Refractive Index Of Magnetic Fluid Research Articles

Vector magnetic field sensor based on coreless D-shaped fiber and magnetic fluid.

A vector magnetic field sensor based on a ferrofluid-encapsulated coreless D-shaped fiber is proposed and demonstrated. The core of the singlemode fiber (SMF) is completely removed by fiber polishing technology, and the remaining part transformed into a multimode interference (MMI) waveguide. The exposed side-polishing plane enable the evanescent field to interact with surrounding magnetic fluid (MF). Relying on the non-circularly symmetric geometry of the coreless D-shaped fiber and the MF refractive index modulation by the orientation and intensity of the applied magnetic field, vector magnetic field sensing is achieved. The magnetic field response characteristics of the coreless D-shaped fibers with different residual thicknesses (RTs) are investigated. The experimental results show that a reduced RT yields enhanced sensitivity, and the magnetic field intensity sensitivity reaches -0.231 nm/mT and -0.483 dB/mT at a RT of 42.7 µm. The developed coreless D-shaped fiber sensor exclusively utilizes SMF, thereby offering a cost-effective scheme for the fabrication of vector magnetic field sensors.

Highly sensitive refractive index and magnetic field sensor based on long-period fiber grating inscribed in tapered optical fiber

A refractive index (RI) and magnetic field sensor based on tapered long period fiber grating (LPFG) is proposed. We prepared two different periods of LPFGs (LPFG1 and LPFG2) using high-frequency CO2 laser point by point method on tapered single-mode fiber. Firstly, LPFG1 is used to measure the RI of sodium chloride solution. LPFG1 is immersed in sodium chloride solutions with different RI to measure the sensitivity of LPFG to RI. The experimental results indicate that LPFG1 is particularly sensitive to changes in environmental RI, with a sensitivity of 381.820 nm/RIU. Due to the special sensitivity of tapered LPFG to environmental RI, in order to eliminate the influence of residual sodium chloride on the surface of LPFG1 on magnetic field measurement, we use LPFG2 with similar parameters to measure the environmental magnetic field. LPFG2 was encapsulated in a glass capillary tube filled with the magnetic fluid (MF). After the environmental magnetic field changed, the RI of MF changed, causing the resonance peak wavelength of LPFG2 to drift. We measured the magnetic field using LPFG2 within the magnetic field range of 0.66 mT to 20 mT. Only in the magnetic field range of 1.95 mT to 4.6 mT, good linear fitting was achieved, with a magnetic field sensitivity of 1.242 nm/mT and a fitting coefficient of 0.9852. The experimental results indicate that LPFG inscribed in tapered optical fiber has high sensitivity to environmental RI and magnetic field. The sensor has a simple structure, small volume, easy production, and high sensitivity, which has certain practical application prospects.

Analysis of Tunable Refractive Index Characteristics of the Magnetic Fluid

The influence of magnetic field intensity(H MF) on the refractive index of magnetic fluid (n MF) at room temperature is analyzed. The optical fiber end reflection method based on the Fresnel principle is used to carry out relevant experiments. The corresponding relationship between n MF and applied magnetic field is studied in detail. n MF controls characteristic curve of magnetic fluid with a volume fraction of 0.36% is obtained. According to the experimental results, the H MF sensitivity of MF is about 0.937~0.948 RIU / T.

High sensitivity and large measurement range magnetic field micro-nano fiber sensor based on Mach-Zehnder interference

High sensitivity and large measurement range magnetic field micro-nano fiber (MFM-NF) sensor based on Mach-Zehnder interference has been proposed and demonstrated. This sensor is composed of micro-nano optical fiber (MNF) and magnetic fluid (MF). MNF is fabricated with rapidly changed cone region and small diameter micro-nano region, the core mode will be coupled to the cladding duo to the small enough diameter of the MNF, and the core mode and the cladding mode will be form Mach-Zehnder interference. The change of magnetic field leads to the change of MF refractive index, and the refractive index near the micro-nano region strongly affects the mode interference. Under the magnetic field increased, the magnetic field sensitivity of the sensor is up to 69 pm/Gs in the range of 50 ∼ 200 Gs. The linearity was 0.9952. Under the magnetic field decreased, the linear correlation is 0.9942 in the range of 200 ∼ 0 Gs, and the magnetic field sensitivity is 29 pm/Gs. The sensor has the advantages of easy fabrication, low cost and simple structure, and it would be have a wide application prospect in the field of magnetic field sensing.

