Fluxgate Magnetometer Research Articles

Latitudinal Distribution of Dayside Magnetospheric Currents Based on Cluster Observations

AbstractBased on the curlometer method, we calculate the azimuthal component of the current density from nearly 19 years of Fluxgate Magnetometer (FGM) data of Cluster and investigate its latitudinal distribution in the dayside noon sector (09:00–15:00 magnetic local time, MLT). A crossing event in the noon meridian plane shows an unexpected eastward current at a geocentric distance of 8 RE, away from the equator with latitudes of 30–40°. Further statistical results of the current distribution show that, the topology of the current can be radially divided into the inner and outer branches over the whole rxy − z plane (rxy = and z are in solar magnetic (SM) coordinates), with the separation point of these two branches at a geocentric distance of about 8 RE. The current variations of the inner and outer branches are different under different Kp, solar wind flow speed Vsw, and solar wind dynamic pressure Pdyn. It is shown that the current densities in both the inner and outer branches increase significantly with the Kp. High solar wind dynamic pressure enhances the current density of the outer branch, while high solar wind speed, on the contrary, enhances that of the inner branch. The formation of the outer branch may be related to the anisotropy of plasma pressure.

Lower magnetic field measurement limit of the coupled dark state magnetometer

Abstract The Coupled Dark State Magnetometer (CDSM) is an optically pumped magnetometer. For the Jupiter Icy Moons Explorer (JUICE) mission, the CDSM and two fluxgate magnetometers are combined in the J-MAG instrument to measure the static and low frequency magnetic field in the Jupiter system. During certain calibration manoeuvres, the CDSM has to be able to measure magnetic field strengths down to 100 nT with an accuracy of 0.2 nT (1 σ). At such low magnetic fields, the CDSM’s operational parameters must be carefully selected to obtain narrow resonance structures. Otherwise, the coupled dark state resonances, used for the magnetic field detection in different instrument modes, overlap and result in a systematic error. In this paper we demonstrate that with the found instrument settings the CDSM is able to measure magnetic field strengths below 100 nT with a systematic error less than 0.2 nT resulting from the overlap of the resonances.

First in situ measurements of the prototype Tesseract fluxgate magnetometer on the ACES-II-Low sounding rocket

First in situ measurements of the prototype Tesseract fluxgate magnetometer on the ACES-II-Low sounding rocket

The Vulcan Mission to Io: Lessons Learned during the 2022 JPL Planetary Science Summer School

A mission to Jupiter's moon Io, the most volcanically active body in the solar system, was suggested as a priority for the New Frontiers program in the 2013 Planetary Science Decadal Survey. We present a New Frontiers–class mission concept, Vulcan, that was designed as an educational exercise through the Jet Propulsion Laboratory’s 2022 Planetary Science Summer School. Vulcan would leverage an instrument suite consisting of wide- and narrow-angle cameras, a thermal infrared spectrometer, two fluxgate magnetometers, and ion and electron electrostatic analyzers to conduct the most thorough investigation of Io to date. Using 78 flybys over a 2 yr primary science mission, Vulcan would characterize the effects of tidal forces on the differentiation state, crustal structure, and volcanism of Io and investigate potential interactions between Io's volcanoes, surface features, and atmosphere. Although Vulcan was developed as an academic exercise, we show that a New Frontiers–class mission to Io could achieve transformative science in both geophysics and plasma physics, unifying typically disparate subfields of planetary science. A dedicated mission to Io, in combination with the Europa Clipper and Jupiter Icy Moons Explorer missions, would address fundamental questions raised by the 2023 Planetary Science Decadal Survey and could complete our understanding of the spectrum of planetary habitability. Lessons learned from Vulcan could be applied to a New Frontiers 5 Io mission concept in the near future.

