Response of an overhead wire near a NEMP simulator

The response of an overhead wire illuminated by a simulated nuclear electromagnetic pulse (NEMP) was experimentally investigated. The wire is 70 m long, 7 mm in diameter, and situated 5 m above the ground. It is located 20 m away from a hybrid-type EMP simulator. The simulator is a resistively loaded elliptical loop structure with its pulse generator located 20 m above the ground. The overhead wire is terminated with various combinations of short circuit, open circuit, and characteristic impedance at the two ends, and the current response is measured at one end and in the middle. The measured responses are compared with calculated values from available analytical models     

Propagation along a wire placed inside a cavity with an aperture: acomparison of measurements and transmission-line modeling (TLM)

There are many practical situations in which a signal propagates along a wire positioned inside an electromagnetic cavity which may or may not contain significant apertures. The paper considers such a situation and the effects which the cavity and any apertures have on a broadband signal propagating along that wire. Results are presented for the phase and magnitude response of the transmitted signal and for the fields produced in an aperture. Two complementary approaches have been used to determine the response, namely direct measurements and simulations using transmission-line modeling (TLM). Good agreement between measurements and simulations was observed     

Integral equation for the fields inside a dielectric cylinder immersed in an incidentE-wave

The scattering of a time-harmonicE-wave by a dielectric cylinder is solved by a single integral equation. Two alternatives are investigated to derive such a single integral equation. Interest is focused on the fields inside the dielectric. In this case the integral equation has only the incident electric field as its source term.     

The physical optics fields of an aperture on a perfectly conducting screen in terms of line integrals

The physical optics fields due to an aperture on a perfectly conducting screen are expressed in terms of line integrals over the boundary of the aperture. These line-integral representations have the same properties as the ones in terms of surface integrals over the aperture; in particular, they admit arbitrary, source distributions, and are continuous everywhere in the source-free half-space, including the geometric optics shadow boundary.     

Susceptibility characterization of a cavity with an aperture by using slowly rotating EM fields: FDTD analysis and measurements

This paper describes the evaluation of the susceptibility of a cavity with an aperture using the finite-difference time-domain (FDTD) method and experimentally. To reduce the computing time, the FDTD method is used for the radiation from the cavity and the susceptibility is obtained by using the reciprocity theorem. The cavity used here is modeled after a full-tower desktop enclosure with a 3.5-in bay. The susceptibility characteristics are evaluated by measuring outputs of a monopole antenna and transmission lines installed in the cavity. The susceptibility characteristics, using a three-dimensional (3-D) map, are studied from the computed and the measured results by applying slowly rotating electromagnetic fields to the cavity on a turntable. Measured and modeled results are in good agreement, indicating the merits of the proposed approach for susceptibility/immunity evaluation. Moreover, some discussions are made to check the susceptibility mechanism.     

利用亚趋附深度Ag膜在双层金属孔径阵列中实现一个显着的透射增强

本文采用理论和实验研究了利用亚趋附深度Ag膜在(Ag@Au)双层金属孔径阵列中实现的一个显着的透射增强现象,这是由于通过倏逝波使银/金界面中的表面等离激元（SPP）耦合作用的结果。结果表明,增强透射率是高度依赖Ag膜的厚度。当Ag膜厚度的增加,透射率峰值先增大,然后减小。此外,其他金属材料的性能也进行了讨论。当Ag膜的厚度为4 nm时,得到一个最高的透射率峰值。时域有限差分法（FDTD）模拟与实验结果吻合良好。这一发现提供了一种有效的方式来控制双层金属孔阵列的增强透射特性,在设计一个高性能的等离子体热发射器方面具有潜在的应用价值。     

Fabricating metallic wire grating inside a polymeric substrate by insertion nanoimprint

This paper proposes a technique called insertion nanoimprint, which features transferring the metallic wire gratings fabricated on a silicon wafer into a flexible polymeric substrate under appropriate temperature and pressure conditions. It is also an innovative process integrating the reversal nanoimprint with conventional nanoimprint process, including transferring metallic structures and defining pattern, respectively. The proposed insertion nanoimprint possesses the advantages of being able to transfer stable metallic wire gratings directly into a flexible substrate and offer flatly finished surface for subsequent processes, such as sealing and packaging. Furthermore, this technique can avoid the embedded nanostructure from damage due to contamination and stresses during packaging process or transportation. In this paper, the Al gratings with 197 nm in linewidth, 335 nm in pitch and 175 nm in height were successfully replicated into the PMMA. Various substrate temperatures were employed to explore the fluidity of PMMA as well as its effects on the mold-filling and demolding. In addition, AFM was utilized to scan the imprinted surface, and the results indicated that the embedded nanostructure underneath a flatly finished surface was obtained.     