Miniaturized FPI-FBG integrated sensor for parallel monitoring of magnetic field and magnetic fluid refractive index

In this paper, a sensor combining Fabry–Perot interferometer (FPI) with fiber Bragg grating (FBG) is designed, fabricated, and experimentally demonstrated as an excellent alternative to traditional sensors to detect the magnetic field and refractive index (RI), simultaneously. The sensor comprises a magnetostrictive Ni-Fe alloy coated on partially-unclad FBG, connecting the two reflecting surfaces of the micro-FPI cavity. The magnetostrictive analysis shows that magnetostriction reaches the maximum value at 59.3% Ni concentration. The sensor performance test was conducted on the RI of magnetic fluid and external magnetic field changes. The probe sensitivity was found to be as high as 625.38 nm/RIU and 7.71 nm mT−1, respectively. A matrix for simultaneous measurement of the magnetic field and RI was constructed using these sensitivity values. The stability of the sensor system over more than 300 h is at a satisfactory level. Considering the accurate FBG modulation and particular design of the experiment proposed by this method, the resolution of 1.69 × 10−4 RIU and 0.016 mT for magnetic fluid and magnetic field could be achieved, respectively, which can meet the sensing demand for a wide range of applications.

Temperature compensated fiber optic magnetic sensor based on the combination interference principle.

In this paper, a highly sensitive temperature compensated fiber optic magnetic field sensor by Sagnac and Mach-Zehnder combination interference (SMZI) is proposed and verified. The sensing structure relies on microstructured exposed core fiber (ECF) filled with ethanol and magnetic fluid (MF). The refractive index of MF and ethanol is affected by the magnetic field and temperature (MFT). SMZI is based on the multimode and birefringence characteristics of ECF. The measurement principle is that the spectra of Sagnac interference and Mach-Zehnder interference have respective sensitivities to the MFT. The magnetic sensitivity can reach 1.17 nm/mT, and the temperature sensitivity is up to -1.93 nm/°C. At the same time, the sensor has good repeatability and low detection limits of 0.41 mT and 0.25°C, respectively. It not only solves the cross-influence of temperature but also makes the spectral analysis more intuitive. The sensor has a broad development prospect in the application of MFT detection.

High-sensitivity detection of magnetic field and temperature based on magnetic fluid coated bi-tapered Mach-Zehnder interferometer

A dual enlarged fiber-tapered magnetic field and temperature detection Mach-Zehnder interferometer which is cladded by magnetic fluid is presented and fabricated. The bi-tapered structure is used to enhance the mode interference intensity. The principle of the sensor is that the refractive index of magnetic fluid is tuned by magnetic field and temperature. Magnetic field and temperature can be detected by monitoring changes in two interference dips with different sensitivity to wavelength. The result shows that the wavelength shift sensitivities for magnetic field and temperature are 264.29 pm/mT and −112 pm/℃, respectively. The sensor has the advantages of easy fabrication, high sensitivity and compact size, which has good potential application in the field of magnetic field and temperature monitoring.

Fiber-optic vector magnetic field sensor based on a magnetic-fluid-infiltrated large-core-offset Mach-Zehnder interferometer.

