Fluxgate Magnetometer Research Articles

DI3 - A New Procedure for Absolute Directional Measurements

The standard observatory procedure for determining a geomagnetic field's declination and inclination absolutely is the DI-flux measurement. The instrument consists of a non-magnetic theodolite equipped with a single-axis fluxgate magnetometer. Additionally, a scalar magnetometer is needed to provide all three components of the field. Using only 12 measurement steps, all systematic errors can be accounted for, but if only one of the readings is wrong, the whole measurement has to be rejected. We use a three-component sensor on top of the theodolites telescope. By performing more measurement steps, we gain much better control of the whole procedure: As the magnetometer can be fully calibrated by rotating about two independent directions, every combined reading of magnetometer output and theodolite angles provides the absolute field vector. We predefined a set of angle positions that the observer has to try to achieve. To further simplify the measurement procedure, the observer is guided by a pocket pc, in which he has only to confirm the theodolite position. The magnetic field is then stored automatically, together with the horizontal and vertical angles. The DI3 measurement is periodically performed at the Niemegk Observatory, allowing for a direct comparison with the traditional measurements.

강관말뚝 탐지를 위한 시추공 3성분 자기탐사

A steel pile often utilized to bear heavy loads of the upper sub-structure, e. g., bridge constructions and tall buildings. As the steel piles are driven in the underground, it is not easy to detect the depth of the existing pile foundation when there is no detailed foundation information available. However, accurate informations of the depths of piles becomes critical required when reinforcing the existing structures or constructing new ones at the adjacent stage to assure the safety of existing structures. In this study, we tested the applicability of the three components borehole fluxgate magnetometer for detecting the depths and locations of steel piles which are commonly used in civil engineering. Results showed that the information of location as well as the depth of steel piles could be obtained by using data from the three components borehole fluxgate magnetometer.

Detection of ULF geomagnetic signals associated with seismic events in Central Mexico using Discrete Wavelet Transform

Abstract. The geomagnetic observatory of Juriquilla Mexico, located at longitude –100.45° and latitude 20.70°, and 1946 m a.s.l., has been operational since June 2004 compiling geomagnetic field measurements with a three component fluxgate magnetometer. In this paper, the results of the analysis of these measurements in relation to important seismic activity in the period of 2007 to 2009 are presented. For this purpose, we used superposed epochs of Discrete Wavelet Transform of filtered signals for the three components of the geomagnetic field during relative seismic calm, and it was compared with seismic events of magnitudes greater than Ms > 5.5, which have occurred in Mexico. The analysed epochs consisted of 18 h of observations for a dataset corresponding to 18 different earthquakes (EQs). The time series were processed for a period of 9 h prior to and 9 h after each seismic event. This data processing was compared with the same number of observations during a seismic calm. The proposed methodology proved to be an efficient tool to detect signals associated with seismic activity, especially when the seismic events occur in a distance (D) from the observatory to the EQ, such that the ratio D/ρ < 1.8 where ρ is the earthquake radius preparation zone. The methodology presented herein shows important anomalies in the Ultra Low Frequency Range (ULF; 0.005–1 Hz), primarily for 0.25 to 0.5 Hz. Furthermore, the time variance (σ2) increases prior to, during and after the seismic event in relation to the coefficient D1 obtained, principally in the Bx (N-S) and By (E-W) geomagnetic components. Therefore, this paper proposes and develops a new methodology to extract the abnormal signals of the geomagnetic anomalies related to different stages of the EQs.

Global spherical harmonic models of the internal magnetic field of the Moon based on sequential and coestimation approaches

Three new models of the global internal magnetic field of the Moon based on Lunar Prospector (LP) fluxgate magnetometer observations are developed for use in understanding the origin of the Moon's crustal magnetic field and for modeling its interaction with the solar wind. The models are at spherical harmonic degree 170, corresponding to 64 km wavelength resolution, from 30 km mean altitude LP observations. Coverage is complete except for a few areas near each pole. Original signal amplitudes are best preserved in the sequential approach map, whereas feature recognition is superior in the coestimation and harmonic wave number correlation maps. Spherical harmonic degrees less than 15, corresponding to 666 km wavelength, are largely absent from the Moon's internal magnetic field. We interpret this bound in terms of the Moon's impact history. A derived magnetization map suggests magnetizations may locally exceed 0.2 A/m in the lunar crust at the survey resolution if the magnetic crust is as thick as 40 km.

