Digital Magnetometer Research Articles

A New Method for Detecting the Abomasal Position and Characteristics of Movement at the Onset of the Left Displacement of the Abomasum in Cows

A new method has been developed by us to observe the movements of the abomasum by using a magnet and digital magnetometer. Four cows with left displacement of the abomasum underwent conventional correction by rolling without tacking. A doughnut-type magnet was sutured to the pyloric region in a routine operation. The same was done in three control cows. The position of the pyloric region was observed with a digital magnetometer from outside the cow's body. The magnets in the pyloric region of the control cows were located at the right side of the abdominal cavity at 10-30 cm anterior to the udder base, and moved slightly in various directions within the span of a day. On the other hand, the magnets in the pyloric region of cows with abomasal displacement moved widely in the abdominal cavity from the normal right side to the abnormal left front side. A large movement of the magnet from the normal right side to the abnormal left side of the abdominal cavity was observed within 12 h of the onset of abomasal displacement.

Delta-sigma digital magnetometer utilizing bistable spin-dependent-tunneling magnetic sensors

A digital magnetometer, utilizing a micron-sized spin-dependent-tunneling (SDT) sensor as a field-dependent bistable difference node within an oversampling first-order delta-sigma (Δ−Σ) analog-to-digital converter, was designed and prototyped. The Δ−Σ magnetometer can be fabricated as a single-chip device. It is intended for integration directly with digital components, facilitating development of low-cost magnetic-field sensing systems for commercial and military navigation, security, and linear-magnetic-field sensing applications. The Δ−Σ magnetometer operates by pulsing the SDT element along its hard axis (HA) in order to set the magnetization of the free layer into an unstable equilibrium orientation along the HA. In the absence of an easy-axis (EA) magnetic field, thermal fluctuations result in an equal probability for the magnetization to relax into one of the two stable orientations along the EA. Application of an EA magnetic field increases the probability for the magnetization to relax into the EA orientation parallel to the applied field. Thus, repeatedly pulsing the SDT sensor along the HA and monitoring the magnetoresistance results in a digital bitstream, where the number of 1s within a fixed length of the bitstream provides a measure of the applied field. The SDT sensor bitstream is thus integrated in order to produce an EA feedback signal. The raw bitstream from the SDT sensor provides the digital output of the magnetometer. The length of the bitstream summing window is the oversampling ratio, which determines the minimum possible digital resolution. A prototype Δ−Σ magnetometer was constructed, and several different bit shapes were tested in order to optimize performance. The digital output of the device was found to provide a count that is linearly proportional to the applied field over a range determined by the EA feedback driver current limit and loop gain.

Electronic transport properties of metallic CNTs in an axial magnetic field at nonzero temperatures: A model of an ultra-small digital magnetometer

We present a complete description of electronic current in metallic single-walled carbon nanotubes under the influence of axially oriented magnetic fields at nonzero temperatures. We include in our model the diameter of the carbon nanotube, the temperature and length of the nanotube. We find that the current in a zigzag carbon nanotube that is metallic at zero magnetic field is strongly modulated by varying the magnitude of an axially oriented magnetic field. We use this property, to propose a design of a carbon nanotube based directional magnetometer that could be designed to sense magnetic fields from 1 to 8T and at temperatures from 0 up to 100K.

Spatiotemporal evaluation of human colon motility using three-axis fluxgates and magnetic markers

An alternative method to study the mechanical activity of the human colon in fasting and postprandial states is presented. The method is based on measurements of the magnetic fields produced by a magnetic marker, a small cylindrical NdBFe magnet, when it was ingested by the subjects. A portable magnetic probe, consisting of two digital three-axis fluxgate magnetometers, arranged in a first-order electronic gradiometer, was implemented for this research. Measurements were taken in 16 healthy male subjects. Contractile activity frequency measurements were taken along the colon length, including the ascending, transverse and descending sections, as well as the rectal sigmoidal section. Values for the contractile activity frequency of 2-5 cycles min(-1) were measured. The set-up is simple, low-cost and suitable for use in an unshielded environment.