A fiber-optic vector magnetic field sensor based on a large-core-offset Mach-Zehnder interferometer (MZI) infiltrated by magnetic fluid (MF) is proposed and demonstrated in this paper. By large-core-offset fusion splicing of a short single-mode fiber (SMF) between a lead-in SMF and a coupling multi-mode fiber, the MZI with a sub-millimeter length is formed, which is then sealed in an MF-infiltrated glass capillary. Through the MF's refractive index modulation by external magnetic field, the phase of the light passing through the MZI is altered. As a result, the transmission spectrum can be monitored for the magnetic field measurement. Furthermore, from the axial-asymmetry of the large-core-offset MZI structure, the proposed sensor possesses vectorial magnetic-field-sensing ability. Experiments show that the MF-infiltrated large-core-offset MZI vector magnetic-field sensor can achieve a high wavelength sensitivity of 96.68 pm/Oe in a magnetic field range of 50-130 Oe.

Fiber in-line magnetic field sensor based on Mach-Zehnder interferometer integrated with magnetic fluid

In this paper, magnetic fluid (MF), a new type of optical functional nanomaterial with interesting optical characteristics under the external magnetic field, is adopted to form a novel fiber-optic magnetic field sensor. The proposed sensor is based on Mach-Zehnder interferometer (MZI) and has a multimode-singlemode-multimode (MSM) fiber structure. The MSM structure was fabricated by splicing a section of uncoated single mode fiber (SMF) between two short sections of multimode fibers (MMFs) using a fiber fusion splicer. The magnetic field sensing probe was made by inserting the fiberoptic structure in an MF-filled capillary tube. Variations in an external magnetic field is seen to cause changes in the refractive index of MF. This tunable change in the refractive index with magnetic field strengths between 0.6 mT to 21.4 mT produces a shift in the peak position of the wavelength. The shift of the valley wavelength with magnetic field intensity has a good linearity of up to 99.6%. The achieved sensitivity of the proposed magnetic field sensor is 0.123 nm/mT, which is improved by several folds compared with those of most of the other reported MF-based magnetic field sensors. Furthermore, we build the corresponding circuit-based measurement system, and the experimental results show that the voltage change indirectly reflects the change of the external magnetic field strength. Therefore, this provides the potential to fiber-based magnetic field sensing applications.

Simultaneous measurement of temperature and magnetic field based on surface plasmon resonance and Sagnac interference in a D-shaped photonic crystal fiber

A novel D-shaped photonic crystal fiber (PCF) sensor based on surface plasmon resonance (SPR) and Sagnac interference technology is proposed to realize the simultaneous measurement of temperature and magnetic field. Two ultra-large air-holes are introduced into the cladding layer to increase the birefringence. Magnetic fluid (MF) material is filled into the cladding air-holes to measure the temperature and magnetic field based on the dependence of the MF refractive index (RI) on temperature and magnetic field. The D-shaped flat surface coated with a gold layer is in direct contact with ethanol to achieve the dual-parameter demodulation and solve the cross-sensitivity problem. The proposed sensor has the advantages of high sensitivity and easy fabrication for the multi-parameter measurement applications.

SPR based magnetic-field sensing in microchannelled PCF: a numerical approach

We propose a surface plasmon resonance (SPR) based magnetic field sensor using a microchannel incorporated side-polished photonic crystal fiber (PCF). A side polished PCF, when exposed to a high energy Gaussian pulse in the transverse direction, engraves a microchannel on the flat surface. The inner surface of the microchannel is assumed to be coated with indium tin oxide (ITO) and the microchannel is to be filled with magnetic fluid (MF). The refractive index (RI) of MF could be varied via application of magnetic field. The principle of the device is based on the excitation of surface plasmon wave at the ITO-MF interface and the corresponding shift in SPR peak due to the change in RI of MF. The presence of ITO helps in excitation of surface plasmon in the near infrared wavelength band. Through numerical analysis, we estimate the magnetic field sensitivity of the proposed device to be 564 pm Oe−1 (5.64 nm/mT) for weaker magnetic field with a maximum resolution of 0.177 Oe. Further, the proposed sensor can be utilized for intensity based magnetic field sensing where its sensitivity is of the order of 0.005/Oe.

