An MPIE-MoM formulation incorporating equivalent volume currents

2003 ◽  
Author(s):  
Y.X. Liu ◽  
L.W. Li ◽  
T.S. Yeo ◽  
M.S. Leong ◽  
P.S. Kooi
Keyword(s):  
Volume Currents

scholarly journals Measuring MEG closer to the brain: Performance of on-scalp sensor arrays

2016 ◽  
Author(s):  
Joonas Iivanainen ◽  
Matti Stenroos ◽  
Lauri Parkkonen
Keyword(s):  
Sensor Arrays ◽  
Element Model ◽  
Magnetic Resonance Images ◽  
Field Pattern ◽  
Optically Pumped ◽  
Point Spread Functions ◽  
Field Patterns ◽  
Compartment Boundary ◽  
Volume Currents ◽  
Squid Magnetometers

AbstractOptically-pumped magnetometers (OPMs) have recently reached sensitivity levels required for magnetoencephalogra-phy (MEG). OPMs do not need cryogenics and can thus be placed within millimetres from the scalp into an array that adapts to the invidual head size and shape, thereby reducing the distance from cortical sources to the sensors. Here, we quantified the improvement in recording MEG with hypothetical on-scalp OPM arrays compared to a 306-channel state-of-the-art SQUID array (102 magnetometers and 204 planar gradiometers).We simulated OPM arrays that measured either normal (nOPM; 102 sensors), tangential (tOPM; 204 sensors), or all components (aOPM; 306 sensors) of the magnetic field. We built forward models based on magnetic resonance images of 10 adult heads; we employed a three-compartment boundary element model and distributed current dipoles evenly across the cortical mantle.Compared to the SQUID magnetometers, nOPM and tOPM yielded 7.5 and 5.3 times higher signal power, while the correlations between the field patterns of source dipoles were reduced by factors of 2.8 and 3.6, respectively. Values of the field-pattern correlations were similar across nOPM, tOPM and SQUID gradiometers. Volume currents reduced the signals of primary currents on average by 10%, 72% and 15% in nOPM, tOPM and SQUID magnetometers, respectively. The information capacities of the OPM arrays were clearly higher than that of the SQUID array. The dipole-localization accuracies of the arrays were similar while the minimum-norm-based point-spread functions were on average 2.4 and 2.5 times more spread for the SQUID array compared to nOPM and tOPM arrays, respectively.

Zur Stabilität zylindersymmetrischer Plasmakonfigurationen mit Volumenströmen

1958 ◽  
Vol 13 (11) ◽  
pp. 936-940 ◽  
Author(s):  
K. Hain ◽  
R. Lüst
Keyword(s):  
Current Distribution ◽  
Wave Length ◽  
Small Perturbations ◽  
Strong Concentration ◽  
Eigen Value ◽  
Eigen Values ◽  
The Stability ◽  
Volume Currents ◽  
Rates Of Growth ◽  
Plasma Configuration

The stability of cylindersymmetric plasma configuration with volume currents is investigated by the method of small perturbations. The problem is reduced to only one eigen-value differential equation of second order. Forspecial current distribution with relativly strong concentration to the axis the eigen-values are computed numerically. For this current distribution specially for long wave lengths instability shows up. The rates of growth for different kinds of pertubations are given as a function of the wave length.

Volume Currents in Forward and Inverse Magnetoencephalographic Simulations Using Realistic Head Models

2003 ◽  
Vol 31 (1) ◽  
pp. 21-31 ◽  
Author(s):  
Robert Van Uitert ◽  
David Weinstein ◽  
Chris Johnson
Keyword(s):  
Volume Currents

scholarly journals An Eigenmode Study of Nanoantennas from Terahertz to Optical Frequencies

Electronics ◽  
2021 ◽  
Vol 10 (22) ◽  
pp. 2782
Author(s):  
Konstantinos D. Paschaloudis ◽  
Constantinos L. Zekios ◽  
Georgios C. Trichopoulos ◽  
Filippos Farmakis ◽  
George A. Kyriacou
Keyword(s):  
Penetration Depth ◽  
Patch Antenna ◽  
State Of The Art ◽  
The State ◽  
Antenna Design ◽  
Surface Currents ◽  
Rectangular Patch ◽  
Full Wave ◽  
Volume Currents

In this work, we present a rigorous full-wave eigenanalysis for the study of nanoantennas operating at both terahertz (THz) (0.1–10 THz), and infrared/optical (10–750 THz) frequency spectrums. The key idea behind this effort is to reveal the physical characteristics of nanoantennas such that we can transfer and apply the state-of-the-art antenna design methodologies from microwaves to terahertz and optics. Extensive attention is given to penetration depth in metals to reveal whether the surface currents are sufficient for the correct characterization of nanoantennas, or the involvement of volume currents is needed. As we show with our analysis, the penetration depth constantly reduces until the region of 200 THz; beyond this point, it shoots up, requiring volume currents for the exact characterization of the corresponding radiating structures. The cases of a terahertz rectangular patch antenna and a plasmonic nanoantenna are modeled, showing in each case the need of surface and volume currents, respectively, for the antenna’s efficient characterization.

scholarly journals Magnetohydrodynamics of Sunspots

1990 ◽  
Vol 142 ◽  
pp. 139-148 ◽  
Author(s):  
N.O. Weiss
Keyword(s):  
Magnetic Field ◽  
Travelling Waves ◽  
Vertical Magnetic Field ◽  
Oscillatory Behaviour ◽  
Filamentary Structure ◽  
Numerical Investigations ◽  
Shallow Layer ◽  
Umbral Dots ◽  
Volume Currents ◽  
Secondary Bifurcations

Recent numerical investigations of fully compressible nonlinear magnetoconvection have clarified the nature of convection in sunspot umbrae. In a shallow layer with a strong vertical magnetic field oscillations give way to travelling waves as the Rayleigh number is increased but in a deep stratified layer oscillatory behaviour only appears after secondary bifurcations. This behaviour leads to a model that explains the formation of umbral dots. Penumbral structure is more difficult to explain owing to the apparent presence of adjacent horizontal and inclined fields in dark and bright filaments. The inner penumbra lies above a transition zone where volume currents are needed to maintain an overall static equilibrium; instabilities in this region may be responsible for filamentary structure in the penumbra as well as for fine structure at the umbral-penumbral boundary.

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