The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
G B Hospodarsky - One of the best experts on this subject based on the ideXlab platform.
-
A Hybrid Fluxgate and Search Coil Magnetometer Concept Using a Racetrack Core
2018Co-Authors: David M Miles, Barry B Narod, D K Milling, I R Mann, David Barona, G B HospodarskyAbstract:<p><strong>Abstract.</strong> A proof-of-concept hybrid magnetometer is presented which simultaneously operates as both a fluxgate and a Search Coil allowing it to sense the magnetic field from DC to two kHz using a single sensor. Historically, such measurements would normally require two dedicated instruments and each would typically require deployment on its own dedicated boom as the instruments mutually interfere. A racetrack fluxgate core combined with a long solenoidal sense winding is shown to be moderately effective as a Search Coil magnetometer and the Search Coil effect can be captured without introducing significant hardware complexity beyond what is already present in a typical fluxgate instrument. Several methods of optimizing the Search Coil action of the hybrid instrument are compared with the best providing sensitivity and noise performance between comparably sized traditional air core and solid core Search Coil instruments. This hybrid sensor topology should miniaturize to platforms such a CubeSats where multiple boom-mounted instruments are generally impractical so a single hybrid instrument providing modest, but scientifically useful, sensitivity from DC to kHz frequencies would be beneficial.</p>
-
Spaced‐based Search Coil magnetometers
Journal of Geophysical Research, 2016Co-Authors: G B HospodarskyAbstract:Search Coil magnetometers are one of the primary tools used to study the magnetic component of low-frequency electromagnetic waves in space. Their relatively small size, mass, and power consumption, coupled with a good frequency range and sensitivity, make them ideal for spaceflight applications. The basic design of a Search Coil magnetometer consists of many thousands of turns of wire wound on a high permeability core. When a time-varying magnetic field passes through the Coil, a time-varying voltage is induced due to Faraday's law of magnetic induction. The output of the Coil is usually attached to a preamplifier, which amplifies the induced voltage and conditions the signal for transmission to the main electronics (usually a low-frequency radio receiver). Search Coil magnetometers are usually used in conjunction with electric field antenna to measure electromagnetic plasma waves in the frequency range of a few hertz to a few tens of kilohertzs. Search Coil magnetometers are used to determine the properties of waves, such as comparing the relative electric and magnetic field amplitudes of the waves, or to investigate wave propagation parameters, such as Poynting flux and wave normal vectors. On a spinning spacecraft, they are also sometimes used to determine the background magnetic field. This paper presents some of the basic design criteria of Search Coil magnetometers and discusses design characteristics of sensors flown on a number of spacecraft.
-
spaced based Search Coil magnetometers
Journal of Geophysical Research, 2016Co-Authors: G B HospodarskyAbstract:Search Coil magnetometers are one of the primary tools used to study the magnetic component of low-frequency electromagnetic waves in space. Their relatively small size, mass, and power consumption, coupled with a good frequency range and sensitivity, make them ideal for spaceflight applications. The basic design of a Search Coil magnetometer consists of many thousands of turns of wire wound on a high permeability core. When a time-varying magnetic field passes through the Coil, a time-varying voltage is induced due to Faraday's law of magnetic induction. The output of the Coil is usually attached to a preamplifier, which amplifies the induced voltage and conditions the signal for transmission to the main electronics (usually a low-frequency radio receiver). Search Coil magnetometers are usually used in conjunction with electric field antenna to measure electromagnetic plasma waves in the frequency range of a few hertz to a few tens of kilohertzs. Search Coil magnetometers are used to determine the properties of waves, such as comparing the relative electric and magnetic field amplitudes of the waves, or to investigate wave propagation parameters, such as Poynting flux and wave normal vectors. On a spinning spacecraft, they are also sometimes used to determine the background magnetic field. This paper presents some of the basic design criteria of Search Coil magnetometers and discusses design characteristics of sensors flown on a number of spacecraft.
A. Roux - One of the best experts on this subject based on the ideXlab platform.
-
The Search-Coil Magnetometer for MMS
Space Science Reviews, 2016Co-Authors: O. Le contel, A. Roux, P. Leroy, C. Coillot, D. Alison, A. Bouabdellah, L. Mirioni, L. Meslier, A. Galic, M. C. VassalAbstract:The tri-axial Search-Coil magnetometer (SCM) belongs to the FIELDS instrumentation suite on the Magnetospheric Multiscale (MMS) mission (Torbert et al. in Space Sci. Rev. ( 2014 ), this issue). It provides the three magnetic components of the waves from 1 Hz to 6 kHz in particular in the key regions of the Earth’s magnetosphere namely the subsolar region and the magnetotail. Magnetospheric plasmas being collisionless, such a measurement is crucial as the electromagnetic waves are thought to provide a way to ensure the conversion from magnetic to thermal and kinetic energies allowing local or global reconfigurations of the Earth’s magnetic field. The analog waveforms provided by the SCM are digitized and processed inside the digital signal processor (DSP), within the Central Electronics Box (CEB), together with the electric field data provided by the spin-plane double probe (SDP) and the axial double probe (ADP). On-board calibration signal provided by DSP allows the verification of the SCM transfer function once per orbit. Magnetic waveforms and on-board spectra computed by DSP are available at different time resolution depending on the selected mode. The SCM design is described in details as well as the different steps of the ground and in-flight calibrations.