Complex refractive index of concentrated magnetic fluids

The spectra of the real and imaginary parts of the refractive index of magnetic fluids based on kerosene with a solids phase concentration of 1% to 35% are experimentally measured. The comparison of calculations results have been made according to Maxwell-Garnett and Bruggeman’s models of effective medium approximation. The influence of refractive index spectra on the extinction of light in magnetic fluids is shown.

Magnetic field sensing using magnetic-fluid-filled optofluidic ring resonator

A magnetic field sensor based on the silica optofluidic ring resonator is proposed and experimentally demonstrated for the first time. Magnetic fluid is filled in the core of the microcapillary to experience the strength change of the applied magnetic field. When the whispering gallery modes circulate in the wall of the microcapillary, it can experience the increasing refractive index of magnetic fluid with the increase in the magnetic field strength, leading to the redshift of the resonant wavelength. The maximum sensitivity of 75.7 pm/mT and figure of merit of 105 T−1 are realized, respectively, corresponding to a large dynamic magnetic field range from 15 to 125 mT. By optimizing the concentration of the kerosene-based magnetic fluid, the detection limit of 2.2 mT and the measurement resolution of 0.9 mT are achieved, respectively. This work provides a novel magnetic field sensing scheme with high performance using the optofluidic ring resonator and further broadens its applications.

Simultaneous measurement of temperature and magnetic field based on cascaded photonic crystal fibers with surface plasmon resonance

Two segments of gold-layer filled photonic crystal fibers (PCF) are joined together to achieve localized Surface Plasmon Resonance (SPR) effect. The cladding air-holes of both two PCFs are selectively filled with magnetic fluid (MF) while only one PCF would be applied a transverse force. The optical field distributions and loss spectra at different wavelengths are calculated and simulated using the finite element method (FEM). Results show that a blue-shift of the loss peaks will be obtained with the increase of applied transverse force. Based on the dependence of the MF refractive index on temperature and magnetic field, the sensitivity of the spectral response of the device to magnetic field and temperature is characterized, and the results of its application as a dual-parameter PCF-based sensor are also presented.

Multi-parameters measurement based on cascaded Bragg gratings in magnetic fluid-infiltrated photonic crystal fibre

Simultaneous measurement of multi-parameters is demonstrated quantitatively using two fibre Bragg gratings inscribed on a high birefringence photonic crystal fibre (PCF) and common PCF, respectively. The birefringence coefficient and the Bragg wavelengths corresponding to the fast-axis mode and slow-axis can be magnetic-controlled by filling magnetic fluid (MF) into several cladding air-holes. Based on the dependence of the MF refractive index on temperature and magnetic field, the sensitivity of the spectral response of the device to longitudinal strain, magnetic field and temperature are characterized, and the results of its application as a multi-parameter sensor are also presented.

Sensing characteristics of a MF-filled photonic crystal fiber Sagnac interferometer for magnetic field detecting

A highly sensitive magnetic field sensor based on Sagnac interferometer consisted of a polarization maintaining photonic crystal fiber (PCF) filled with magnetic fluid (MF) is proposed and demonstrated. The refractive index of MF is sensitive to magnetic field H and the fiber Sagnac interferometer is sensitive to refractive index, so the sensing structure of our magnetic field sensor is designed. The water-based nanoparticles Fe3O4 is used which possesses low refractive index. The refractive index of MF follows the Langevin function and changes linearly with magnetic field H in our considerable magnetic field region. The parameters of λ, B(λ, H) on the influences of sensitivity are analyzed. We find a new phenomenon the two dip wavelengths shift in the opposite direction as magnetic field increases. The phenomenon is explained by group birefringence Bg which decreases and its sign changes as magnetic field increases. The sensitivity increases infinitely near the special wavelength related with zero-point Bg. The average sensitivities are 384pm/Oe (51,569nm/RIU), −430pm/Oe (−57,747nm/RIU) which turn out pretty well and the R-squares are 0.98113, 0.98415 respectively for the detected range 410–600Oe.

