Triode Operation Research Articles

Computer Model of Thyratron TGI1-270/12

The issues of developing the computer model of a thyratron - an electronic tube triode operating in a switching mode - are considered. A detailed description of the composition of the model is given. The computer model of a single-grid thyratron was developed in the form of a hierarchical block by means of OrCAD. The test circuit for the computer model of a thyratron is suggested. The simulation results of the test circuit operation including a thyratron model are presented (simulated currents and voltages, dynamic characteristics of the thyratron - anode current as a function of the grid voltage). The computer model demonstrated adequacy to the product data sheet.

Investigations of photoresponse characteristics of ultrasonic spray pyrolysis deposited zinc oxide-based phototransistors at different quiescent points

How quiescent-points affect the performance of the ultrasonic spray pyrolysis deposited zinc oxide-based phototransistor is investigated in this study. It is well known that gate bias and drain bias control quiescent-points. By changing gate bias, strong accumulation, weak accumulation, weak depletion, and strong depletion in the active layer of the phototransistor are obtained. Meanwhile, by changing drain bias, either triode or saturation operation regions of the phototransistor is obtained. Therefore, total 8 different quiescent-points are investigated in this study. The material characteristics such as crystal structure, oxygen deficiency, bandgap, and trap energy levels are characterized. Moreover, the performance of the phototransistor at different quiescent-points are investigated. The present phototransistor shows four operation modes, including high responsivity, high UV-to-visible rejection ratio, fast response speed, and high specific detectivity, and each mode corresponds to a specific quiescent point.

A new active resistor and its application to a CMOS transconductor

In this paper a new active resistor is proposed which is suitable for tunable linear voltage to current converters. The proposed resistor is composed of the main and auxiliary triode-mode transistors in which the resistance of auxiliary transistor adds to that of main transistor at a specific tune voltage. By this way the triode operation of both transistors is ensured throughout the tuning range. The proposed resistor is used in a tunable linear transconductor. The proposed transconductor which is implemented in 0.13 μm CMOS technology works with 1.2 V supply voltage and its power consumption changes between 682 and 980 μW. Simulation results show 20 dB improvement in THD of transconductor thanks to using proposed resistor rather than conventional one for input voltage amplitude of 1Vpp at 1 MHz. The transconductance can be tuned from 68 to 177.4 μA/V and the THD remains less than −55 dB for input voltage amplitudes up to 1.2Vpp and for the entire tuning range.

Experimental investigation and mathematical modeling of triode PEM fuel cells

The triode operation of humidified PEM fuel cells has been investigated both with pure H2 and with CO poisoned H2 feed over commercial Vulcan supported Pt(30%)-Ru(15%) anodes. It was found that triode operation, which involves the use of a third, auxiliary, electrode, leads to up to 400% power output increase with the same CO poisoned H2 gas feed. At low current densities, the power increase is accompanied by an increase in overall thermodynamic efficiency. A mathematical model, based on Kirchhoff’s laws, has been developed which is in reasonably good agreement with the experimental results. In order to gain some additional insight into the mechanism of triode operation, the model has been also extended to describe the potential distribution inside the Nafion membrane via the numerical solution of the Nernst-Planck equation. Both model and experiment have shown the critical role of minimizing the auxiliary-anode or auxiliary-cathode resistance, and this has led to improved comb-shaped anode or cathode electrode geometries.

Triode Solid Oxide Fuel Cell Operation Under Sulfur‐Poisoning Conditions

AbstractThe triode solid oxide fuel cell (SOFC) is a three electrodes configuration. The third electrode, so‐called auxiliary, is connected in a way to run in electrolysis mode, while cathode and anode operate in normal fuel cell mode. This mixed operation allows to reach anode–cathode potential differences which are not accessible in normal operation. In this work, the benefits of triode operation under sulfur‐poisoning conditions are shown. In particular, the difference between conventional and triode operation mode under 2ppm of H2S in H2 are analyzed. The partial reversibility of sulfur poisoning is investigated and the observed regeneration processes are discussed for both the conventional and triode operation. After each sequence of exposure and regeneration, IV and EIS characteristics are taken. The electrochemical impedance spectra are further processed by computing the distribution of relaxation times (DRT). During triode operation, less degradation during exposure and faster stabilization after exposure and regeneration with respect to conventional operation mode are observed.

