Magnetic Field Sensitivity Research Articles

Numerical study of a tapered fiber magnetic field sensor based on the ENZ mode

This study introduces what we believe to be a novel magnetic field sensor that utilizes a tapered optical fiber coated with indium tin oxide (ITO) and titanium dioxide (TiO2), operating on an epsilon-near-zero (ENZ) mode. The evanescent field around the tapered optical fiber can excite the ENZ mode of the ITO film, and the TiO2 layer can ensure the phase matching between the fiber core mode and the ENZ mode. The sensor, immersed in magnetic fluid, leverages the unique properties of ENZ materials to achieve a high sensitivity and resolution in the near-infrared (NIR) region. Through a simulation, the sensor demonstrated a maximum sensitivity of 6900 nm/RIU and a magnetic field sensitivity of 370 pm/Oe. The findings suggest that ENZ mode-based optic sensing presents a promising alternative to traditional plasmonic sensing methods, offering potential applications in various fields requiring precise magnetic field measurements.

Magnetic field sensor based on multiple Fano resonance in metal-insulator-metal waveguide coupled with cross-shape resonator

Abstract In this paper, an innovative plasmonic magnetic field sensor (MFS) that exploits a Metal-insulator-Metal (MIM) waveguide configuration with an asymmetric cross-shaped resonator is constructed. The design enables the observation of double Fano resonance in the transmission spectrum, resulting from the coupling between continuous spectrum and discrete spectrum. By incorporating magnetic fluid in the asymmetric cross-shape resonator, the Fano line shapes can be tuned by the external magnetic field. Finite-Difference Time-Domain (FDTD) is used to simulate the spectra response to external magnetic fields and geometrical sizes. The proposed structure exhibits remarkable magnetic field sensitivity of 12.1 p m / O e within the detection range of 15 O e to 199 O e . The resolution of MIM magnetic field sensors can reach 0.0826 O e . The optimal figure of merit (FOM) and maximum Q factor of the Fano dip are about 6.9 × 10 − 4 / O e and 66.74, respectively. Meanwhile, The proposed Fano resonance MFS has some advantages, including compact size, high sensitivity, and cost-effectiveness. A strong linear relationship between the magnetic field and resonance wavelength indicates that the proposed structure can find potential applications in diverse fields such as magnetic field sensors, aircraft navigation, and even nuclear energy generation.

Study of magnetic field error suppression methods based on atomic parameters of cell in atomic co-magnetometer rotation measurement

Abstract We propose a new model for magnetic field errors based on the rotation measurement of the K-Rb-$^{21}{\rm{Ne}}$ co-magnetometer, considering the density ratio and spin collisions. The spin polarization characteristics of different alkali metal density ratios were analyzed by creating five cells with different density ratios, and the correctness of the magnetic field error model was verified experimentally. Moreover, the effects of five different alkali metal density ratios of cells on the sensitivity, long-term stability and magnetic field error suppression of the K-Rb-$^{21}{\rm{Ne}}$ co-magnetometer were investigated experimentally. When the density ratio is 1:107, there can be the optimal magnetic field error suppression effect, sensitivity and long-term stability. According to the derived magnetic field error equation, the magnetic noise error of the K-Rb-$^{21}{\rm{Ne}}$ co-magnetometer with an optimized density ratio is reduced by nearly 5 times from 260$^{\circ}$/h/nT to 56.5$^{\circ}$/h/nT, the sensitivity is improved from 2.9$\times$10$^{-5}$ $^{\circ}$/s/Hz$^{1/2}$ to 7.0$\times$10$^{-6}$ $^{\circ}$/s/Hz$^{1/2}$ at 1 Hz, and the long-term stability Allan variance over two hours is improved from 1.9$\times$10$^{-2}$ $^{\circ}$/h to 8.9$\times$10$^{-3}$ $^{\circ}$/h. This result provides a theoretical basis for designing the parameters of the K-Rb-$^{21}{\rm{Ne}}$ co-magnetometer cell.

