Linear Transmission Line Research Articles

Acoustic echo cancellation system based on Laguerre method and neural network

Acoustic echo cancellation (AEC) is a fundamental requirement of signal processing to increase the quality of teleconferences. In this paper, a system that combines the Laguerre method with neural networks is proposed for AEC. In particular, the signal is processed using the Laguerre method to effectively handle nonlinear transmission line system. The results after applying the Laguerre method are then fed into a neural network for training and acoustic echo cancellation. The proposed system is tested on both linear and nonlinear transmission lines. Simulation results show that combining the Laguerre method with neural networks is highly effective for AEC in both linear and nonlinear transmission lines system. The AEC results obtained by the proposed method achieves a significant improvement in nonlinear transmission lines and it is the basis for building a practical echo cancellation system.

Acoustic echo cancellation system based on Laguerre method and neural network

Acoustic echo cancellation (AEC) is a fundamental requirement of signal processing to increase the quality of teleconferences. In this paper, a system that combines the Laguerre method with neural networks is proposed for AEC. In particular, the signal is processed using the Laguerre method to effectively handle nonlinear transmission line system. The results after applying the Laguerre method are then fed into a neural network for training and acoustic echo cancellation. The proposed system is tested on both linear and nonlinear transmission lines. Simulation results show that combining the Laguerre method with neural networks is highly effective for AEC in both linear and nonlinear transmission lines system. The AEC results obtained by the proposed method achieves a significant improvement in nonlinear transmission lines and it is the basis for building a practical echo cancellation system.

Hole transport mechanism at high temperatures in p-GaN/AlGaN/GaN heterostructure

This Letter reports an investigation of hole transport in p-GaN/AlGaN/GaN heterostructures through experimental and theoretical analyses under varied conditions. Highly non-linear current–voltage (I–V) characteristics, obtained via the linear transmission line method measurements, are utilized for this study. At low bias voltage, the transport can be ascribed to the Schottky nature of the contact, while at high bias, the conduction is observed to be governed by space-charge limited current (SCLC). The Schottky characteristics (Schottky barrier height and non-ideality factor) and the SCLC exponent were analyzed for devices with varying contact spacings and at different high temperatures. The SCLC exponent, m, is in the range of 2≤m≤4 depending on the applied voltage range, revealing the existence of the trap states in the channel region. The findings of this work indicate that the charge injection, field-induced ionization, and trap states in the p-GaN channel are critical factors in the current transport of p-GaN/AlGaN/GaN heterostructure.

Implementation & simulation of fault locating algorithm and localization for linear transmission lines on PMU based two terminal system.

The demand of electricity is increasing rapidly. Among all, electricity is most reliable and sustainable source. With the growth in demand, power system will be more complex and sophisticated. Transmission lines are backbone for supplying electricity to every consumer. Transmission line are mostly prone to faults. So, clearing the fault of transmission in least possible time is most important to reduce the damage occurred due to fault. The protection of the transmission line could benefit tremendously from the capacity to locate and identify the issue. The Phasor Measurement Unit is used in this work to offer a contemporary method of fault localization and detection. The PMU transmission line and fault have been modelled using MATLAB/Simulink. The detection of fault uses discrete wavelet transform, PMU uses discrete Fourier transform and the localization of fault is done using Universal algorithm. In general, this paper provides the concept of PMU and its application in fault detection and locating the fault point in transmission as well as distribution line. The approach taken in this paper has been tested for different line length, source impedance and different types of faults.

Broadband reduction of phase noise in a spatially extended tunnel‐diode oscillator through multiple self‐injection locking

SummaryA self‐injection locking scheme is proposed to reduce phase noise in a spatially extended oscillator that uses a tunnel‐diode (TD) transmission line. When a linear transmission line is connected to each cell of the TD line, a part of the oscillating edge flows through the linear line. This wave on the linear line is reflected at its far end and flows back to the point of connection of the TD and linear transmission lines. By matching the time taken by the reflected wave on the linear transmission line to reach the point of connection with the time taken by the forward‐moving oscillating edge to return to the point, the edge can be synchronized with the wave that flows back through each linear line. This multiple self‐injection locking significantly reduces the phase noise of the oscillating edge. In this work, the technique of phase noise reduction is explained through numerical phase noise analysis using the perturbation projection vector of the system. Several experimental observations were made to validate the reduction of the phase noise in the oscillating edge traveling on the TD line.

A hybrid transmission-line model for the resolution of the heat equation in stratified structures under non-linear regime and periodic excitation: its applications to microwave radiometry of the Moon

We here propose a method that, through linear transmission lines and time-domain non linear sub-circuits, solves the heat equation for one-dimensional problems in the periodic regime, involving layered structures and boundary conditions and/or media with a non-linear behavior. As an example, we provide its application to the lunar crust, represented by a layered structure, that is exposed to solar radiation and transfers heat to the sky by means of radiation. The proposed model allows then to determine the Moon temperature at different depths and in time. It represents the starting point for determining the microwave electromagnetic emission from the Moon, whose remote observation is of considerable importance in the study of its characteristics. Microwave brightness data from recent lunar missions are in good agreement with the proposed model results.

