Simple Transmission Line Model Research Articles

Layer by Layer: Improved Tortuosity in High Loading Aqueous NMC811 Electrodes

Thick electrode production is a key enabler for realizing high energy density Lithium-ion batteries. Therefore, the investigation of tortuosity as a crucial limiting parameter was conducted in this work. A thickness threshold (>150 μm) for a drastic increase in tortuosity for aqueous processed LiNi0.8Mn0.1Co0.1O2 (NMC811) electrodes was determined. Symmetrical cells, under blocking conditions, were analyzed via electrochemical impedance spectroscopy. To counteract this phenomenon, multi-layer coated electrodes with varying binder concentrations were investigated. This novel coating method, combined with the reduction of binder material, leads to a tortuosity decrease of more than 80%, when compared to high-loading electrodes (>8.5 mAhcm−2) coated with the conventional doctor-blade technique. Additionally, a simplified transmission line model is opposed to a linear fitting method for analyzing the impedance data.

A Platinum Micro-Reference Electrode for Impedance Measurements in a PEM Water Electrolysis Cell

We present a platinum wire micro-reference electrode (Pt-WRE) suitable for recording individual electrochemical impedance spectra of both the anode and the cathode in a proton exchange membrane water electrolyzer (PEM-WE). For this purpose, a thin, insulated Pt-wire reference electrode (Pt-WRE) was laminated centrally between two 50 μm Nafion® membranes, whereby the potential of the Pt-WRE is determined by the ratio of the local H2 and O2 permeation fluxes at the tip of the Pt-WRE. Impedance analysis with the Pt-WRE allows determination of the proton sheet resistance of the anode, the anode catalyst layer capacitance, and the high-frequency resistance (HFR) of both electrodes individually, using a simple transmission-line model. This new diagnostic tool was used to analyze performance degradation during an accelerated stress test (AST), where low and high current densities were alternated with idle periods without current (i.e., at open circuit voltage (OCV)), mimicking the fluctuating operation of a PEM-WE with renewable energy. Our analysis revealed that the increasing HFR that was observed over the course of the OCV-AST, which is the main cause for the observed performance decrease, can unequivocally be assigned to an increasing contact resistance between the anode electrode and the porous transport layer.

Polarization twist reflector antenna — A systematic design approach

In this paper, we present an easy and systematic design approach to realize a polarization twist reflector antenna. Detail description has been provided on how to design a transreflector antenna and its constituents including the transreflector, the polarization twist-reflector, and the feed horn. Simple relations for calculation of reflection coefficients of the trans-reflector and the twist- reflector with plane wave incidence have been considered. Simple transmission line model based analyses have been presented. As it does not involve any integral equation or summation of series of some functions, the final results can be obtained within few seconds with the minimum computational resource requirement. Conductive gratings have been conceived for both trans-reflector and twist-reflector. Their performances have been optimized individually in terms of their grating parameters. A linearly polarized pyramidal horn located at the prime focus of the transreflector has been used for the excitation. A prototype of the complete antenna has been designed at Ka-band, fabricated and experimentally measured. 19% impedance bandwidth with average gain of ≈32.3 dBi has been demonstrated.

Shielded open-circuited probe for in-situ measurements of soil permittivity in Very high frequency (VHF) and Ultra high frequency (UHF) bands

In this paper, the shielded open-circuited probe operating in the wide frequency range from 75MHz to 2GHz is proposed. The probe is made of an SubMiniature version A (SMA) flange connector. The central rod of the SMA connector emerges from a coaxial transition in the flange and shielded by four rods. The robe design allows us to calculate of the probe reflection coefficient S11 used simple analytical transmission line model (TEM wave mode), the parameters of which were calibrated on a set of substances with a known frequency spectrum of permittivity. The refractive index (RI) and normalized attenuation coefficient (NAC) retrieval technique is based on solving the inverse problem of minimizing the residual norm between measured and calculated frequency spectra of reflection coefficient S11. After calibration, the root-mean-square error (determination coefficient) between the measured and calculated module and phase of the reflection coefficient S11 for the sets of calibration media air, distilled water, butanol, pure ice, water solution with NaCl of salinity of 8.9% do not exceed 0.26dB (0.995) and 0.03 rad (0.999), respectively, in the frequency range from 75MHz to 2GHz. The root-mean-square error (determination coefficient) between the measured RI and NAC spectra for four soil cover samples (variation of the clay fraction from 10.5 g/g to 47.6 g/g) using the proposed probe and a precision coaxial cell not exceeds 0.109 (0.993) and 0.057 (0.986), respectively, in the frequency range from 75 MHz to 2 GHz. As a result, it is experimentally shown that RI и NAC can be measured by the proposed non-precision probe with an error comparable to the precision coaxial cell.