Potential distributions through an annular aperture with a floatinginner conductor

The potential distributions through an annular aperture in a thick conducting plane are considered when an inner conductor is electrically floating. The charge conservation is used to relate the potential in terms of the total charge on an inner conductor. Numerical calculations are performed to illustrate the behavior of potential distribution, capacitances, and polarizabilities in terms of the aperture geometry and incident field     

Radiation from an aperture in a conducting cylinder coated with a moving plasma sheath

The electromagnetic radiation from an aperture on a conducting cylinder coated with a moving isotropic plasma sheath is considered. Numerical results are presented to illustrate the radiation patterns as functions of sheath velocity and plasma frequency for the circumferential slot and axial slot apertures. It is found for the circumferential slot aperture that the radiation is enhanced in the direction of sheath motion when the plasma is overdense and that relatively little change occurs when the sheath is underdense. For the axial slot, it is found that an electromagnetic field is radiated whose polarization is normal to that of the field radiated under stationary conditions, in addition to a field of the usual polarization. Significant alterations of radiation patterns from their form when the sheath is stationary can occur at relatively small velocities if the wave frequency is near the plasma frequency.     

Electron diffraction through an aperture in a potential wall

We study the diffraction of a two-dimensional Gaussian wavepacket through a rectangular aperture in a finite potential wall (one slit experiment). For wavepacket with incident wavevector k₀ satisfying the diffraction condition, k₀ = 2π/w, w being the slit width, the near field (Fresnel-like) diffraction pattern behind the slit can be clearly seen for small time duration (<0.2ps). At later time steps, the diffracted beam is fragmented into lobes (perpendicular to the direction of incidence of the wavepacket) as a result of the multiple reflections of the wavepacket inside the slit (assumed to be of finite thickness). At later time, no far-field Fraunhoffer diffraction pattern is observed in our numerical simulations.     

Coupling of power from a circular confocal laser with an output aperture

An iteration technique is used for a theoretical study of the field distributions and diffraction losses at the reflectors of an asymmetric confocal cylindrical resonator having an output hole in one mirror for the low-loss TEM00and TEM10modes with Fresnel numbers ofN = 0.8and 1.2. A digital computer is used to numerically iterate an initially launched uniform distribution as it reflects back and forth between the mirrors until a steady-state field distribution occurs. The edge and coupling hole diffraction losses and the power coupled from an output hole in one mirror are also computed. The presence of the coupling hole produces a perturbation of the field distribution with distortion of the field increasing for increasing Fresnel number and for low-order modes. The relationship between hole radius and power output is presented. An optimum-size coupling hole may be selected from this data, which will yield maximum power output in the mode of operation desired. It has been found that, with the use of a coupling hole, mode selection of the lowest order TEM00mode is possible for resonators having large Fresnel numbers (N > 1.0).     

Wide-band microstrip antenna with an H-shaped coupling aperture

Theoretical and experimental results of a wide-band planar antenna are presented. This antenna can achieve a wide bandwidth, low cross-polarization levels, and low backward radiation levels. For wide bandwidth and easy integration with active circuits, it uses aperture-coupled stacked square patches. The coupling aperture is an H-shaped aperture. Based on the finite-difference time-domain method, a parametric study of the input impedance of the antenna is presented, and effects of each parameter on the antenna impedance are illustrated. One antenna is also designed, fabricated, and measured. The measured return loss exhibits an impedance bandwidth of 21.7%. The cross-polarization levels in both E and H planes are better than 23 dB. The front-to-back ratio of the antenna radiation pattern is better than 22 dB. Both theoretical and experimental results of S parameters and radiation patterns are presented and discussed     

Model of the electromagnetic fields inside a cuboidal enclosurepopulated with conducting planes or printed circuit boards

We examine the extension of a simple and versatile model of the electromagnetic fields in an equipment enclosure with an aperture to include the effects of loading the enclosure with conducting planes or printed circuit board structures (PCB). Modeling results are compared with experimental measurements of the shielding effectiveness in a cuboidal enclosure loaded with both grounded and ungrounded conducting planes and/or PCBs with a range of grounded and ungrounded tracks. Measurement results are compared with full electromagnetic simulations and the simple model to demonstrate the accuracy and range of validity of the simple model     