Novel step selection analyses on energy landscapes reveal how linear features alter migrations of soaring birds.

Human modification of landscapes includes extensive addition of linear features, such as roads and transmission lines. These can alter animal movement and space use and affect the intensity of interactions among species, including predation and competition. Effects of linear features on animal movement have seen relatively little research in avian systems, despite ample evidence of their effects in mammalian systems and that some types of linear features, including both roads and transmission lines, are substantial sources of mortality. Here, we used satellite telemetry combined with step selection functions designed to explicitly incorporate the energy landscape (el-SSFs) to investigate the effects of linear features and habitat on movements and space use of a large soaring bird, the golden eagle Aquila chrysaetos, during migration. Our sample consisted of 32 adult eagles tracked for 45 spring and 39 fall migrations from 2014 to 2017. Fitted el-SSFs indicated eagles had a strong general preference for south-facing slopes, where thermal uplift develops predictably, and that these areas are likely important aspects of migratory pathways. el-SSFs also provided evidence that roads and railroads affected movement during both spring and fall migrations, but eagles selected areas near roads to a greater degree in spring compared to fall and at higher latitudes compared to lower latitudes. During spring, time spent near linear features often occurred during slower-paced or stopover movements, perhaps in part to access carrion produced by vehicle collisions. Regardless of the behavioural mechanism of selection, use of these features could expose eagles and other soaring species to elevated risk via collision with vehicles and/or transmission lines. Linear features have previously been documented to affect the ecology of terrestrial species (e.g. large mammals) by modifying individuals' movement patterns; our work shows that these effects on movement extend to avian taxa.

Optimization of ohmic contact on n-type GaAs by screen-printing silver paste

We used printed electronics technology to print silver paste (SP) on n-GaAs as an electrode replacing conventional alloy electrodes to simplify the fabrication process of solar cell and to reduce cost. The linear transmission line model was used to characterize the performances of SP/semiconductor ohmic contact at different annealing temperatures. The lowest specific contact resistance between SP and n-GaAs of 1.8 × 10−4 Ω cm2 was achieved after annealing at 560 °C, which indicates the appropriate annealing temperature can not only ensure the close contact of silver particles, but also reduce the barrier height of metals and semiconductors to a certain extent. On the basis of these results, n-GaAs with an SP electrode can be promisingly applied to realize highly efficient and simple-manufacturing III–V solar cells.

Structural and electrical properties of Pd/p-GaN contacts for GaN-based laser diodes

In this paper, the properties of Pd-based p-contacts on GaN-based laser diodes are discussed. Pd is often the metal of choice for ohmic contacts on p-GaN. However, for Pd/p-GaN ohmic contacts, nanovoids observed at the metal/semiconductor interface can have a negative impact on reliability and also reproducibility. The authors present a thorough analysis of the microstructure of the Pd/p-GaN interface by x-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM). STEM data show that the microvoids at the p-GaN/Pd interface form during rapid thermal annealing. A combination of the following effects is suggested to support the void formation: (1) the differences in thermal expansion coefficients of the materials; (2) excess matrix or impurity atoms in the semiconductor, at the interface, and in the metals, which are released as gases; and (3) the strong antisurfactant effect of Pd on Ga-rich p-GaN surfaces. A slow temperature ramp during contact annealing reduces the formation of voids likely by suppressing the accumulation of gases at the interface. XPS data show that the Ga/N ratio can be reduced by suitable cleaning of the p-GaN surface, which enhances Pd adhesion. As a result, the quality of the contact system is improved by the systematic optimization of the surface cleanliness as well as the annealing parameters, leading to void-free and clean Pd/p-GaN interfaces. The specific contact resistance, extracted from linear transmission line method measurements, is reduced by an order of magnitude to 2 × 10−3 Ω cm² at 1 mA for the same epitaxial layer stack.

Simplifying Through-Forest Propagation Modelling

Propagation analysis and modeling is critical for radio systems design, but remains a challenge for most through-vegetation situations, including forests. Transmission through such inhomogeneous mixed media is complicated by the many different propagation mechanisms and the complexity of the randomness. This means that accurate, purely physics-based analysis is unlikely to be practical (conveniently computed), and similarly, that practical, purely random modeling is unlikely to be accurate. Through-vegetation propagation models, including the standard radiative energy transfer (RET), are not very accurate in the sense that the uncertainty can be tens of dB, and this seems to be an accepted limitation for vegetation. A simpler propagation model, which maintains or improves accuracy, but keeps a reasonable association with the physics, would be insightful. This paper discusses such a model. It comprises two parallel transmission mechanisms: direct transmission through a succession of trees, which is modeled by a simple linear transmission line; and transmission across the forest top, which is modeled by simplified multiple-edge diffraction. The model is examined using recently-published experiments over a long path-length. It is demonstrated that this two-mechanism model can provide an accurate fit to the dual-slope profile of through-forest propagation over a long distance which is not possible with the RET model.