Reply to comment by John Shaw on “A new high‐precision furnace for paleomagnetic and paleointensity studies: Minimizing magnetic noise generated by heater currents inside traditional thermal demagnetizers”

Reply to comment by John Shaw on “A new high‐precision furnace for paleomagnetic and paleointensity studies: Minimizing magnetic noise generated by heater currents inside traditional thermal demagnetizers”

Geometrical analysis of planar coil design for fluxgate magnetometer

This paper presents geometrical analysis on the design of planar coupled coils for use as magnetic sensors. Inductance and magnetic coupling of the coil are analyzed using field solver analyzer ASITIC. Effects of different coil parameters, such as winding number, spacing, and width are discussed in detail. As results, the coil design considers not only the inductance value and the height of magnetic coupling, but also the geometrical area consumed. The analysis is verified by experimental data from coupled coil fabricated using surface micromachining techniques. An outer coil area having a typical dimension of 1.8 × 1.8 mm2 and a fix inner coil diameter of 500 μm was fabricated. Coupling factor of about 0.7 and self inductance of 12.7 nH were achieved, which show a reasonably good agreement with the simulated results. The coil platform developed offers an integrated solution for the design of fluxgate magnetometer.

A solution of fluxgate excitation fed by squarewave voltage

Different types of fluxgate excitation circuits were used and some simplified models were proposed for the analysis of excitation. This paper presents an analytical solution of the non-linear circuit which is fed by a squarewave voltage source. Experimental results show that this solution can be used to evaluate the overall excitation performance. Special attention is drawn to the effect of the amplitude and phase of the excitation current on the efficiency and offset stability. The solution serves as a tool for fluxgate magnetometer designers.

Victor Vacquier (1907–2009)

Ingenious geophysicist Victor Vacquier died on 11 January 2009 at the age of 101. He is widely known for developing the fluxgate magnetometer. When modified for use at sea, it, and the later proton precession magnetometer, made the observations that established plate tectonics. In Victor's view, however, his most significant achievement was the gyrocompass for dead reckoning navigation.

Conjugate ground and multisatellite observations of compression‐related EMIC Pc1 waves and associated proton precipitation

We present coordinated ground satellite observations of solar wind compression‐related dayside electromagnetic ion cyclotron (EMIC) waves from 25 September 2005. On the ground, dayside structured EMIC wave activity was observed by the CARISMA and STEP magnetometer arrays for several hours during the period of maximum compression. The EMIC waves were also registered by the Cluster satellites for half an hour, as they consecutively crossed the conjugate equatorial plasmasphere on their perigee passes at L ∼ 5. Simultaneously, conjugate to Cluster, NOAA 17 passed through field lines supporting EMIC wave activity and registered a localized enhancement of precipitating protons with energies >30 keV. Our observations suggest that generation of the EMIC waves and consequent loss of energetic protons may last for several hours while the magnetosphere remains compressed. The EMIC waves were confined to the outer plasmasphere region, just inside the plasmapause. Analysis of lower‐frequency Pc5 waves observed both by the Cluster electron drift instrument (EDI) and fluxgate magnetometer (FGM) instruments and by the ground magnetometers show that the repetitive structure of EMIC wave packets observed on the ground cannot be explained by the ultra low frequency (ULF) wave modulation theory. However, the EMIC wave repetition period on the ground was close to the estimated field‐aligned Alfvénic travel time. For a short interval of time, there was some evidence that EMIC wave packet repetition period in the source region was half of that on the ground, which further suggests bidirectional propagation of wave packets.

Experimental Study of the Active Compensation to a Full-Size Separate-Shell Magnetic Shield

Shielding efficiency of a full-size separate-shell magnetic shield equipped with active compensation coils is presented. Its size is 135 cm in height, 100 cm in width, and 240 cm in depth. With respect to active compensation two control schemes, i.e., feedback and feedforward, are compared. The shielding efficiency is estimated from the measurements of the attenuation of environmental magnetic fields in two axial directions (horizontal and vertical). In the case of feedback, a reference sensor that measures the incoming magnetic fields is positioned inside the shield, whereas in the case of feedforward the reference sensor is positioned outside the shell. In both axial directions, the environmental magnetic noise can be reduced to less than 500 pT: the noise floor measured by a fluxgate magnetometer is approximately 10 pT/?Hz in the frequency range from 10 to 100 Hz.

