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Reducing the electrical resistance of films of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate).

Yoshida, Satoru; Ito, Renato Hamakawa; Blackaby, Stuart Tyler; Noguchi, Henrique Kenji Formaggio; Takimoto, Herick Garcia; Santos, Emerson Roberto; Hui, Wang Shu
Fonte: Associação Brasileira de Polímeros; Porto de Galinhas Publicador: Associação Brasileira de Polímeros; Porto de Galinhas
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
36.37%
Semi-conductive polymer thin films were prepared from solutions of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT/PSS) by spin coating. A commercial solution of PEDOT/PSS was submitted to different modification by addition of organic polar compounds, namely ethylene glycol, dimethylformamide, N-methy-2-pyrrolidone, triethylamine, dimethylsulfoxide and sorbitol, and of solutions of nanosilver precursor at different concentrations. Films were prepared from the solutions by spin-coating and their electrical resistances and optical transmittances were measured. Alternatively, deposited thin films were submitted to additional chemical treatments and then heat cured. Additional chemical treatment of the films was carried out using solutions of methanesulfonic acid and p-toluenesulfonic acid at various concentrations. The electrical resistances of the films were reduced from 5-60 MΩ, for those films prepared from original PEDOT/PSS solution, to 10-50 kΩ and 110 kΩ for those from PEDOT/PSS solution modified with organic polar compounds and nanosilver precursor, respectively, and, finally, to 60 kΩ for those films treated with a solution of toluenesulfonic acid. The films presented excellent optical transparency and transmittances at 550 nm in the range 84 - 92 % were found by UV-Vis spectroscopy.; CAPES; CNPq

Anisotropia de resistividade elétrica em filmes finos nanoestruturados.; Electrical resistivity anisotropy in nanostructured thin films.

Teixeira, Fernanda de Sá
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 18/05/2007 PT
Relevância na Pesquisa
46.19%
O objetivo principal deste trabalho foi desenvolver um dispositivo de filme fino com anisotropia de resistividade elétrica. A idéia foi usar um efeito quântico presente em filmes muito finos de materiais condutores ou semicondutores com morfologia anisotrópica na superfície. A morfologia foi um perfil unidirecional quase-senoidal. As resistividades foram determinadas medindo-se as resistências elétricas destes materiais em direções ortogonais, levando-se em conta a geometria da amostra e suas dimensões. O material condutor usado foi Polimetilmetacrilato (PMMA) com ouro implantado na superfície. A profundidade média de implantação foi 2,7 nm. Na fabricação do dispositivo foi utilizada micro e nanolitografia, caracterização por Microscopia Eletrônica de Varredura e Microscopia de Força Atômica e implantação de ouro por MePIIID (Metal Plasma Immersion Ion Implantation and Deposition).; The main purpose of this work was to develop a thin film device with electrical anisotropic resistivity. The idea was to use a quantum effect which is present in very thin films of conductor or semiconductor materials with anisotropic morphology on the surface. The morphology was a sinusoidal-like unidirectional profile. The resistivities were determined measuring the electrical resistances of theses materials in orthogonal directions...

Study of ITO@PMMA composites by transmission electron microscopy

Arlindo, Elen P. S.; Orlandi, Marcelo O.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 183-188
ENG
Relevância na Pesquisa
36.22%
ITO nanowires were synthesized by carbothermal reduction process, using a co-evaporation method, and have controlled size, shape, and chemical composition. The electrical measurements of nanowires showed they have a resistance of about 102 Ω. In order to produce nanocomposites films, nanowires were dispersed in toluene using an ultrasonic cleaner, so the PMMA polymer was added, and the system was kept under agitation up to obtain a clear suspension. The PMMA polymer was filled with 1, 2, 5 and 10% in weight of nanowires, and the films were done by tape casting. The results showed that the electrical resistance of nanocomposites changed by over 7 orders of magnitude by increasing the amount of filler, and using 5 wt% of filler the composite resistance decreased from 1010 Ω to about 104 Ω, which means that percolation threshold of wires occurred at this concentration. This is an interesting result once for nanocomposites filled with ITO nanoparticles is necessary about 18% in weight to obtain percolation. The addition of filler up to 10 wt% decreased the resistance of the composite to 103 Ω, which is a value close to the resistance of wires. The composites were also analyzed by transmission electron microscopy (TEM), and the TEM results are in agreement with the electrical ones about percolation of nanowires. These results are promising once indicates that is possible to produce conductive and transparent in the visible range films by the addition of ITO nanowires in a polymeric matrix using a simple route. © 2011 Materials Research Society.