Methods—Understanding Porous Electrode Impedance and the Implications for the Impedance Analysis of Li-Ion Battery Electrodes

Two of the main factors influencing the performance of Li-ion battery (LIB) electrodes are the kinetic losses due to the charge transfer resistance of the active material () and the ionic transport resistance in the electrolyte phase within the electrode pores (). Seeking to increase the energy density of LIBs, ever higher active material loadings are applied, resulting in thicker electrodes for which becomes dominant. As electrochemical impedance spectroscopy is commonly used to quantify of electrodes, understanding the impact of on the impedance response of thick electrodes is crucial. By use of a simplified transmission line model (TLM), we simulate the impedance response of electrodes as a function of electrode loading. This will be compared to the impedance of graphite anodes (obtained using a micro-reference electrode), demonstrating that their impedance response varies from purely kinetically limited at 0.6 mAh cm−2 to purely transport limited at 7.5 mAh cm−2. We then introduce a simple method with which and can be determined from the electrode impedance, even under transport limited conditions. Finally, we show how the initially homogenous ionic current distribution across porous electrodes under kinetically limited conditions becomes severely inhomogeneous under transport limited conditions.

Compact dual-wideband bandpass filter for wireless applications

In this paper, a compact dual-wideband bandpass filter with two reflection zeros in both passbands and two transmission zeros in the stopband, based on a signal interference technique is presented. The proposed filter is formed by a transmission line connected in parallel with a series connection of transmission lines and a short circuited edge coupled line. A simple lossless transmission line model is used to derive the condition for transmission zeros. To validate the theoretical predictions, a compact dual-wideband bandpass filter has been fabricated to operate at GPS and INSAT Satellite bands. The measured 3 dB passband fractional bandwidths are 82.16% and 41.52%, respectively.

Analysis of Arbitrarily Curved Microstrip Lines for Radiated Emission

In the context of printed circuit design, microstrip interconnects pose a great challenge in terms of radiated emission, signal integrity, and intertrace interference. Curved and bent microstrip lines are integral part of such high-frequency circuit design. In this paper, internal fields of an arbitrarily curved microstrip line are calculated using a sequential mode matching technique with piecewise circular discretization. Transverse asymmetry of the electric field is observed due to unequal curvatures of the two side edges of the microstrip line. A dynamic co-ordinate system based on Serret–Frenet reference frame is developed. A simple transmission line model is formulated in this new co-ordinate system to calculate the radiated far fields from the line. The developed model is applied to compute radiation from a sinusoidal line as well as that of a planar spiral. The model is also applied to compute the radiation efficiencies from various microstrip bends and it is observed that circular bends exhibit minimum leakage amongst others. A sinusoidal line and a planar spiral are fabricated and measured. Results are shown to be in good agreement with those predicted by the analytical model.

Transmission line model for analysis of microstrip travelling wave antennas with right angled bends

A simple but accurate transmission line model for the analysis of microstrip travelling wave antennas based on microstrip lines and right angle bends is described. Radiated far fields from the antenna are calculated using magnetic current on the antenna sidewalls and electric current on the strip surface. Local reflections from the right angle discontinuity are considered in internal field calculations. An equivalent decay constant to accommodate the radiated power from the antenna is introduced which is iteratively computed to improve impedance and radiation characteristics calculated by the model. Total power lost in the line due to this equivalent decay constant is equal to the total power radiated from the antenna. A rampart line antenna having three unit cells is fabricated in the C band and the results from the model are compared with those from full wave MoM simulations and practical measurement with good agreement. This simple yet accurate model would be valuable in computer aided design for optimal microstrip line based antennas with minimal computational resources.

A Novel Broadband Band-pass Filter Based on Spoof Surface Plasmon Polaritons.

In this paper, we present a novel broadband bandpass filter based on spoof surface plasmon polaritons (SSPPs) in the microwave frequency band. The proposed bandpass filter includes three parts: (1) coplanar waveguide (CPW); (2) matching transition; and (3) coupled structure that is an asymmetric coupled filter constructed by five grooved strips. The proposed bandpass filter realizes excellent low loss performance from 7 to 10 GHz, in which its insertion loss is around 1.5 dB in the same frequency band. Meanwhile, this filter has a good band stop characteristic from 3 to 7 GHz. A simple but accurate transmission line model was proposed to evaluate the proposed broadband SSPPs filter. The measured data, simulated results and the results obtained from the transmission line model have shown a very good agreement. The proposed planar broadband filter plays an important role for filtering surface plasmon polaritons (SPPs) waves in plasmonic circuits and systems.

