Modified Transmission Line Research Articles

Design Considerations of a Pair of Power Leads for Fast-Cycling Superconducting Accelerator Magnets Operating at 2 Tesla and 100 kA

Recently proposed injector accelerator, Low Energy Ring (LER) for the LHC and fast cycling accelerators for the proton drivers, SF-SPS at CERN and Dual Super-Ferric-Main Ring (DSF-MR) at Fermilab of neutrino sources require that a new magnet technology be developed. In support of this accelerator program, a pair of power leads needs to be developed to close the loop between the power supply and accelerator system. The magnet proposed to be used will be a modified transmission line magnet technology that would allow for accelerator quality magnetic field sweep of 2 T/s. The transmission line conductor will be using HTS technology and cooled with supercritical helium at 5 K. The power leads consist of two sections; upper one is a copper and lower section will be using HTS tapes. The accelerator magnet will be ramped to 100 kA in a second and almost immediately ramped down to zero in one second. This paper outlines the design considerations for the power leads to meet the operational requirements for the accelerator system. The power leads thermal analysis during the magnet powering cycle will be included.

Expressions for far electric fields produced at an arbitrary altitude by lightning return strokes

Electromagnetic fields produced at high altitudes by return strokes in cloud‐to‐ground lightning are needed in studies of transient luminous events in the mesosphere. Such calculations require the use of a lightning return stroke model. Two of the widely used return stroke models are (1) the modified transmission line model with exponential decay (MTLE) of current with height and (2) the modified transmission line model with linear decay (MTLL) of current with height. In this paper, simplified expressions based on the MTLE and MTLL models are derived for calculating far (radiation) electric fields produced at an arbitrary elevation angle by lightning return strokes. It is shown that different (for example, containing either spatial or time integral), but equivalent equations can be derived for each of the models. Predictions of simplified expressions are compared with electric fields computed using exact expressions, including all the field components, and the validity of simplified expressions for distances that are much greater than the radiating channel length is confirmed.

On return stroke currents and remote electromagnetic fields associated with lightning strikes to tall structures: 2. Experiment and model validation

In this paper, simultaneous GPS time‐stamped measurements of the electric and magnetic fields at three distances and of the return stroke current associated with lightning strikes to the Toronto CN Tower (553 m) during the summer of 2005 are presented. The lightning return stroke current was measured using a Rogowski coil installed at a height of 474 m above ground level (AGL). The vertical component of the electric field and the azimuthal component of the magnetic field were measured simultaneously at distances of 2.0 km, 16.8 km, and 50.9 km from the CN Tower. The propagation path from the CN Tower to the first two stations (2.0 and 16.8 km) was along the soil and through the Toronto city, whereas for the third location (50.9 km) the propagation path was nearly entirely across Lake Ontario. The waveforms of the electric and magnetic fields at 16.8 km and 50.9 km exhibit a first zero crossing about 5 μs after the onset of the return stroke. This early zero crossing is part of a narrow undershoot. For fields at 50.9 km the expected zero crossing at about 40 μs is also observed. Metallic beams and other conducting parts in buildings on which electric and magnetic field sensors were located cause an enhancement effect on the measured fields. Although an enhancement can be identified both on the electric and the magnetic fields, the degree of enhancement is actually more significant for the electric field than for the magnetic field. It is shown that the value of the wave impedance (E‐field peak to H‐field peak ratio) could give an estimate of the enhancement effect of the building on the electric field. Propagation effects (decrease of field amplitude and increase of its risetime) can also be observed in experimental records. It is shown that the fields at 50.9 km are less affected by such attenuation, compared to those at 16.8 km, presumably because the path of propagation is mostly across Lake Ontario. Measured waveforms are compared with theoretical predictions obtained using the five engineering return stroke models extended to include the presence of the strike object, namely, transmission line (TL), modified transmission line (MTLL and MTLE), Bruce‐Golde (BG), and traveling current source (TCS) models. A reasonable agreement is found with all five engineering models for the magnetic field waveforms at the three considered distances, although the peak values of the computed fields are systematically about 25% lower than measured values. None of the models was able to reproduce the early zero crossing and the narrow undershoot. As far as the electric field is concerned, larger differences have been observed between simulations and measurements. This may be due to the fact that the enhancement effect of the building on the electric field is stronger than that on the magnetic field. The expression relating current and field peaks associated with strikes to tall structures is also tested versus obtained sets of experimental data. The overall agreement between the theoretically predicted and the experimentally observed field‐to‐current ratio is reasonable, although the formula of Bermudez et al. (2005) appears also to underestimate the experimentally measured ratio (by about 25%). This may be due, at least in part, to the enhancement effect of the buildings on which the field measurement antennae were installed.

