On the Applicability of the Surface Impedance Integral Equation for Optical and Near Infrared Copper Dipole Antennas

The applicability of the surface impedance integral equation (SI-IE) method for the analysis of optical and near-infrared copper dipole antennas is assessed, and some issues relative to resonant half-wavelength optical dipoles are highlighted. Since at these frequencies the conductivity of copper (and of all metals) is relatively small, the appropriateness of using the standard integral equation method for imperfectly conducting wires, based on a surface impedance boundary condition, needs to be examined. Here it is found that the SI-IE method yields accurate results in the near-infrared regime, and for suitably small wire radius values at low optical frequencies. For the middle and upper optical frequencies the approximate SI-IE is not generally valid. Some results are presented for a half-wave dipole resonant in the upper near-infrared/low optical range, and a discussion of the trade-off between maintaining good polarization selectivity and radiation efficiency is provided     

Development of Short Electrical Pulses in a Schottky Line Periodically Loaded with Resonant Tunneling Diodes

The characteristics of a Schottky line periodically loaded with resonant tunneling diodes (RTDs) are discussed for the development of short electrical pulses. RTDs act as electronic switches and exhibit a pronounced N-shaped I-V characteristic even at millimetre wave frequencies. The dynamics of the line is reduced to an extended KdV equation. These dynamics are considered both within the method of perturbation and the numerical integration of the transmission equation of the line.     

Computations of Frequencies and Intrinsic Q Factors of TE/sub 0nm/ Modes of Dielectric Resonators (Short Papers)

The Rayleigh-Ritz method is described, which is used to calculate the resonant frequencies and intrinsic Q factors due to dielectric losses of quasi TE/sub onm/ modes of dielectric resonators. Electromagnetic fields of an auxiliary post dielectric resonator are taken as an electrodynamics basis for approximate solutions of this problem. The method provides upper bounds for true resonant frequencies. Numerical results are compared with previously published complementary calculations. The influence of a dielectic substrate on resonant frequencies and intrinsic Q values is demonstrated.     

A comparison of integral equations with unique solution in theresonance region for scattering by conducting bodies

A comparison of integral equations, for problems involving scattering by arbitrary-shape conducting bodies, having a unique solution in the resonance region is presented. The augmented electric and magnetic field integral equations and the combined field integral equation, in their exact and approximate versions, are considered. The integral equations and the basis and test functions used in the method of moments to solve them are reviewed. Their implementation in a computer code is analyzed, mainly the relation between the matrix properties and the CPU time and memory. Numerical results (condition number and backscattering cross section) are presented for the cube. It is shown that the combined field integral equation, and the approximate (symmetric) combined field integral equation, are the most efficient equations to use in the neighborhood of resonant frequencies, because the overdetermined augmented integral equations require an extra matrix multiplication     

Design of MMICs employing whispering-gallery mode dielectric resonators at microwave and millimeter wave frequencies

A simple theoretical model for predicting the resonant frequencies of the modes of the whispering — gallery (WG) mode dielectric resonators MICs (Microwave Integrated Circuits) at microwave and millimetre wave frequencies is presented. The unsymmetric field distribution for WGE mode in the axial direction is taken into account. The theoretical results are found to be in good agreement with the practical results taken at microwaves C-X bands. In addition, the variation of resonant modes against dielectric resonator's dimensions and dielectric constant is modelled. The effect of the width of dielectric substrate on resonant modes is also illustrated.     

Spectral Domain Analysis of Coaxial Cavities

Coaxial cavities are used in high power gyrotrons as the beam-wave interaction structure. Much research has been devoted to their mode selective properties. A coaxial cavity lacks a sharp boundary at its open end, so it has some physical features that can only be observed using a spectral model, such as frequency-dependent field profiles and mode overlapping effects. These properties are important since cold tests are usually conducted in the frequency domain. This study applies the incident/reflected wave boundary condition to the wave equation of a weakly irregular coaxial waveguide. The resistivity of the wall is considered in the analysis. Calculations reveal that the fixed-position spectrum yields an uncertain resonant frequency and quality factor. Although the maximum-field spectrum can uniquely determine the properties of the coaxial cavity, the resonant frequency obtained using the maximum-field spectral model is inconsistent with that obtained using the temporal model. The field-energy spectrum explains the low Q nature of the coaxial cavity. Moreover, resonant frequencies evaluated using the field-energy spectrum agree precisely with those evaluated using the temporal model.     