Bandwidth compensation for ultra-high-sensitivity SERF magnetometers in magnetocardiac sensing

The trade-off between sensitivity and bandwidth has limited the clinical application of spin exchange relaxation-free (SERF) atomic magnetometers in magnetocardiac measurements. This research addresses the issue by modeling the SERF magnetometer as a first-order inertial link and proposing a method that integrates transient response with tracking signals. The tracking-differential link enables the simultaneous acquisition of both transient and tracking signals, leading to effective noise suppression. Empirical mode decomposition is employed to extract features and filter out noise, ensuring high signal quality. This method extends the bandwidth of dual-beam magnetometers from 9.77 Hz to 240 Hz and single-beam magnetometers from 139 Hz to 289 Hz, while preserving sensitivities of 1 fT/Hz1/2 and 10 fT/Hz1/2, respectively. This research enables high-bandwidth measurements with sub-femtotesla magnetic field sensitivity, presenting promising application opportunities.

DESIGN AND FABRICATION OF SHAPE MORPHING MAGNETO-IMPEDANCE MAGNETIC SENSOR

The magnetoimpedance (MI) effect is characterized by the alteration in the impedance of soft magnetic materials when subjected to a magnetic field while a high-frequency alternating current flows through them. In this study, we engineered two distinct sensor architectures utilizing amorphous FeCSi magnetic ribbon: a single-bar structure with the dimension of 10 mm × 90 μm × 20 μm and a meander structure consisting of 13 parallel single bars. These structures were miniaturized through advanced techniques combining laser engraving and chemical etching. The magnetic analysis reveals that the meander structure exhibits a pronounced dependency on the angle θ between the magnetic field and the sensor orientation, enhancing its soft magnetic properties by up to fivefold compared to the single-bar design. This enhancement might be attributed to a reduction in the demagnetization effect and shape anisotropy energy within the meander sensor. Furthermore, the analysis of the MI effect indicates that the resonance frequency remains unaffected by external magnetic fields for both sensor types. Notably, the meander sensor demonstrates exceptional MI ratio values exceeding 82%, representing a remarkable 24-fold increase over the 3.5% observed in the single-bar sensor. Additionally, the isotropy - quantified as the MI ratio's dependence on angle θ, and magnetic field sensitivity are significantly improved in the meander configuration. These advancements in soft magnetic and physical properties are correlated to the domain structure of the sensor, particularly its transverse magnetic permeability, as evidenced by micromagnetic simulations conducted using Mumax3. With its superior MI ratio, isotropy, and heightened magnetic field sensitivity, the meander-type magnetic field sensor presents substantial potential for applications across diverse fields, ranging from biological systems to specialized practical missions.

Utilizing the multifrequency resonances of the electron spins in diamond nitrogen-vacancy centers under strong radio frequency driving for quantum sensing

Multifrequency resonances in the pulsed-optically detected magnetic resonance (ODMR) spectra of electron spins in ensemble nitrogen-vacancy (NV) centers in diamonds are investigated under strong radio frequency (RF) driving at a MHz frequency range and weak microwave driving at a GHz frequency range in a bias static magnetic field for quantum sensing applications. First, we demonstrate that the coherent destruction of tunneling, which leads to the disappearance of the main resonance peaks, can be utilized for precise calibration of the RF amplitude. Next, we clarify the condition for enhancing the sensitivity of a DC magnetic field under strong RF driving at the RF frequency that matches the split frequency due to the hyperfine interaction between 15N nuclear spins and the NV electron spins. Our findings indicate that strong RF driving increases the sensitivity of the DC magnetic field by enhancing the ODMR contrast and reducing the linewidth. The above results contribute to certifying the quantitative accuracy of RF imaging and enhancing the sensitivity of the DC magnetic field imaging using ensemble NV centers in diamonds.

Functionalized Nanodiamonds for Targeted Neuronal Electromagnetic Signal Detection.

