Specific features of ballistic electron transport in double-level open systems in a large-amplitude high-frequency electric field

Analytical expressions for electron coefficients of transmission and reflection in a large-amplitude high-frequency electric field, with a frequency close to resonance, for asymmetric double- and triple-barrier resonant tunneling structures with thin high barriers forming open two-level systems are reported. The dependences of the width and shape of resonant levels on the high-frequency field amplitude are investigated. It is shown that, in these structures there are almost always conditions at which nonresonant scattering channels near the quantum levels can become absolutely transparent.     

Reducing the Electric Field in Coil Systems Used for Environmental Research

Series resonant coil systems are being used to study the effects of ELF magnetic fields on living systems. High inductive voltages generate electric fields that prevent the separation of magnetic and electric field effects. These electric fields can be reduced by using multiple capacitor banks and connecting the coils and capacitors so that the electric fields cancel each other.     

The absorption and coupling of an electromagnetic wave incident ona microstrip circuit with superstrate

The absorption of an electromagnetic wave incident on a microstrip circuit covered with a dielectric layer is studied. The exact analytical expression for the plane-wave reflection coefficient at the air-superstrate interface of a four-layer model for a superstrate-loaded microstrip circuit is given. Numerical results illustrating the power absorption by the microstrip circuit and the electric and magnetic fields on the surface of the circuit as a function of wave frequency, superstrate thickness, superstrate permittivity, and incident angle are presented. It is found that the power absorption by the circuit at resonant frequencies increases with increasing superstrate permittivity. Higher superstrate thickness and permittivity can both cause more resonant power absorption peaks in the frequency spectrum. Significant intensities of electric or magnetic fields can also exist on the surface of the circuit for almost all the frequencies, which may couple to the circuit and cause malfunctions or interference. Details of the numerical results are presented     

Piezoelectric effects in strained layer heterostructures grown on novel index substrates

III–V and II–VI semiconductors are piezoelectric and therefore electric fields can be generated in strained layer heterostructures formed from these materials. The strain induced electric fields depend on the symmetry of the strain, which in turn depends on the orientation of the substrate on which the heterostructure is grown. For strain generated electric fields to occur in a zincblende structure semiconductor, the strain must distort the angles of the cubic unit cell away from 90°. Strains in (100) oriented heterostructures do not distort the 90° angles of the cubic unit cell and no electric fields are generated. However, for other substrate orientations, electric fields can be generated in the strained layers. These electric fields can lead to large changes in the optical properties of the heterostructure which can be externally. modulated to.make, for example, electro-optic devices. They can also cause charge accumulation which can be used in field effect transistor and resonant tunneling structures.     

Resonant modes of a concentric spherical cavity with conicallystratified medium

An analysis on electromagnetic fields of a cavity formed by two concentric conducting spheres with a conically stratified medium is presented in this paper. Angular transmission formulation and the radial eigenfunction expansion are used to formulate the field components. Boundary matching methods are applied to obtain the characteristic equations containing various infinite series of spherical Hankel functions and Legendre functions of complex order for resonant frequencies. The first two resonant frequencies and field expansion coefficients are determined numerically. The distribution pattern of angular field components and the forms of typical electric field lines and magnetic field lines for the first resonant fields are also indicated     

用改进基函数分析缝隙阵频率选择表面电磁特性

提出了一组有效的改进基函数用于分析缝隙阵频率选择表面的电磁传输特性。规则的中心连接和环形两种类型频率选择单元可以划分为直线段和弯曲段，切向电场基函数在直线段按照波导模式展开，而在弯曲段幅值不变且连续变化。以Y形和六边环形缝隙阵频率选择表面结构作为算例，应用较少的基函数和Floquet模预测的频率响应曲线与试验结果吻合得很好，与使用传统的基函数相比，谐振频率不随Floquet模数的增加而变动，具有良好的稳定性，同时计算时间大大减少。     

Resonant scattering from weak fluctuations in plane stratified dielectric media

The distorted wave Born approximation (DWBA) breaks down near points of vanishing permittivity in fluctuating media. For plane stratified media, a modified DWBA theory based on a single realization of propagating magnetic fields rather than electric fields adequately treats resonant scattering from points of vanishing permittivity.     