-
the Search Coil magnetometer for themis
Space Science Reviews, 2008Co-Authors: A. Roux, Christophe Coillot, Abdel Bouabdellah, Bertrand De La Porte, Dominique Alison, Sébastien Ruocco, Le O Contel, Marie-cécile VassalAbstract:THEMIS instruments incorporate a tri-axial Search Coil Magnetometer (SCM) designed to measure the magnetic components of waves associated with substorm breakup and expansion. The three Search Coil antennas cover the same frequency bandwidth, from 0.1 Hz to 4 kHz, in the ULF/ELF frequency range. They extend, with appropriate Noise Equivalent Magnetic Induction (NEMI) and sufficient overlap, the measurements of the fluxgate magnetometers. The NEMI of the SearchCoil antennas and associated pre-amplifiers is smaller than 0.76 pT \(/\sqrt{\mathrm{Hz}}\) at 10 Hz. The analog signals produced by the SearchCoils and associated preamplifiers are digitized and processed inside the Digital Field Box (DFB) and the Instrument Data Processing Unit (IDPU), together with data from the Electric Field Instrument (EFI). SearchCoil telemetry includes waveform transmission, FFT processed data, and data from a filter bank. The frequency range covered depends on the available telemetry. The SearchCoils and their three axis structures have been precisely calibrated in a calibration facility, and the calibration of the transfer function is checked on board, usually once per orbit. The tri-axial SearchCoils implemented on the five THEMIS spacecraft are working nominally.
-
first results of the themis Search Coil magnetometers
Space Science Reviews, 2008Co-Authors: Le O Contel, A. Roux, Christophe Coillot, Abdel Bouabdellah, Bertrand De La Porte, Dominique Alison, Sébastien Ruocco, P Robert, V Angelopoulos, K R BromundAbstract:We present the first data from the THEMIS Search Coil Magnetometers (SCM), taken between March and June 2007 while the THEMIS constellation apogee moved from the duskside toward the dawnside. Data reduction, especially the SCM calibration method and spurious noise reduction process, is described. The signatures of magnetic fluctuations in key magnetospheric regions such as the bow shock, the magnetopause and the magnetotail during a substorm, are described. We also discuss the role that magnetic fluctuations could play in plasma transport, acceleration and heating.
-
The Search Coil Magnetometer for THEMIS
Space Science Reviews, 2008Co-Authors: A. Roux, Olivier Le Contel, Christophe Coillot, Abdel Bouabdellah, Bertrand De La Porte, Dominique Alison, Sébastien Ruocco, Marie-cécile VassalAbstract:THEMIS instruments incorporate a tri-axial Search Coil Magnetometer (SCM) designed to measure the magnetic components of waves associated with substorm breakup and expansion. The three Search Coil antennas cover the same frequency bandwidth, from 0.1 Hz to 4 kHz, in the ULF/ELF frequency range. They extend, with appropriate Noise Equivalent Magnetic Induction (NEMI) and sufficient overlap, the measurements of the fluxgate magnetometers. The NEMI of the SearchCoil antennas and associated pre-amplifiers is smaller than 0.76 pT/ p Hz at 10 Hz.The analog signals produced by the SearchCoils and associated preamplifiers are digitized and processed inside the IDPU, together with data from the EFI instrument. SearchCoil telemetry includes waveform transmission, FFT processed data, and data from a filter bank. The frequency range covered in waveform depends on the available telemetry. The SearchCoils and their three axis structures have been precisely calibrated in a quiet site, and the calibration of the transfer function is checked on board usually once per orbit. The tri-axial SearchCoils implemented on the five THEMIS spacecraft are working nominally.
-
improvements on the design of Search Coil magnetometer for space experiments
Sensor Letters, 2007Co-Authors: C. Coillot, Paul Leroy, Joel Moutoussamy, Gerard Chanteur, A. RouxAbstract:Search Coils despite of their bulk, are still used on space experiments thanks to their ability to measure weak magnetic fields and also to their robustness. This paper will focus on the Search Coil modeling and design. We propose an original shape of the magnetic core allowing an improvement of their performances. Models for the demagnetizing factor for this shape as well as for the winding behavior are proposed. Then, we present a formulation of the optimization problem needed to achieve a low mass sensor. This is a critical issue for space instruments. The optimization problem is solved by using a Newton algorithm combined with an efficient formulation of the cost function. Finally, we discuss the solution obtained via this optimization procedure and indicate the performances of the sensor. A sensitivity as low as 15fT / √ Hz at a few kHz is obtained.