Experimental analysis of a digital SQUID device at 4.2 K

The application of superconducting rapid single-flux quantum (RSFQ) digitalelectronics for highly sensitive measurement of magnetic fields can provide significantadvantages in the use of conventional analogue SQUIDs, especially in terms ofoperation speed and dynamic range. Furthermore, utilizing an unconventionalgeneralized single-flux-quantum (SFQ) logic with a bidirectional operation principleallows an additional decrease in effort in superconducting electronics. Our novelfully digital SQUID based on the SFQ technique can be assumed to be operatingat frequencies in the gigahertz range corresponding to slew rates of several109 Φ0 s−1. We present first experimental results for the proper digital function as a preliminary stagefor a digital SQUID magnetometer device. The measurements presented are performed fora reliable low temperature superconductor technology at liquid helium temperature;nevertheless the very low complexity of the superconducting digital circuitry holds promiseas regards prospects for a working digital SQUID based on high temperaturesuperconductor technology.

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.

Study of Decomposition of Supercooled Austenite of Powder Steels with the Help of a Novel Digital Magnetometer

A magnetometric complex for studying the decomposition of supercooled austenite is described. The kinetics of phase transformations is studied by the developed method. The kinetic parameters are determined and kinetic diagrams of phase transformations for conditions of stage hardening are plotted. A mathematical model of decomposition of supercooled austenite under conditions of isothermal and stage hardening is developed on the basis of these kinetic parameters and diagrams. An experimental check of adequacy of the models obtained is performed for the whole temperature and time range of the transformation.

Gastric activity studies using a magnetic tracer

A magnetic pulse generator has been set up in order to study gastric activity. Two coils 1.05 m in diameter, arranged in a Helmholtz configuration, were used. The system generated magnetic field pulses higher than 15 mT, of duration 17.3 ± 1.2 ms. Measurements were performed in 11 male volunteers, with average age 29.3 ± 6.4 years and body mass index 26.0 ± 4.8 kg m−2. Magnetite (Fe3O4) particles with diameters from 75 to 125 µm were used as magnetic tracers, which were mixed in 250 ml of yogurt in concentrations from 2 to 5 g. Signals were registered by using a high speed 3 axis fluxgate digital magnetometer and processed to determine the relaxation of the magnetic tracers by fitting a first-order exponential function to the data, a mean relaxation constant κ = 116 ± 40 s−1 was obtained. Also, an average gastric peristaltic frequency was measured; a value of 3.2 ± 0.3 cpm was determined.

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.

Interball-1 and MIR orbital station coordinated magnetic field and energetic particles measurements

Magnetic field measurements in solar wind and outer magnetosphere onboard the INTERBALL-1 spacecraft were performed by the following magnetometers: MIF-M magnetometer with both DC sensor (BPP) having 0.2 nT threshold sensitivity at DC and 5 pT at 1 Hz and AC sensor (DM2) with the sensitivity about 0.2 nT at 1 Hz and 0.4 pT at 100 Hz; FGM-I DC magnetometer with threshold sensitivity of 5 pT at 1 Hz; FM-31 DC magnetometer with two sensors having 0.1 nT (sensor MI) and 1.0 nT (sensor M2) threshold sensitivity. During INTERBALL-1 operation the ionosphere experiment SPRUT-VI onboard the MIR station was performed from 06/13–08/26/1999. The measurements of DC magnetic field, electron and ion fluxes at energies between 50 keV–2.5 MeV and 50 keV–30 MeV were made. The SPRUT-MAG digital magnetometer for this experiment is based on the one developed for the ESA Rosetta Lander device ROMAP which threshold sensitivity was about 5 pT/(Hz)1/2 at 1 Hz. This paper discusses the possibility of signals processing with the aim to separate the artificial (technical, connected with the MIR onboard system operation) and natural origin signals as well as to estimate the level of ULF/ELF magnetic field disturbances and particle flows bursts.