The insulated conductor as a scattering antenna in a relatively dense medium

A simple formula is derived for the current induced in an insulated conducting cylinder when embedded in an isotropic homogeneous dissipative medium and excited by a periodic electric field with uniform amplitude and phase along its axis. The currents on electrically short, resonant, and terminated insulated conductors are discussed.     

Equations of motion for a free-electron laser with an electromagnetic pump field and an axial electrostatic field

The equations of motion for a free-electron laser (FEL) with an electromagnetic pump field and a static axial electric field are derived using a Hamiltonian formalism. Equations governing the energy transfer between the electron beam and each of the electromagnetic fields are given, and the phase shift for each of the electromagnetic fields is derived from a linearized Maxwell wave equation. The relation between the static axial electric field and the resonant phase is given. Laser gain and the fraction of the electron energy converted to photon energy are determined using a simplified resonant particle model. These results are compared to those of a more exact particle simulation code.     

Electric current and electric field induced in the human body whenexposed to an incident electric field near the resonant frequency

The electric field and current density induced in the human body when this is exposed to electric fields near the resonant frequency, 53 MHz, are determined analytically. Since this frequency range includes an important amateur radio band of 50-60 MHz and exposure to electric fields at this frequency has been shown to be hazardous, the study has a specific motivation. A cylindrical model of the body is used to derive formulas for the total axial current and current density induced in the body subject to skin effect. Tabulations and graphical representations illuminate the results     

Ultrashort electrical pulses open a new gateway into biological cells

An electrical model for biological cells predicts that for pulses with durations shorter than the charging time of the outer membrane, there is an increasing probability of electric field interactions with intracellular structures. Experimental studies in which human cells were exposed to pulsed electric fields of up to 300-kV/cm amplitude, with durations as short as 10 ns, have confirmed this hypothesis. The observed effects include the breaching of intracellular granule membranes without permanent damage to the cell membrane, abrupt rises in intracellular free calcium levels, and enhanced expression of genes. At increased electric fields, the application of submicrosecond pulses induces apoptosis (programmed cell death) in biological cells, an effect that has been shown to reduce the growth of tumors. Possible applications of the intracellular electroeffect are enhancing gene delivery to the nucleus, controlling cell functions that depend on calcium release (causing cell immobilization), and treating tumors.     

Determination of Power Absorption in Man Exposed to High Frequency Electromagnetic Fields by Thermographic Measurements on Scale Models

When the body of man, small compared to a wavelength, is exposed to high frequency (HF) electromagnetic (EM) fields, the absorbed power density patterns and total absorbed power may be approximated by the simple superposition of the internal electric fields obtained from the quasistatic coupling characteristics of the electric and magnetic field components determined independently. These characteristics were obtained for full scale man by thermographic studies of power absorption in scale models of man exposed to fields at frequencies scaled up inversely proportional to the model size. A VHF resonant cavity was used to provide the necessary field strengths for producing measurable power absorption patterns under simulated HF exposure conditions. The results indicate that peak power absorption densities as high as 5.63 W/kg can be produced in man exposed to 10 mW/cm2 31 MHz radiation fields. The results show that the absorption decreases as the square of the frequency as predicted by theory for frequencies below 31 MHz.     

垂直电偶极子在地-电离层波导中场的球级数解

在非理想导电地面与电离层条件下,我们导出了ELF/SLF垂直电偶极子在球形地-电离层壳体中产生的电磁场的球谐级数表达式,采用一种加速收敛算法,算出了波导中的电磁场分布.根据计算结果,在SLF频段,地面与电离层之间的电磁场可理解为二个"行波"的叠加,且与SLF频段的球面二阶近似算法计算结果吻合很好.在ELF频段,壳体中的电磁场是驻波,其频率变化规律能正确反映出"舒曼"谐振现象.     

Resonance propagation of electrons through three-barrier structures in a two-frequency electric field

The solution of the Schrödinger equation that describes resonance transitions between three equidistant quantum levels in asymmetric three-barrier resonance-tunnel structures in a high one-frequency electric field is extended to the case of differently separated levels and a two-frequency field, with the frequencies corresponding to resonance transitions in each of the coupled quantum wells. It is shown that, in the conditions of coherent electron transport, irrespective of the parameters of the structure, for any amplitude of the high resonance field in one well, there exists an amplitude of the resonance field in the other well such that the structure is absolutely transparent and most electrons (in the limiting case, all electrons) incident on the upper resonance level can emit two photons with different frequencies and leave the structure through the lower level with no intermediate interaction with phonons. The probability of the transitions substantially depends on the amplitudes of the fields and does not depend on the phase difference between the fields. It is found that the possibility exists of almost complete blocking of resonance transitions in one of the wells by a high-frequency field in the other well.     

