Equivalent dipole moment method to characterize magnetic fields generated by electric appliances: extension to intermediate frequencies of up to 100 kHz

A previously proposed simple method to characterize magnetic fields near electric appliances was extended to intermediate frequencies of up to 100 kHz. The method consists of identification of the magnetic dipole moment that is equivalent to a magnetic field source of an electric appliance and simple estimation of the magnetic field distribution around the appliance. In addition, frequency characteristics of the magnetic field were taken into account by considering the harmonic components in the magnetic-field waveform for both power frequency and intermediate frequency ranges. For the application of the method, a wide-frequency range (from power frequency to 100 kHz) magnetic-field measuring instrument was developed and applied to appliances that generate intermediate frequency magnetic fields, i.e., an induction heating cooker, a TV set, and a metal detector. The results revealed that the method is adequate to quantify the magnetic field near the electric appliances at frequencies of up to 100 kHz.     

Numerical study on an equivalent source model for inhomogeneous magnetic field dosimetry in the low-frequency range

A new equivalent numerical source model is proposed for efficient dosimetric investigations in the low-frequency range. This approach allows the reproduction of complicated inhomogeneous magnetic field distributions around electronic appliances with full generality (i.e., supports three-dimensional vector fields). This paper investigates the accuracy of the equivalent source model using the geometry-based numerical reference model of a current loop to simulate the magnetic field distribution of a real electronic appliance. Good agreement between the equivalent source model and the reference is obtained with regard to the magnetic field distribution and the induced electric current density in a homogeneous human body model, respectively.     

Equivalent source estimation based on the calculation of theelectric field from depth EEG data

This paper describes a method for the estimation of equivalent source position and strength based on the estimation of the electric field from depth electroencephalographic (EEG) data. The calculation method for the electric field is based on a tetrahedral geometry. The proposed approach for source parametrization is twofold. Firstly, the distribution of electrical energy by the squared norm of the electric field vector can give an estimate of the source position, without having to assume a dipole source. Secondly, the average electric field can be related to the dipole magnitude and orientation of the equivalent source. Simulation results demonstrate the potential usefulness of the method. The effects of noise and sampling, and the geometry of the measurement system (i.e., implanted electrodes) relative to the source are also investigated through simulations.     

Effect of torso boundaries on electric potential and magnetic fieldof a dipole

A numerical model of a human torso was used to study and compare the effect of outer torso, lung, and intracavitary blood mass boundaries on the body surface distribution of electric potential and normal component of magnetic field due to a single current dipole placed at various locations in the heart. Results are presented in the form of isopotential and isofield maps and are also compared to the maps of a dipole in a semi-infinite homogenous model in the context of single dipole inverse solutions. The inclusion of the boundaries has a large effect on the magnitudes of the maps and modest effects on their topology. The electric and magnetic maps show similar responses to the boundaries for X (leftward) and Y (upward) directed dipoles. The electric maps of Z (back-to-front) dipoles are comparatively unaffected by the boundaries, unlike the magnetic maps of Z dipoles, to which the outer boundary makes a substantial contribution. The results indicate electric and magnetic maps have complementary sensitivities for certain dipole components in the presence of realistic boundaries     

Low-frequency dosimetry of inhomogeneous magnetic fields using the coil source model and the household appliance

In this paper, the magnetic field properties and the dosimetry at ELF (50 Hz) are investigated using a coil model, which is prescribed in the European standard EN50366 (CENELEC) as a substitute source model for real household appliances. The accuracy of magnetic field vectors and values of the induced current density, which is achieved with the coil model, were compared with the results of two test appliances (a drilling machine and a hand mixer) obtained from the equivalent source model. It was demonstrated that the magnetic fields obtained (dominant component and strength) using the coil model and the real appliance show an agreement with each other with a maximum difference of 5 dB. The calculated induced current densities in the numerical human body models (homogeneous and anatomical body models) and the real appliances also show a good agreement with each other with a maximum difference by a factor of 1.6 (by the anatomical body model). Furthermore, the values of both field vectors and induced current density values calculated using the coil model were shown to be higher than those calculated in the case of the real appliances. Based on these results, the applicability of the coil model prescribed in EN50366 confirms that of the two applied test appliances.     