Using the electrochemical impedance spectroscopy to characterize carbon steel in biodiesel medium

Akita, A. H.; Fugivara, C. S.; Aoki, I. V.; Benedetti, A. V.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Conferência ou Objeto de Conferência Formato: 71-77
ENG
Relevância na Pesquisa
36.15%
Electrochemical impedance spectroscopy measurements using two carbon steel electrodes in soybean biodiesel medium, produced by methylic route, were performed in an electrochemical cell that allows positioning the two electrodes face-to-face. To retain the biodiesel between the electrodes and prevent its leakage a porous membrane soaked in biodiesel was used. The amplitude of the AC potential and the area of the electrodes were varied. The linearity between disturbance and response signals was observed for tests when the amplitude of the AC potential was lower than 1500 mV (rms). The electrical resistance of biodiesel dominates the global response and carbon steel presents low corrosion, which is observed only at low frequency, and was confirmed by chemical tests performed in the membrane. In conclusion the electrical resistance of biodiesel can be estimated using electrochemical impedance spectroscopy with two electrodes set up. ©The Electrochemical Society.

Electrical Resistances of Corn Root Segments 12

Anderson, W. P.; Higinbotham, Noe
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1976 EN
Relevância na Pesquisa
46.48%
Longitudinal electrical resistances have been measured on 2-centimeter segments of corn (Zea mays L.) roots, cut at varying distances from the root apex. The segment resistances vary from 400 to 100 kilohms per centimeter along the root length (apex to 18 cm), with the maximum occurring in the 2- to 4-centimeter segment, and decreasing thereafter toward the root base. Measurements of isolated root cortical sleeves and steles show that the pathway of least resistance is in the cortex, which has a greater cross-sectional area; the specific resistance of the older stele is less than that of the cortex. The anatomical state of the xylem cannot be inferred from electrical resistance determinations.

Comparison of Three Methods for Measuring Electrical Resistances of Plant Cell Membranes 1

Etherton, Bud; Keifer, David W.; Spanswick, Roger M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1977 EN
Relevância na Pesquisa
36.16%
The reliability of two different membrane resistance-measuring methods that use a single intracellular microelectrode was tested against a conventional method that uses two intracellular microelectrodes. The first single-electrode method used a single square current pulse and required a constant microelectrode resistance. This method was unreliable because the electrode resistance changed markedly on cell penetration and changed with time within the cell. The second method used a high frequency square wave for injecting current into the cell and depended upon the membrane having a much longer RC (resistance × capacitance)-time constant than the microelectrode. The resistance values obtained by this latter method were usually different from membrane resistances obtained at the same time on the same cells using two intracellular microelectrodes. Therefore, neither single intracellular microelectrode method was as reliable as the conventional method. All tests were with coleoptile cells of Avena sativa var. Victory.

Cell membranes and paracellular resistances in isolated renal proximal tubules from rabbit and Ambystoma.

Bello-Reuss, E
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1986 EN
Relevância na Pesquisa
36.45%
Transepithelial specific resistance (Re) was measured in isolated and perfused rabbit proximal convoluted tubules by cable analysis and intracellular micro-electrode techniques were used to calculate the electrical resistances of the cell membranes and of the paracellular pathway. Re was 16 +/- 2 omega cm2 and the space constant was 130 +/- 14 micron, n = 29. Re was significantly increased by a decrease in temperature from 37 to 10 degrees C, and was practically abolished by nominal removal of Ca2+ from the bathing solution (to 2.0 +/- 0.3 omega cm2, P less than 0.001, n = 6). The apparent ratio of cell membrane resistances (luminal to basolateral) was 3.1 +/- 0.3. The control values of apical and basolateral membrane resistances (Ra and Rb) were calculated from the values of (1) Re, (2) the apparent ratio of cell membrane resistances, and (3) the effects of addition of either Ba2+ (1 mM) to the bath solution or glucose (8 mM) to the perfusate on basolateral and apical membrane voltages (assuming that the initial effects of Ba2+ and glucose are restricted to the ipsilateral membrane). Control values of Ra (omega cm2 of epithelium) were 249 +/- 68 (Ba2+ method) and 227 +/- 42 (glucose method). Values of Rb were 70 +/- 11; and 66 +/- 12 respectively. The low paracellular resistance values obtained with the Ba2+ and glucose methods...