Intracellular sensing technologies necessitate a delicate balance of spatial resolution, sensitivity, biocompatibility, and stability. While existing methods partially fulfill these criteria, none offer a comprehensive solution. Nanodiamonds (NDs) harboring nitrogen-vacancy (NV) centers have emerged as promising candidates due to their sensing capabilities under biological conditions and their ability to meet all aforementioned requirements. This study focuses on expanding the application of NDs and NV center-based sensing to neuronal contexts by investigating their functionalization and subsequent effects on three distinct cell lines relevant to neurodegenerative disease research. Our study concentrates on positioning fluorescent NDs (FNDs) with NV center point defects onto neuronal cell surfaces. Achieving this through specific antibody attachment enhances the proximity of FND to neurites, facilitating the detection of local action potentials. Targeting voltage-dependent calcium channels (Cav2.2) with biotin-streptavidin-bound antibodies enables the precise positioning of FNDs. The functionalized FNDs (f-FNDs) show increased size and zeta potential, confirming the antibody presence without compromising cell viability. Two-color confocal imaging and co-localization algorithms are employed to further attest to the success of the functionalization. The f-FNDs are applied to cell cultures of three cell lines: SH-SY5Y, differentiated dopaminergic neurons, and hippocampal rat neurons; their biocompatibility and effects on synaptic activity are explored. Moreover, preliminary total internal reflection fluorescence - optically detected magnetic resonance (TIRF-ODMR) experiments across cellular sites demonstrate the magnetic field sensitivity of our sensor network. The successful establishment of this sensor network provides a platform for characterizing neuronal signaling in healthy models and conditions mimicking Parkinson's disease.

Simultaneous vector magnetometry based on fluorescence polarization of NV centers ensemble in diamond

The nitrogen-vacancy (NV) centers ensemble has extensive application prospects in vector-magnetic-field measurement due to its accurate and fixed spatial orientations along the crystallographic axes of diamonds. However, to address signals of NV centers along all four axes, a large bias magnetic field sufficient to spectrally separate their resonances is typically inevitable, which may affect the magnetic substance under test and require multiple-frequency microwaves to interrogate signals of the four axes. Here, we demonstrate an NV-based simultaneous vector magnetometer that works at a bias field as low as just separating the resonant peaks of |ms=±1 states and utilizes a single-frequency microwave. By simultaneously detecting the fluorescence at specific optical polarization angles in three orthogonal directions and determining the transformation matrix in advance, all the Cartesian components of the magnetic field under test are distinguished. The experimentally achieved magnetic-field sensitivity is 63 nT/Hz, and the bias field is reduced to around 11 Gauss (still reducible by narrowing the linewidth) in ambient conditions. The proposed methods dramatically reduce the bias field for NV-based simultaneous vector magnetometers and potentially expand their applications in biological science, materials science, and industrial noninvasive detection.

Dual-channel photonic crystal fiber dual-parameter sensor exploiting surface plasmon resonance

A surface plasmon resonance (SPR) based sensor using a negative curvature circular side-polished photonic crystal fiber was proposed. The sensor’s sensitivity was analyzed using the finite element method. The impact of structural parameters was investigated. The sensor exhibits an average wavelength sensitivity (WS) of 7846 nm/RIU in the refractive index range of 1.370–1.396 and 2350 nm/RIU in the range of 1.330–1.370, with maximum WS of 46000 nm/RIU. For refractive index and magnetic field dual-parameter sensing, the simultaneously obtained magnetic field sensitivity is 0.84 nm/mT. The proposed SPR sensor demonstrates remarkable sensitivity, making it suitable for refractive index and magnetic field sensing applications.

A quantum-enhanced magnetometer using a single high-spin nucleus in silicon

Abstract Quantum enhanced metrology has the potential to go beyond the standard quantum limit and eventually to the ultimate Heisenberg bound. In particular, quantum probes prepared in nonclassical coherent states have recently been recognized as a useful resource for metrology. Hence, there has been considerable interest in constructing magnetic quantum sensors that combine high resolution and high sensitivity. Here, we explore a nanoscale magnetometer with quantum-enhanced sensitivity, based on 123Sb (I = 7/2) nuclear spin doped in silicon, that takes advantage of techniques of spin-squeezing and coherent control. With the optimal squeezed initial state, the magnetic field sensitivity may be expected to approach 6 aT⋅Hz−1/2⋅cm−3/2 and 603 nT⋅Hz−1/2 at the single-spin level. This magnetic sensor may provide a novel sensitive and high-resolution route to microscopic mapping of magnetic fields as well as other applications.

