes bonded on a Terfenol-D base. We show the relation between the MFL and the width and depth of the crack, the lift-off of the sensor away from the surface of the workpiece, and the angle between the orientation of the sensor and the magnetization direction. The experimental results are very consistent with those obtained from finite element analysis simulations. The sensitivity of the sensor is increased to 81.11pm/mT for increasing magnetic fields and 91.55pm/mT for decreasing magnetic fields. The MFL test demonstrates that the sensor can identify a crack with a width of 0.5mm and depth of 2mm in an 8mm thick workpiece. To the best of our knowledge, the magnetic field sensor proposed in this work has the highest sensitivity compared with the same types of sensors. Moreover, the application of an FBG-Terfenol-D based magnetic field sensor in the MFL test shows good performance. Compared with traditional electrical MFL testing technologies, the sensitivity-enhanced optical fiber magnetic field sensor has a higher resolution and longer survival time in harsh environments.

Computational Modeling of Magnetic Field Optical Fiber Sensor Considering Temperature Effects

Due to the vast area of application and reliability, fiber optic magnetic field sensors have been the subject of several studies, however, some of these application areas are submitted to temperature variations, which can hinder the sensors in monitoring the magnetic field. With this panorama, this work analyzes through computational modeling a fiber optical magnetic field sensor, using the magneto-optical Faraday effect and observing temperature effects in the sensor response. For modeling, a numerical model built in COMSOL Multiphysics is used. The results show a value for cross-sensitivity of 3.27 mT/°C in a non-optimized configuration of the sensor and of 2.47 mT/°C for an optimized configuration. A methodology for optimizing the sensor to operate in a certain temperature range, 55 to 75 °C, is also discussed. The results presented in this work show that the temperature is an important factor to be considered to improve the selectivity and to obtain the correct sensitivity of the sensor.

Optical Fiber Magnetic Field Sensors Based on 3 × 3 Coupler and Iron-Based Amorphous Nanocrystalline Ribbons

Optical fiber interferometric magnetic field sensors based on magnetostrictive effects have several advantages, e.g., high sensitivity, strong adaptability to harsh environments, long distance transmission, etc. They also have great application prospects in deep wells, oceans, and other extreme environments. In this paper, two optical fiber magnetic field sensors based on iron-based amorphous nanocrystalline ribbons and a passive 3 × 3 coupler demodulation system were proposed and experimentally tested. The sensor structure and the equal-arm Mach-Zehnder fiber interferometer were designed, and the experimental results showed that the magnetic field resolutions of the optical fiber magnetic field sensors with sensing length of 0.25 m and 1 m were 15.4 nT/√Hz @ 10 Hz and 4.2 nT/√Hz @ 10 Hz, respectively. This confirmed the sensitivity multiplication relationship between the two sensors and the feasibility of improving the magnetic field resolution to the pT level by increasing the sensing length.

Fiber Optic All-Polarization Weak Magnetic Field Sensor Based on Sagnac Interferometer

A novel fiber-optic magnetic field sensor, based on a Sagnac structure, is proposed with the approach of polarization interference detection. The sensor takes advantage of common path interference, combining with a high magnetic field sensitivity sensing unit, composed of magneto-optical crystal, and magnetic field concentrators, to achieve high resolution, high stability, and large dynamic measurement of DC magnetic field signals. In this paper, the theoretical model is established and the related theory is derived in detail. The key technologies in the system are thoroughly investigated and verified. Experimental research on the proposed system is demonstrated and the results show that a DC magnetic field resolution of 5.6 nT and a dynamic range of larger than 70 dB is achieved. Furthermore, the linearity of the system is greater than 99.8% and the instability is less than 0.5%.

High-sensitivity optical fiber magnetic field sensor based on multimode optical fiber multi Fabry-Perot interference cavities.

A high-sensitivity optical fiber magnetic field sensor based on a multi-Fabry-Perot interference (F-P) cavity in an etched multimode optical fiber (MMF) was proposed. The MMF was etched along the fiber axis and a hole with the length of about 250 µm formed in the MMF. The multi-F-P cavity in the MMF is a sandwich structure, which is composed of UV glue, magnetic fluid and UV glue. The refractive index and effective cavity length of the magnetic fluid cavity change with the changing of the external magnetic field, which will result in changes of the reflection spectra of the multi-F-P. Thus, the external magnetic field could be detected by the changes of spectra. Experimental results showed that the high magnetic field sensitivity of 299.7 pm/mT and 0.164 dB/mT were obtained in the range of 0∼8 mT weak magnetic induction intensity by using the wavelength and intensity demodulations, respectively. The proposed sensor shows the potential applications in the magnetic field measurement in the weak magnetic environment.