The magnetic diagnostics subsystem of the LISA Technology Package

The Magnetic Diagnostics Subsystem of the LISA Technology Package (LTP) on board the LISA Pathfinder (LPF) spacecraft includes a set of four tri-axial fluxgate magnetometers, intended to measure with high precision the magnetic field at the positions they occupy. However, their readouts do not provide a direct measurement of the magnetic field at the positions of the test masses. Therefore, an interpolation method must be implemented to obtain this information. However, such interpolation process faces serious difficulties. Indeed, the size of the interpolation region is excessive for a linear interpolation to be reliable, and the number of magnetometer channels does not provide sufficient data to go beyond that poor approximation. Recent research points to a possible alternative to address the magnetic interpolation problem by means of neural network algorithms. The key point of this approach is the ability neural networks have to learn from suitable training data representing the magnetic field behaviour. Despite the large distance to the test masses and the insufficient magnetic readings, artificial neural networks are able to significantly reduce the estimation error to acceptable levels. The learning efficiency can be best improved by making use of data obtained from on-ground measurements prior to mission launch in all relevant satellite locations and under real operation conditions. Reliable information on that appears to be essential for a meaningful assessment of magnetic noise in the LTP.

Field-Programmable Gate Array-based fluxgate magnetometer with digital integration

In this paper, a digital magnetometer based on printed circuit board fluxgate is presented. The fluxgate is pulse excited and the signal is extracted by gate integration. We investigate the possibility to perform integration on very narrow gates (typically 500 ns) by using digital techniques. The magnetometer is based on field-programmable gate array (FPGA) card: we will show all the advantages and disadvantages, given by digitalization of fluxgate output voltage by means of analog-to-digital converter on FPGA card, as well as digitalization performed by external digitizer. Due to very narrow gate, it is shown that a magnetometer entirely based on a FPGA card is preferable, because it avoids noise due to trigger instability. Both open loop and feedback operative mode are described and achieved results are presented.

Small Fluxgate Magnetometers: Development and Future Trends in Spain

In this paper, we give an overview of the research on fluxgate magnetometers carried out in Spain. In particular we focus in the development of the planar-type instruments. We summarize the fabrication processes and signal processing developments as well as their use in complex systems and space.

An example of operation for a partly manned Antarctic geomagnetic observatory and the development of a radio link for data transmission

The experience acquired from more than ten years of operation of an Antarctic geomagnetic observatory is described along with the development of data transmission facilities. The observatory was deployed at the Spanish Antarctic Station in 1996. The main instrument was an Overhauser magnetometer deployed in dual axis Helmholtz coils, a δD/δI configuration. The site is only manned during the summer, with the magnetometer left recording throughout the rest of the year. During the 2007-2008 survey the observatory instrumentation has been upgraded with a DMI suspended triaxial fluxgate magnetometer, new sampling hardware and data logging software. Both sampling and timing are carried out under the control of a PIC based microcontroller and GPS receiver. Data presentation, trans- mission and archiving are performed under the control of a low power embedded PC. For real time access to the da- ta two options have been provided and rigorously tested during the last 10 years: METEOSAT and GOES Data Col- lection Systems, and recently, a high frequency (HF) digital radio-link, using ionospheric propagation between Antarctica and Spain, has been developed. This latest transmission system is being continuously upgraded, and it would be possible to extend its application to other remote stations. Measurements have been made during the last four years in order to determine the channel characteristics and its variability, mainly the multipath and Doppler spread and the link availability for a given SNR in the receiver. These measurements are being used to design the physical layer of a radiomodem intended to maximize the link capacity keeping the emitted power low.

Melt-Spun Fe–Co–B–Cu Alloys With High Magnetic Flux Density for Relax-Type Magnetometers

Melt-spun Fe63 Co21 B15Cu ribbons were annealed at temperatures between 573 K and 623 K in longitudinal and transverse-magnetic field in order to prepare a representative set of relaxed amorphous and partially crystallized samples having uniaxial anisotropy. The optimal magnetic characteristics for the relaxation sensor were obtained after longitudinal field annealing for 1 h at 593 K, which corresponds to early crystallization stage in the heat treated amorphous material. The magnetic flux density after such heat treatment reaches 1.83 T and the value of coercive field is 4.2 A/m. The corresponding relaxation characteristics obtained by using ferroprobe designed as a flat, double-layer coil tightly surrounding the ribbon core with the dimensions of 60 × 3 mm show good prospects for the potential use of these alloys as core materials in the relax-type fluxgate magnetometers mainly due to the extending of their linear measuring range as compared to the currently used commercial materials while keeping the similar sensitivity.

