Digital Fluxgate Magnetometer Research Articles

Alex magnetometer and telluric station in Egypt: First results on pulsation analysis

This study presents the first results of a newly installed ground-based station Alex Magnetometer and Telluric Station (AMTS) located in Alexandria governorate in Egypt (geographic coordinate: 30° 51.68′ N, 29° 33.67′ E). The station consists of a fluxgate digital magnetometer and a two-channel digital Long Period Telluric Recorder (LPTR). The station commenced operation on October 12th, 2021, by providing real-time data of the geoelectric and geomagnetic field components. Despite the low solar activity, the AMTS detected several signatures of geomagnetic storms. An illustrative case study was conducted on the strong geomagnetic storm of November 4th, 2021. The magnetic field components recorded by the station demonstrated a prompt increase synchronized with the Sudden Storm Commencement (SSC) captured by the ACE satellite arriving at 19:42 UT on November 3rd, 2021. The three geomagnetic field components recorded by the AMTS during the storm were consistent with the nearby INTERMAGNET stations. The digital fluxgate magnetometer’s high sampling frequency (400 Hz) and the LPTR with a sampling frequency (1 Hz), allowed us to capture all ULF pulsations. The structural pearl-shaped Pc1 pulsation was obtained in all phases of the geomagnetic storm with repetitive oscillations in the main storm phase. The wavelet analysis of micropulsations recorded at AMTS showed a high coherence with the nearby-four INTERMAGNET stations demonstrating high data integrity and reliability. The magnetometer and telluric measurements at the AMTS will fill the data gap in the northern section of Africa and allow us to study geoelectric and geomagnetic micropulsations in the region.

The Experimental Albertan Satellite #1 (Ex-Alta 1) Cube-Satellite Mission

The Experimental Albertan satellite #1 (Ex-Alta 1) was a three-unit cube satellite (CubeSat) developed at the University of Alberta (UAlberta). As the first ‘made in Alberta’ spacecraft, the Ex-Alta 1 CubeSat was the Canadian contribution to the international QB50 CubeSat constellation mission ( www.qb50.eu ). Ex-Alta 1’s mission incorporated four science objectives, two technical objectives, and one educational outreach objective. These are reviewed in the context of the Ex-Alta 1 mission design, as well as future CubeSat constellation missions that may follow demonstration missions such as Ex-Alta 1 and the experiences of the QB50 project. In support of its objectives, Ex-Alta 1 flew the multi-needle Langmuir probe (m-NLP) QB50 standardized payload, a UAlberta developed miniaturized digital fluxgate magnetometer (DFGM) mounted on a two-element articulated deployable boom, a radiation dosimeter from Teledyne, and an open source onboard computer (OBC) developed at UAlberta. Ex-Alta 1 was released by a NanoRacks deployer from the International Space Station on May 26, 2017, and commanded and controlled from a ground-station developed and operated at UAlberta. Ex-Alta 1 operated continuously throughout its mission until it burned up in the atmosphere on November 14, 2018. The last two-way contact occurred on that day at 07:49:29 UTC, when the spacecraft reported an onboard temperature of 47 °C in eclipse at an altitude of 152 km and which marked the effective end of the mission. This paper provides an overview of the Ex-Alta 1 mission, its development, the spacecraft and mission design, and reports preliminary results from the payload focusing on the DFGM instrument. We also report briefly on related education and outreach activities, including the development and delivery of curriculum-targeted and CubeSat focused classroom sessions inspired by the Ex-Alta 1 mission to school pupils in Alberta.

Effect of second harmonic in pulse-width-modulation-based DAC for feedback of digital fluxgate magnetometer

Digital fluxgate magnetometers employ processing of the measured pickup signal to produce the value of the compensation current. Using pulse-width modulation with filtering for digital to analog conversion is a convenient approach, but it can introduce an intrinsic source of nonlinearity, which we discuss in this design note. A code shift of one least significant bit changes the second harmonic content of the pulse train, which feeds into the pick-up signal chain despite the heavy filtering. This effect produces a code-dependent nonlinearity. This nonlinearity can be overcome by the specific design of the timing of the pulse train signal. The second harmonic is suppressed if the first and third quarters of the excitation period pulse train are repeated in the second and fourth quarters. We demonstrate this principle on a digital magnetometer, achieving a magnetometer noise level corresponding to that of the sensor itself.