First Observation of Harmonics of Magnetosonic Waves in Martian Magnetosheath Region

AbstractThe present study provides an evidence for the generation of harmonics of magnetosonic waves in the Martian magnetosheath region. The wave signatures are manifested in the magnetic field measurements recorded by the fluxgate magnetometer instrument onboard the Mars Atmosphere and Volatile Evolution missioN (MAVEN) spacecraft in the dawn sector around 5–10 LT at an altitude of 4,000–6,000 kms. The wave that is observed continuously from 19.1 to 20.7 UT below the proton cyclotron frequency (fci ≈ 46 mHz) is identified as fundamental mode of the magnetosonic wave. Whereas harmonics of the magnetosonic wave are observed during 19.7–20.3 UT at frequencies that are multiple of fci. The ambient solar wind proton density and plasma flow velocity are found to vary with a fundamental mode frequency of 46 mHz. It is noticed that the fundamental mode is mainly associated with the left‐hand (LH), and higher frequency harmonics are associated with the right‐hand (RH) circular polarizations. A clear difference in the polarization and ellipticity is noticed during the time of occurrence of harmonics. The magnetosonic wave harmonics are found to propagate in the quasi‐perpendicular directions to the ambient magnetic field. The results of linear theory and Particle‐In‐Cell simulation performed here are in agreement with the observations. The present study provides a conclusive evidence for the occurrence of harmonics of magnetosonic wave in the close vicinity of the magnetosheath region of the unmagnetized planet Mars.

Design and Simulation of Conventional Rod Core Fluxgate Magnetometer and Analysis of Performance with Different Core Materials

Design and Simulation of Conventional Rod Core Fluxgate Magnetometer and Analysis of Performance with Different Core Materials

Copper permalloys for fluxgate magnetometer sensors

Abstract. Fluxgate magnetometers are commonly used to provide high-fidelity vector magnetic field measurements. The magnetic noise of the measurement is typically dominated by that intrinsic to a ferromagnetic core used to modulate (gate) the local field as part of the fluxgate sensing mechanism. A polycrystalline molybdenum–nickel–iron alloy (6.0–81.3 Mo permalloy) has been used in fluxgates since the 1970s for its low magnetic noise. Guided by previous investigations of high-permeability copper–nickel–iron alloys, we investigate alternative materials for fluxgate sensing by examining the magnetic properties and fluxgate performance of that permalloy regime in the range 28 %–45 % Cu by weight. Optimizing the alloy constituents within this regime enables us to create fluxgate cores with both lower noise and lower power consumption than equivalent cores based on the traditional molybdenum alloy. Racetrack geometry cores using six layers of ∼30 mm long foil washers consistently yield magnetic noise around 4–5 pT/Hz at 1 Hz and 6–7 pT/Hz at 0.1 Hz, meeting the 2012 1 s INTERMAGNET standard of less than 10 pT/Hz noise at 0.1 Hz.

Magnetic field generator for the calibration of magnetometers and electromagnetic compatibility (EMC) and electromagnetic interference (EMI) compliance

A standard magnetic field generation system from 1 to 30 μT between DC and 20 kHz has been demonstrated for the calibration of DC/AC magnetometers. The system includes a laboratory-designed Helmholtz coil, shunt resistor, digital multimeter, and dedicated power source. The DC coil constant of the Helmholtz coil was determined to be 10.586 μT/A using a single-axis fluxgate magnetometer. The homogeneity analysis was carried out for the Helmholtz coil to identify the uniformity along the x, y, and z axes. The system for DC generation was standardized and compared by measuring the field values using a single-axis fluxgate magnetometer. Further, the system was validated for AC generation by a search coil with a known turn area (1.3767 ± 0.0027 m2). Moreover, the measured magnetic field values using a search coil were compared with a commercial magnetometer to identify the variation in generated and measured magnetic fields. The described system can have significant utilities in calibration, electromagnetic interference electromagnetic interference/electromagnetic compatibility (EMI/EMC) testing, magnetic susceptibility testing, and magnetic field therapy applications. The expanded uncertainty of the Helmholtz coil in generating a magnetic field was 0.2–1.6% (at k = 2) from DC to 20 kHz.

Advances in small-scale resistance spot welding of the Ni-15 %Fe-4 %Mo-1 %Mn permalloy in the production of low-noise ring cores for fluxgate magnetometers

The aim of this study was to assess the possibility of improving control of small-scale resistance spot welding (SSRSW) of the Ni-15 %Fe-4 %Mo-1 %Mn permalloy in the production of low-noise ring cores for fluxgate magnetometers. It was found that the range of the optimal current–time parameters (weld lobe) was within current amplitudes of 1–2 kA and pulse durations of 6–14 ms, which allowed to form sound nuggets with sufficient diameters but without expulsions in most cases. A preheating stage (a pulse with an amplitude of about 1 kA and a duration of 3–4 ms) had a positive effect on the stability of both dimensions and mechanical characteristics of the investigated nuggets. A decrease in the solidification rate slightly improved the stability of tensile shear strength values of the SSRSW joints despite the absence of fundamental differences in the microstructure and phase composition of the weld metals. To determine the reliability of predicting the quality of the SSRSW joints by assessing dynamic resistances measured during the formation of nuggets, a comparative statistical analysis of their diameters and the tensile shear strength values was carried out. The obtained results did not reveal any strong correlation between these parameters.