Some Aspect of Using a Magnetoresistive Transducer

The results of investigating the lower sensitivity threshold of a magnetoresistive transducer converting the magnetic field induction into an electric signal are presented. The voltage fluctuation amplitude measured in terms of the magnetic field induction units amounts to 25 × 10–9 T at the transducer output. It is found that after termination of the action of the magnetic field the output transducer voltage returns to the zero level with a delay. The duration of this return may amount to tens of minutes (depending on the induction and duration of the field action). A digital magnetometer with the scale of ±200 μT graduated to 0.1 μT is fabricated on the basis of the magnetoresistive transducer.

High sensitivity digital SQUID magnetometers

A single-chip digital SQUID magnetometer integrates a sensitive analog SQUID sensor with a comparator gate and feedback circuitry on the same chip. The comparator gate is an asymmetric SQUID gate driving two DC-to-SFQ converters in series with the feedback coil. In an optimized digital magnetometer chip, sensitivity and noise level are determined by the input analog SQUID. The dynamic range of such digital chips is extremely wide enabling them to be operated in a relatively high magnetic field environment without extensive magnetic shielding. Their slew rate is determined by the frequency of an external two-phase clock. This chip simplifies room temperature electronics and, due to its digital output, can be easily multiplexed on-chip. In this paper, we describe this digital SQUID magnetometer chip and summarize our experimental results demonstrating a digital SQUID chip with sensitivity of 20 /spl mu//spl Phi//sub 0///spl radic/(Hz) and a system slew rate of 5/spl times/10/sup 6/ /spl Phi//sub 0//s at the pick up coil.

Auroral electrojets during geomagnetic storms

On the basis of digital magnetometers from the International monitor auroral geomagnetic effects (IMAGE) and European incoherent scatter (EISCAT) meridional chains in Scandinavia dynamics of the eastward and westward electrojets during the main phase of magnetic storms are considered. For the intense magnetic storm on May 10–11, 1992, with Dst = −300 nT, magnetograms of subauroral and midlatitudinal stations Leningrad, Borok, and Moscow were examined. It is found that the eastward electrojet center during the storm main phase shifts equatorward as |Dst| increases. The electrojet center is located at the corrected geomagnetic latitude Φ ∼ 59°–60° when Dst ∼ −100 nT and at Φ ∼ 54°–55° when Dst ∼ −300 nT. Data from meridional chains of magnetometers support earlier results pertaining to the relationship between the westward electrojet center position and the ring current intensity for intervals between substorms. During substorms expansive phases the westward electrojet expands poleward covering auroral latitudes Φ ∼ 65°. The electrojets location during the storm main phase and their dynamics in connection with substorms allow for interpretations of effects described in the literature: the AE indices saturation during the main phase of magnetic storms; approximately equal values of AU and AL indices during the storm initial phase and AL ≫ AU during the storm main phase.

Digital detection and feedback fluxgate magnetometer

A new full Earth's field dynamic feedback fluxgate magnetometer is described. It is based entirely on digital signal processing and digital feedback control, thereby replacing the classical second harmonic tuned analogue electronics by processor algorithms. Discrete mathematical cross-correlation routines and substantial oversampling reduce the noise to 71 pT root-mean-square in a 0.25 - 10 Hz bandwidth for a full Earth's field range instrument.

