Magnetic Field Emission Research Articles

Suppression measures for electromagnetic emission interference in low frequency range in hybrid electric vehicles

Limit–exceeding problems exist in electric field and magnetic field emission level in a type of hybrid electric vehicles. Characteristics of main electromagnetic interference source in the vehicles are analysed, production mechanism of radiated electric filed and magnetic field in the whole vehicle is discussed and the conclusion that the main interference sources of whole vehicle electromagnetic emission are three–phase working current of drive motor and electric motor controller is cleared up. Additionally, considering the properties of interference source, corresponding suppression measures for interference are proposed and applied. In the end, comparison validations with experiments are made to show that the whole vehicle electric field in low frequency range and the level of magnetic emission can be decreased by the suppression measures applied. The measures can also provide a reference for electromagnetic compatibility improvement in other hybrid electric vehicles.

Space-Frequency Analysis and Experimental Measurement of Magnetic Field Emissions Radiated by High-Speed Railway Systems

This paper shows that in the radiated emission spectrum of high-speed railway systems, a low-frequency range exists in which the magnetic field space-frequency distribution is determined, to a large extent, by the railway infrastructure features. To prove this, electromagnetic modeling of a suitably long stretch of the railway infrastructure is developed, and an ad hoc experimental campaign is carried out for comparison. Modeling and experimental measurements refer to a 50 km stretch of the Italian 2 × 25 kV ac railway system. Infrastructure simulation is obtained by resorting to a simplified approach based on multiconductor transmission line. To this end, short segments of uniform lines are cascade-connected with lumped networks representing equipment and electrical devices placed along the line, and the radiated magnetic field is evaluated from the corresponding noise-current distributions. Since the emission source, i.e., the train, has unknown electrical properties, it is represented as a unit-current source. Thus, the proposed model provides a transfer ratio between the radiated magnetic field and the current source. As a result, the maximum values of train current corresponding to magnetic field limits provided by the International Standards can be readily derived. An optimized measurement procedure is used to show that in the frequency band 60-120 kHz, transient emissions due to random and unpredictable phenomena are negligible. In such a frequency range, where continuous and persistent emissions are present, the structure of time-frequency measurement data is readily explained, and the role of the railway infrastructure on the radiated magnetic field is unambiguously identified.

Fabrication of porous anodic aluminum oxide by hybrid pulse anodization at relatively high potential

Anodic aluminum oxide (AAO) containing high-aspect ratio pore channels has been widely used as a template for fabricating nanowires or other 1D nanostructures. For AAO prepared in oxalic acid, the anodizing potential is set as 40 V in order to balance the oxidation and dissolution rates. In practice, a higher potential is beneficial in increasing the pore size. However, a higher potential increases the local electrolyte temperature and therefore damages the pore structure. In this article, this problem is resolved by means of a high-potential hybrid pulse anodization (HPA) technique, in which a period of small negative potential is applied to suppress the Joule heating effect during the AAO preparation process. The scanning electron microscope results showed that HPA with an anodizing potential of 60 V resulted in an intact pore structure on the AAO surface. By contrast, the AAO formed using conventional direct current anodization with the same anodizing potential contained many small irregular pores around each original pore. The present results suggest that HPA has significant potential for the fabrication of high-quality nanowires with various diameters for such applications as magnetic recording, super capacitors or field emission devices.

Surface and volume effects in micro-scale plasma evolution

Micro-scale plasmas are extremely interesting due to the spectrum of applications potentially feasible for these small scale plasmas. Due to the small physical size and short temporal scales, simulations can provide complementary and insightful tools to help understand the underlying physical processes. The present paper discusses a numerical model coupling the plasma, metastable species and gas dynamics in atmospheric microcavities in helium at atmospheric pressure. The self-consistent and time-dependant model is described with emphasis on terms involved in the close coupling among species (plasma, metastable and gas) and the applied field – both electric and magnetic fields. The microplasmas are studied from an initial cloud and transients are particularly important in the evolution. Gas heating, neutral depletion initiation and electrohydrodynamic effects are observed, highlighting the interaction between neutral gas and plasma species in governing the microplasmas. The crucial effects of the applied magnetic field and secondary emission are discussed – and surface and volume effects are compared in terms of spatial and temporal evolutions of the plasma and gas dynamics in atmospheric microplasmas.