Phase‐noise reduction by self‐injection locking in spatially extended tunnel‐diode oscillator

A scheme is proposed for reducing phase noise in a spatially extended oscillator using tunnel-diode (TD) transmission line. It is observed that a voltage edge oscillates on a TD line when supplied by an appropriate DC voltage at the end. When the TD line is bypassed by a linear transmission line, part of the oscillating edge is inputted to and moves on the linear line to interact with the oscillating edge at the another crosspoint. The proper length of the linear line makes the bypassed voltage arrive at the crosspoint at the same time as the oscillating edge. It results in significant phase-noise reduction of the oscillating edge through self-injection locking. Herein, the principle of operation is described with its experimental validation.

Theory of Terminated Nonlinear Transmission Lines

Properly terminating a transmission line, in order to transfer the maximum available power to the load, is an important issue. The problem, fully analyzed in linear lines, is still considered as a persisting problem in the area of nonlinear transmission lines (NLTLs). In this paper, an accurate analysis is presented which gives a closed-form formula for the matching efficiency of the NLTLs. Using this analysis, optimal resistive terminating load for the NLTLs was extracted. These results will considerably ease the design of all kinds of the NLTL-based systems, such as high-frequency oscillators and ultrashort pulse generators. This consistent analysis also gives the reflection coefficient for the waves reflecting from the NLTLs load. It is shown that the NLTLs are far different from linear transmission lines in the both cases of matching efficiency and reflection coefficient. The obtained analytical results are verified with experimental measurements and SPICE simulations. Excellent agreements are obtained. It is also shown that the results of the introduced analysis make it possible to design the NLTL-based systems without any trial-and-error efforts.

Sheet resistance underneath the Au ohmic-electrode on hydrogen-terminated surface-conductive diamond (001)

The sheet resistance (Rsk) underneath ohmic Au-electrodes on hydrogen-terminated surface-conductive diamond (001) surfaces was examined by a special current-voltage measurement. It has been found that Rsk is about ~200 times larger than the sheet resistance, Rsh, in the open areas without Au-electrodes. The specific contact resistance, RC, of ohmic Au-electrodes on H-terminated surface-conductive diamonds as determined by linear transmission line models must be corrected accordingly. As the results of this, RC is suggested to be of the order of 1×10−3–1×10−4Ωcm2.

The effects of bifacial deposition of ALD AlOx on the contact properties of screen-printed contacts for p-type PERC solar cells

Most c-Si solar cells adopt monofacial thin film structures and consequently much effort, particularly at the equipment design level, is devoted to ensure monofacial thin film processing. This often leads to more complex production equipment with lower throughput. However, in some cases, bifacial processing can be tolerated, and it is shown that a bifacial deposition of aluminium oxide (AlOx) using atomic layer deposition (ALD) can even result in improved performance of the solar cell. The merits of ALD AlOx at the rear of p-type PERC solar cells are well established and this work shows that a thin AlOx layer on the front of a PERC solar cell can also significantly reduce the contact resistance of screen printed Ag without affecting the optical properties of the solar cell. In this work, a equidistant linear transmission line method (TLM) pattern is used to characterise the contact resistance and specific contact resistivity. This technique has the advantage of being able to measure the fingers of completed cells, and this also explores the error introduced by measuring the resistance across interjacent fingers. A 3 or 5 nm AlOx film reduces the contact resistivity to 0.06 mΩ.cm2 and 0.11 mΩ.cm2, respectively, significantly lower than a value of 0.25 mΩcm2 achieved with an uncapped reference. Also, the peak temperatures required to achieve a good contact was lower, and the optimum firing temperature window was found to be wider, in comparison to the reference. A 10 nm ALD AlOx film is found to have a detrimental effect on the contact resistance which cannot be mitigated by a higher firing temperature.