Effects of changes in the composition of the serosal solution on the electrical properties of the toad urinary bladder epithelium.

Finn, A L; Reuss, L
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1975 EN
Relevância na Pesquisa
36.48%
1. The potential profile and the cellular and paracellular transepithelial resistances of the toad urinary bladder were measured, by means of micro-electrode techniques, as functions of the osmolality of the serosal solution. 2. Reductions in serosal osmolality (that increase the rate of active sodium transport) produced proportional decreases in the electrical resistances of the apical and basal-lateral cell membranes, while the changes in resistance of the paracellular pathway were more complex. The apical membrane potential increased. 3. Increases in serosal osmolality (that decrease sodium transport) produced increases in the electrical resistances of both cell membranes, and moderate reduction in the paracellular resistance. The polarity of the apical membrane potential reversed. 4. These results indicate that reductions in serosal solution osmolality stimulate sodium transport by increasing both the sodium permeability of the luminal cell membrane (thus increasing sodium entry), and the electromotive force generated at the serosal border of the cell, thus enhancing the rate of sodium pumping. Conversely, increases in osmolality reduced sodium transport by reducing both the sodium permeability of the luminal membrane and the serosal membrane electromotive force.

Failure of the Nernst-Einstein Equation to Correlate Electrical Resistances and Rates of Ionic Self-Exchange across Certain Fixed Charge Membranes

Gottlieb, Melvin H.; Sollner, Karl
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1968 EN
Relevância na Pesquisa
46.59%
The electrical resistances and rates of self-exchange of univalent critical ions across several types of collodion matrix membranes of high ionic selectivity were studied over a wide range of conditions. The relationship which was observed between these quantities with membranes of a certain type, namely those activated with poly-2-vinyl-N-methyl pyridinium bromide, cannot be explained on the basis of current concepts of the movement of ions across ion exchange membranes. Rates of self-exchange across these membranes were several times greater than those calculated from the electrical resistances of the membranes on the basis of an expression derived by the use of the Nernst-Einstein equation. The magnitude of the discrepancy was greatest at low concentrations of the ambient electrolyte solution and was independent of the species of both critical and noncritical ions. The data obtained with other types of collodion matrix membranes were, at least approximately, in agreement with the predictions based on the Nernst-Einstein equation. Self-exchange rates across the anion permeable protamine collodion membranes, and across the cation permeable polystyrene sulfonic acid collodion membranes, were about 20% less than those calculated from the electrical resistances. The direction and magnitude of these differences...

Passive Electrical Properties of Toad Urinary Bladder Epithelium : Intercellular Electrical Coupling and Transepithelial Cellular and Shunt Conductances

Reuss, Luis; Finn, Arthur L.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/07/1974 EN
Relevância na Pesquisa
36.37%
The electrical resistances of the transcellular and paracellular pathways across the toad urinary bladder epithelium (a typical "tight" sodium-transporting epithelium) were determined by two independent sets of electrophysiological measurements: (a) the measurement of the total transepithelial resistance, the ratio of resistance of the apical to the basal cell membrane, and cable analysis of the voltage spread into the epithelium; (b) the measurement of the total transepithelial resistance and the ratio of resistances of both cell membranes before and after replacing all mucosal sodium with potassium (thus, increasing selectively the resistance of the apical membrane). The results obtained with both methods indicate the presence of a finite transepithelial shunt pathway, whose resistance is about 1.8 times the resistance of the transcellular pathway. Appropriate calculations show that the resistance of the shunt pathway is almost exclusively determined by the zonula occludens section of the limiting junctions. The mean resistance of the apical cell membrane is 1.7 times that of the basal cell membrane. The use of nonconducting materials on the mucosal side allowed us to demonstrate that apparently all epithelial cells are electrically coupled...