Temperature and vibration insensitive fiber optic vector magnetic field sensor

We propose and demonstrate a fiber optic vector magnetic field sensor based on the magneto-optical Faraday effect. The sensor has excellent environmental adaptability. Due to the polarization dependence of Faraday effect in polarization-maintaining fiber coil, the sensor uses two orthogonal polarization states to detect the direction and intensity of magnetic field. By establishing the magnetic sensitivity model of the sensor through the Jones matrix, we analyze the magnetic field-induced phase difference in the two orthogonal polarization states theoretically. Then the influence of environmental temperature and vibration on the output of the two polarization states of the sensor is analyzed, and the sensor can theoretically achieve complete suppression of environmental temperature and vibration errors. The experimental results show that the sensor sensitivity is 0.507 mV/mT. The directivity of the vector magnetic field sensor reaches 21 dB with the orientation error of ±0.4°. The sensor also has excellent robustness. It is insensitive to environmental temperature changes between 30 °C and 50 °C and environmental vibrations within 1 g. The suppression effect of environmental errors can reach 9.8 times with high anti-interference capability in experiments. The proposed sensor has potential applications in navigation, vehicle detection, and current sensing.

Design of an Er-doped surface plasmon resonance-photonic crystal fiber to improve magnetic field sensitivity.

In order to meet the demand for large-scale magnetic field testing, this paper proposes a D-shaped magneto-refractive photonic crystal fiber (MRPCF) based on surface plasmon resonance (SPR) by using the erbium-doped materials. The four different structures of Models A, B, C, and D are designed by changing the diameter, the position, and the number of layers of the air holes, and the corresponding magnetic field sensing characteristics are analyzed. The results show that in the magnetic field range of 5-405 mT, the magnetic field sensitivities of Models A, B, C, and D are 28 pm/mT, 48 pm/mT, 36 pm/mT, and 21 pm/mT, respectively. Meanwhile, the figure of merit (FOM) of the four MRPCF-SPR sensors is investigated, which have FOMs of 4.8 × 10-4 mT-1, 6.4 × 10-4 mT-1, 1.9 × 10-4 mT-1, 0.9 × 10-4 mT-1. Model B has higher sensitivity and larger FOM. In addition, the effect of the structural parameters of Model B on the sensing performance is also studied. By optimizing each parameter, the magnetic field sensitivity of the optimized Model B is increased to 53 pm/mT, and its magneto-refractive sensitivity and FOM are 2.27 × 10-6 RIU/mT and 6.2 × 10-4 mT-1, respectively. It shows that the magneto-refractive effect of MRPCF can be effectively enhanced by optimizing the structural design of fiber. The proposed MRPCF is an all-solid-state fiber, which solves the instability problem of the magnetic fluid-filled fiber and reduces the complexity of the fabrication process. The all-solid-state MRPCF can be used in the development of quasi-distributed optical fiber magnetic field sensors and has broad applications in the fields of geological exploration, earthquake and tsunami monitoring, and military navigation.

A large bandwidth optical fiber magnetic field sensor based on Sagnac interferometer

In this paper, a fiber magnetic field sensor is proposed based on Terfenol-D and Sagnac interferometer. The mechanism of the sensor is deduced theoretically. As the frequency of the magnetic field increases, on the one hand, the sensitivity is enhanced because the response to the high-frequency non-reciprocal phase differences is intensified in the Sagnac interferometer. On the other hand, the sensitivity is suppressed by the eddy current effect. Then it exhibits significant linear response to alternating magnetic field in a certain frequency range. The sensor performances, such as frequency response, linear range, and noise, are analyzed theoretically and demonstrated experimentally. Experimental results show that the sensor has a 3 dB bandwidth from 100 Hz to 2500 Hz, and the excellent linearity and reversibility from 0 to 274.05 μT (rms). The high sensitivity of 1.34 mV/μT (rms) and minimum detectable magnetic field of 25 nT/√Hz (rms) are achieved at 500 Hz. The sensor with large bandwidth and wide measuring range is suitable for detecting weak alternating magnetic field.

Temperature-compensated optical fiber magnetic field sensor with cascaded femtosecond laser micromachining hollow core fiber and fiber loop

A fiber magnetic field sensor with temperature compensation is put forward and experimentally verified by utilizing Fabry-Perot interferometer (FPI) and multimode interferometer (MI). The FPI with ultra-short cavity (about 20 μm), which is proposed to improve the spectrum contrast after being filled with oil-based magnetic fluids (MF) and achieve the sensing of magnetic field, is drilled through by femtosecond laser. The FPI is composed of two sections of single mode fiber and a hollow core fiber, which is named as single mode fiber-hollow core fiber-single mode fiber (SHS). The MI composed of the coated-fiber-loop, which is only sensitive to temperature, is proposed to compensate the temperature on the sensing of magnetic field. The fiber loop is fabricated by only bending a section of coated single mode fiber (SMF). According to the experiment results, the spectrum visibility of magnetic field sensing part can be improved by 3.1 times by shortening the Fabry-Perot (FP) cavity length. The interference wavelength increases nonlinearly from 0 to 69.1 Gs while linearly from 69.1 to 137.7 Gs. In addition, its temperature sensitivity is −0.20 nm/℃ from 23.0 to 42.9 ℃. Moreover, the sensitivity of MI is −2.31 nm/℃ from 23.0 to 42.9 ℃. It could be used to compensate the temperature influence effectively. The structure boasts characteristics of simple manufacture, low cost and highly-sensitive, which can be applied in the fields of magnetic field sensing.