Equivalent Currents on an Anisotropic Material Backed by a Metal Surface and Their Relation

Based on a first-order state-vector differential equation representation of Maxwell's equations, an analytical formulation is derived for the equivalent currents on an anisotropic material backed by a metal surface, and the relation between two currents is also considered. These expressions are degenerated into the common forms for some simple cases. This effort will provide the theoretical preparation for the approximate calculation of electromagnetic scattering from a conducting object coated by an anisotropic material.

Electric Potential in a Dielectric Sphere Head Produced by a Time-Harmonic Equivalent Current Dipole

A time-harmonic equivalent current dipole model is proposed to simulate EEG source which deals with the problem concerning the capacitance effect. The expressions of potentials in both homogeneous infinite dielectric medium and dielectric sphere on the electroquasistatic condition are presented. The potential in a 3-layer inhomogeneous spherical head is computed by using this model. The influences on potential produced by time-harmonic character and permittivity are discussed. The results show that potentials in dielectric sphere are affected by frequency and permittivity.

Improved method to derive equivalent current systems from global MHD simulations

Derivation of equivalent current systems(ECS)from a global magnetospheric magnetohydrodynamics(MHD)model is very useful in studying magnetosphere-ionosphere coupling,ground induction effects,and space weather forecast.In this study we introduce an improved method to derive the ECS from a global MHD model,which takes account of the obliqueness of the magnetic field lines.By comparing the ECS derived from this improved method and the previous method,we find that the main characteristics of the ECS derived from the two methods are generally consistent with each other,but the eastward-westward component of the geomagnetic perturbation calculated from the ECS derived from the improved method is much stronger than that from the previous method.We then compare the geomagnetic perturbation as a function of the interplanetary magnetic field(IMF)clock angle calculated from the ECS derived from both methods with the observations.The comparison indicates that the improved method can improve the performance of the simulation.Furthermore,it is found that the incomplete counterbalance of the geomagnetic effect produced by the ionospheric poloidal current and field-aligned current(FAC)contributes to most of the eastward-westward component of geomagnetic perturbation.

Relationship Between Noise Figure and Equivalent Input Noise Current Spectral Density for Optical Receiver Design

Based on the equivalent circuit model of a two-port optical receiver front-end,the relationship between the equivalent input noise current spectral density and the noise figure is analyzed. The derived relationship has universal validity for determining the equivalent input noise current spectral density for optical receiver designs, as verified by measuring a 155Mb/s high-impedance optical receiver front.end. Good agreement between calculated and simulated results has been achieved.

Application of the method of equivalent edge currents to composite scattering from the cone-cylinder above a dielectric rough sea surface

Compared with scattering from a rough surface only, composite scattering from a target above a rough surface has become so practical that it is a subject of great interest. At present, this problem has been solved by some numerical methods which will produce an enormous calculation amount. In order to overcome this shortcoming, the reciprocity theorem （RT） and the method of equivalent edge currents （MEC） are used in this paper. Due to the advantage of RT, the difficulty in computing the secondary scattered fields is reduced. Simultaneously, MEC, a high-frequency method with edge diffraction considered, is used to calculate the scattered field from the cone-cylinder target with a high accuracy and efficiency. The backscattered field and the polarization currents of the rough sea surface are evaluated by the Kirchhoff approximation （KA） method and physical optics （PO） method, respectively. The effects of the backscattering radar cross section （RCS） and the Doppler spectrum on the size of the target and the windspeed of the sea surface for different incident angles are analysed in detail.

Application of improved equivalent edge currents in synthetic aperture radar imaging

Target modeling and scattering function calculating are important prerequisites and groundwork for the synthetic aperture radar（SAR） imaging simulation.According to the difficult problems that normal methods cannot calculate the scattering function of electrically large object under the condition to wideband,an effective method of improved equivalent edge currents is presented and applied to SAR imaging simulation for the first time.This method improves calculating velocity and has relatively high precision.The concrete steps of applying the method are given.By way of the simulation experiment,the effectiveness of the method is verified.

THEORETICAL INVESTIGATION ON BY-ONLY-CURRENT ELECTROMAGNETIC SEPARATION OF INCLUSION FROM MOLTEN METALS

The electromagnetic field under applied AC and DC current in round and rectangular pipe was systematically investigated, then a concept of 'equivalent current density' was proposed for evaluating the inhomogeneous electromagnetic pinch force, and the mono-component removal efficiency and the overall removal efficiency of inclusion were formulated. It is founded that flat pipe is superior to round pipe for the electromagnetic removal of inclusion, and DC current can get a higher removal efficiency than A C current due to absence of skin phenomenon. Under usual condition, a removal efficiency of 52% for 10μm inclusion or more than 92% for 20μm inclusion can be achieved by imposing a current density of 3×106A/m2 in a flat pipe.

A study on the multi-componentsubstrom current

A new technique of eigen mode analysis, Method of Natural Orthogonal Components (MNOC) is used to analyze the ionospheric equivalent current systems obtained on the basis of magnetic data at six meridian magnetometer chains in the northern hemisphere during March 17 19, 1978. The results show that the whole current pattern for any given instant consists of a few eigen modes with different intensities. The first eigen mode exhibits a two cell current construction, characterizing the large scale magnetospheric convection and directly driven process, while the second eigen mode shows a concentrated westward electrojet at midnight sector, characterizing the substorm current wedge and the loading unloading process. The first mode consistently exists whenever during quiet periods or at substorms, and its intensity increases from the beginning of the growth phase of substorms, then quickly intensifies in the expansion phase, followed by a gradual decrease in the recovery phase. On the other hand, the intensity of the second mode remains to be near zero during both quiet time and the growth phase of substorms. Its rapid enhancement occurs in the expansion phase. These characteristics in the current patterns and the intensity variations coincide with the defined physical processes of the directly driven and loading unloading components.