Analysis of TE scattering from dielectric cylinders using amultifilament magnetic current model

A moment solution is presented for the problem of transverse electric (TE) scattering from homogeneous dielectric cylinders. The moment solution uses fictitious filamentary magnetic currents to simulate both the field scattered by the cylinder and the field inside the cylinder and in turn point-matches the continuity conditions for the tangential components of the electric and magnetic fields across the cylinder surface. The procedure is simple to execute and is general in that cylinders of arbitrary shape and complex permittivity can be handled effectively. Metallic cylinders are treated as reduced cases of the general procedure. Results are given and compared with available analytic solutions, which demonstrate the very good performance of the procedure     

电偶极子和磁偶极子场分布相似性的一种解释

电偶极子电场与磁偶极子磁场具有相似的空间分布。然而,这种相似性并非显而易见：电偶极子由一对等量异号电荷组成,而磁偶极子则是一个电流回路。本文从矢量场边值问题的唯一性定理出发,得出了面散度源和面旋度源产生的矢量场分布的一种等价关系,进而对电偶极子电场与磁偶极子磁场空间分布的相似性进行了解释。     

A spatio-temporal dipole simulation of gastrointestinal magnetic fields

We have developed a simulation of magnetic fields from gastrointestinal (GI) smooth muscle. Current sources are modeled as depolarization dipoles at the leading edge of the isopotential ring of electrical control activity (ECA) that is driven by coupled cells in the GI musculature. The dipole moment resulting from the known transmembrane potential distribution varies in frequency and phase depending on location in the GI tract. Magnetic fields in a homogeneous volume conductor are computed using the law of Biot-Savart and characterized by their spatial and temporal variation. The model predicts that the natural ECA frequency gradient may be detected by magnetic field detectors outside the abdomen. It also shows that propagation of the ECA in the gastric musculature results in propagating magnetic field patterns. Uncoupling of gastric smooth muscle cells disrupts the normal magnetic field propagation pattern. Intestinal ischemia, which has been experimentally characterized by lower-than-normal ECA frequencies, also produces external magnetic fields with lower ECA frequencies.     

Spatio-temporal cortical source imaging of brain electrical activity by means of time-varying parametric projection filter

In the present study, we explore suitable spatio-temporal filters for inverse estimation of an equivalent dipole-layer distribution from the scalp electroencephalogram (EEG) for imaging of brain electric sources. We propose a time-varying parametric projection filter (tPPF) for the spatio-temporal EEG analysis. The performance of this tPPF algorithm was evaluated by computer simulation studies. An inhomogeneous three-concentric-spheres model was used in the present simulation study to represent the head volume conductor. An equivalent dipole layer was used to represent equivalently brain electric sources and estimated from the scalp potentials. The tPPF filter was tested to remove time-varying noise such as instantaneous artifacts caused by eyes-blink. The present simulation results indicate that the proposed time-variant tPPF method provides enhanced performance in rejecting time-varying noise, as compared with the time-invariant parametric projection filter.     

Estimating equivalent dipole polarizabilities for the inductive response of isolated conductive bodies

Away from a conductive body, secondary magnetic fields due to currents induced in the body by a time-varying external magnetic field are approximated by (equivalent) magnetic dipole fields. Approximating the external magnetic field by its value at the location of the equivalent magnetic dipoles, the equivalent magnetic dipoles' strengths are linearly proportional to the external magnetic field, for a given time dependence of external magnetic field, and are given by the equivalent dipole polarizability matrix. The polarizability matrix and its associated equivalent dipole location are estimated from magnetic field measurements made with at least three linearly independent polarizations of external magnetic fields at the body. Uncertainties in the polarizability matrix elements and its equivalent dipole location are obtained from analysis of a linearized inversion for polarizability and dipole location. Polarizability matrix uncertainties are independent of the scale of the polarizability matrix. Dipole location uncertainties scale inversely with the scale of the polarizability matrix. Uncertainties in principal polarizabilities and directions are obtained from the sensitivities of eigenvectors and eigenvalues to perturbations of a symmetric matrix. In application to synthetic data from a magnetic conducting sphere and to synthetic data from an axially symmetric elliptic conducting body, the estimated polarizability matrices, equivalent dipole locations, and principal polarizabilities and directions are consistent with their estimated uncertainties.     