Vector magnetic field characteristics of magneto-shape effect with high figure of merit based on fiber optic vernier effect

The vector magnetic field structures utilizing magnetic fluid (MF) mainly rely on the magneto-refractive index effect (MRI), which has the low spatial resolution due to the long sensitive length. In this article, the vector magnetic field characteristics of the magneto-shape effect (MSE) are simulated and experimentally studied based on the fiber optic vernier effect. The high vector magnetic field sensitivity can be achieved under the condition of Φ128*73 μm in the sensitive area by combine the MSE and vernier effect. The distribution of magnetic field on the concavity of MF varies with magnetic field direction, giving rising to MF concavity different deformations. The magnetic field observation structure based on fiber optic vernier effect are fabricated to verify the vector magnetic field characteristics of MSE. The observation structure is subjected to one-dimensional and two-dimensional magnetic field. The test results demonstrate that the magnetic field sensibility can reach 2.36 nm/Gs, 3.88 nm/Gs and 4.52 nm/Gs under 0–55.0 Gs, 55.0–91.7 Gs and 91.7–119.2 Gs in Y direction field. The magnetic field sensibility is 0.91 nm/Gs in Z direction field. The magnetic field direction sensitivity can reach 1.16 nm/° in XY dimensional field. The structure of the MSE is very compact and the size is very small, which is very helpful for detecting the narrow space and gradient magnetic field.

Photonic Crystal Fiber Based on Surface Plasmon Resonance Used for Two Parameter Sensing for Magnetic Field and Temperature

This paper presents a photonic crystal fiber (PCF) sensor that can be used to measure the temperature and magnetic field simultaneously, and to monitor the changes in them in the environment. When we designed the fiber structure, two circular channels of the same size were added to the fiber to facilitate the subsequent addition of materials. A gold film is added to the upper channel (ch1), and the channel is filled with a magnetic fluid (MF). The sensor can reflect changes in the temperature and magnetic field strength. The two channels containing MF and PDMS in the proposed fiber are called ch1 and ch2. The structure, mode and properties (temperature and magnetic field) were analyzed and discussed using the finite element method. By using the control variable method, the influence of Ta2O5 or no Ta2O5, the Ta2O5 thickness, the diameter of the special air hole, the distance from the fiber core and the distance between them in the displacement of the loss spectrum and the phase-matching condition of the coupling mode were studied. The resulting maximum temperature sensitivity is 6.3 nm/°C (SPR peak 5), and the maximum magnetic field sensitivity is 40 nm/Oe (SPR peak 4). Because the sensor can respond to temperature and magnetic field changes in the environment, it can play an important role in special environmental monitoring, industrial production and other fields.

3D modeling of deep borehole electromagnetic measurements with energized casing source for fracture mapping at the Utah Frontier Observatory for Research in Geothermal Energy

AbstractWe present a 3D numerical modelling analysis evaluating the deployment of a borehole electromagnetic measurement tool to detect and image a stimulated zone at the Utah Frontier Observatory for Research in Geothermal Energy geothermal site. As the depth to the geothermal reservoir is several kilometres and the size of the stimulated zone is limited to several 100 m, surface‐based controlled‐source electromagnetic measurements lack the sensitivity for detecting changes in electrical resistivity caused by the stimulation. To overcome the limitation, the study evaluates the feasibility of using a three‐component borehole magnetic receiver system at the Frontier Observatory for Research in Geothermal Energy site. To provide sufficient currents inside and around the enhanced geothermal reservoir, we use an injection well as an energized casing source. To efficiently simulate energizing the injection well in a realistic 3D resistivity model, we introduce a novel modelling workflow that leverages the strengths of both 3D cylindrical‐mesh‐based electromagnetic modelling code and 3D tetrahedral‐mesh‐based electromagnetic modelling code. The former is particularly well‐suited for modelling hollow cylindrical objects like casings, whereas the latter excels at representing more complex 3D geological structures. In this workflow, our initial step involves computing current densities along a vertical steel‐cased well using a 3D cylindrical electromagnetic modelling code. Subsequently, we distribute a series of equivalent current sources along the well's trajectory within a complex 3D resistivity model. We then discretize this model using a tetrahedral mesh and simulate the borehole electromagnetic responses excited by the casing source using a 3D finite‐element electromagnetic code. This multi‐step approach enables us to simulate 3D casing source electromagnetic responses within a complex 3D resistivity model, without the need for explicit discretization of the well using an excessive number of fine cells. We discuss the applicability and limitations of this proposed workflow within an electromagnetic modelling scenario where an energized well is deviated, such as at the Frontier Observatory for Research in Geothermal Energy site. Using the workflow, we demonstrate that the combined use of the energized casing source and the borehole electromagnetic receiver system offer measurable magnetic field amplitudes and sensitivity to the deep localized stimulated zone. The measurements can also distinguish between parallel‐fracture anisotropic reservoirs and isotropic cases, providing valuable insights into the fracture system of the stimulated zone. Besides the magnetic field measurements, vertical electric field measurements in the open well sections are also highly sensitive to the stimulated zone and can be used as additional data for detecting and imaging the target. We can also acquire additional multiple‐source data by grounding the surface electrode at various locations and repeating borehole electromagnetic measurements. This approach can increase the number of monitoring data by several factors, providing a more comprehensive dataset for analysing the deep‐localized stimulated zone. The numerical analysis indicates that it is feasible to use the combination of the energized casing and downhole electromagnetic measurements in monitoring localized stimulated zone at large depths.