INTERPRETING THE ROLE OF THE MAGNETIC FIELD FROM DUST POLARIZATION MAPS

Dust polarization observations from the Submillimeter Array (SMA) and the Caltech Submillimeter Observatory (CSO) are analyzed with the goal of providing a general tool to interpret the role of the magnetic field in molecular clouds. Magnetic field and dust emission gradient orientations are observed to show distinct patterns and features. The angle $\delta$ between these two orientations can be interpreted as a magnetic field alignment deviation, assuming the emission gradient orientation to coincide with the density gradient orientation in the magnetohydrodynamics (MHD) force equation. In SMA high-resolution (collapsing) cores, additional symmetry properties in $\delta$ can reveal accretion and outflow zones. All these observational findings suggest the angle $\delta$ to be a relevant quantity that can assess the role of the magnetic field. Indeed, when comparing this angle with the (projection-free) magnetic field significance \Sigma_B (Koch et al. 2012a), it is demonstrated that |\delta| yields an approximation to the change in \Sigma_B. Thus, changes in the magnetic field alignment deviation $\delta$ trace changes in the role of the magnetic field. The angle $\delta$ is observationally straightforward to determine, providing a tool to distinguish between zones of minor or significant magnetic field impact. This is exemplified by the CSO M+0.25+0.01, Mon R2, CO+0.02-0.02, M-0.02-0.07 sources and by the SMA high-resolution data from W51 e2, W51 North, Orion BN/KL and g5.89. Additional CSO sources are analyzed, providing further support of this result. Finally, based on the different features found in our sample of 31 sources in total, covering sizes from large-scale complexes to collapsing cores, a schematic evolutionary scenario is proposed (abridged).

Excessive magnetic field flux density distribution from overhead isolated powerline conductors due to neutral line current

Overhead isolated powerline conductors (hereinafter: “OIPLC”) are the most compact form for distributing low voltage currents. From the known physics of magnetic field emission from 3-phase power lines, it is expected that excellent symmetry of the 120° shifted phase currents and where compact configuration of the 3-phase+neutral line exist, the phase current vectorial summation of the magnetic field flux density (MFFD) is expected to be extremely low. However, despite this estimation, an unexpectedly very high MFFD was found in at least three towns in Israel. This paper explains the reasons leading to high MFFD emissions from compact OIPLC and the proper technique to fix it. Analysis and measurement results had led to the failure hypothsis of neutral line poor connection design and poor grounding design of the HV–LV utility transformers. The paper elaborates on the low MFFD exposure level setup by the Israeli Environmental Protection Office which adopted a rather conservative precaution principal exposure level (2 mG averaged over 24 h).

Sunspots and geomagnetic storms during solar cycle-23

Geo-magnetic storms generally occur due to abnormal conditions in the interplanetary magnetic field (IMF) and solar wind plasma emissions caused by various solar activities. The Disturbance storm time (Dst) index is used to identify more than 220 storms which occurred in time interval 1996–2007, the span of solar cycle-23. Using the minimum Dst value as an indicator, we classify the storms as moderate (138), strong (67), severe (11), and great (4). We have analyzed and studied them statistically. We have found that yearly occurrences of geomagnetic storm are strongly correlated with 11 year sunspot cycle, but no significant correlation between the maximum and minimum phase of solar cycle-23 has been found. It is also found that solar cycle-23 is remarkable for occurrence of intense geomagnetic storms during its declining phase. It is also observed that Halo CME is the main cause to produce geomagnetic storms. The results are discussed in the present paper.