Implicit Common-Mode Resonance in <italic>LC</italic> Oscillators

The performance of a differential LC oscillator can be enhanced by resonating the common mode of the circuit at twice the oscillation frequency. When this technique is correctly employed, Q-degradation due to the triode operation of the differential pair is eliminated and flicker noise is nulled. Until recently, one or more tail inductors have been used to achieve this common-mode resonance. In this paper, we demonstrate that additional inductors are not strictly necessary by showing that common-mode resonance can be obtained using a single tank. We present an NMOS architecture that uses a single differential inductor and a CMOS design that uses a single transformer. Prototypes are presented that achieve figure-of-merits of 192 and 195 dBc/Hz, respectively.

Enhanced Carbon Deposition Tolerance of SOFC Anodes Under Triode Operation

The triode fuel cell design and operation concept was applied as an alternative means for controlling and enhancing the carbon tolerance of state-of-the-art solid oxide fuel cell (SOFC) anodes. The triode cell configuration entails the introduction of a third electrode in addition to the anode and cathode, driven by an auxiliary circuit which is run in electrolytic mode. In this way the cell is forced to operate at controlled potential differences that are inaccessible under standard operation, and thus introduces a controllable variable into fuel cell operation. In the present study, the effectiveness of the triode approach was evaluated for the in situ control of the rate of carbon deposition in commercial multilayer NiO–GDC and NiO–YSZ SOFC anodes. The study involved typical and triode operation of SOFC button cells under CH4 steam reforming conditions, and it was found that the application of a small electrolytic current under triode operation resulted in significantly less carbon built-up on the anode compared to the standard SOFC operation.

Electrochemical Model of a Triode Solid Oxide Fuel Cell

A Triode Solid Oxide Fuel Cell is a novel cell architecture that aims to control the electrocatalytic activity under low steam reforming conditions, or poisoning conditions. This fuel cell design introduces a third electrode (auxiliary electrode) of the same nature of the cathode while the anode is common between the two circuits (Figure 1). The auxiliary circuit, which electrically connects the anode with the auxiliary electrode, is operated in electrolysis mode while the fuel cell circuit runs in its conventional way. During the triode operation, performance enhancement is recorded especially when a significant electrode overpotential is presented; this can be the case for SOFC anode feeds with natural gas and gasoline fuels, or when it is being poisoned from impurities. A two-dimensional stationary isothermal model is developed and implemented in commercial software, COMSOL Multiphysics (version 4.3b). The model is based on composite electrodes, where the equations for mass, momentum and charge transport, along with electrochemical global kinetics (Butler-Volmer equation) and charge conservation are solved simultaneously. Exchange current densities are fitted from experimental data to reproduce the observed behavior of the cell. The model, able to predict conventional and triode operation, gives guidelines for the electrodes geometry design that needs to be adopted in order to favor the expected improvements. In particular, it is noted that the aspect ratio between the electrodes distance cathode-auxiliary and the electrolyte thickness is a key parameter. The interaction between the main and auxiliary circuits is then discussed in terms of equipotential and current lines in a cross section of the cell for two different geometries: anode and electrolyte supported cells. The improvements achievable in triode operation are also calculated in terms of electric current surplus that is possible to obtain in the fuel cell circuit while imposing an electrolysis voltage of 1.7 V in the auxiliary circuit. Figure 1

Electrochemical Model of a Triode Solid Oxide Fuel Cell

A Triode Solid Oxide Fuel Cell is a novel cell architecture that consists of two circuits: an auxiliary circuit, operated in electrolysis mode, and a conventional main fuel cell circuit. During triode operation, performance enhancement can be expected especially when a significant electrode overpotential is present. A two-dimensional stationary isothermal model is implemented in a commercial software, COMSOL Multiphysics. The model, able to predict conventional and triode operation, gives guidelines for the electrodes geometry design that needs to be adopted in order to favor the expected improvements. The interaction between the main and auxiliary circuits is then discussed in terms of equipotential and current lines in a cross section of the cell for two different geometries: anode and electrolyte supported cells. The improvements achievable in triode operation are also calculated in terms of electric current surplus that is possible to obtain in the fuel cell circuit.