Enhanced axial strain and vector magnetic field sensitivity in MZI utilizing dual cascaded air bubbles with tapered fiber

Enhanced axial strain and vector magnetic field sensitivity in MZI utilizing dual cascaded air bubbles with tapered fiber

Enhanced sensitivity of magnetic field sensing using L-shaped dual Terfenol-D-FBGs based on the Vernier effect and a dual-loop optoelectronic oscillator

We proposed and successfully validated improved the sensitivity of magnetic field sensing using the Vernier effect in a dual-loop optoelectronic oscillator (OEO) incorporating cascaded L-shaped Terfenol-D-FBGs. Thanks to the time delay introduced by the dispersion compensating fiber (DCF) in the OEO cavity, precise conversion between the sensing FBG wavelength changes and the OEO oscillation frequency can be achieved. The central wavelengths of the sensing Terfenol-D-FBG change along with the magnetic field. Therefore, the magnetic field can be monitored by measuring the oscillating frequency of the OEO. In the proposed scheme, two reflection signals from the cascaded FBGs pass through two fiber paths with slightly different lengths, inducing the Vernier effect in the OEO, which significantly enhances the sensitivity of the sensor. Additionally, a bias magnetic field is applied to the sensing Terfenol-D alloy to further improve the sensitivity. Experimental results demonstrate that by applying a bias magnetic field on both sides of the sensing Terfenol-D, the sensitivity of the single-loop OEO is increased from 421 Hz/mT to 560 Hz/mT. Utilizing the Vernier effect, the magnetic field sensitivity of the dual-loop OEO reaches up to −16.54 kHz/mT, with a 29-times improvement over the single-loop OEO's 560 Hz/mT. By finely adjusting the path length difference, we further enhance the performance of the sensor, achieving sensitivities of −24.58 kHz/mT, −28.49 kHz/mT and −35.94 kHz/mT, respectively, which are 44 times, 51 times and 64 times higher than the single-loop OEO structure. Besides, to overcome the influence of temperature, a temperature compensation sensor is designed using a pair of L-shaped Terfenol-D alloys to host the cascaded sensing FBG and reference FBG. The experimental results show that the proposed L-shaped Terfenol-D with cascaded FBG can reduce the magnetic field error caused by temperature crosstalk to 0.03 mT.

The study on the magnetic interaction between the duel magnetic layers and the FINEMET ribbon

Due to the sensitive magnetic field response of the GMI effect, the peak field in magneto impedance curves obtained from the composite magnetic ribbons shows great dependence on the magnetic interaction, which has gained intensive attention in the study of the diversity and the mechanism of magnetic interaction. In this work, FINEMET/Fe20Ni80/SiO2/Fe20Ni80 composite ribbons with a fixed thickness of outer Fe20Ni80 layer (200 nm) and variable thickness ratio of the inner Fe20Ni80 and SiO2 layers, ranging from the 1:4 to 4:1 were prepared. Then the GMI response was utilized to investigate the influence of the exchange couple and the dipole interaction to magnetic properties of the base ribbon. The experimental results indicated that additional SiO2 layer can successfully induce slight magnetic differences of the two Fe20Ni80 layers, which results in the emergence of four-peak GMI profiles. Besides, the frequency-dependent nature of the peaks was explored, revealing that both dipole interaction and exchange couple influence the magnetic properties, contributing to the occurrence of four-peak GMI curves. Thus, the insights presented in this work are thought to be valuable for understanding the mechanisms of multilayer composite ribbons in future sensing applications.