금속격지구조의 누설특성을 이용한 새로운 광 결합용 필터

광 평면 유전체 기판 위에 형성된 금속격자구조의 누설특성을 이용한 새로운 광 결합용 필터를 제안하였고, Bragg 조건들을 모드 전송선로 이론을 사용하여 정확하게 분석하였다. 수치해석 결과, 유전체격자구조로 구성된 기존의 DFB는 전송 모드들의 피드백특성에 기인한 차단대역을 형성하지만 금속격자구조는 누설파특성에 기인한 차단대역을 형성하는 것으로 나타났다. 결국, 누설파 필터특성을 적용한 광 결합용 필터는 LD나 광섬유와 같은 광통신용 소자들과 집적이 가능함을 보였다. A novel optical coupling filter with finite-thickness metal-strip gratings printed on optical planar dielectric slabs is proposed, and Bragg conditions of the device are rigorously evaluated by using Modal Transmission-Line Theory (MTLT). The numerical results reveal that the guiding structures have filtering properties due to a leaky-wave stop-band while conventional DFB guiding structures consisted of dielectric gratings depend on a feedback-wave stop-band. Consequently, it shows that the optical coupling titter dependent on the leaky-wave filtering characteristics can be compounded of such optical devices as LD and optical fiber.

Plasmon polaritons in slot waveguides: Simple model calculations and a full nonlocal quantum mechanical treatment

We study the propagation of electromagnetic waves in a slot waveguide made of a simple (Al) as well as a complex (Ag) metal for frequencies around and below the surface plasmon frequency. Simple model calculations are compared with the full, nonlocal, quantum mechanical treatment based on Feibelman's $d$-function formalism. We show that for frequencies sufficiently lower than the surface plasmon frequency, but still in the infrared or visible range, the waveguide supports a plasmon polariton mode that resembles, and indeed reduces to, the conventional TEM mode of the conventional slot transmission line, known in the radiotechnology. This opens up the possibility of employing ideas of the radiotechnology in the visible range.

ODD Modes of a New Transmission Line Based on Semi−open Dielectric Rod

ODD Modes of a New Transmission Line Based on Semi−open Dielectric Rod

Modified transmission line model to investigate non-Ohmic contact behavior and its application on GaN

In this article we proposed a modified transmission line model method to analyze non-Ohmic contact. It can differentiate the contact resistance while the current flows into and out of the contact. When the earlier two factors are equal, this method degenerate to traditional method. By this method, we obtained contact parameters for both p-GaN and n-GaN and revealed the validity of this method. To further study the contact characteristics and transportation mechanism between alloyed Ni/Au and p-GaN, we also measured barrier information at different temperature and current. The result indicates the hole passes through the barrier by thermionic emission and the barrier may lowered by image force.

Distortion of pulsed signals in carbon nanotube interconnects

This paper investigates the distortion of DC and radio frequency (RF) pulsed signals in carbon nanotube interconnects. A modified transmission line model for single-walled carbon nanotubes is employed for the simulation. Comparisons with the conventional AlCu interconnect are performed.

An approach for small omnidirectional microstrip antennas based on the backward waves of double negative metamaterials

In this paper, a small omnidirectional microstrip antenna (MSA) is proposed based on a compact double negative (DNG) metamaterial, which is constructed by modified split ring resonators (MSRRs) and metal strips. First, the backward wave property of the DNG slab is investigated and illustrated by full-wave simulations. It is shown that the slab can exhibit double negative parameters and support backward wave in a broadband of 8.45 GHz∼11.05 GHz, so the existence of the DNG band is proven. Then the DNG unit cells are stacked and embedded into a host substrate to construct a phase-compensating substrate for the small MSA. By using the modified transmission line model (MTLM) and 3D full-wave simulation, a small MSA is modeled and characterized. Results show that the presence of the DNG fillings can indeed greatly reduce the physical dimensions from 0.5λ to 0.17λ, while its farfield pattern is significantly different from that of a conventional half-wave-length MSA. Lastly, the E-field distributions of the small MSA and a conventional half-wave-length MSA are contrasted and discussed to explain the functional mechanism of the small omnidirectional SMA.