Au-free ohmic Ti/Al/TiN contacts to UID n-GaN fabricated by sputter deposition

The fabrication and characterization of an Au-free Ti/Al/TiN (20/100/100 nm) contact stack to unintentionally doped n-GaN with TiN serving as the diffusion barrier is presented. Sputter deposition and lift-off in combination with post deposition annealing at 850 °C are used for contact formation. After annealing, contact shows ohmic behavior to n-GaN and a specific contact resistivity of 1.60 × 10−3 Ω cm2. To understand the contact formation on the microscopic scale, the contact was characterized by current–voltage measurements, linear transmission line method, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The results show the formation of Ti-N bonds at the GaN/Ti interface in the as-deposited stack. Annealing leads to diffusion of Ti, Al, Ga, and N, and the remaining metallic Ti is fully consumed by the formation of the intermetallic tetragonal Al3Ti phase. Native oxide from the GaN surface is trapped during annealing and accumulated in the Al interlayer. The TiN capping layer, however, was chemically stable during annealing. It prevented oxidation of the Ti/Al contact bilayer successfully and thus proved to be a well suitable diffusion barrier with ideal compatibility to the Ti/Al contact metallization.

Modified Rogowski coil for the detection of fast plane currents

Rogowski coils are used to diagnostic currents of cylindrical configuration, therefore they are known to have a toroidal geometry. Nowadays, also linear transmission lines can be developed to get planar beams. Therefore, linear Rogowski coil to detect current pulses inside the linear conductors are necessary. For large devices, the theory necessary to study the system is that of the transmission lines, especially if the pulse width is comparable to the propagating time of signal inside the detector. The device we developed is able to record pulses more than 80ns long with rise time near 500ps. The former depends on the inductance value, load impedance and resistance of the coil; while the second on the mechanical configuration of coil loops. Theoretically, the attenuation coefficient depends exclusively on the turn number of the coil, while experimentally it is found to depend also on the current distribution inside the line.

The effect of non-linear capacitances in the localization properties of aperiodic dual electric transmission lines

This study investigates the localization properties of dual electric transmission lines with non-linear capacitances. The VC,n voltage across each capacitor is selected as a non-linear function of the electric charge qn, i.e., VC,n = qn(1/Cn -en|qn|2) where Cn is the linear part of the capacitance and en the amplitude of the non-linear term. We follow a binary distribution of values of en, according to the Thue-Morse m-tupling sequence. The localization behavior of this non-linear case indicates that the case m = 2 does not belong to the m ≥ 3, family because when m changes from m = 2 to m = 3, the number of extended states diminishes dramatically. This proves the topological difference of the m = 2 and m = 3 families. However, by increasing m values, localization behavior of the m-tupling family resembles that of the m = 2, case because the system begins to regain its extended states. The exact same result was obtained recently in the study of linear direct transmission lines with m-tupling distribution of inductances. Consequently, we state that the localization behavior of the m-tupling family as a function of the m value is independent of both the linear and the non-linear system under study, but independent of the kind of transmission line (dual or direct). This is curious behavior of the m-tupling family and thus deserves more scholarly attention.

Mask registration and lithography platform portability for nitride fin-based field effect transistors prototyping

The authors report on the integration of a hybrid lithography process for AlGaN/GaN high-electron-mobility nanoscaled, fin-based field effect transistors with an Au-free contact. The integration consists of electron beam lithography (EBL) and optical photolithography to minimize prototyping cost and time while maximizing resolution and device array density. I-line direct photolithography is performed using standard photoresist, while EBL is accomplished using 2% polymethyl methacrylate for high resolution of fin structure patterning. Au-free contact is characterized using linear transmission line method (TLM) and is deposited along with registration marks via electron beam evaporation. The registration marks and TLM structures are used for alignment in the EBL process. Details of the device fabrication process and electrical results are discussed and show possible parallel processing of GaN and Si devices.

Polar semiconductor heterojunction structure energy band diagram considerations

The unique nature of built-in electric field induced positive/negative charge pairs of polar semiconductor heterojunction structure has led to a more realistic device model for hexagonal III-nitride HEMT. In this modeling approach, the distribution of charge carriers is dictated by the electrostatic potential profile instead of Femi statistics. The proposed device model is found suitable to explain peculiar properties of GaN HEMT structures, including: (1) Discrepancy in measured conventional linear transmission line model (LTLM) sheet resistance and contactless sheet resistance of GaN HEMT with thin barrier layer. (2) Below bandgap radiation from forward biased Nickel Schottky barrier diode on GaN HEMT structure. (3) GaN HEMT barrier layer doping has negligible effect on transistor channel sheet charge density.

Modified Linear Transmission Line Model Test Structure for Determining Specific Contact Resistance

ABSTRACTA modified design of the transmission line model test structure uses the simple calculation of specific contact resistance, ρc, based on a two contact linear pattern but without the requirement of a mesa etch. This modified structure uses a linear TLM with semicircular terminations at each end. The function of the semicircular terminations is to confine the fringing fields at the ends of the linear TLM contacts. Simple analytical equations for determining ρc have been developed on the basis of the modified linear TLM pattern. These calculations have shown good agreement with a finite element model (FEM) of the modified TLM test structure using typical parameters for metal/ SiC contacts.