Triode operation for enhancing the performance of H2S-poisoned SOFCs operated under CH4–H2O mixtures

Performances of Solid Oxide Fuel Cells (SOFCs) were investigated in triode operation mode under methane steam reforming in the presence of H2S. Both the catalytic performances for methane steam reforming and the electrochemical properties for the electrochemical oxidation of hydrogen of a Ni/GDC anode drastically dropped in the presence of 1ppm H2S. Poisoned catalytic sites are different from those for the hydrogen electrochemical oxidation. Triode operation, i.e. application of moderate negative currents between the anode and an auxiliary electrode, can improve electrochemical properties, as a result of a local production of H2 coming from H2O electrolysis. Some specific triode operations were found to achieve a thermodynamic efficiency close to the unity to avoid any energy overconsumption.

Enhanced Oxygen Reduction Using Triode Fuel Cells

Keywords: Triode fuel cells, oxygen reduction, auxiliary electrode, overpotential minimization, SOFC, PEMFC INTRODUCTIONThe power output and thermodynamic efficiency of electrochemical power producing devices, batteries and fuel cells, depend critically on the minimization of overpotential losses at the anode and cathode [1]. Significant overpotential, caused by inefficient electrocatalysis at the anode and cathode, remains the main obstacle for commercialization of the technologies of solid oxide fuel cells (SOFC) and polymer electrolyte membrane (PEM) fuel cells [1]. < style="text-align: justify;"> EXPERIMENTAL The introduction of a third electrode together with an auxiliary circuit which is run in the electrolytic mode permits fuel cell operation under previously inaccessible anode-cathode potential difference. This introduces a new controllable variable in fuel cell operation and can lead to significant reduction of the anodic and cathodic overpotential and thus in an enhancement of power output and overall thermodynamic efficiency. The triode operation has been tested both with SOFC and with PEMFCs, the latter with CO poisoned H2 feeds. In both cases significant, up to 800% and 400% respectively increases in power output have been obtained [2,3]. The new design is shown schematically in Figure 1 for the case of a PEM fuel cell. In the present study two reference electrodes added in order to measure the anodic and cathodic overpotential. RESULTS AND DISCUSSIONTwo parameters have been introduced to quantify the results of triode operation. The first is the power enhancement ratio, rP, defined as:ρp=Pfc /Po fc (1)where Po fc is the cell power output for normal (Iaux=0) operation. The second parameter is the power gain ratio, ΛP , defined as ΛP=(Pfc - Po fc)/Paux (2) When ΛP>1 then the thermodynamic efficiency of the triode unit is higher than that corresponding to conventional fuel cell operation. In the case of PEM fuel cells it has been found [3] that the cell power output can be enhanced by a factor of four with a concomitant 30% increase in thermodynamic efficiency. It was found that the applied auxiliary potential affects the charged transfer kinetics both at the anode and at the cathode and can enhance significantly the cathodic reduction of oxygen. CONCLUSIONS The triode fuel cell appears to be a promising concept under conditions of significant anodic or cathodic overpotential.Significant enhancement in cell performance is possible only when anode and cathode are is at least partly polarizable. Mathematical modeling is underway to optimize cell geometry. Application of the triode operation in suitably modified PEMFC stacks also appears feasible [3]. Figure 1.Schematic of the triode fuel cell, showing (a) the fuel cell and auxiliary circuits. (b) The exact geometry of the triode PEM fuel cell tested [3] and the electrical circuits. The fuel cell cathode acts simultaneously as an electrode of the auxiliary circuit where current or potential are controlled via a galvanostat-potentiostat.ACKNOWLEDGMENTWork supported under the ARISTEIA Programme. ReferenceS [1] W. Vielstich, A. Lamm and H. Gasteiger, in Handbook of Fuel Cells, Fundamentals Technology and Applications, Vol. 2, Wiley, New York (2003).[2] S.P. Balomenou and C.G. Vayenas, J. Electrochem. Soc., 151(11) (2004) A1874.[3] F.M. Sapountzi, S.C. Divane, M.N. Tsampas, C.G. Vayenas, Electrochim. Acta 56 (2011) 6966.