Resonant tunneling assisted propagation and amplification of plasmons in high electron mobility transistors

A rigorous theoretical and computational model is developed for the plasma-wave propagation in high electron mobility transistor structures with electron injection from a resonant tunneling diode at the gate. We discuss the conditions in which low-loss and sustainable plasmon modes can be supported in such structures. The developed analytical model is used to derive the dispersion relation for these plasmon-modes. A non-linear full-wave-hydrodynamic numerical solver is also developed using a finite difference time domain algorithm. The developed analytical solutions are validated via the numerical solution. We also verify previous observations that were based on a simplified transmission line model. It is shown that at high levels of negative differential conductance, plasmon amplification is indeed possible. The proposed rigorous models can enable accurate design and optimization of practical resonant tunnel diode-based plasma-wave devices for terahertz sources, mixers, and detectors, by allowing a precise representation of their coupling when integrated with other electromagnetic structures.

Simple transmission line model suitable for the electromagnetic pulse coupling analysis of twisted-wire pairs above ground

Simple transmission line model suitable for the electromagnetic pulse coupling analysis of twisted-wire pairs above ground

A Compact Meander Line-Resonator Hybrid Structure for Wideband Common-Mode Suppression

In this paper, a novel compact and wideband common-mode suppression structure is proposed, which is composed of a meander line and several quarter wavelength resonators. A simple and accurate transmission line model is employed to describe the stopband behavior of the proposed structure. The resonance frequencies and harmonics of quarter wavelength resonators are employed to form stopbands of the common mode. Those stopbands together with the stopband of the meander line are connected in series, which are useful to expand the common-mode suppression bandwidth. Meanwhile, compensation strips are proposed to reduce the insertion loss of the differential mode. A reduction of 15 dB of common-mode propagation above 0.8 GHz is obtained by using the proposed hybrid structure. The measurement results of printed circuit boards, which are designed and fabricated on the simulation model, show good correlation with the simulation results.

Free-electron THz-reabsorption in distributed photodiode structures

Ultra-fast photodiodes based on vertical p–i–n or uni-traveling (UTC) mesa structures require a highly doped base layer that makes a well-conducting transverse connection between the mesa bottom layer and the bottom metal contacts. To reach the lowest possible THz loss, the question arises on what doping levels would be optimal for this layer. Doping levels of up to cm−3 can be reached in InP, corresponding to conductivities of around S m−1, which is still much lower than those of metal conductors. A full-wave analysis, which is executed in HFSS™ and CST Microwave Studio™ and reported here, shows that a valley of low loss exists around a conductivity of S m−1 (estimated doping value cm−3), in the middle of a conductivity range of excessive terahertz absorption, making this value the best choice for the whole frequency range up to 2000 GHz. The results are supported by an analytical solution in a simplified transmission line model. The results are expected to be significant for designing future distributed photonic devices such as traveling-wave (TW) photodiodes.

Optical emission and peak electromagnetic power radiated by negative return strokes in rocket-triggered lightning

Calibrated measurements of the optical radiation produced by negative return strokes in rocket-triggered lightning (RTL) have been made in the visible and near infrared (VNIR) spectral region in correlation with currents measured at the channel base. Using a simple transmission-line model, the currents have been used to estimate the peak electromagnetic (EM) fields and Poynting power that are radiated in the time-domain (i.e. from about 1kHz to 3MHz). The results show that the optical power radiated by RTL at the time of the peak current has a mean and standard deviation of 130±120MW, a value that is only about 5% of the Poynting power that is radiated into the upper half-space at that time. These results are in good agreement with similar measurements made on the subsequent return strokes in natural lightning that remain in a pre-existing channel. Our methods and assumptions are similar to those of (Guo and Krider, 1983; Krider and Guo, 1983; Quick and Krider, 2013).

Breakup length of AC electrified jets in a microfluidic flow-focusing junction

Electroactuation of liquid–liquid interfaces offers promising methods to actively modulate droplet formation in droplet-based microfluidic systems. Here, flow-focusing junctions are coupled to electrodes to control droplet production in the well-known jetting regime. In this regime, a convective instability develops leading to droplet formation at the end of a thin and uniform, long liquid finger. We show that in AC electric fields, the jet length is a function of both the magnitude of the applied voltage and the electrical parameters such as the frequency of the AC field and the conductivity of the dispersed phase. We explain that dependency using a simple transmission line model along the liquid jet. An optimum frequency to maximize the liquid ligament length is experimentally observed. Such length simply cannot be obtained by other means under the same operating conditions, in the absence of the AC signal. At low frequency, we reach a transition from a well-behaved, uniform jet brought about near the optimum frequency to highly unstable liquid structures in which axisymmetry is lost rather abruptly.