A novel flexible optical fiber magnetic field sensor based on integrated Fe3O4 nanoparticles

We propose a new flexible optical fiber magnetic field sensor (FOMS) based on the combination of Michelson interferometer and the PDMS polymer-based optical fiber. The flexible optical fiber magnetic field sensor is made of stretchable elastomer. It uses a stepped refractive index core-cladding structure to achieve effective light confinement, thus enabling stable transmission of light in the waveguide. When the magnitude of the external magnetic field is changed, the micro bending of the sensing region of the optical fiber causes its equivalent refractive index to change, which leads to a drift in the interference spectrum. It is shown that the magnetic field sensitivity of this optical fiber magnetic field sensor reaches −62.8 pm/mT for wavelength detection in the measurement range of 0–200 mT. The FOMS has the characteristics of high sensitivity, good linearity, good temperature response capability, sensitive response, and resistance to electromagnetic interference. In the future, the sensor will have a broad application prospect in medical, geography, aerospace and other fields.

Superconducting Quantum Magnetometer Based on Flux Focusing Effect for High-Sensitivity Applications.

A superconducting quantum magnetometer for high-sensitivity applications has been developed by exploiting the flux focusing of the superconducting loop. Unlike conventional dc SQUID magnetometers that use a superconducting flux transformer or a multiloop design, in this case, a very simple design has been employed. It consists of a bare dc SQUID with a large washer-shaped superconducting ring in order to guarantee a magnetic field sensitivity BΦ less than one nT/Φ0. The degradation of the characteristics of the device due to an inevitable high value of the inductance parameter βL was successfully compensated by damping the inductance of the dc SQUID. The size of the magnetometer, coinciding with that of the washer, is 5 × 5 mm2 and the spectral density of the magnetic field noise is 8 fT/√Hz with a low frequency noise knee of two Hz. The excellent performance of this simple magnetometer makes it usable for all high-sensitivity applications including magnetoencephalography.

High Sensitivity Magnetic Field Sensor Based on Magneto-Optical Surface Plasmon Resonance

High Sensitivity Magnetic Field Sensor Based on Magneto-Optical Surface Plasmon Resonance

Magnetic field mapping along a NV-rich nanodiamond-doped fiber

Integration of NV−-rich diamond with optical fibers enables guiding quantum information on the spin state of the NV− color center. Diamond-functionalized optical fiber sensors have been demonstrated with impressive sub-nanotesla magnetic field sensitivities over localized magnetic field sources, but their potential for distributed sensing remains unexplored. The volumetric incorporation of diamonds into the optical fiber core allows developing fibers sensitive to the magnetic field over their entire length. Theoretically, this makes distributed optical readout of small magnetic fields possible, but does not answer questions on the addressing of the spatial coordinate, i.e., the location of the field source, nor on the performance of a sensor where the NV− fluorescence is detected at one end, thereby integrating over color centers experiencing different field strength and microwave perturbation. Here, we demonstrate distributed magnetic field measurements using a step-index fiber with the optical core volumetrically functionalized with NV− diamonds. A microwave antenna on a translation stage is scanned along a 13 cm long section of a straight fiber. The NV− fluorescence is collected at the fiber's far end relative to the laser pump input end. Optically detected magnetic resonance spectra were recorded at the fiber output for every step of the antenna travel, revealing the magnetic field evolution along the fiber and indicating the magnetic field source location. The longitudinal distribution of the magnetic field along the fiber is detected with high accuracy. The simplicity of the demonstrated sensor would be useful for, e.g., magnetic-field mapping of photonics- and/or spintronics-based integrated circuits.