Current propagation model for a narrow bipolar pulse

Narrow bipolar pulses (NBPs) are a class of high‐altitude, high‐energy discharges that occur during some thunderstorms. We use a modified transmission line model (called MTLEI) with a current that increases exponentially along the propagation channel to test mechanisms that might produce NBPs. Model outputs were compared to measured E data from a single NBP collected at near and far field locations. We were unable to fit the measured data using the fast current propagation speeds appropriate for a runaway breakdown/extensive air shower mechanism. Instead, by using currents that travel relatively slowly (6 × 107 m/s), the MTLEI model fit the data reasonably well. This result is compatible with a mechanism that uses runaway breakdown to produce charge carriers along with a moving electric field to drive the main NBP current. Using this model for the measured NBP, we estimate a charge moment of 0.6 C·km.

Even Modes of a New Transmission Line Based on Semi–Open Dielectric Rode

An original transmission line based on a planar waveguide splitter with central dielectric filling is considered. A rigorous electrodynamics model is presented for calculating propagation parameters of odd eigenmodes. It was determined that the physics of the wave processes of the line for odd modes is identical to the physics of closed structures, though the structure geometry is of semi-open character. Numerical experiments prove that new line is very promising for different millimeter wave applications, such as band pass filters, test fixture, antennae and three-dimensional integrated circuits (TDIC).

Effective medium approach for subwavelength resolution

In a wire medium there can propagate ordinary and extraordinary waves. In a single-wire medium the line source excites two extraordinary modes: TM and TEM fields. In the far-field region one of them is the transmission-line mode, which can be used for transfer of an image to a long distance with a resolution that is determined by the ratio of the operating and the plasma frequency in wire medium. Subwavelength resolution is achieved with sufficiently high plasma frequencies.

Three-band Modified Transmission Line Antennas for Mobile Communication

Three-band Modified Transmission Line Antennas for Mobile Communication

Vertical conductivity of p-Al xGa 1−xN/GaN superlattices measured with modified transmission line model

The vertical conductivity of the p-Al 0.11Ga 0.89N/GaN SLs has been measured and calculated. The measured result (1.35×10 −5 S cm −1) is in good agreement with the calculated result (2.26×10 −5 S cm −1), indicating that the adoption of Fermi–Dirac distribution and sequential tunneling model in our calculation is very plausible. As a result, it is suggested that in p-AlGaN/GaN SLs the Fermi–Dirac distribution need to be considered in calculation related to hole distribution.

On the applicability of conventional transmission line theory within cavities

Abstract. We investigate whether or not conventional transmission line theory needs to be modified if transmission lines are considered that are located in a cavity rather than in free space. Our analysis is based on coupled Pocklington's equations that can be reduced to integral equations for the antenna mode and the transmission line mode. Under the usual assumptions of conventional transmission line theory these modes do approximately decouple within a cavity. As a result, cavity properties will primarily influence the antenna mode but not the transmission line mode.

격자구조형 광섬유 결합기에서 최적 전력결합을 결정하기 위한 새로운 조건

A grating-assisted fiber coupler(GAFC), which consists of a thin-film waveguide with grating and circular optical fiber, is proposed and the optimized power coupling is evaluated by using a technique amenable to rigorous longitudinal modal transmission-line theory(L-MTLT). In addition, novel criteria to couple an optical signal incident through the grating waveguide to a single-mode optical fiber are proposed. The numerical result reveals that the optimized power coupling occurs at minimum-gap condition between rigorous modes rather than for the conventional phase-matching condition.