QUANTIFYING THE SIGNIFICANCE OF THE MAGNETIC FIELD FROM LARGE-SCALE CLOUD TO COLLAPSING CORE: SELF-SIMILARITY, MASS-TO-FLUX RATIO, AND STAR FORMATION EFFICIENCY

Dust polarization observational results are analyzed for the high-mass star formation region W51 from the largest parent cloud ($\sim$ 2~pc, JCMT) to the large-scale envelope ($\sim$ 0.5~pc, BIMA) down to the collapsing core e2 ($\sim$ 60~mpc, SMA). Magnetic field and dust emission gradient orientations reveal a correlation which becomes increasingly more tight with higher resolution. The previously developed polarization - intensity gradient method (Koch et al. 2012) is applied in order to quantify the magnetic field significance. This technique provides a way to estimate the local magnetic field force compared to gravity without the need of any mass or field strength measurements, solely making use of measured angles which reflect the geometrical imprint of the various forces. All three data sets clearly show regions with distinct features in the field-to-gravity force ratio. Azimuthally averaged radial profiles of this force ratio reveal a transition from a field dominance at larger distances to a gravity dominance closer to the emission peaks. Normalizing these profiles to a characteristic core scale points toward self-similarity. Furthermore, the polarization intensity-gradient method is linked to the mass-to-flux ratio, providing a new approach to estimate the latter one without mass and field strength inputs. A transition from a magnetically supercritical to a subcritical state as a function of distance from the emission peak is found for the e2 core. Finally, based on the measured radius-dependent field-to-gravity force ratio we derive a modified star formation efficiency with a diluted gravity force. Compared to a standard (free-fall) efficiency, the observed field is capable of reducing the efficiency down to 10\% or less.

Statistical Study of Geomagnetic Storms during Year 1996-2007

A geomagnetic storm is a global disturbance in Earth’s magnetic field usually occurred due to abnormal conditions in the interplanetary magnetic field (IMF) and solar wind plasma emissions caused by various solar phenomenon. A study of 220 geomagnetic storms associated with disturbance storm time (Dst) decreases of more than -50 nT to -300 nT, observed during 1996-2007, the span of solar cycle 23. We have analyzed and studied them statistically. We find yearly occurrences of geomagnetic storm are strongly correlated with 11-year sunspot cycle, but no significant correlation between the maximum and minimum phase of solar cycle-23 have been found. It is also found that solar cycle-23 is remarkable for occurrence of Intense geomagnetic storm during its declining phase. The detailed results are discussed in this paper.

Integration of HTS Cables in the Future Grid of the Netherlands

ue to increasing power demand, the electricity grid of the Netherlands is changing. The future transmission grid will obtain electrical power generated by decentralized renewable sources, together with large scale generation units located at the coastal region. In this way electrical power has to be distributed and transmitted over longer distances from generation to end user. Potential grid issues like: amount of distributed power, grid stability and electrical loss dissipation merit particular attention. High temperature superconductors (HTS) can play an important role in solving these grid problems. Advantages to integrate HTS components at transmission voltages are numerous: more transmittable power together with less emissions, intrinsic fault current limiting capability, lower ac loss, better control of power flow, reduced footprint, less magnetic field emissions, etc. The main obstacle at present is the relatively high price of HTS conductor. However as the price goes down, initial market penetration of several HTS components (e.g.: cables, fault current limiters) is expected by year 2015. In the full paper we present selected ways to integrate EHV AC HTS cables depending on a particular future grid scenario in the Netherlands.