An integrated digital SQUID magnetometer with high sensitivity input

A single chip SQUID magnetometer is described that integrates a SQUID-based pre-amplifier with a high sensitivity comparator gate and feedback circuitries on the same chip. The comparator gate is an asymmetric SQUID gate driving two SQUID quantizers in series with the feedback coil. The chip's sensitivity and noise level are primarily determined by the pre-amplifier SQUID. The pick up coil is in series with the feedback transformer. Since the current in the feedback coil is maintained close to zero, the dynamic range of the chip can be extremely wide and is independent of the SQUID pre-amplifier or comparator architectures. The chip's slew rate is determined by the bipolar clock biasing the comparator gate. Clocks running in the tens of MHz result in a magnetometer system with slew rate exceeding 10/sup 5/ /spl Phi//sub 0//s (/spl Phi//sub 0/=2.07/spl times/10/sup -7/ Gauss-cm/sup 2/). This chip simplifies room temperature electronics and, due to its digital output, can be easily multiplexed on-chip. A system based on this chip can be operated in a relatively high magnetic field environment without extensive magnetic shielding. The details of the chip as well as preliminary measurement results for the pre-amplifier as well as the digital circuit will be presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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.

Magnetic observatories at the turn of the century: a forward look

Accurate measurements from standard observatories and repeat stations will continue to be essential for modelling the geomagnetic field for navigation and scientific purposes. The technology of data base management increasingly calls for the use of digitally recording magnetometer systems at observatories, and suggests that absolute and repeat station observations should be made with compatible equipment. The cost of such equipment is reducing and its reliability is increasing. Digital equipment relieves operators of the tedious scalings which often result in backlogs of years in the presentation of data to the community. There is, therefore, every reason to recommend that observatories should buy and operate digital magnetometers and adopt digital processing systems. Those countries which are not yet able to adopt digital methods are usually poor in financial terms and in commercially available technology and trained manpower. They are almost all located in the areas of the Earth where the distribution of observatories is sparse and are, thus, all the more important. It is essential that observations in these areas continue. It is also very desirable that national or regional magnetic surveys are carried out in coordination with the observatory operations. In the 1990s and the 21st century satellite magnetic surveys will supplement the work done by ground observatories. The effectiveness of satellite surveys will depend on base data from ground stations operated to the highest standard.

The unmanned geophysical data collection platform based on the digital magnetometer CMVS-6

The polar geomagnetic research laboratory of Izmiran carries out construction on the automated digital data collection platform for operation in the remote regions including Antarctica. In view of the experience with previous instruments such as CMVS-2, a new digital magnetometer CMVS-6 was designed. CMVS-6 consists of a few separate modules: quartz sensors unit, electronic unit with cassette tape recorder, control and adjustment unit and radioisotopic thermoelectric generator (RITEG). Data sample rate is 1, 10 or 60 s (selectable) and the system includes the measurement of D, H and Z components of the magnetic field and has three channels for additional sensors with electric output. Resolution is 0.5 nT for magnetic field and 1.25 mV for electric channels. The dynamic range is 4000 nT for a magnetometer and 10 V for electric channels, but CMVS-6 can operate properly in dynamic range 1.8 times greater. The data are stored on the cassette tape recorder. Control and adjustment are necessary only for initial installation of the platform and for the data flow checking. It is planned to use the riometer, d.c. electric meter and thermometer as additional sensors. The first platform is installed in the Antarctic for testing in 1987–1988 season.

On the digital geomagnetic observatory at Lunping, Taiwan

A permanent Lunping Observatory was established by the author in 1965 at Lunping (25°00′ N; 121°10′ E), Taiwan. A set of Ruska magnetographs, a proton precession magnetometer and a GSI 1st Order Precession Magnetometer have been used to measure the hourly mean values of the geomagnetic three components, H, Z, D, and to determine the three hourly geomagnetic K indices from the daily magnetograms. The purpose of this paper is to show how a set of fluxgate digital magnetometers has been introduced at Lunping Geomagnetic Observatory to automate the routine work of the observatory to save the time spent for the tedious routine manual data production. To maintain the fluxgate digital magnetometers at their best conditions, it has been found that the temperatures of the sensors as well as the electronic parts of the fluxgate magnetometers have to be kept constant. Even though these temperatures have been kept constant, the aging effects of the sensors and electronic parts require absolute measurements of the geomagnetic field to obtain the accurate baseline values of the fluxgate magnetometers. The computer assisted determination of K indices is also presented and discussed.