Orthogonal Magnetic Field Components Research Articles

Functional Multisensor for Temperature and Subsequent 3D Magnetic-field Measurement

A novel functional multisensor for temperature and subsequent measurement of three orthogonal magnetic-field components using the same transducer zone is presented. One central emitter, two symmetrically positioned base contacts and two pairs of output ohmic terminals on a silicon substrate, close to the bases, are implemented. Three subsequent coupling arrangements of the output terminals use the same element at different times. Temperature is measured through the voltage on the forward biased p+-n emitter junction at constant supply current. The channel sensitivities are Sx = 7V/AT, Sy = 9V/AT and Sz = 11.3V/AT. The thermo-sensitivity is KEB = 1.82mV/°C at supply current of 1mA. Magnetic induction does not perturb thermometric voltage within a wide range, - 0.8 T ≤ B ≤ 0.8 T. The spatial resolution reaches about 110 х 90 х 40μm3.

Three-dimensional magnetometer based on subsequent measurement principle

A novel single-chip 3-D multidimensional Hall device for subsequent measurement of the three orthogonal magnetic-field components using one and the same transducer zone is presented. The magnetometer includes n-Si microsensor and simple and reliable interface circuitry which contains power supply and original signal extraction and conditioning circuitry. In the 3-D microsensor, six ohmic planar contacts on silicon substrate are implemented. Two of them are used for power supply. The other four are used to obtain the full information about the magnetic field vector components, by three successive coupling arrangements realizing two in-plane sensitive and one orthogonal Hall effect devices. The proposed approach employs the same element, but at different time. The sensor operation is determined by the direction of individual parts of nonlinear carriers’ trajectory in the substrate and the Lorentz force action on them. The effective sensor minimum operational volume is 90μm×60μm×30μm. The respective channel-magnetosensitivities consist Sx≈35V/AT, Sy≈26V/AT, and Sz≈18V/AT, the channel cross-talk at induction B≤1T reaches no more than 3% and the lowest detected magnetic field of the three channels is about 10μT in the frequency range f≤102Hz. The instrument ensures the measurement of the full magnetic field vector with rate 20,000Hz and the output signal is in range [−5V, 5V].

Calibration of SQUID vector magnetometers in full tensor gradiometry systems

Measurement of magnetic vector or tensor quantities, namely of field or field gradient, delivers more details of the underlying geological setting in geomagnetic prospection than a scalar measurement of a single component or of the scalar total magnetic intensity. Currently, highest measurement resolutions are achievable with superconducting quantum interference device (SQUID)-based systems.Due to technological limitations, it is necessary to suppress the parasitic magnetic field response from the SQUID gradiometer signals, which are a superposition of one tensor component and all three orthogonal magnetic field components. This in turn requires an accurate estimation of the local magnetic field. Such a measurement can itself be achieved via three additional orthogonal SQUID reference magnetometers. It is the calibration of such a SQUID reference vector magnetometer system that is the subject of this paper.A number of vector magnetometer calibration methods are described in the literature. We present two methods that we have implemented and compared, for their suitability of rapid data processing and integration into a full tensor magnetic gradiometry, SQUID-based, system.We conclude that the calibration routines must necessarily model fabrication misalignments, field offset and scale factors, and include comparison with a reference magnetic field. In order to enable fast processing on site, the software must be able to function as a stand-alone toolbox.

Compact fluxgate magnetic full-tensor gradiometer with spherical feedback coil

The magnetic tensor gradiometer, which is used for measuring the spatial derivatives of three orthogonal magnetic field components, is an important magnetic field characterization tool. Here, the construction of a magnetic full-tensor gradiometer is described, which utilizes four fluxgates arranged on a planar cross structure, and a single, triaxial, spherical feedback coil assembly. In this arrangement, one of the fluxgates is used as a reference, controlling the currents through the feedback coils. Since the fluxgates are working in the near-zero magnetic field environment, the magnetic tensor gradiometer is stable and of an improved accuracy. This design avoids the crosstalk normally caused by individual feedback coils for each fluxgate, and reduces the orthogonality and orientation errors. Moreover, the calibration parameters can be directly inferred using the spherical feedback coil. The measured gradient tensor magnitude can reach 0.52 nT/m/Hz(1/2) @ 1 Hz in unshielded laboratory conditions, while exhibiting good noise immunity. The functionality of the system is verified by locating a small, single, permanent, and dipole magnet in space. The gradiometer is compact, while employing global feedback, and therefore it is especially suitable for deployment on space-constrained moving platforms.