In-plane magnetic properties and anisotropy of scandium substituted thulium iron garnet thin films for fluxgate magnetometer

In-plane easily magnetized scandium substituted thulium iron garnet films(Tm3Fe5-xScxO12) with soft magnetic properties have recently attracted attention for fluxgate magnetometer applications. In this paper, thin Tm3Fe5-xScxO12 films were prepared on gadolinium gallium garnet substrates by liquid phase epitaxial(LPE) method. Microstructural properties, composition, magnetic properties and the in-plane anisotropy of the films were discussed. We found that the films turned from tensile stress to compressive stress as the Sc3+ substitution decreased, and the in-plane anisotropy was mainly caused by stress reducing as Sc3+ declined. By analyzing the in-plane magnetic hysteresis loops, the magnetic performance was the best when x = 0.75. Tm3Fe4.25Sc0.75O12 film had the lowest in-plane coercive field(0.006 Oe) and the highest initial magnetic permeability(378), which was more beneficial to realize fluxgate magnetometers.

A Closer Cooperation between Space and Seismology Communities – a Way to Avoid Errors in Hunting for Earthquake Precursors

The space physicists and the earthquake (EQ) prediction community exploit the same instruments – magnetometers, but for different tasks: space physicists try to comprehend the global electrodynamics of near-Earth space on various time scales, whereas the seismic community develops electromagnetic methods of short-term EQ prediction. The lack of deep collaboration between those communities may result sometimes in erroneous conclusions. In this critical review, we demonstrate some incorrect results caused by a neglect of specifics of geomagnetic field evolution during space weather activation. The considered examples comprise: Magnetic storms as a trigger of EQs; ULF waves as a global EQ precursor; Geomagnetic impulses before seismic shocks; Long-period geomagnetic disturbances generated by strong EQs; Discrimination of underground ULF sources by amplitude-phase gradients; Depression of ULF power as a short-term EQ precursor; and Detection of seimogenic emissions by satellites. To verify the reliability of the above widely disseminated results data from available arrays of fluxgate and search-coil magnetometers have been re-analyzed. In all considered events, the “anomalous” geomagnetic field behavior can be explained by global geomagnetic activity, and it is apparently not associated with seismic activity. This critical review does not claim that ULF electromagnetic field cannot be used as a sensitive indicator of the EQ preparation processes, but we suggest that both communities must cooperate their studies more tightly using data exchange, combined usage of magnetometer networks, organization of CDAW for unique events, etc.

Validating a UK Geomagnetically Induced Current Model Using Differential Magnetometer Measurements

AbstractExtreme space weather can damage ground‐based infrastructure such as power lines, railways and gas pipelines through geomagnetically induced currents (GICs). Modeling GICs requires knowledge about the source magnetic field and the electrical conductivity structure of the Earth to calculate ground electric fields during enhanced geomagnetic activity. The electric field, in combination with detailed information about the power grid topology, enable the modeling of GICs in high‐voltage (HV) power lines. Directly monitoring GICs in substations is possible with a Hall probe, but scarcely realized in the UK. Therefore we deployed the differential magnetometer method (DMM) to measure GICs at 12 sites in the UK power grid. The DMM includes the installation of two fluxgate magnetometers, one directly under a power line affected by GICs, and one as a remote site. The difference in recordings of the magnetic field at each instrument yields an estimate of the GICs in the respective power line segment via the Biot‐Savart law. We collected data across the UK in 2018–2022, monitoring HV line segments where previous research indicated high GIC risk. We recorded magnetometer data during several smaller storms that allow detailed analysis of our GIC model. For the ground electric field computations we used recent magnetotelluric (MT) measurements recorded close to the DMM sites. Our results show that there is strong agreement in both amplitude and signal shape between measured and modeled line and substation GICs when using our HV model and the realistic electric field estimates derived from MT data.