Analysis of a cylindrical antenna containing an aperture coupledload

In this paper we present the basis for the analysis of shielded tuning networks coupled to wire antenna elements. The structure analyzed comprises three conducting cylindrical tubes that form an aperture-fed circular coaxial waveguide. Two methods are presented for formulating and solving integral equations for the structure. The first method is based on the mixed potential electric field integral equation enforced on the three cylindrical tubes, and the second is based on aperture theory. An end correction capacitance is used to adjust the reflection coefficient in the eigenmode expressions of the aperture method. The data obtained by the two methods are in close agreement. Differences in actual currents and equivalent currents obtained from solutions are discussed and reconciled     

核电磁脉冲与开孔金属腔体耦合特性研究

利用基于时域有限差分法(FDTD)的电磁仿真软件XFDTD,研究了核电磁脉冲与开孔腔体的耦合规律。分析了不同极化方向的核电磁脉冲入射时,矩形孔洞长宽比对耦合特性的影响;讨论了核电磁脉冲照射下,腔体谐振和孔缝与腔体的耦合谐振现象;给出了腔体内部电场分布的截面图,讨论了核电磁脉冲入射时腔体内外电场的空间分布情况。研究结果表明:当核电磁脉冲的极化方向与开孔矩形短边平行时,耦合的电场强度比正方形开孔时的要大,且长宽比越大,耦合的电场强度越大;当核电磁脉冲的极化方向与开孔矩形长边平行时,耦合的电场强度比正方形开孔时的小,且长宽比越大,耦合的电场强度越小。极化方向与矩形开孔短边平行时,腔体内产生了腔体谐振和孔缝与腔体的耦合谐振,开孔尺寸的变化会引起谐振频率的偏移;极化方向平行于长边时无明显电磁谐振发生。核电磁脉冲对屏蔽体内的影响主要局限于开孔附近。     

Estimation of wave fields of incident beams in a transmission electron microscope by using a small selected-area aperture

The direction of an electron beam in a nanometer-sized area is measured directly by utilizing a selected-area aperture. By the measurements at several areas in a beam, the wavefront curvature and thus the defocus value of the beam are detected. From the defocus value, the wave field at the specimen plane is also reproduced in consideration of the influences of the condenser aperture and spherical aberration of the illumination lens. The result shows that phase deviation of 2π is caused only at about 10?nm apart from the beam center in a beam with a typical diameter for high-resolution transmission electron microscopy. Based on the defocus value, the convergence angle of the beam is also estimated to be about 6?mrad without being influenced by the partial coherence, that is, independently of the type of the electron gun. Measuring the defocus values for only two beam diameters enables us to determine geometrical parameters peculiar to the illumination system, based on which wave fields of any beam diameters by any condenser aperture sizes can be estimated. The technique proposed in this paper is effective in evaluating the influence of wavefront curvature of incident beams on various kinds of precise measurements conducted in transmission electron microscopes.     

Equivalent currents for an aperture in an impedance surface

Expressions of equivalent magnetic and electric currents for an aperture in an impedance surface is derived in a self-consistent manner. Each equivalent current consists of the combination of the tangential electric and magnetic fields in the aperture, and is placed in front of the original aperture where the surface is extended to close the aperture. The result is particularly useful for problems involving apertures in an impedance ground plane     

Electron-phonon energy exchange and local fields in island metallic films

A theory is developed to account for the emission of electrons from island metallic films as a result of CO₂ laser irradiation, even though the incident photon energy is much less than the work function of the metal.     

TE scattering by an inhomogeneously filled aperture in a thickconducting plane

The electromagnetic characterization of the transmission and scattering properties of an aperture in a thick conducting plane filled with an inhomogenous composite material for transverse electric polarization is discussed. Of particular interest in this analysis is the introduction of a new technique that combines the finite element and boundary integral methods. To allow the treatment of large apertures, the conjugate gradient method (CGM) and fast Fourier transform (FFT) are also incorporated for the solution of the resulting system. Numerical examples that demonstrate the validity, versatility, and capability of the technique are presented     

Radiation from an aperture in an infinite conducting wedge

In this paper the problem of the far field radiation of an infinite aperture occupying one side of an infinite conducting wedge is solved. For uniform illuminations as well as for illuminations tapered to zero at the edges, it is shown that the radiated field can be effectively represented by line sources situated along the edge of the wedge. Also, for the special case of illuminations which taper to zero at the edges within a few wavelengths, it is shown that the shadow region radiation is proportional to the rate of taper.