Analytical and Experimental Considerations on the Resonant Frequency and the Quality Factor of Dielectric Resonators

A dielectric pillbox resonator placed on a dielectric substrate is analyzed by a new method, the approximate mode matching method, in which the cross section of such a resonator is subdivided into several sub-sections having a simple geometry of the boundaries, i.e., dielectric slab radial waveguides, and the continuity condition of fields between subsections is treated in the least-squares sense. The resonant frequencies and the intrinsic Q values due to the leakage loss through the dielectric substrate calculated by this method are presented together with experimental results obtained in the 50-GHz region. As a result, it is found that the experimental results for both the resonant frequencies and the Q values agree better with our calculated ones than with the results by other approximate method, and so it will be concluded that the analytical method presented here is almost enough to discuss precisely the resonant characteristics of a dielectric pillbox resonator.     

Field-induced coupled quantum-well oscillators

A study of field-induced coupled quantum-well oscillators due to the interwell coherent oscillation is presented. The evolution of an electron wave packet in an asymmetric coupled quantum-well structure is described by the application of the time-development operator of the time-dependent Schrodinger equation. By adjusting the applied field, various resonant conditions giving rise to different oscillation frequencies can be obtained in a single device. Direct frequency tuning, amplitude variation, and dipole matrix element due to the external field are also investigated     

Resonant modes in shielded uniaxial-anisotropic dielectric rodresonators

Rigorous field analysis by the mode-matching method is presented for dielectric rod resonators, including such uniaxial dielectrics as sapphire, which are placed between two parallel conducting plates or in a conducting cavity. The wave equations for E_Z and H_Z in a uniaxial anisotropic dielectric medium are derived in a cylindrical coordinate system. Based on these wave equations, the characteristic equations for the two resonator structures are derived and can be used to calculate the resonant frequencies of any resonant mode. Cutoff conditions of the resonant modes are discussed for parallel-plate-type resonators. Resonant frequencies of some lower order modes are calculated for both types of resonator. Mode charts useful for designing the resonators are presented. It is verified that the mode-matching method used commonly for the analysis of isotropic-dielectric resonators can be applied successfully to uniaxial-dielectric resonators     

Muscle sounds are emitted at the resonant frequencies of skeletalmuscle

The changes in mechanical resonant frequency of whole muscles during twitch and tetanic contractions were compared to changes in frequency components of the pressure wave produced by muscles during contraction. Resonant frequencies were determined by imposing sinusoidal length changes on a muscle and observing transverse standing waves when the frequency of length change matched the muscle's resonant frequency or a harmonic of the resonant frequency. Acoustic signal instantaneous frequency spectrums were calculated using time-frequency transformations including the Wigner transform and the exponential distribution. During a tetanic muscle contraction, the peak instantaneous frequency initially increased and then became constant as the force plateau was reached. The resonant frequencies determined during the force plateau and during relaxation spanned the same range as the peak instantaneous frequency of the acoustic signal. These results suggest that the acoustic signal may be useful as a non-invasive monitor of muscle resonant frequency during contraction.     

Ray-mode analysis of complex resonances of an open cavity [radartargets]

Complex resonances furnish valuable inputs for classification of radar signatures from irregularly shaped objects. An important class of targets involves open-ended enclosures with exterior-interior coupling. If the interior has waveguide-like properties, modal expansions can model the wave phenomena there, while ray methods can be employed to account for multiple diffraction at the aperture edges, and for wave interactions around the exterior boundary. By self-consistent ray-mode coupling in a hybrid format, one can construct a global resonance equation whose solutions yield the complex resonant frequencies for the composite object. The importance of evanescent modes and of coupling to nearest neighbor modes is investigated, as is the contribution from low-Q interactions around the external circumference     

Spectral domain analysis of a coupled slot antenna

The characteristics of a coupled slot resonator suitable for novel design of an integrated planar antenna are analyzed. The analysis is based on the spectral domain immittance matrix approach, and all the wave phenomena associated with the structure are incorporated. The resonant frequencies in the even and odd resonance modes are evaluated from the numerical solution of the characteristic equation, and the radiation patterns are calculated. The numerical results are compared with experimental data with good agreement     

计算多层介质中微带环谐振器谐振频率的频域方法

本文介绍计算多层介质微带环谐振器谐振频率的一种频域方法。它是基于电磁场理论中“反应原理”,由求解不同区域中满足边界条件的波动方程出发,通过傅立叶－汉克尔变换得到频域中的一个广义积分方程。根据该方程的数值结果,可获得各种模式下的谐振频率随第二层介质层厚度及介电常数的变化曲线。与变分法比较,一致性很好。这种微带环谐振器在微波热疗中有着广阔的应用前景,本文结果将对临床应用起到一定的指导意义。     

Scattering by a thin wire parallel to a ground plane using the singularity expansion method

A thin wire parallel to a ground plane is analyzed using moment methods to find the complex natural resonant frequencies and modal current distributions. The resonant frequencies are found as functions of the wire radius and distance above the ground. The complex frequencies appear to be divisible into two classes: 1) those associated with the resonant length of the dipole and 2) those associated with interactions of the dipole and its image. For large dipole radii, the two classes interact and some anomalies, which appear, are investigated. The time domain response to a step-function plane wave is computed using the singularity expansion method and the results compare favorably with the Fourier transform solution.     