Single-board low-noise fluxgate magnetometer

Low-noise fluxgate magnetometers are normally comprised of three separate devices: a power supply, the sensor head/electronics and an analog-to-digital converter (ADC). This paper presents a parallel rod fluxgate magnetometer in a single printed circuit board of size=5×12 cm, weight=45 g, and sensor head average power dissipation = 40 mW. The open-loop noise spectral density =5pTrms/Hz@1Hz, competitive with state-of-the-art devices. This is realized using a new amorphous wire core material and programmable mixed-signal electronics with low amplifier and ADC noise. We have compared the sensor performance to a low-noise observatory magnetometer and found sub-nT correlation when tracking the Y (East-West) component of the Earth’s geomagnetic field.

Performance of Fluxgate Magnetometer with Cu-Doped CoFeSiB Amorphous Microwire Core.

In this study, we investigated the effects of Cu doping on the performance of CoFeSiB amorphous microwires as the core of a fluxgate magnetometer. The noise performance of fluxgate sensors primarily depends on the crystal structure of constituent materials. CoFeSiB amorphous microwires with varying Cu doping ratios were prepared using melt-extraction technology. The microstructure of microwire configurations was observed using transmission electron microscopy, and the growth of nanocrystalline was examined. Additionally, the magnetic performance of the microwire and the noise of the magnetic fluxgate sensors were tested to establish the relationship between Cu-doped CoFeSiB amorphous wires and sensor noise performance. The results indicated that Cu doping triggers a positive mixing enthalpy and the reduced difference in the atomic radius that enhances the degree of nanocrystalline formation within the system; differential scanning calorimetry analysis indicates that this is due to Cu doping reducing the glass formation capacity of the system. In addition, Cu doping affects the soft magnetic properties of amorphous microwires, with 1% low-doping samples exhibiting better soft magnetic properties. This phenomenon is likely the result of the interaction between nanocrystalline organization and magnetic domains. Furthermore, a Cu doping ratio of 1% yields the best noise performance, aligning with the trend observed in the material's magnetic properties. Therefore, to reduce the noise of the CoFeSiB amorphous wire sensor, the primary goal should be to reduce microscopic defects in amorphous alloys and enhance soft magnetic properties. Cu doping is a superior preparation method which facilitates control over preparation conditions, ensuring the formation of stable amorphous wires with consistent performance.

Yttrium-Iron Garnet Film Magnetometer for Registration of Magnetic Nano- and Submicron Particles: In Vitro and In Vivo Studies.

In the current article, we present a new kind of magnetometer for quantitative detection of magnetic objects (magnetic nano- and submicron particles) in biological fluids and tissues. The sensor is based on yttrium-iron garnet film with optical signal registration system. Inheriting the working principle of a fluxgate magnetometers, the sensor works at a room-temperature, its wide dynamic range allows the measurements in an unshielded environment. A small size of sensitive element combined with a short recovery time after the excitation coils are off provide us with a potentially high spatial and temporal resolution of measurements. We show the feasibility of the developed devices by sensing the remanent magnetization of magnetic nanoparticles (MNPs) both in vitro (test tubes, dry MNPs) and in vivo (local injection of the MNPs into mice).

Calibration of the Zero Offset of the Fluxgate Magnetometer on Board the Tianwen‐1 Orbiter in the Martian Magnetosheath

AbstractHigh‐precision measurements of the magnetic field are critical to explore the near‐Mars environment. The Mars Orbiter MAGnetometer (MOMAG) is one of seven payloads on board the Tianwen‐1 orbiter. Its zero offset needs regular calibration, and the Wang‐Pan method I is applied to the MOMAG when the Tianwen‐1 orbiter is in the solar wind. The orbiter will remain out of the solar wind over tens of days each year, a method is necessary to ensure the accuracy of the zero offset during this period. Recently, a new method was proposed by Wang (2022b), https://doi.org/10.3847/1538-4357/ac822c, which is referred to as the Wang method II for ease of description. Here, we test the performance of this method using the MOMAG data measured in the Martian magnetosheath. We find that the zero offset Ow determined by the Wang method II varies around the zero offset Owp calculated by the Wang‐Pan method I using the potential Alfvénic fluctuations in the solar wind. After smoothing with a temporal window of 27 days, Ow is able to achieve an accuracy close to Owp. If the data segment has no gaps and its duration is < 27 days, the smoothed Ow might have an error >2 nT, but the error tends to be smaller if the segment's duration is longer. Our tests suggest that the Wang method II is suitable for the in‐flight calibration of the MOMAG when the Tianwen‐1 orbiter remains out of the solar wind.