Variation of surface electric field during geomagnetic disturbed period at Maitri, Antarctica

The paper discusses on the variations of the atmospheric vertical electric field measured at sub-auroral station Maitri (70∘75′S, 11∘75′E), and polar station Vostok (78.5∘S, 107∘E) during the geomagnetic disturbances on 25–26 January 2006. Diurnal variation of surface electric field measured at Maitri shows a similar variation with worldwide thunderstorm activity, whereas the departure of the field is observed during disturbed periods. This part of the field corresponds to the magnetospheric/ionospheric (an additional generator in the polar regions) voltage generators. Solar wind parameters and planetary indices represent the temporal variation of the disturbances, and digital fluxgate magnetometer variation continuously monitored to trace the auroral movement at Maitri. We have observed that the electrojet movement leaves its signature on vertical and horizontal components of the DFM in addition; the study infers the position of auroral current wedge with respect to Maitri. To exhibit the auroral oval, OVATION model is obtained with the aid of DMSP satellite and UV measurements. It is noted that the Maitri is almost within the auroral oval during the periods of disturbances. To examine the simultaneous changes in the vertical electric field associated with this magnetic disturbance, the dawn–dusk potential is studied for every UT hours; the potential was obtained from Weimer model and SuperDARN radar. The comparison reveals the plausible situation for the superposition of dawn–dusk potential on surface electric field over Maitri. This observation also shows that the superposition may not be consistent with the phase of the electrojet. Comparison of surface electric field at Maitri and Vostok shows that the parallel variation exhibits with each other, but during the period of geomagnetic disturbances, the influence is not much discerned at Vostok.

Digital fluxgate magnetometer: design notes

We presented an approach to understanding the performance of a fully digital fluxgate magnetometer. All elements of the design are important for the performance of the instrument, and the presence of the digital feed-back loop introduces certain peculiarities affecting the noise and dynamic performance of the instrument. Ultimately, the quantisation noise of the digital to analogue converter is found to dominate the noise of the current design, although noise shaping alleviates its effect to some extent. An example of magnetometer measurements on board a sounding rocket is presented, and ways to further improve the performance of the instrument are discussed.

Characteristic ULF Band Magnetic Field Variations at MPGO, Ghuttu for the 20 June 2011 Earthquake in Garhwal Himalaya

Magnetic field variations recorded at the Multi Parameter Geophysical Observatory (MPGO), Ghuttu, using digital fluxgate magnetometer are studied in the frequency band 0.03-1 Hz and for 19-20 h UT for June 2011. Polarization analysis based on planar wave assumption for far field is applied in order to discriminate seismo-magnetic signatures. The dynamics of earthquake processes, considering them as selforganized critical systems, is also studied using fractal dimension of ultra-low frequency band geomagnetic field variations. Marginal increase in polarization ratio and fractal dimension a few days before the earthquake is significant against the background of global geomagnetic activity. At the same time, the effect of post-seismic readjustment of seismogenic processes is clearly marked by significant changes in fractal dimension and increased polarization ratio after the earthquake.

A radiation hardened digital fluxgate magnetometer for space applications

Abstract. Space-based measurements of Earth's magnetic field are required to understand the plasma processes responsible for energising particles in the Van Allen radiation belts and influencing space weather. This paper describes a prototype fluxgate magnetometer instrument developed for the proposed Canadian Space Agency's (CSA) Outer Radiation Belt Injection, Transport, Acceleration and Loss Satellite (ORBITALS) mission and which has applications in other space and suborbital applications. The magnetometer is designed to survive and operate in the harsh environment of Earth's radiation belts and measure low-frequency magnetic waves, the magnetic signatures of current systems, and the static background magnetic field. The new instrument offers improved science data compared to its predecessors through two key design changes: direct digitisation of the sensor and digital feedback from two cascaded pulse-width modulators combined with analog temperature compensation. These provide an increase in measurement bandwidth up to 450 Hz with the potential to extend to at least 1500 Hz. The instrument can resolve 8 pT on a 65 000 nT field with a magnetic noise of less than 10 pT/√Hz at 1 Hz. This performance is comparable with other recent digital fluxgates for space applications, most of which use some form of sigma-delta (ΣΔ) modulation for feedback and omit analog temperature compensation. The prototype instrument was successfully tested and calibrated at the Natural Resources Canada Geomagnetics Laboratory.