Exposure to Electromagnetic Fields From Laptop Use of “Laptop” Computers

ABSTRACT Portable computers are often used at tight contact with the body and therefore are called “laptop.” The authors measured electromagnetic fields (EMFs) laptop computers produce and estimated the induced currents in the body, to assess the safety of laptop computers. The authors evaluated 5 commonly used laptop of different brands. They measured EMF exposure produced and, using validated computerized models, the authors exploited the data of one of the laptop computers (LTCs) to estimate the magnetic flux exposure of the user and of the fetus in the womb, when the laptop is used at close contact with the woman's womb. In the LTCs analyzed, EMF values (range 1.8–6 μT) are within International Commission on Non-Ionizing Radiation (NIR) Protection (ICNIRP) guidelines, but are considerably higher than the values recommended by 2 recent guidelines for computer monitors magnetic field emissions, MPR II (Swedish Board for Technical Accreditation) and TCO (Swedish Confederation of Professional Employees), and those considered risky for tumor development. When close to the body, the laptop induces currents that are within 34.2% to 49.8% ICNIRP recommendations, but not negligible, to the adult's body and to the fetus (in pregnant women). On the contrary, the power supply induces strong intracorporal electric current densities in the fetus and in the adult subject, which are respectively 182–263% and 71–483% higher than ICNIRP 98 basic restriction recommended to prevent adverse health effects. Laptop is paradoxically an improper site for the use of a LTC, which consequently should be renamed to not induce customers towards an improper use.

Modelling the very high energy flare of 3C 279 using one-zone leptonic model

We model the simultaneous observations of the flat spectrum radio quasar 3C 279 at radio, optical, X-ray and very high energy (VHE) gamma ray energies during 2006 flare using a simple one zone leptonic model. We consider synchrotron emission due to cooling of a non-thermal electron distribution in an equipartition magnetic field and inverse Compton emission due to the scattering off synchrotron photons (SSC) and external soft photons (EC) by the same distribution of electrons. We show that the VHE gamma ray flux cannot be explained by SSC process thereby suggesting the EC mechanism as a plausible emission process at this energy. The EC scattering of BLR photons to VHE energies will be in Klein-Nishina regime predicting a steep spectrum which is contrary to the observations. However the infrared photons from the dusty torus can be boosted to VHE energies with the scattering process remaining in the Thomson regime. Though EC process can successfully explain the observed VHE flux, it require a magnetic field much lower than the equipartition value to reproduce the observed X-ray flux. Hence we attribute the X-ray emission due to SSC process. We derive the physical parameters of 3C 279 considering the above mentioned emission processes. In addition we assume the size of emission region constrained by a variability timescale of one day. This model can successfully reproduce the broadband spectrum of 3C 279 but predicts substantially large flux at MeV-GeV energies.

ANATOMY OF A SOLAR FLARE: MEASUREMENTS OF THE 2006 DECEMBER 14 X-CLASS FLARE WITH GONG,HINODE, ANDRHESSI

Some of the most challenging observations to explain in the context of existing flare models are those related to the lower atmosphere and below the solar surface. Such observations, including changes in the photospheric magnetic field and seismic emission, indicate the poorly understood connections between energy release in the corona and its impact in the photosphere and the solar interior. Using data from Hinode, TRACE, RHESSI, and GONG we study the temporal and spatial evolution of the 2006 December 14 X-class flare in the chromosphere, photosphere, and the solar interior. We investigate the connections between the emission at various atmospheric depths, including acoustic signatures obtained by time-distance and holography methods from the GONG data. We report the horizontal displacements observed in the photosphere linked to the timing and locations of the acoustic signatures we believe to be associated with this flare, their vertical and horizontal displacement velocities, and their potential implications for current models of flare dynamics.

The close classical T Tauri binary V4046 Sgr: complex magnetic fields and distributed mass accretion

We report here the first results of a multi-wavelength campaign focussing on magnetospheric accretion processes within the close binary system V4046 Sgr, hosting two partly-convective classical T Tauri stars of masses ~0.9 Msun and age ~12 Myr. In this paper, we present time-resolved spectropolarimetric observations collected in 2009 September with ESPaDOnS at the Canada-France-Hawaii Telescope (CFHT) and covering a full span of 7d or ~2.5 orbital/rotational cycles of V4046 Sgr. Small circularly polarised Zeeman signatures are detected in the photospheric absorption lines but not in the accretion-powered emission lines of V4046 Sgr, thereby demonstrating that both system components host large-scale magnetic fields weaker and more complex than those of younger, fully-convective cTTSs of only a few Myr and similar masses. Applying our tomographic imaging tools to the collected data set, we reconstruct maps of the large-scale magnetic field, photospheric brightness and accretion-powered emission at the surfaces of both stars of V4046 Sgr. We find that these fields include significant toroidal components, and that their poloidal components are mostly non-axisymmetric with a dipolar component of 50-100G strongly tilted with respect to the rotation axis; given the similarity with fields of partly-convective main-sequence stars of similar masses and rotation periods, we conclude that these fields are most likely generated by dynamo processes. We also find that both stars in the system show cool spots close to the pole and extended regions of low-contrast, accretion-powered emission; it suggests that mass accretion is likely distributed rather than confined in well defined high-contrast accretion spots, in agreement with the derived magnetic field complexity.