Plane-wave scattering by a magnetoplasma cylinder

The scattering of H-polarised plane waves by an infinitely long axially magnetised cylinder of uniform plasma is investigated for the case in which the radius of the cylinder is small in comparison with the wavelength of the incident wave. The scattering amplitude is found to be a maximum at two frequencies, which are shown to be related to the familiar dipolar resonant frequency of an isotropic plasma column. Approximate expressions for the two resonant frequencies are derived.     

一种基于缝隙天线阻抗的带缝腔体谐振频率计算方法

电磁波经缝隙进入机箱腔体后,会在某些频率点形成驻波而发生电磁谐振,导致腔体屏蔽效能急剧下降.为快速准确预测谐振频率以指导屏蔽腔体设计,本文基于缝隙天线阻抗理论提出一种带缝腔体谐振频率的计算方法.将电磁场用自由空间和腔体格林函数表示,根据缝隙处的边界条件建立等效磁流源的积分方程.通过矩量法求解积分方程,计算出腔体输入阻抗.根据谐振发生时电抗为零或电阻最小,可从频率-阻抗曲线获得谐振频率.本文方法不仅能预测缝隙谐振和低阶模式腔体谐振,还能预测出高阶谐振.与实验和CST仿真结果对比验证了本文方法的准确性及快速性.最后用本文方法分析了腔体和缝隙尺寸以及缝隙位置对谐振频率的影响.     

电导率调制体声波谐振器FDTD仿真研究

该文基于FDTD数值仿真法研究了电导率对ZnO体声波谐振器谐振频率的影响规律,为体声波声放大器、可调滤波器及探测器的优化设计提供指导。电导率的影响通过连续性方程引入,为了提高仿真精度,连续性方程采用四阶Adams-Bashforth差分格式。仿真结果表明,电导率在1～30 mS/m时,对谐振器谐振频率具有显著的调制效果。     

W 波段回旋管谐振腔特性参数测量方法的研究*

W 波段回旋振荡管是一种重要的高功率毫米波源,它通常采用圆柱开放式谐振腔作为其高频结构。 谐振腔所具有的特性参数,如谐振频率和品质因数影响了整管的性能。在W 波段,特性参数对于尺寸的变化特别敏 感,因此,有必要对加工好的开放式谐振腔的特性参数进行测量。利用直接耦合法实现了对5 组开放式谐振腔谐振 频率和品质因数的无损检测,实验结果验证了该方法的可行性与有效性。同时,分析了加工误差对谐振腔性能造成 的影响,结果表明,当开放式谐振腔渐变角度的加工误差达到7%以上时,谐振频率将偏移0.2GHz。     

Spectral Domain Analysis of an Elliptical Microstrip Ring Resonator (Comments)

Along with the above paper several other papers have been published recently by Sharma and his co-workers [2]-[3] on the analysis of the resonant frequencies of a microstnp disk using the quasi-static approach. The quasi-static approach has been proven to be incorrect in [4] and [5]. The quasi-static argument on the correction to the resonant frequencies of a microstrip disk is based on some intuitive arguments that are not rigorous. The only thing it predicts correctly is that the resonant frequencies of a microstrip disk should decrease compared to that of a magnetic-wall model. The author may argue that since the correction to the magnetic-wall model is small, any approximate method is viable. However, we have found that the quasi-static correction could be as much as 50 percent in error. Even when this correction is small, if we bother to caIculate it, I think we should calculate it correctly. The author's quasi-static correction has a new twist compared to earlier authors, but when epsilon/sub r/ = 1, it does not differ from the quasi-static correction of earlier work.     

Resonant Frequencies of Rectangular Dlekctric Resonators

The resonant frequencies of isolated dielectric resonators of rectangular shape are calculated using the dielectric waveguide model. The waveguide treatment of the rectangular dielectric rod is solved using the approximate semianalytical techniques of Marcatili, Knox, and Toulios. The accuracy with measured frequencies appear satisfactory with the former approach.