Analysis of S^(p)_(q) current systems by using corrected geomagnetic coordinates

The S^p_q equivalent current system of the quiet day geomagnetic variation in the polar region is very complicated. It is composed of several currents, such as the ionospheric dynamo current and the auroral electrojet caused by the field aligned current. S p q is unsymmetrical in both polar regions. In this paper, the S p q current systems are analyzed in the corrected geomagnetic coordinates (CGM) instead of the conventional geomagnetic coordinates (GM), and the symmetries of the S p q current in different systems are compared. Then the causes of S p q asymmetry in the GM coordinates are discussed; the effects of each component in S p q are determined.

The Principle of Calibration Using the Ionic Current——A New Calibration Method for Electro-Magnetic Flowmeters

An equivalent relationship between electro magnetic flowmeters (EMFs) and the Hall effect is discussed in principle and three equivalent conclusions about their measuring equations are derived. Thereby,the calibration using the ionic current (CUIC) is introduced to the calibration of EMFs in a special Hall effect system. A basic system with these equations is specially given and discussed for realizing the method. Two key points about CUIC are proved by a simple experiment.

Performance enhancement of CMOS terahertz detector by drain current

In this paper, we study the effect of the drain current on terahertz detection for Si metal-oxide semiconductor fieldeffect transistors（MOSFETs） both theoretically and experimentally. The analytical model, which is based on the smallsignal equivalent circuit of MOSFETs, predicts the significant improvement of the voltage responsivity Rv with the bias current. The experiment on antennas integrated with MOSFETs agrees with the analytical model, but the Rv improvement is accompanied first by a decrease, then an increase of the low-noise equivalent power（NEP） with the applied current. We determine the tradeoff between the low-NEP and high-Rv for the current-biased detectors. As the best-case scenario, we obtained an improvement of about six times in Rv without the cost of a higher NEP. We conclude that the current supply scheme can provide high-quality signal amplification in practical CMOS terahertz detection.

Changes of auditory evoked magnetic fields in patients after acute cerebral infarction using magnetoencephalography

Auditory evoked magnetic fields were recorded from 15 patients with acute cerebral infarction and 11 healthy volunteers using magnetoencephalography.The auditory stimuli of 2 kHz pure tone were binaurally presented with an interstimulus interval of 1 second.The intensity of stimuli was 90 dB and the stimulus duration was 8 ms.The results showed that the M100 was the prominent response, peaking approximately 100 ms after stimulus onset in all subjects.It originated from the area close to Heschl’s gyrus.In the patient group,the peak latency of M100 responses was significantly prolonged,and the mean strength of equivalent current dipole was significantly smaller in the affected hemisphere.The three-dimensional inter-hemispheric difference of the M100 positions was increased in the patient group.Our experimental findings suggested that impairment of cerebral function in patients with acute ischemic stroke can be detected using magnetoencephalography with the higher spatial resolution and temporal resolution.Magnetoencephalography could provide objective and sensitive indices to estimate auditory cortex function in patients with acute cerebral infarction.

CHARACTERISTICS OF Sq VARIATION OF GEOMAGNETIC FIELD AT THE GREAT WALL STATION, ANTARCTICA IN WINTER

In this paper the characteristics of Sq variation of geomagnetic field in the region of the Chinese Great Wall Station (CGWS), Antarctica, in winter are analyzed from geomagnetic data obtained at the Geomagnetic Observatory of CGWS. The result enables us to reveal the following aspects: (1) The pattern of Sq variation at CGWS in early (Apr.) and Late winter (Sep.) is similar to that at Beijing Geomagnetic Observatory (BJO) at the middle latitude in the Northern Hemisphere. It may be controlled by the midlatitudinal ionospheric dynamo current. Amplitude of Sq variation is very small, and the harmonics in 8 hours or shorter periods in midwinter (June and July) is predominant because of the decreased effect of solar ultraviolet radiation and the dominant geomagnetic disturbance at high latitudes. (2) The vectors of Sq-equivalent current in the daytime are about five times more than that in the night. The direction of the vectors is clockwise in the daytime (08-15h) and counterclockwise in the night in early and late winter. Both of the vectors are very small because of the effect of the current density in the ionosphere is relatively weak in midwinter. The direction of vectors of Sq-equivalent current at CGWS in early and late winter is different from that in midwinter. It may be affected by the ionospheric current and field-aligned current in the polar region.

Analysis on the effectiveness of decoupling capacitor on mitigating radiated emission from power ground planes by BEM

The radiation emission （RE） of multilayer primed circuit board （PCB） will cause electromagnetic compatibility problem. An efficient numerical method for evaluating the effectiveness of decoupling capacitors in reducing RE from power ground （P/G） planes in PCB was presented. A two-dimensional boundary-element method （BEM） was used to establish the radiation model. Then, the RE was calculated by equivalent magnetic current of edge field around P/G planes. Furthermore, the radiation and input impedance of P/G planes mounted decoupling capacitors were calculated for frequency up to 5 GHz The results were compared to those of the case without decoupling capacitors. It shows that the decoupling capacitors can effectively decrease RE except for anti-resonant frequency. At higher frequencies, the decoupling effectiveness mainly depends on the parasitic inductance of capacitor pin rather than the value.