Propagation of Partial Discharge Signals in Stator Windings of Turbine Generators

We studied the propagation of partial discharge pulses in a stator winding by means of measurements on a dismantled 35-MW generator and found that a stator winding acts as a transmission line. Therefore, a partial-discharge (PD) signal manifests itself at the generator terminals after a transit time that depends on the location of the discharge. Due to capacitive and inductive couplings in the end-winding region, a second propagation mode is present for higher frequencies. This "fast mode" manifests itself at the terminals without appreciable time delay. The capacitive and inductive couplings also cause crosstalk between the phases. As a consequence, a signal measured in one phase does not necessarily originate from a discharge in that phase. The amplitudes of the fast mode and, to a lesser extent, the slow mode (or transmission-line mode) are heavily damped when the discharge occurs further away from the measuring terminal. The consequence is that only discharges close to the measuring terminal can be observed. The propagation of a PD signal is not only influenced by the construction of the generator but also by its external connections.

천이영역을 갖는 원통형 격자필터 설계를 위한 간단한 해석적 방법

협대역 천이영역을 갖는 원통형 격자전송구조 (Circular Bragg Grating: CBG) 가 최근 DWDM을 위한 광통신용 대역통과 필터로 널리 사용되고 있다. 이 원통형 Bragg 격자 구조들의 광 필터특성을 분석하기 위하여 본 논문에서는 Floquet-Babinet의 원리에 의존하는 새로운 해석적인 모드 전송선로 이른 (Modal Transmission-Line Theory: MTLT)을 제시하였다. 수치해석 결과, 제안한 해석법은 CBG의 필터특성을 분석하기 위한 유용한 프로그래밍 알고리즘을 제공하고, 다층 원통형 주기 구조들의 그 전송특성을 분석하기 위하여 쉽게 발전시킬 수 있음을 보였다. Circular Bragg gratings(CBGs) canbe incorporated in most of the semiconductor laser devices because of the frequency-selective property applicable as an optical narrowband-pass filter in DWDM optical communications. In this paper, the optical filtering characteristics of CBGs are evaluated by a novel and simple analytic modal transmission-line theory(MTLT), which is based on Floquet-Babinet's principle. The numerical results reveal that this method offers a simple and convenient algorithm to analyze the filtering characteristics of CBGs as well as is extended conveniently to evaluate the guiding problems of circular multi-layered periodic structures.

Quasi-TM MoL/MoM approach for computing the transmission-line parameters of lossy lines

This paper presents a quasi-TM approach for the fundamental mode of transmission lines with semiconductor substrates and nonperfect metallic conductors. The approach has allowed us to develop a transmission-line model by properly defining frequency-dependent parameters in terms of the quasi-static electric potential and the electric current density along the propagation direction in the line. The previous quasi-TM analysis avoids the involved numerical root finding process typical in full-wave analysis, and overcomes the limitations of the conventional quasi-TEM approach to account for the effects of the longitudinal currents present both in the lossy substrates and in the nonperfect conductors. The transmission-line parameters have been computed by a hybrid technique that combines the method of lines with the method of the moments (MoM). The total CPU effort has been considerably reduced thanks to the possibility of finding closed-form expressions for the reaction integrals appearing in the MoM. Comparisons with previous computed and measured results show the validity of the present model

Frequency-Selective Transmission by a Leaky Parallel-Plate-Like Waveguide

The phenomena of high frequency-selective transmission of a plane wave by a dielectric two-dimensional (2-D) periodic waveguide, comprising a uniform dielectric layer sandwiched by two finite thickness 2-D periodic structures served as the waveguide wall is described. This structure is termed a leaky parallel-plate-like waveguide because the waveguide walls are not perfect reflection mirrors. The scattering characteristics and dispersion relation, including the phase and attenuation constants, of the 2-D periodic waveguide are thoroughly analyzed with the modal transmission-line method and Floquet theory. The extraordinary open stopbands caused by the contra-flow coupling between a leaky parallel-plate-like waveguide and the leaky waves, which are generated by 2-D periodic structures (waveguide walls), are displayed in the form of the Brillouin diagram. The phase-match condition is used to verify the resonant coupling between the incident plane wave and the leaky parallel-plate-like waveguide modes. Specifically, the transmission peak frequencies are accurately predicted.