The near field of dipole antennas, part I: Theory

The theoretical and experimental evaluation of the electromagnetic fields in the immediate vicinity of resonant dipole antennas is presented. This type of antenna is widely used with portable and mobile radio transmitters. The work presented herein has been motivated by the concern that future Radio Frequency Protection Guides with respect to human exposure to nonionizing electromagnetic radiation might be expressed strictly in terms of the intensity squared of the electric or magnetic fields. It is shown in the results that it is possible to detect relatively high intensity electromagnetic (EM) fields in close proximity to resonant dipoles even for very low levels of radiated power (1 mW and less). The paper is divided into a theoretical section and an experimental section because its goals are twofold. First, the formulas for the correct evaluation of the EM fields in the close proximity to dipole antennas are established. Second, it is shown that such EM fields, which can be theoretically predicted and experimentally verified with satisfactory accuracy, are indeed strong enough to violate proposed Radio Frequency Protection Guides even for very low levels of radiated power. Thus portable radios are rendered virtually useless, although the same guides permit exposures to much higher levels of power in the far field. Part I of the paper is essentially theoretical and expresses the fields near dipole antennas in terms of cylindrical waves, which lend themselves to closed form integration. The asymptotic expressions of some components of the field are particularly simple for close distances (in terms of wavelength) from the antenna. The correctness of the solution is checked by evaluating how closely boundary conditions are satisfied. Results have shown that previously used formulas for evaluating field intensity very near dipole antennas can give incorrect values.     

数字调制谐振式光纤陀螺中阶梯波复位误差的分析

谐振式光纤陀螺(R-FOG)是采用环形谐振腔来增强Sagnac效应的，其检测方案可以分为开环和闭环，在电路实现上，根据相位调制器控制信号的不同，又分为模拟调制和数字调制。相比而言，其数字闭环检测方案具有动态范围大、灵敏度高的特点。在数字调制的谐振式光纤陀螺中，其阶梯波的复位高度V2π是否精确，会对旋转角速度的测量和标度因数的线性度产生影响。从理论上分析了不精确的复位高度V2π对系统的影响，指出不精确的V2π将使谐振腔中的交叉耦合电场和直通耦合电场之间不会形成最佳相消干涉，从而产生误差。利用探测器输出总电场的表达式，以双频率调制的谐振式光纤陀螺为例，对引入的误差作了定量的数值计算，最后给出了克服误差的几种方法。     

Small Resonant Scatterers and Their Use for Field Measurements

A general formulation for the back-scattered field from loaded objects is given. It is shown that small resonant objects produce a much greater back-scattered field than small nonresonant ones. The theory is applied to short dipoles and small loops. The use of small resonant scatterers to measure electric and magnetic fields by scattering techniques is discussed. Resonant scatterers are found to have several advantages over nonresonant scatterers when used for field measurements.     

Protecting EFIE-based scattering computations from effects ofinterior resonances

A numerical method, based on the standard matrix formulation of the electric field integral equation (EFIE) for calculating the scattering from conducting bodies near resonant frequencies, is given for both stabilizing the numerical calculations and finding the form of the resonant fields. When this method is used along with a direct solution to the original matrix equation, it requires insignificant additional computation. An additional advantage of this approach is that it can easily be implemented in existing computer codes by using a single, standard but general, plug-in module     

Radiation from ring sources of electric or magnetic dipoles with different orientations in free space

Radiation from a horizontal ring of radial electric dipoles, the strength of which varies as exp (jn?), is calculated for an unbounded medium by the saddle-point method of approximation. The cylindrical components of the radiated fields due to ring sources composed of radial, angular and vertical electric or magnetic dipoles, the amplitude of which varies as cos n? (or sin n?), are presented in a tabular form.     

Superconducting microwave bandpass filter using spiral resonatorswith no air bridges

A very compact superconducting bandpass filter using spiral resonators has been designed and demonstrated. No air bridges are required, an important feature for superconductors. The electric and magnetic fields are such that errors in track width have relatively little effect on resonant frequency and resonator coupling