3-D Silicon Hall Device with Subsequent Magnetic-field Components Measurement

Abstract A novel single-chip 3-D multidimensional device for subsequent measurement of the three orthogonal magnetic-field components using one and the same transducer zone is presented. Six ohmic planar contacts on silicon substrate are implemented both as supply and four to obtain the full information about the vector components by three successive coupling arrangements realizing two in-plane sensitive and one orthogonal Hall effect devices. The proposed approach employs the same element, but at different time. The sensor operation is determined by the direction of individual parts of nonlinear carriers’ trajectory in the substrate and the Lorentz force action on them. The effective sensor resolution is 90x60x30 μm 3 . The respective channel- magnetosensitivities consists S x ≈ 35 V/AT, S y ≈ 26 V/AT, and S z ≈ 18 V/AT, the channel cross-talk at induction B ≤ 1 T reaches no more than 3% and the lowest detected magnetic field of the three channels is about 10 μT in the frequency range f ≤ 10 2 Hz.

Circular polarization of obliquely propagating whistler wave magnetic field

The circular polarization of the magnetic field of obliquely propagating whistler waves is derived using a basis set associated with the wave partial differential equation. The wave energy is mainly magnetic and the wave propagation consists of this magnetic energy sloshing back and forth between two orthogonal components of magnetic field in quadrature. The wave electric field energy is small compared to the magnetic field energy.

Characterization of gastric electrical activity using magnetic field measurements: a simulation study.

Gastric disorders are often associated with abnormal propagation of gastric electrical activity (GEA). The identification of clinically relevant parameters of GEA using noninvasive measures would therefore be highly beneficial for clinical diagnosis. While magnetogastrograms (MGG) are known to provide a noninvasive representation of GEA, standard methods for their analysis are limited. It has previously been shown in simplistic conditions that the surface current density (SCD) calculated from multichannel MGG measurements provides an estimate of the gastric source location and propagation velocity. We examine the accuracy of this technique using more realistic source models and an anatomically realistic volume conductor model. The results showed that the SCD method was able to resolve the GEA parameters more reliably when the dipole source was located within 100 mm of the sensor. Therefore, the theoretical accuracy of SCD method would be relatively diminished for patients with a larger body habitus, and particularly in those patients with significant truncal obesity. However, many patients with gastric motility disorders are relatively thin due to food intolerance, meaning that the majority of the population of gastric motility patients could benefit from the methods developed here. Large errors resulted when the source was located deep within the body due to the distorting effects of the secondary sources on the magnetic fields. Larger errors also resulted when the dipole was oriented normal to the sensor plane. This was believed to be due to the relatively small contribution of the dipole source when compared to the field produced by the volume conductor. The use of three orthogonal magnetic field components rather than just one component to calculate the SCD yielded marginally more accurate results when using a realistic dipole source. However, this slight increase in accuracy may not warrant the use of more complex vector channels in future superconducting quantum interference device designs. When multiple slow waves were present in the stomach, the SCD map contained only one maximum point corresponding to the more dominant source located in the distal stomach. Parameters corresponding to the slow wave in the proximal stomach were obtained once the dominant slow terminated at the antrum. Additional validation studies are warranted to address the utility of the SCD method to resolve parameters related to gastric slow waves in a clinical setting.

Epitaxial yttrium iron garnet film as an active medium of an even-harmonic magnetic field transducer

The use of epitaxial yttrium iron garnet (YIG) films in transducers excited by a magnetic field rotating in the film plane is considered. The circular excitation of the film allows one to keep it in the saturated monodomain state and exclude the Barkhausen noise. Using the ferrodielectric material enables one to avoid eddy-current losses, which limit the excitation frequency—and thus the magnetometer sensitivity—and are also an additional source of noise. Conditions of simultaneous measuring of three orthogonal magnetic field components by the YIG single-crystal film have been established. Theoretical analysis of the intrinsic noises of the magnetic material and coils is performed. The prospective way is described to design the magnetometer with noise of several fT Hz−1/2 at room temperature. The prototype of the 3D magnetometer was experimentally tested, demonstrating the detection level below 1 pT Hz−1/2 at frequencies above 0.1 Hz. It looks feasible to reach with such sensors at room temperature the detection level of cooled SQUIDs.