Miniaturized digital fluxgate magnetometer for small spacecraft applications

A novel design of an Earth field digital fluxgate magnetometer is presented, the small magnetometer in low-mass experiment (SMILE). The combination of a number of new techniques results in significant miniaturization of both sensor and electronics. The design uses a sensor with volume compensation, combining three dual rod cores in a Macor® cube with the side dimension of 20 mm. Use of volume compensation provides high geometrical stability of the axes and improved performance compared to component compensated sensors. The sensor is operated at an excitation frequency of 8 kHz. Most of the instrument functionality is combined in a digital signal processing core, implemented in a field programmable gate array (FPGA). The pick-up signal is digitized after amplification and filtering, and values of compensation currents for each of the axes are determined by a digital correlation algorithm, equivalent to a matched filter, and are fed to a hybrid pulse-width modulation/delta-sigma digital-to-analogue converter driving the currents through the compensation coils. Using digital design makes the instrument very flexible, reduces power consumption and opens possibilities for the customization of the operation modes. The current implementation of the design is based on commercial off-the-shelf components. A calibration of the SMILE instrument was carried out at the Nurmijärvi Geophysical Observatory, showing high linearity (within 6 nT on the whole ±50 µT scale), good orthogonality (22 arcmin) and very good temperature stability of the axes.

Digitalization of highly precise fluxgate magnetometers

This paper describes the theory behind all three known ways of digitalizing the fluxgate magnetometers: analogue magnetometers with digitalized output using high resolution ADC, application of the delta–sigma modulation to the sensor feedback loop and fully digital signal detection. At present time the Δ–Σ ADCs are mostly used for the digitalization of the highly precise fluxgate magnetometers. The relevant part of the paper demonstrates some pitfalls of their application studied during the design of the magnetometer for the new Czech scientific satellite MIMOSA. The part discussing the application of the Δ–Σ modulation to the sensor feedback loop theoretically derives the main advantage of this method—increasing of the modulation order and shows its real potential compared to the analog magnetometer with consequential digitalization. The comparison is realized on the modular magnetometer allowing configurations with modulator inside and outside the feedback loop. The last principle is demonstrated on the project of the fully digital fluxgate magnetometer based on the digital signal processor (DSP). The results of the presented projects are compared with recently published competitive projects. The main objective of the paper is then to discuss the potential, real advantages and weakness of each concept and to examine their convenience for future implementations.

Towards fully digital magnetometer

Abstract New topology of digital fluxgate magnetometer is proposed. The main target is to achieve high dynamic range by using fast analog-to-digital converter (ADC) for the detection and precise delta–sigma (Δ–Σ) digital-to-analog converter (DAC) in the feedback. First results show that the electronics can match 20-bit (120 dB) precisions of the sensors.

Concept and first results of a digital fluxgate magnetometer

The feasibility and first results of a near sensor digitalization of fluxgate signals (digital fluxgate magnetometer) are presented. Applying the usual magnetometer electronics we have substituted the analogue section by a digital processing unit (DPU). The 2f0 signal is digitized at its second harmonic and mean values are online phase-sensitively calculated. Based on this development we present a completely redesigned magnetometer experiment for applications on planetary surfaces. Sensor and electronics including serial interface have to be in one housing, its weight is less than 150 g and the number of electrical connections is limited to four (power lines+serial link). Applications for the digital magnetometer on Earth are also discussed.

Upgraded Norwegian magnetic observatories in the Arctic

A description is given of a new digital fluxgate magnetometer system to be run at the following stations in the Norwegian Arctic region: Ny-Ålesund, Bjørnøya, Jan Mayen, Ramfjordmoen, and the Auroral Observatory in Tromsø. Summaries of the annual quiet mean values of the H- and D-components as well as the total field strength F observed at Tromsø, Bjørnøya and Ny-Ålesund for the last decades are also presented. The magnetic field strength reached a maximum at all three stations in the period 1975–1977. The maximum was first reached at the northernmost station indicating a phase shift from north to south.

A microprocessor based digital fluxgate magnetometer for geomagnetic deep sounding studies.

A three component digital fluxgate magnetometer is described for use in Geomagnetic Deep Sounding experiments. The magnetometer is small, completely self contained and requires only a few minutes to install in the field. The design incorporates an INTEL 8748 microprocessor which allows the power consumption to be reduced such that three months of data, at 1min sampling interval are obtained using only two small 10 AH lead acid gel batteries. The data are recorded digitally on a magnetic C-60 cassette tape, and transferred via a specially designed tape reader, to a main frame computer within a few hours. The magnetometer has a resolution of 1nT, and its drift, when properly thermostatted by burial, is less than 1nT per day. Noise is about 0.6nT and variations with periods greater than 5min are faithfully recorded. The magnetometer has a dynamic range of ±80, 000nT. Its low cost allows 2-D arrays to be constructed with a modest budget.