An analysis of piecewise homogeneous dielectric rod antennas

The radiation characteristic of piecewise homogeneous dielectric rod antennas is studied by using the volume equivalence principle. Experimental results are presented for comparison.     

Electric field distribution for a surface

A closed form expression is obtained for the electric field distribution that results when a voltage is impressed on a system of surface wave interdigital electrodes. The conventional assumptions of weak piezoelectric coupling and of electrodes long compared with acoustic wavelength are made. Equivalence with previously reported results derived by a spatial harmonics method is explicitly demonstrated.     

Hall effect in a non homogeneous magnetic field

The purpose of this paper is to investigate the influence of a non homogenous magnetic field on the characteristics of a Hall generator. For a particular shape of the magnetic field strength the problem can be solved without further approximations by an integral equation technique. This offers the advantage that the problem can be analysed for extreme values of the non homogeneous component of the magnetic field. This fact is checked by means of the Hall voltage generated in a rectangular sample.     

Electric potential produced by a dipole in a homogeneous conducting sphere

The potential produced by a dipole in a homogeneous conducting sphere is useful in simulation study, and the current available solutions still suffer from some shortcomings. In this communication, a closed solution is developed for the precise calculation of the potential anywhere in the spherical model.     

横流CO2激光器大体积均匀放电的研究

根据磁场稳定气体放电的原理,设计了一套电极结构,对这种二轴正交式横流CO2激光器的放电特性进行了研究,获得了大体积均匀放电,放电注入功率为15kW。     

Optical transitions in a quantized cylindrical layer in the presence of a homogeneous electric field

Variations in the charge carrier energy spectrum in the presence of a transverse electric field in a cylindrical semiconductor layer are considered using the one-electron approximation. The explicit dependences of the Stark shift on an external field and on nanoradial sample dimensions are obtained. The absorption factors are calculated and the selection rules are obtained for both interband and intraband-intersubband optical transitions in the presence of an external electric field.     

Electric field bounds over a phased array aperture

In the following, a bound on the electric field magnitude existing over a phased array antenna is presented. Use of this bound in predicting the power handling capability of the array is discussed. It is shown that, although the overall array is large with respect to wavelength, the narrow beamwidth often required significantly affects the near field over the aperture and just outside the antenna. The result is compared to a previously existing bound obtained for a single rectangular aperture.     

Electric field of a transmission line over multilayered media

The two-dimensional Fourier transform is used to derive an expression for the electric field and impedance associated with a transmission line with a multilayered earth return. The expressions are based on a model of the earth which includes arbitrary horizontal stratification with differing resistivities and permeabilities. A method is proposed to extend the applicability of these results to conductors over multilayered media with varying permitivities such as semiconductor devices.     

Mathematical analysis of lead field expansions

The solution to the bioelectromagnetic inverse problem is discussed in terms of a generalized lead field expansion, extended to weights depending polynomially on the current strength. The expansion coefficients are obtained from the resulting system of equations which relate the lead field expansion to the data. The framework supports a family of algorithms which include the class of minimum norm solutions and those of weighted minimum norm, including FOCUSS (suitably modified to conform to requirements of rotational invariance). The weighted-minimum-norm family is discussed in some detail, making explicit the dependence (or independence) of the weighting scheme on the modulus of the unknown current density vector. For all but the linear case, and with a single power in the weight, a highly nonlinear system of equations results. These are analyzed and their solution reduced to tractable problems for a finite number of degrees of freedom. In the simplest magnetic field tomography (MFT) case, this is shown to possess expected properties for localized distributed sources. A sensitivity analysis supports this conclusion.     

Electric field induced ferroelectric-surface modification for high mobility organic field effect transistors

Inherent spontaneous polarization in ferroelectric-dielectric polymer PVDF-TrFE (Poly[(vinylidenefluoride-co-trifluoroethylene]) and an external electric field induced surface modification procedure are utilized to enhance organic field effect transistor (OFET) characteristics. The increase in the carrier mobility of the electric-field (EF) treated device correlates with the EF magnitude and evolution of dielectric microstructure and exhibits an enhancement beyond 300%. The enhanced interfacial transport property appears to have its origin in the dipolar orientation and nanostructure evolution at the interface.     

Electric field switching in a resonant tunneling diodeelectroabsorption modulator

The basic mechanism underlying electric field switching produced by a resonant tunneling diode (RTD) is analyzed and the theory compared with experimental results; agreement to within 12% is achieved. The electroabsorption modulator (EAM) device potential of this effect is explored in an optical waveguide configuration. It is shown that a RTD-EAM can provide significant absorption coefficient change, via the Franz-Keldysh effect, at appropriate optical communication wavelengths around 1550 nm and can achieve up to 28-dB optical modulation in a 200-μm active length device. The advantage of the RTD-EAM over the conventional reverse-biased p-n junction EAM, is that the RTD-EAM has, in essence, an integrated electronic amplifier and, therefore, requires considerably less switching power     

A deterministic particle method for the kinetic model of semiconductors: The homogeneous field model

We present a new particle method for the simulation of the semiconductor Boltzmann equation—the weighted particle method. This method differs from the Monte-Carlo method by the approximation of the collision operator—we allocate each particle a weight which varies in time according to the collision integral. This integral is evaluated by means of a quadrature formula, which does not require the use of random numbers. The aim of this paper is to show that this method gives accurate results on physically relevant problems. Linear as well as non-linear collision integrals can be handled the same way by this method. Precise representations of the distribution functions are available, which allow a good insight into the physical processes. In this paper, we only consider the homogeneous field model with an emphasis on the collision operator. Numerical results are presented with a comparison with the Monte-Carlo method.     