Experimental Investigation of the Magnetic Shielding Effect of Mineral Powders in a Drilling Fluid

Magnetic contamination of the drilling fluid shields the Earth's magnetic field measured by the magnetic sensors, and may contribute significantly to errors in directional surveying of a wellbore. A series of laboratory measurements were performed to investigate such magnetic shielding effects. In the measurement, a single axis fluxgate magnetometer was immersed in model drilling fluids prepared by mixing powders of known magnetic properties (magnetite and pure iron) into a solution of xanthan gum in fresh water, whereafter the vertical component of the Earth's field inside the fluid was measured. It was found that the strong shielding effect of dry iron powder essentially vanished when was suspended in the drilling fluid. The magnetic shielding caused by magnetite, however, remained significant also in solution, showing a complex dynamical behaviour. Initially the magnetic field was significantly damped, and this shielding was found to increase further for the next hour or so, reaching a fairly sharp maximum. The shielding then started to decay slowly and irregularly again over the next few days.

Nonlinear sensors: An approach to the residence time detection strategy

The monitoring of the residence time difference in bistable sensors has been recently proposed as a valid scheme for improving the detection capabilities of sensors as diverse as fluxgate magnetometers, ferroelectric sensors and mechanical sensors. In this paper we propose an approach to the residence time based detection strategy based on the measurement of the slope m of the sensor output integral. We demonstrate that such a method, far from degrading the detection performances can provide an easier way to realize fast and reliable sensors without the computationally demanding task related with the computation of the residence time difference. We introduce the receiver operating characteristic curve as a quantitative estimator for the comparison of the two methods and show that the detector performances increase with increasing the periodic bias amplitude A up to a maximum value. This condition has potentially relevant consequences in the future detectors design.

Theory and modelling of the magnetic field measurement in LISA PathFinder

The magnetic diagnostics subsystem of the LISA Technology Package (LTP) on board the LISA PathFinder (LPF) spacecraft includes a set of four tri-axial fluxgate magnetometers, intended to measure with high precision the magnetic field at their respective positions. However, their readouts do not provide a direct measurement of the magnetic field at the positions of the test masses, and hence an interpolation method must be designed and implemented to obtain the values of the magnetic field at these positions. However, such an interpolation process faces serious difficulties. Indeed, the size of the interpolation region is excessive for a linear interpolation to be reliable while, on the other hand, the number of magnetometer channels do not provide sufficient data to go beyond the linear approximation. We describe an alternative method to address this issue, by means of neural network algorithms. The key point in this approach is the ability of neural networks to learn from suitable training data representing the behaviour of the magnetic field. Despite the relatively large distance between the test masses and the magnetometers, and the insufficient number of data channels, we find that our artificial neural network algorithm is able to reduce the estimation errors of the field and gradient down to levels below 10%, a quite satisfactory result. Learning efficiency can be best improved by making use of data obtained in on-ground measurements prior to mission launch in all relevant satellite locations and in real operation conditions. Reliable information on that appears to be essential for a meaningful assessment of magnetic noise in the LTP.

Ultrasensitive core for magnetooptical fluxgate magnetometer with high space resolution

New type of fluxgate magnetometer core on the basis of magnetooptical uniaxial Bi-substituted garnet film was designed, numerically modeled and investigated experimentally. Magnetooptical garnet film with weak magnetization exhibits extremely high sensitivity with relation to external magnetic field. High sensitivity is achieved by single domain wall displacement in film area restricted by potential barriers. High amplitude magnetooptical response was received from garnet film element with special shape in space region 20–200 mcm. Magnetic field value for sensitive element saturation and garnet film coercive field were found in the same range 20–200 /m. Used in fluxgate regime garnet film sensitive element can provide space resolution better 10 mcm with magnetic field sensitivity higher than that one of traditional fluxgate. Presented approach possesses to avoid temperature adjustment and inductive coils application in high sensitive magnetometers.

RTD Fluxgate behavioral model for circuit simulation

SPICE simulation is universally recognized as a powerful tool in the field of electronic engineering. Simulations are strategic when dealing with a strong non-linear behavior that cannot be easily handled analytically. Magnetic hysteresis is one example of non-linearity that founds many practical applications, especially in the field of magnetometers and magnetic sensors. The aim of this paper is to present a behavioral model of RTD Fluxgate magnetometers easy to implement and adaptive with respect to the dynamic of the driving signal. Even if the whole work is focused on a specific magnetometer, the developed methodology can generalized to the wide class of hysteretic devices.