Gaussian statistics for palaeomagnetic vectors

SUMMARY With the aim of treating the statistics of palaeomagnetic directions and intensities jointly and consistently, we represent the mean and the variance of palaeomagnetic vectors, at a particular site and of a particular polarity, by a probability density function in a Cartesian three-space of orthogonal magnetic-field components consisting of a single (unimodal) non-zero mean, spherically-symmetrical (isotropic) Gaussian function. For palaeomagnetic data of mixed polarities, we consider a bimodal distribution consisting of a pair of such symmetrical Gaussian functions, with equal, but opposite, means and equal variances. For both the Gaussian and bi-Gaussian distributions, and in the spherical three-space of intensity, inclination, and declination, we obtain analytical expressions for the marginal density functions, the cumulative distributions, and the expected values and variances for each spherical coordinate (including the angle with respect to the axis of symmetry of the distributions). The mathematical expressions for the intensity and off-axis angle are closed-form and especially manageable, with the intensity distribution being Rayleigh–Rician. In the limit of small relative vectorial dispersion, the Gaussian (bi-Gaussian) directional distribution approaches a Fisher (Bingham) distribution and the intensity distribution approaches a normal distribution. In the opposite limit of large relative vectorial dispersion, the directional distributions approach a spherically-uniform distribution and the intensity distribution approaches a Maxwell distribution. We quantify biases in estimating the properties of the vector field resulting from the use of simple arithmetic averages, such as estimates of the intensity or the inclination of the mean vector, or the variances of these quantities. With the statistical framework developed here and using the maximum-likelihood method, which gives unbiased estimates in the limit of large data numbers, we demonstrate how to formulate the inverse problem, and how to estimate the mean and variance of the magnetic vector field, even when the data consist of mixed combinations of directions and intensities. We examine palaeomagnetic secular-variation data from Hawaii and Reunion, and although these two sites are on almost opposite latitudes, we find significant differences in the mean vector and differences in the local vectorial variances, with the Hawaiian data being particularly anisotropic. These observations are inconsistent with a description of the mean field as being a simple geocentric axial dipole and with secular variation being statistically symmetrical with respect to reflection through the equatorial plane. Finally, our analysis of palaeomagnetic acquisition data from the 1960 Kilauea flow in Hawaii and the Holocene Xitle flow in Mexico, is consistent with the widely held suspicion that directional data are more accurate than intensity data.

Conductivity anomalies in the Baltic Shield in Finland

In 1981–84 six arrays of 30 or 31 magnetometers were operated on the Baitic Shield in central and southern Finland to deduce information about the electrical conductivity within the Earth's crust. The magnetometer sites cover the area with 20–60 km spacing allowing the identification of large-scale electrical structures within the crust. Each array recorded the three orthogonal magnetic field components on analogue film for about two months simultaneously at all the stations. Altogether 17 magnetic variation events of 2–6hr length have been digitized and analysed. This paper includes results of the last array in south-western Finland, a comparison of two methods of induction vector estimation and combination of results from all the arrays. Four zones of anomalously high electrical conductivity have been observed. They are all interpreted as lying at depths greater than 5 km. The ‘Oulu Anomaly’ is wider than the others and rather short, about 100 km. The ‘Southern Finland Anomaly’ is probably a 500 km-long narrow zone. This and the ‘Ostrobothnian Anomaly’ surround three sides of the large Central Finland Granite area. The ‘Outokumpu Anomaly’ is probably deeper lying than the others. Blocks separated by these anomalies are presented. The blocks have different average resistivities.

Magnetic field measurements near RF induction heaters.

We discuss initial magnetic field strength measurements made around radiofrequency (RF) induction heaters. These measurements were made with a monitor developed for the National Institute for Occupational Safety and Health (NIOSH) by the National Bureau of Standards (NBS). The monitor has a dynamic range of .01 to 10,000 A2/m2, a frequency range of 300 kHz to 100 MHz, an isotropic response (+/- .3 dB) with three mutally orthogonal loop antennas that have the ability to measure and display each of three orthogonal magnetic field components, a high probe burnout protection level of 20,000 A2/m2, and an accuracy of +/- 1.0 dB at 13 calibration frequencies. The portable survey monitor was used to measure the magnetic field strengths in the vicinity of 16 RF induction heaters. Typically these induction heaters are operated continuously for several hours. The maximum field strengths (without duty factor correction) ranged from 15 to 4,500 A2/m2 and were measured 5 to 51 cm from the loop applicators of the induction heaters. At locations commonly occupied by workers (ie, approximately 30 to 76 cm from heaters), the fields ranged from .01 to 300 A2/m2 (without duty factor correction).