Transmission through dielectric-filled slots in a conductingcylindrical shell of arbitrary cross section: TE case

A simple moment solution is summarized for the problem of electromagnetic transmission through dielectric-filled slots in a conducting cylindrical shell of arbitrary cross section. The system is excited by a plane-wave polarized transverse electric (TE) to the axis of the shell. The equivalence principle is used to replace the shell and the dielectric by equivalent electric and magnetic surface currents radiating into an unbounded medium. Two different sets of coupled integral equations involving the surface currents are obtained by enforcing the boundary conditions on the tangential components of the total electric and magnetic fields. The method of moments is used to solve the integral equations. Pulses are used for both expansion and testing functions. Special attention is paid to circular and rectangular shells. Results for shell surface current, the internal field, and the aperture field are presented. For the case of air dielectric filling, the results computed using the electric field and/or the magnetic field formulation are in very good agreement with published data. In general, it is observed that the effect of filling a slot with a dielectric is not predictable from a simple theory     

Method for determining the electric and magnetic polarizability ofarbitrarily shaped conducting bodies

The paper deals with polarization properties of arbitrarily shaped conducting bodies in quasistatic electric fields and quasisteady magnetic fields within the strong-skin-effect approximation. Based on measuring the capacitance (inductance) of a field-forming system before and after introducing an arbitrary conducting body into it, a method for determining its electric (magnetic) polarizability is proposed. The method permits one to find eigenvalues and directions of the principal axes of the polarizability tensors of any conducting body. The results obtained are useful in solving two practical problems of the electromagnetic compatibility: estimation of a measurement error induced by coupling the transducers of an electric and magnetic field to the conducting surfaces, and estimation of an additional field induced by coupling the objects to the field-forming system electrodes in electromagnetic susceptibility tests     

An Intercommunication Home Energy Management System with Appliance Recognition in Home Network

In present days there are wide varieties of household electric appliances along with different power consumption habits of consumers, making identifying electric appliances without presetting difficulty. This paper introduces smart appliance management system to recognize electric appliances in home networks, which uses sensing devices that measure current to calculate the power consumption of the appliances. The system will set the characteristics and categories of each electric appliance, and then uses the classifications of the electronic energy features in order to recognize different appliances. The system searches the cluster data while eliminating noise for recognition functionality and error detection mechanism or the electric appliances using the current clustering algorithm. Afterwards the recognition are used to build a control list of appliances on the platform to provide appliance intercommunication. Simultaneously, the household appliance automatic control services are integrated by the system to control appliances based on userspower consumption plans to realize a bidirectional monitoring services. In actual experiments, the proposed system achieves a recognition rate or 95% as well as successfully controls general household electric appliances in home network.     

Radial field retrieval in spherical scanning for currentreconstruction and NF-FF transformation

A near-field to far-field (NF-FF) transformation is addressed for the case of spherical scanning using equivalent magnetic currents (EMCs) and matrix methods. It is based on the decoupling of the field components and the iterative retrieval of the radial component of the electric field. The technique is applied for far-field calculation as well as for the estimation of the current distribution of the antenna under test (AUT) using spherical near-field facilities. Results from measured near-field data of several antennas are presented and compared to those of the analytical solution via a spherical wave mode expansion method     

Extended boundary condition integral equations for perfectly conducting and dielectric bodies: Formulation and uniqueness

The equivalence theorem is used to derive novel generalized boundary condition (GBC) integral equations for the tangential components of the electric and magnetic fields on the interfaces of a finite number of dielectric or conducting scatterers. Closed surface, plane, and line extended boundary conditions (EBC) equivalent to the GBC are introduced. The GBC integral equations can now be replaced by any of these EBC integral equations whose solutions are unique and easy to obtain numerically using the moment method. A perfectly conducting sphere and a dielectric sphere in the electrostatic field of two equal and opposite point charges are presented as simple examples of the general procedure.     