An appraisal of the electrical resistance method for assessing root surface area

Cao, Yang; Repo, Tapani; Silvennoinen, Raimo; Lehto, Tarja; Pelkonen, Paavo
Fonte: Oxford University Press Publicador: Oxford University Press
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
36.22%
Electrical resistances of roots and stems of hydroponically raised willows (Salix schwerinii) were studied and related to root morphology. Willow cuttings with and without roots were set in a constant electric field (effective voltage of 0.1 V, sine-AC, 128 Hz) in a hydroponic solution. The electrical resistance of different components in the measurement system was measured and analysed in relation to root surface area in contact with the cultivation solution. Axial resistivities of single root segments and of stems were measured. The results showed that the resistance decreased in relation to an increase in the contact surface area of the roots with the solution. The resistance depended strongly on the contact area of the stem with the solution, however, thus causing bias in the evaluation of root surface area. This work is a new contribution for the understanding of current pathways in the root system as exposed to an external electric field and for developing a non-destructive method to study plant roots accordingly. It may be concluded that the electrical resistance method is a useful non-destructive method to study roots and their physiological properties. Electrical analogues for roots and stem comprising resistors are discussed in relation to in situ measurements.

Electrochemical Reduction of Silver Vanadium Phosphorous Oxide, Ag2VO2PO4: Silver Metal Deposition and Associated Increase in Electrical Conductivity

Marschilok, Amy C.; Kozarsky, Eric S.; Tanzil, Kevin; Zhu, Shali; Takeuchi, Kenneth J.; Takeuchi, Esther S.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/10/2010 EN
Relevância na Pesquisa
36.48%
This report details the chemical and associated electrical resistance changes of silver vanadium phosphorous oxide (Ag2VO2PO4, SVPO) incurred during electrochemical reduction in a lithium based electrochemical cell over the range of 0 to 4 electrons per formula unit. Specifically the cathode electrical conductivities and associated cell DC resistance and cell AC impedance values vary with the level of reduction, due the changes of the SVPO cathode. Initially, Ag+ is reduced to Ag0 (2 electrons per formula unit, or 50% of the calculated theoretical value of 4 electrons per formula unit), accompanied by significant decreases in the cathode electrical resistance, consistent with the formation of an electrically conductive silver metal matrix within the SVPO cathode. As Ag+ reduction progresses, V5+ reduction initiates; once the SVPO reduction process progresses to where the reduction of V5+ to V4+ is the dominant process, both the cell and cathode electrical resistances then begin to increase. If the discharge then continues to where the dominant cathode reduction process is the reduction of V4+ to V3+, the cathode and cell electrical resistances then begin to decrease. The complex cathode electrical resistance pattern exhibited during full cell discharge is an important subject of this study.

Circuit design and technological limitations of silicon RFICs for wireless applications

Hitko, Donald A. (Donald Anthony)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 206 p.; 21553012 bytes; 21552769 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
36.15%
Semiconductor technologies have been a key to the growth in wireless communication over the past decade, bringing added convenience and accessibility through advantages in cost, size, and power dissipation. A better understanding of how an IC technology affects critical RF signal chain components will greatly aid the design of wireless systems and the development of process technologies for the increasingly complex applications that lie on the horizon. Many of the evolving applications will embody the concept of adaptive performance to extract the maximum capability from the RF link in terms of bandwidth, dynamic range, and power consumption-further engaging the interplay of circuits and devices is this design space and making it even more difficult to discern a clear guide upon which to base technology decisions. Rooted in these observations, this research focuses on two key themes: 1) devising methods of implementing RF circuits which allow the performance to be dynamically tuned to match real-time conditions in a power-efficient manner, and 2) refining approaches for thinking about the optimization of RF circuits at the device level. Working toward a 5.8 GHz receiver consistent with 1 GBit/s operation, signal path topologies and adjustable biasing circuits are developed for low-noise amplifiers (LNAs) and voltage-controlled oscillators (VCOs) to provide a facility by which power can be conserved when the demand for sensitivity is low. As an integral component in this effort...