An Exact Method for the Extraction of Effective Bulk and Surface Parameters of Periodic Artificial Media

A new method is presented for the extraction of the bulk and surface parameters of a periodic artificial medium which uses the eigenvectors of the generalized transfer matrix of a unit layer. These eigenvectors correspond to the Bloch modes of the periodic structure. The eigenvector related to the propagating Bloch mode directly yields an expression for the effective, intrinsic wave impedance of the medium. Moreover, the interface between the artificial material and a surrounding, conventional (dielectric) region is described by an interface impedance matrix which accounts for the excitation of higher order, nonpropagating Bloch modes at the interface. Although these modes do not propagate into the bulk of the artificial material, they affect the reflection and transmission coefficients of incident waves. From the bulk and surface impedances derived, and with the aid of a simple transmission line model, the scattering parameters of a slab of an artificial medium are computed. Results are in excellent agreement with those of exact full-wave simulations.

OMNIDIRECTIONAL RADIATION IN THE PRESENCE OF HOMOGENIZED METASURFACES

Analytical and numerical approaches are presented for modeling the interaction of azimuthally symmetric fields with omnidirectional metasurfaces, based on the use of locally homogenized equivalent sheet impedances. Radially uniform metasurfaces on layered dielectric media are described in terms of a spectral impedance dyadic, thus allowing for the derivation of the field excited by omnidirectional sources through a simple transmission-line model. In a first approximation, the effect of circular edges in laterally truncated structures is taken into account through an efficient physical- optics method. Then, truncated and radially non-uniform homogenized layered structures are treated numerically with the method of moments, by suitably extending a recently developed spectral-domain formulation. Numerical results are presented for planar radiating structures based on omnidirectional metasurfaces, comparing the radiation patterns obtained through the proposed homogenized models with those calculated by means of full-wave simulations. The discussion emphasizes the validity of the proposed approaches and their usefulness in the analysis of two-dimensional leaky-wave antennas based on printed omnidirectional metasurfaces.

Electrochemically Self-Doped TiO2 Nanotube Arrays for Supercapacitors

The application of highly ordered TiO2 nanotube arrays (NTAs) for energy storage devices such as supercapacitors has been attractive and of great interest owing to their large surface area and greatly improved charge-transfer pathways compared to those of nonoriented structures. Modification of the semiconductor nature of TiO2 is important for its application in constructing high-performance supercapacitors. Hence, the present study demonstrates a novel method involving fabrication of self-doped TiO2 NTAs by a simple cathodic polarization treatment on the pristine TiO2 NTAs to achieve improved conductivity and capacitive properties of TiO2. The self-doped TiO2 NTAs at −1.4 V (vs SCE) exhibited 5 orders of magnitude improvement on carrier density and 39 times enhancement in capacitance compared to those of the pristine TiO2 NTAs. Impedance analysis based on a proposed simplified transmission line model proved that the enhanced capacitive behavior of the self-doped TiO2 NTAs was due to a decrease of charge-...

Transient Behaviour of Grounding System in a Two-Layer Soil Using the Transmission Line Theory

The present work deals with modeling of the transient behavior of grounding systems in the presence of layered media. A simple and efficient Transmission Line (TL) model featuring the use of the Finite Difference Time Domain (FDTD) is proposed. The proposed approach easily accounts for the influence of semi-infinite media (soil or air) and imposes conditions at the interfaces. The TL model is verified through the direct solution of the Maxwell's equations in the time domain by means of the FDTD method. Some illustrative computational examples addressing some engineering applications stemming from industry are given in the paper.

A new diagnostic tool for the percolating carbon network in the polymer matrix

Percolating carbon conduction network is not only a long-time pursued scientific topic but also becomes more and more technologically important. Yet no established diagnostic tool is available. A simple two-wire transmission line (TL) model with symmetric boundary condition is suggested as working equivalent circuit model for the percolating carbon network in the insulating matrix such as polymer materials. Spatially distributed shunt capacitors of TL network are determined by the spacing between percolating backbone pathways of resistors. Deviation from the ideal RC TL behavior of the real network due to the non-uniform geometry, dangling network, random distribution of carbon fillers between the backbone pathways, etc. can be represented by modified yet parametric TL models featured by the generalization of the shunt capacitors to constant phase elements.