Planar near-field to far-field transformation using an array ofdipole probes

A method is presented for computing far-field antenna patterns from measured near-field data measured by an array of planar dipole probes. The method utilizes the near-field data to determine some equivalent magnetic current sources over a fictitious planar surface which encompasses the antenna. These currents are then used to find the far fields. The near-field measurement is carried out by terminating each dipole with 50 Ω load impedances and measuring the complex voltages across the loads. An electric field integral equation (EFIE) is developed to relate the measured complex voltages to the equivalent magnetic currents. The mutual coupling between the array of probes and the test antenna modeled by magnetic dipoles is taken into account. The method of moments with Galerkin's type solution procedure is used to transform the integral equation into a matrix one. The matrix equation is solved with the conjugate gradient-fast Fourier transformation (CG-FFT) method exploiting the block Toeplitz structure of the matrix. Numerical results are presented for several antenna configurations to show the validity of the method     

On the magnetic dipole representation of small loop antenna

The use of a magnetic dipole to represent a small loop antenna is examined by comparing their field components. Particular attention is paid to the dipole approximation in the near field, and curves are presented which allow an accurate and rapid assessment to be made of the error as a function of angle and distance from the loop. The curves, which apply to any loop with a circumference between 0.0001 λ and 0.1 λ, enable the correction to the dipole field to be estimated. The difference between the loop and magnetic dipole fields is expressed algebraically for large distances from the loop, and for near-axial angles.     

Air to undersea communication with magnetic dipoles

Simplified expressions are derived for the electromagnetic fields produced by a vertical or horizontal magnetic dipole (loop antenna) located in air above the sea. The expressions hold over the quasi-near range in both media subject to certain mild restrictions. The solutions are obtained by first applying the boundary conditions to determine the magnetic Hertz potentialbar{pi}^{ast}in the form of Sommerfeld integrals, and then relating these to two auxiliary integralsU, Vand their derivatives, asymptotic series for which are obtained by extending the work of Baños and Wesley. The horizontal magnetic dipole (loop in the vertical plane) is found to be superior to the vertically-oriented dipole of the same size and excitation from the point of view of field strength induced in the sea at large distances from the source. A comparison with previously published results for the electric dipole shows the magnetic dipole to be better, provided the number of turns in the loop exceeds a certain minimum. An approximate analysis on the basis of equal powers also shows the magnetic dipole to be better except for points near the outer rim of the quasi-near range, where the two types of dipoles are equivalent.     

Transient radiation field of a circular loop antenna

For a circular loop antenna excited by a frequency-hand-limited rectangular voltage pulse, the time variation of the electric field at remote points in various directions has been computed. The computations are for a loop of radiusbmade from wire of radiusa, for which the thickness parameterOmega = 2 ln (2pi b/a) = 15. The moment method was used in obtaining the current distribution on the loop due to each harmonic component in the excitation. Then the transient field is obtained by using the harmonic current distribution due to each frequency component of the exciting voltage pulse.     

电小线圈近场分析

天线的近场分析在近场通信(NFC)、电磁兼容(EMC)、阵列天线设计等领域越来越受到关注。准确高效的近场分析方法对于近场的分布控制和引导机制等有着重要的作用。本文针对典型天线磁偶极子(电小线圈)的近场进行了初步的理论研究,主要分析了磁偶极子的近场平均能量密度分布、有功功率和无功功率的关系和分布。并通过磁偶极子的场分量计算平均坡印廷矢量,从而定性分析了线圈"储能"和"辐射能量"的关系,同时根据平均坡印廷矢量给出了电小线圈的近场"储能"中能量流动的物理图像。本文还计算了磁偶极子的平均电场能量密度和平均磁场能量密度,并进一步分析了二者的分布以及比较了二者的大小关系。