Double layer capacitors : automotive applications and modeling

New, David Allen, 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 227 p.; 15027449 bytes; 15056891 bytes; application/pdf; application/pdf
EN_US
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36.15%
This thesis documents the work on the modeling of double layer capacitors (DLCs) and the validation of the modeling procedure. Several experiments were conducted to subject the device under test to a variety of charging/discharging profile and temperatures in an effort to simulate the various conditions such a device might encounter in an automotive type application. High and low current charging profiles were performed for both charge/discharge and charge/hold/discharge type experiments. Low temperature ([approx.] -25 ⁰C), room temperature ([approx.] 21 ⁰C), and high temperature experiments ([approx.] 50 ⁰C) were performed for the investigation of temperature effects on these devices. The derived DLC model was used in PSpice® and Matlab® simulations to determine how accurately the model could predict the performance of the device. The nonlinear characteristics of the device were also investigated and the nonlinear modeling information presented as an addition to the basic DLC model. Device variation was explored for a small sample of these devices in an effort to gain insight on the range of tolerances for modern devices. This work also presents an extensive look into the variety of electrochemical capacitor devices under investigation and in use today. An explanation of these devices and their distributed resistances and capacitance is included. This thesis gives a detailed look into the experimental setups and testing procedures used to test the devices...

Copper wafer bonding in three-dimensional integration

Chen, Kuan-Neng, 1974-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 176 p.; 7404641 bytes; 7426947 bytes; application/pdf; application/pdf
ENG
Relevância na Pesquisa
36.15%
Three-dimensional (3D) integration, in which multiple layers of devices are stacked with high density of interconnects between the layers, offers solutions for problems when the critical dimensions in integrated circuits keep shrinking. Copper wafer bonding has been considered as a strong candidate for fabrication of three-dimensional integrated circuits (3-D IC). This thesis work involves fundamental studies of copper wafer bonding and bonding performance of bonded interconnects. Copper bonded wafers exhibit good bonding qualities and present no original bonding interfaces when the bonding process occurs at 400⁰C/4000 mbar for 30 min, followed by nitrogen anneal at 400⁰C for 30 min. Oxide distribution in the bonded layer is uniform and sparse. Evolution of microstructure morphologies and grain orientations of copper bonded wafers during bonding and annealing were studied. The bonded layer reaches steady state after post-bonding anneal. The microstructure morphologies and bond strengths of copper bonded wafers under different bonding conditions were investigated.A map summarizing these results provides a useful reference on process conditions suitable for three-dimensional integration based on copper wafer bonding. Similar microstructure morphology of copper bonded interconnects was observed to that of copper bonded wafers. Specific contact resistances of bonded interconnects of approximately 10⁻⁸ [ohms]-cm² were measured by using a novel test structure which can eliminate the errors from misalignment during bonding. The bonding qualities of different interconnect sizes and densities have been investigated. In addition to increasing the bonding temperature and duration...

Deeply scaled CMOS for RF power applications

Scholvin, Jörg, 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 140 p.
ENG
Relevância na Pesquisa
36.15%
The microelectronics industry is striving to reduce the cost, complexity, and form factor of wireless systems through single-chip integration of analog, RF and digital functions. Driven by the requirements of the digital system components, the 90 nm and 65 nm technology nodes are currently emerging as platforms for highly integrated systems. Achieving such integration while minimizing the cost of adding specialized RF modules places high demands on the base CMOS technology. In this regard, the integration of the power amplifier (PA) function becomes an increasing challenge as technology geometries and supply voltages scale down. Gate length (Lg) scaling yields improved frequency response, promising higher power-added efficiency (PAE), a key RF PA consideration. This benefit comes at the cost of a lower drain voltage, which demands a higher output current and thus wider devices in order to produce a given output power level (Po,,). In this work, we have investigated the potential of deeply scaled CMOS for RF power applications, from 0.25 um down to 65 nm. We demonstrate the frequency and power limitations that the different CMOS technologies face, and describe the physical mechanisms that give rise to these limitations.; (cont.) We find that layout considerations...

Electric field engineering in GaN high electron mobility transistors

Zhao, Xu, S.M. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 70 leaves
ENG
Relevância na Pesquisa
36.37%
In the last few years, AlGaN/GaN high electron mobility transistors (HEMTs) have become the top choice for power amplification at frequencies up to 20 GHz. Great interest currently exists in industry and academia to increase the frequency to mm-wave frequencies. The goal of this thesis has been to identify new solutions to some of the main challenges to increase this frequency performance even further. Electron velocity is a critical parameter affecting the transistor performance. In standard GaN transistors, the extremely high electric fields present in the channel of the device reduce the average electron velocity well below the peak electron velocity, resulting in low cutoff frequencies. In this thesis, we introduced a partial recess in the drain access region of the transistor to engineer the electric field along the channel of the device without introducing parasitic capacitances. By reducing the peak electric field, the average electron velocity is increased by 50%. This new technology has the potential to improve not only the cutoff frequencies, but also the breakdown voltage of GaN transistors. To successfully engineer the electric field in GaN devices, an accurate, reliable and low damage etching technology is needed. However none of the traditional GaN dry etching technologies meets these requirements. This lack of suitable technology has motivated us to develop a new atomic layer etching technique of AlGaN/GaN structures. This technology has been shown to be a self limited process with very high reliability and low damage...