Magnetic field sensor based on cascaded microfiber coupler with magnetic fluid

A kind of magnetic field sensor based on cascaded microfiber coupler with magnetic fluid is proposed and experimentally demonstrated. The magnetic fluid is utilized as the cladding of the fused regions of the cascaded microfiber coupler. As the interference valley wavelength of the sensing structure is sensitive to the ambient variation, considering the magnetic-field-dependent refractive index of magnetic fluid, the proposed structure is employed for magnetic field sensing. The effective coupling length for each coupling region of the as-fabricated cascaded microfiber coupler is 6031 μm. The achieved sensitivity is 125 pm/Oe, which is about three times larger than that of the previously similar structure based on the single microfiber coupler. Experimental results indicate that the sensing sensitivity can be easily improved by increasing the effective coupling length or cascading more microfiber couplers. The proposed magnetic field sensor is attractive due to its low cost, immunity to electromagnetic interference, as well as high sensitivity, which also has the potentials in other tunable all-fiber photonic devices, such as filter.

An All-Fiber Magnetic Field Sensor Based on Dual-S-Shaped Optic Fiber Integrated With Magnetic Fluid

In this paper, magnetic fluid (MF), a new type of optical functional nanomaterial with interesting optical characteristics under the external magnetic field is adopted to form a novel fiber-optic magnetic field sensor. The proposed sensor is based on Mach-Zehnder interferometer and has a dual-S-shaped structure. The S-shaped structure is fabricated by splicing two overlapping single-mode fibers with a fiber fusion splicer. The magnetic field sensing probe was made by inserting the fiber-optic micro-structure in an MF-filled capillary tube. Variations in an external magnetic field is seen to cause changes in the refractive index of MF. This tunable change in the refractive index with magnetic field strengths between 0 and 20 mT produces a shift in the position of the peak of the wavelength. The shift of the valley wavelength with magnetic field intensity has a good linearity of up to 99.634%. The achieved sensitivity of the proposed magnetic field sensor is 0.2904 nm/mT, which is a several-fold improvement on most of the other reported MF-based magnetic field sensors. Furthermore, we have built the corresponding circuit-based measurement system and have shown that a voltage change, associated with the results, indirectly reflects the change of the external magnetic field strength. This, therefore, provides the potential to fiber-based magnetic field sensing applications.

Single-beam Mach–Zehnder micro-interferometer based on magnetic fluids

The single-beam Mach–Zehnder micro-interferometers are proposed. Magnetic fluid is utilized to constitute the interferometers. Due to the tunable refractive index of magnetic fluid under external magnetic field, the interference intensity of the Mach–Zehnder interferometer can be adjusted by the magnetic field. Through turning on and turning off the magnetic field alternatively, the repeatability and tunability of the micro-interferometer are verified. The results in this work can be employed to design unique optical devices based on magnetic fluids, such as optical modulator, optical switches.

A Novel Long-Tail Fiber Current Sensor Based on Fiber Loop Ring-Down Spectroscopy and Fabry-Perot Cavity Filled With Magnetic Fluid

A novel long-tail optical fiber current sensor based on fiber loop ring-down spectroscopy (FLRDS) and magnetic-tunable refractive index properties and magnetic-tunable transmission properties of magnetic fluid is proposed and demonstrated for the first time. In the sensing system, a Fabry-Perot (F-P) cavity filled with magnetic fluid is used as the sensing head, and the sensitivity of current-sensing has been enhanced significantly. Relations between magnetic field and refractive index of magnetic fluid are measured. Refractive index of magnetic fluid increases linearly as the magnetic field increases and according to the F-P interferometer principle, the best gap length of F-P cavity is obtained. In this paper, the FLRDS sensing system has been theoretically modeled, and a new mathematical model developed for optimizing the coupling ratio of couplers has been presented, and the best coupling ratio has been obtained. The new mathematical model could also be used in the similar ring-down systems. Finally, the performances of the current-sensing system are tested by applying different measured currents. The final results indicate that a sensitivity of 14.88 mA/ $\mu $ s is achieved.