Miniaturized digital fluxgate magnetometer for small spacecraft applications

Abstract

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 R 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.

A radiation hardened digital fluxgate magnetometer for space applications

“…SMILES (Forslund et al, 2008) is a miniaturised digital fluxgate magnetometer designed for small spacecraft applications. This design uses a sophisticated hybrid of pulse width modulation (PWM) and sigma-delta ( ) modulation to provide digital feedback.…”

The effect of winding and core support material on the thermal gain dependence of a fluxgate magnetometer sensor

“…The specific materials used in sensor construction are often not provided in instrument publications. However, MACOR is explicitly mentioned or known to be used in the NASA MAGSAT satellite (Acuña et al, 1978); the S100, STE, and PC104 observatory magnetometers developed by Narod Geophysics Ltd. (Narod and Bennest, 1990); both the Canadian CARISMA ground network (Mann et al, 2008) and the US EMScope magnetotelluric network (Schultz, 2009); the Danish Oersted satellite (Nielsen et al, 1995); the miniaturised SMILE instrument (Forslund et al, 2007); the Vector Fluxgate Magnetometer (VMAG) for the Demonstration and Science Experiment program (Moldwin, 2010); a prototype radiation tolerant fluxgate (Miles et al, 2013); and the Canadian Space Agency Cassiope/e-POP satellite (Wallis et al, 2015). Unfortunately, MACOR is expensive, difficult to machine, and brittle.…”

Digital fluxgate magnetometer: design notes

“…A joint team of KTH and LCISR previously developed such a digital FGM-the Small Magnetometer In Low mass Experiment (SMILE) [8]. This paper briefly describes the original design, and focuses on solving the specific problems and trade-offs between the sensitivity, response and stability.…”

“…Using digital technology is even more crucial because of the usual lack of data transmission channel throughput for small satellites with limited ground support. At the same time the digital implementation of an actual analogue device creates problems related to the discretisation of internal data processing [6,7].A joint team of KTH and LCISR previously developed such a digital FGM-the Small Magnetometer In Low mass Experiment (SMILE) [8]. This paper briefly describes the original design, and focuses on solving the specific problems and trade-offs between the sensitivity, response and stability.…”