Seleção de parâmetros de soldagem a ponto por resistência, baseado na medição da resistência elétrica entre chapas; Selection of resistance spot welding parameters, based on the measurement of the electrical resistance between sheets

Nascimento, Vinicius Castanheira do
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Dissertação
POR
Relevância na Pesquisa
46.48%
A aplicação da solda a ponto por resistência elétrica em produção em série pode vir a requerer uma programação prévia de variação da regulagem de parâmetros, em função da demanda por mudança seqüencial, tanto devido ao tipo de material como a de sua espessura. Caso a operação seja manual, o operador é quem terá de fazer a troca de programa sempre que identificar diferentes condições numa mesma seqüência de pontos. Por se tratar de uma operação “on-line”, torna-se uma fonte de erro em potencial. Dessa forma, a principal motivação deste trabalho foi a verificação da possibilidade de se regular os parâmetros de soldagem para soldas a ponto em produção, baseado na medição da resistência elétrica das combinações entre chapas. Uma série de experimentos foi realizada para verificar os parâmetros e o número mínimo de ciclos ideal para se medir a resistência elétrica entre chapas de aço com e sem revestimentos com diferentes combinações de espessura. Verificou-se que é possível se determinar a resistência elétrica de uma combinação de espessuras de chapas com apenas seis ciclos e que a variação da resistência era suficientemente repetitiva e diferenciada para justificar o uso deste princípio na separação de combinações por regiões definidas pela resistência elétrica...

Effects of electromagnetic waves on the electrical properties of contacts between grains

Dorbolo, S.; Merlen, A.; Creyssels, M.; Vandewalle, N.; Castaing, B.; Falcon, E.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.44%
A DC electrical current is injected through a chain of metallic beads. The electrical resistances of each bead-bead contacts are measured. At low current, the distribution of these resistances is large and log-normal. At high enough current, the resistance distribution becomes sharp and Gaussian due to the creation of microweldings between some beads. The action of nearby electromagnetic waves (sparks) on the electrical conductivity of the chain is also studied. The spark effect is to lower the resistance values of the more resistive contacts, the best conductive ones remaining unaffected by the spark production. The spark is able to induce through the chain a current enough to create microweldings between some beads. This explains why the electrical resistance of a granular medium is so sensitive to the electromagnetic waves produced in its vicinity.; Comment: 4 pages, 5 figures

Functional carbon nanotubes for electrical conductors

Schauerman, Christopher
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Dissertação
EN_US
Relevância na Pesquisa
36.41%
Carbon nanotube (CNT) conductors are an enabling technology for advancing the efficacy of sustainable energy systems. In parallel, proactive consideration for each of the phases in the material life cycle can enhance device performance while minimizing unwanted impacts. Increasing the yield of CNTs through advances in synthesis will help reduce the electricity, chemicals, and costs associated with their production. Modifications to the nanoscale morphology (alignment, bundling, density and lower contact resistances) are needed to improve the CNT material properties to meet or exceed those of conventional metallic conductors. Also, a robust evaluation of methods for contacting carbon-based wires is needed when interfacing with metallic contacts. Finally, it's important to begin looking at upstream options for proper treatment of waste streams containing CNT conductors when they reach the end of their useable life. Therefore, the subject of this dissertation focuses on the development of functional CNT conductors and considers approaches to improve each phase of their life cycle. Specifically, progress towards using more efficient catalysts in the laser vaporization process has led to a 50% increase in SWCNT yield and simplified the purification procedure. The use of chemical dopants such as KAuCl4 has increased the electrical conductivity up to 1x106 S/m which is over an order of magnitude higher than the pre-doping baseline value. Alternatively...