Jorge Oteromillan - One of the best experts on this subject based on the ideXlab platform.
-
simultaneous recordings of human microsaccades and drifts with a contemporary video eye tracker and the Search Coil technique
PLOS ONE, 2015Co-Authors: Michael B Mccamy, Jorge Oteromillan, John R Leigh, Susan King, Rosalyn Schneider, Stephen L Macknik, Susana MartinezcondeAbstract:Human eyes move continuously, even during visual fixation. These “fixational eye movements” (FEMs) include microsaccades, intersaccadic drift and oculomotor tremor. ReSearch in human FEMs has grown considerably in the last decade, facilitated by the manufacture of noninvasive, high-resolution/speed video-oculography eye trackers. Due to the small magnitude of FEMs, obtaining reliable data can be challenging, however, and depends critically on the sensitivity and precision of the eye tracking system. Yet, no study has conducted an in-depth comparison of human FEM recordings obtained with the Search Coil (considered the gold standard for measuring microsaccades and drift) and with contemporary, state-of-the art video trackers. Here we measured human microsaccades and drift simultaneously with the Search Coil and a popular state-of-the-art video tracker. We found that 95% of microsaccades detected with the Search Coil were also detected with the video tracker, and 95% of microsaccades detected with video tracking were also detected with the Search Coil, indicating substantial agreement between the two systems. Peak/mean velocities and main sequence slopes of microsaccades detected with video tracking were significantly higher than those of the same microsaccades detected with the Search Coil, however. Ocular drift was significantly correlated between the two systems, but drift speeds were higher with video tracking than with the Search Coil. Overall, our combined results suggest that contemporary video tracking now approaches the Search Coil for measuring FEMs.
N K Logothetis - One of the best experts on this subject based on the ideXlab platform.
-
a novel functional magnetic resonance imaging compatible Search Coil eye tracking system
Magnetic Resonance Imaging, 2007Co-Authors: A Oeltermann, Shihpi Ku, N K LogothetisAbstract:Measuring eye movements (EMs) using the Search-Coil eye-tracking technique is superior to video-based infrared methods [Collewijn H, van der Mark F, Jansen TC. Precise recording of human eye movements. Vision Res 1975;15(3):447-50], which suffer from the instability of pupil size, blinking behavior and lower temporal resolution. However, no conventional functional magnetic resonance imaging (fMRI)-compatible Search-Coil eye tracker exists. The main problems for such a technique are the interaction between the transmitter Coils and the magnetic gradients used for imaging as well as the limited amount of space in a scanner. Here we present an approach to overcome these problems and we demonstrate a method to record EMs in an MRI scanner using a Search Coil. The system described has a spatial resolution of 0.07° (visual angle) and a high temporal resolution (22 kHz). The transmitter Coils are integrated into the visual presentation system and the control/analysis unit is portable, which enables us to integrate the eye tracker with an MRI scanner. Our tests demonstrate low noise in the recorded eye traces and scanning with minimal artifact. Furthermore, the induced current in the Search Coil caused by the RF pulses does not lead to measurable heating. Altogether, this MR-compatible Search-Coil eye tracker can be used to precisely monitor EMs with high spatial and temporal resolution during fMRI. It can therefore be of great importance for studies requiring accurate fixation of a target, or measurement and study of the subject's oculomotor system.
William T Newsome - One of the best experts on this subject based on the ideXlab platform.
-
tracking the eye non invasively simultaneous comparison of the scleral Search Coil and optical tracking techniques in the macaque monkey
Frontiers in Behavioral Neuroscience, 2012Co-Authors: Daniel L Kimmel, Dagem Mammo, William T NewsomeAbstract:From human perception to primate neurophysiology, monitoring eye position is critical to the study of vision, attention, oculomotor control, and behavior. Two principal techniques for the precise measurement of eye position—the long-standing sclera-embedded Search Coil and more recent optical tracking techniques—are in use in various laboratories, but no published study compares the performance of the two methods simultaneously in the same primates. Here we compare two popular systems—a sclera-embedded Search Coil from C-N-C Engineering and the EyeLink 1000 optical system from SR ReSearch—by recording simultaneously from the same eye in the macaque monkey while the animal performed a simple oculomotor task. We found broad agreement between the two systems, particularly in positional accuracy during fixation, measurement of saccade amplitude, detection of fixational saccades, and sensitivity to subtle changes in eye position from trial to trial. Nonetheless, certain discrepancies persist, particularly elevated saccade peak velocities, post-saccadic ringing, influence of luminance change on reported position, and greater sample-to-sample variation in the optical system. Our study shows that optical performance now rivals that of the Search Coil, rendering optical systems appropriate for many if not most applications. This finding is consequential, especially for animal subjects, because the optical systems do not require invasive surgery for implantation and repair of Search Coils around the eye. Our data also allow laboratories using the optical system in human subjects to assess the strengths and limitations of the technique for their own applications.