The boundary-residual method for three-dimensional homogeneous field problems with boundaries of arbitrary geometry

Boundary-residual methods are extended to include three-dimensional homogeneous field problems applicable to millimeter-wave problems. Their connection to pointmatching methods is shown, and the reason why pointmatching fails and boundary residual methods do not is explained. A numerical example is used to demonstrate the validity of these methods. A discussion of the limitations of these methods is also included.     

Electric field stimulation of excitable tissue

Examines the transmembrane voltage response of an unmyelinated fiber to a stimulating electric field from a point current source. For subthreshold conditions, analytic expressions for the transmembrane potential, v_m, are developed that include the specific effects of fiber-source distance, h, and time from the onset of the stimulus, T. Suprathreshold effects are determined for two examples by extending the analytical results with a numerical model. The v_m , response is a complex evolution in time, especially for small h, that differs markedly from the “activating function”. In general, the subthreshold response is a good predictor of the wave shape of the suprathreshold v_m but a poor predictor of its magnitude. The subthreshold response also is a good (but not a precise) predictor of the region where excitation begins     

Electric field distributions of waveguide arrays for local tumor hyperthermia

Total electric field distributions in muscle and fat tissues, due to colinear rectangular waveguide arrays at 2.45 GHz and 915 MHz were calculated. The effect of phase difference between incident phases on the field pattern is shown. Phase adjustment is capable of furnishing control of either field-size or focused-field performance of the multi-element, direct-contact applicator. The tissue-applicator junction is analyzed by means of the Generalized Scattering Matrix (GSM) of the generalized 2-port discontinuity, assuming that the lossy homogeneous tissue is immersed in a large waveguide. This method provides an exact calculation of multimodal fields, as well as reflection and coupling coefficients in the apertures.     

熔融石英的热及电场诱导机理

详细分析了熔融石英样品经热及电场诱导后 ,建立二阶极化率的机理。该机理表明 ,二阶极化率是由样品耗尽区中偶极子的定向和三阶极化率经强静电场作用共同形成的。在一般条件下诱导 ,前者是主要因素 ;在较高电压诱导时 ,后者是主要因素。推导了二阶极化率的表达式 ,并进行了数值计算。数值结果表明 ,在一般情况下 ,χ3 3 ( 2 ) 约 1pm/V ,χ3 3 ( 2 ) ∶χ3 1( 2 ) 约为 3。理论证明提高诱导的外加电压和选用Na和OH杂质浓度较大的石英材料能提高二阶极化率。     

长椭球介质人头模型中的场分布

文中给出一长椭球介质人头模型中的电磁场全波解。运用并矢格林函数和散射叠加原理 ,求解的电磁场表示为椭球矢波函数。导出了在人头模型中的耦合系数 ,最后给出了数字结果的讨论。     

Electric field integral equation formulation for a dynamic analysisof nonuniform microstrip multi-conductor transmission lines

A moment-method technique based on using a combined quasi-dynamic, dynamic, and asymptotic approach is presented for the analysis of nonuniform microstrip transmission lines and discontinuities. It uses the grounded dielectric slab Green's functions. The regions of validity of the quasi-dynamic and asymptotic approximations are determined in terms of the required accuracy in the Green's functions. Numerical examples are presented and compared with available data to check the accuracy of the technique     

Registration of head volume images using implantable fiducialmarkers

Describes an extrinsic-point-based, interactive image-guided neurosurgical system designed at Vanderbilt University, Nashville, TN, as part of a collaborative effort among the Departments of Neurological Surgery, Computer Science, and Biomedical Engineering. Multimodal image-to-image (II) and image-to-physical (IP) registration is accomplished using implantable markers. Physical space tracking is accomplished with optical triangulation. The authors investigate the theoretical accuracy of point-based registration using numerical simulations, the experimental accuracy of their system using data obtained with a phantom, and the clinical accuracy of their system using data acquired in a prospective clinical trial by 6 neurosurgeons at 4 medical centers from 158 patients undergoing craniotomies to respect cerebral lesions. The authors can determine the position of their markers with an error of approximately 0.4 mm in X-ray computed tomography (CT) and magnetic resonance (MR) images and 0.3 mm in physical space. The theoretical registration error using 4 such markers distributed around the head in a configuration that is clinically practical is approximately 0.5-0.6 mm. The mean CT-physical registration error for the: phantom experiments is 0.5 mm and for the clinical data obtained with rigid head fixation during scanning is 0.7 mm. The mean CT-MR registration error for the clinical data obtained without rigid head fixation during scanning is 1.4 mm, which is the highest mean error that the authors observed. These theoretical and experimental findings indicate that this system is an accurate navigational aid that can provide real-time feedback to the surgeon about anatomical structures encountered in the surgical field     

Electric field intensity at surface of a coronating wire above a ground plane

An assumption commonly used in the solution of the DC corona equations is that the electric field intensity at the coronating wire is always constant at the onset value. However, the validity of this assumption has been questioned in the literature. An algorithm in which this difficulty is alleviated is proposed.