Measurement of the extremely low frequency (ELF) magnetic field emission from a ship

The electromagnetic (EM) fields radiating from a ship are widely recognized as important components of underwater detection. Galvanic currents flowing in the water around the hull and in the hull generate an underwater electric field. This field is responsible for the extremely low frequency (ELF) EM emission. The rotation of the shaft(s) modulates the galvanic current passing through the shaft-bearing-hull and thus an ELF EM signal is generated into the water. The ELF EM signal from ships was analyzed using the cross wavelet transform and wavelet coherence. The phase angle statistics demonstrated the presence of an additional ELF magnetic field component that was identified as being generated by a rotating vertical permanent magnet. The only vertical part of the ship rotating with the same frequency as the shaft is the nickel aluminum bronze propeller, which contains 3–5% iron. The paper presents the measurements and the investigation methodology that led to the separation of an additional ELF component, and to the calculation of the magnetic moment that caused it.

THE DISCOVERY OF A STRONG MAGNETIC FIELD AND COROTATING MAGNETOSPHERE IN THE HELIUM-WEAK STAR HD 176582

We report the detection of a strong, reversing magnetic field and variable H-alpha emission in the bright helium-weak star HD 176582 (HR 7185). Spectrum, magnetic and photometric variability of the star are all consistent with a precisely determined period of 1.5819840 +/- 0.0000030 days which we assume to be the rotation period of the star. From the magnetic field curve, and assuming a simple dipolar field geometry, we derive a polar field strength of approximately 7 kG and a lower limit of 52 degrees for the inclination of the rotation axis. However, based on the behaviour of the H-alpha emission we adopt a large inclination angle of 85 degrees and this leads to a large magnetic obliquity of 77 degrees. The H-alpha emission arises from two distinct regions located at the intersections of the magnetic and rotation equators and which corotate with the star at a distance of about 3.5 R* above its surface. We estimate that the emitting regions have radial and meridional sizes on the order of 2 R* and azimuthal extents (perpendicular to the magnetic equator) of less than approximately 0.6 R*. HD 176582 therefore appears to show many of the cool magnetospheric phenomena as that displayed by other magnetic helium-weak and helium-strong stars such as the prototypical helium-strong star sigma Ori E. The observations are consistent with current models of magnetically confined winds and rigidly-rotating magnetospheres for magnetic Bp stars.

Ground observation of electromagnetic emissions related to clusters of earthquakes

Ultra-low frequency (ULF) and very low frequency (VLF) data obtained from three ground-based experiments at Agra station (latitude 27.2° N, longitude 78.0° E) in India, namely measurement of ULF magnetic field emissions using a three-component search coil magnetometer, the vertical component of VLF electric field emissions with a borehole antenna, and the phase and amplitude of fixed frequency VLF transmitter signals using an Absolute Phase and Amplitude Logger (AbsPAL) receiver, were analysed in search of possible precursors of two major seismic activities that occurred in Sumatra (Indonesia) during the post-tsunami period between January and April 2005. These two major seismic events occurred as clusters of earthquakes during 27–29 January and 28–30 March 2005. The results show that, apart from the borehole antenna, all the experiments showed precursors due to these clusters of earthquakes. Such precursors were not seen in the case of isolated large-magnitude earthquakes. Furthermore, the precursory duration was influenced by a magnetic storm that occurred about a week before the clusters. The mechanism of ULF propagation to long distances between Sumatra and Agra and perturbations in the ionosphere before the clusters are discussed.