Development of a high-sensitivity orthogonal fluxgate sensor

Fluxgate magnetometers are one of the most common magnetometers to use as they offer a reliable solution for magnetic anomaly detection. These magnetometers are used in room temperature, exhibiting high sensitivity, making them ideal for several applications. In this paper, a new fluxgate magnetometer design is presented, that is based on a sinusoidal signal for the excitation of the magnetic core and offers improved sensitivity and low power consumption. The developed device is able to operate as a standalone fluxgate sensor based on the orthogonal topology, consisting of one sensing coil, an amorphous magnetic wire core, as well as a microcontroller along with the required electronics for its operation and signal process.

GEOLOGICAL AND GEOPHYSICAL STUDIES AND EXPLORATORY DRILLING OF PALEOZOIC SEDIMENTS IN THE TASBULAK GRABEN

Despite the half-century history of prospecting, the geological and geophysical knowledge of the Shu-Sarysu basin does not exceed 50%. At the same time, the Tasbulak graben remains the most unstudied. From 1941 to 1969 Regional and exploratory aeromagnetic surveys using Z-aerial magnetometers and fluxgate magnetometers at scales of 1:500,000-1:100,000 covered the areas of the western, northwestern and partially central parts of the Shu-Sarysu depression. From 1969 to the present, up to 70% of the area of the Shu-Sarysu depression has been covered with high-precision surveys using proton, fluxgate and quantum aeromagnetometers on a scale of 1:50,000-1:25,000. In fact, the entire territory of the Shu-Sarysu depression is covered by areal gravimetric surveys on a scale of 1:200,000, scales of 1:50,000-1:100,000 - about 70-75% of the area. In the west and southeast of this depression, individual areas were worked out by detailed surveying on a scale of 1:25,000. Over the entire period of satellite surveys (from 1972 to the present), a significant archive of high, medium and low-resolution images has been accumulated. Seismic exploration of the territory of the Tasbulak graben using the CDP and CDP methods was carried out in the period from 1968 to 1993. Seismic exploration using the CDP - 3D method was not carried out. With a total area of the basin of more than 150 thousand square kilometers, the degree of its drilling exploration is extremely low (about 1 well per 375-475 square kilometers). The degree of study of the Tasbulak graben is even less. As a result of prospecting and exploration work, 12 gas and gas condensate deposits were identified, including: 6 in the Moyynkum graben, 3 in the Kokpansor graben and 3 on the Talas uplift (helium). The totality of geophysical work carried out within the Tasbulak graben indicates a premature cessation of oil and gas exploration in the region and the need for detailed work to verify the presence of more complex structures and their reservoir properties.

Korea Pathfinder Lunar Orbiter Magnetometer Instrument and Initial Data Processing

The Korea Pathfinder Lunar Orbiter (KPLO), the first South Korea lunar exploration probe, successfully arrived at the Moon on December, 2022 (UTC), following a 4.5-month ballistic lunar transfer (BLT) trajectory. Since the launch (4 August, 2022), the KPLO magnetometer (KMAG) has carried out various observations during the trans-lunar cruise phase and a 100 km altitude lunar polar orbit. KMAG consists of three fluxgate magnetometers capable of measuring magnetic fields within a ± 1,000 nT range with a resolution of 0.2 nT. The sampling rate is 10 Hz. During the originally planned lifetime of one year, KMAG has been operating successfully while performing observations of lunar crustal magnetic fields, magnetic fields induced in the lunar interior, and various solar wind events. The calibration and offset processes were performed during the TLC phase. In addition, reliabilities of the KMAG lunar magnetic field observations have been verified by comparing them with the surface vector mapping (SVM) data. If the KPLO’s mission orbit during the extended mission phase is close enough to the lunar surface, KMAG will contribute to updating the lunar surface magnetic field map and will provide insights into the lunar interior structure and lunar space environment.

A magnetic falling-sphere viscometer

We present a falling-sphere viscometer with a magnetized sphere and fluxgate magnetometers continuously measuring the magnetic field produced at the sensor positions by the falling sphere. With a fluid volume of 15 ml and within a few seconds, we directly measure dynamic viscosities in a range between 200 and 3000 cP with a precision of 3%.