Measurements of Magnetic Field Emission of Various Digital Circuit Layouts

Signal or power to ground traces on a printed circuit board (PCB) of digital products may act as an efficient loop antenna radiating magnetic field when the length is greater than the wavelength of the high frequency current. Employment of proper routing of the return current path, filtering and damping resistor is best practices in the design criteria to minimise sources of electromagnetic emission at PCB level. It is important to indicate that the use of guard traces, filtering at supply network of critical component and damping resistor on signal traces can be the options of emission reduction techniques on double sided assemblies as it will reduce the emission level. In this paper, three double sided test boards are developed to evaluate the impact of the aforementioned mitigation methods on near magnetic field emission. The magnetic field distributions over each layout are measured in order to reveal the profile of radiation to gain further understanding on the net current distribution on the traces of the digital circuit. It is seen that by proper design of return current path, the magnetic field is reduced by average of 16.5 dB.

Non-stationary dynamo and magnetospheric accretion processes of the classical T Tauri star V2129 Oph

We report here the first results of a multi-wavelength campaign focussing on magnetospheric accretion processes of the classical TTauri star (cTTS) V2129Oph. In this paper, we present spectropolarimetric observations collected in 2009 July with ESPaDOnS at the Canada-France-Hawaii Telescope (CFHT). Circularly polarised Zeeman signatures are clearly detected, both in photospheric absorption and accretion-powered emission lines, from time-series of which we reconstruct new maps of the magnetic field, photospheric brightness and accretion-powered emission at the surface of V2129Oph using our newest tomographic imaging tool - to be compared with those derived from our old 2005 June data set, reanalyzed in the exact same way. We find that in 2009 July, V2129Oph hosts octupolar & dipolar field components of about 2.1 & 0.9kG respectively, both tilted by about 20deg with respect to the rotation axis; we conclude that the large-scale magnetic topology changed significantly since 2005 June (when the octupole and dipole components were about 1.5 and 3 times weaker respectively), demonstrating that the field of V2129Oph is generated by a non-stationary dynamo. We also show that V2129Oph features a dark photospheric spot and a localised area of accretion-powered emission, both close to the main surface magnetic region (hosting fields of up to about 4kG in 2009 July). We finally obtain that the surface shear of V2129Oph is about half as strong as solar. From the fluxes of accretion-powered emission lines, we estimate that the observed average logarithmic accretion rate (in Msun/yr) at the surface of V2129Oph is -9.2+-0.3 at both epochs, peaking at -9.0 at magnetic maximum. It implies in particular that the radius at which the magnetic field of V2129Oph truncates the inner accretion disc is 0.93x and 0.50x the corotation radius in 2009 July and 2005 June respectively.

A Correlative Study of Geomagnetic Storms Associated with Solar Wind and IMF Features During Solar Cycle 23

A geomagnetic storm is a global disturbance in Earth's magnetic field usually occurred due to abnormal conditions in the interplanetary magnetic field (IMF) and solar wind plasma emissions caused by various solar phenomenon. Furthermore the magnitude of these geomagnetic effects largely depend upon the configuration and strength of potentially geo-effective solar/interplanetary features. In the present study the identification of 220 geomagnetic storms associated with disturbance storm time (Dst) decrease of more than -50 nT to -300 nT, have been made, which are observed during 1996-2007, the time period spanning over solar cycle 23. The study is made statistically between the Dst strength (used as an indicator of the geomagnetic activity) and the peak value obtained by solar wind plasma parameters and IMF B as well as its components. We have used the hourly values of Dst index and the wind measurements taken by various satellites. Our results inferred that yearly occurrences of geomagnetic storms are strongly correlated with 11-year sunspot cycle. We observed that IMF B is highly geo-effective during the main phase of magnetic storms, while it more significant at the time of storm peak, which is further contributed by southward component of IMF Bz, substantiating earlier findings. The correlation between Dst and wind velocity is higher, as compared with IMF Bz and ion density. It has been verified that geomagnetic storm intensity is correlated well with the total magnetic field strength of IMF better than with its southward component.