Triode operation of CO poisoned PEM fuel cells: Fixed and cyclic potential triode operation

An alternative approach for enhancing the Polymer Electrolyte Membrane Fuel Cell (PEMFC) performance under CO poisoning conditions was investigated by the use of the recently developed triode fuel cell design and operation. In this mode of operation a third, auxiliary, electrode is introduced in addition to the anode and cathode electrodes. It is shown that the application of electrolytic potential between the cathode and an auxiliary electrode can affect the performance of the fuel cell circuit in a controllable and reversible manner. The applied electrolytic current or potential can be fixed (steady-state) or can be cycled between chosen limits. In the present study, both triode operation modes were investigated and it was found that the time-averaged power output of the fuel cell can be increased up to three times.

Enhanced performance of CO poisoned proton exchange membrane fuel cells via triode operation

The effect of triode operation on the performance of CO poisoned PEM fuel cells was investigated. In this mode of operation a third, auxiliary, electrode is introduced in addition to the anode and the cathode. Application of electrolytic current in the auxiliary circuit, comprising the cathode and the auxiliary electrode was found to significantly enhance the time-averaged power output of a state-of-the-art PEMFC unit operating with a 70 ppm CO in H 2 atmospheric pressure mixture. Both normal and triode operation were found to lead to self-sustained current and potential oscillations in the fuel cell circuit over wide ranges of external resistive load. The time averaged increase in power output was found to be typically a factor of three higher than the power output in conventional fuel cell operation and up to a factor of 1.32 larger than the power sacrificed in the auxiliary circuit. The mechanism of the enhanced anodic electrocatalysis was investigated via the use of two reference electrodes and the results are discussed together with a possible design for application of the triode concept in stacks.

Bulk-Quantity Synthesis of Ultralong SnO&lt;sub&gt;2&lt;/sub&gt; Nanowires and their Application to a Backgated Triode Emission Device

A high yield of ultralong SnO2 nanowires is successfully achieved by a simple thermal evaporation of SnO powders under air ambient. The as-synthesized SnO2 nanobelts are single crystals with rutile structure. A backgated triode device for high-current applications has been developed with beltlike SnO2 field emitters. The devices have confirmed triode operation with low turn-on gate voltage (about 170 V) and stable electron emission with brightness of 30 cd/m2.

Development and Characterization of Repetitive 1-kJ Marx-Generator-Driven Reflex Triode System for High-Power Microwave Generation

This paper presents the design and development of a repetitive Marx generator rated at 1 kJ, 300 kV, 12 kA, and 10 Hz and which is suitable to drive the load directly. Bipolar charging of a Marx generator scheme has been adopted to get the following: 1) faster rise time and 2) relatively low charging voltage. The faster rise time is due to the reduced number of spark gaps down to six for 12 in-series capacitors (0.15 μF and 50 kV) of a six-stage bipolar-charging Marx generator. Interstage inductive charging further enhances the efficiency of the overall system as compared to resistive charging. The generator is characterized by an aqueous resistive load for both polarities at the output voltage. Output voltages of the same magnitude have been achieved for both polarities. The matched impedance is found to be 25 Ω for which a suitable reflex triode is designed. Intense electron beams and high-power microwaves have been generated using this Marx generator and reflex triode system. Experimental results demonstrating the Marx generator and the reflex triode operation are presented and discussed.

Triode Operation of a Proton Exchange Membrane (PEM) Methanol Electrolyser

Triode operation was shown to improve the PEM electrolysis of liquid methanol and water in a non-flowing system at ambient conditions in the galvanostatic and potentiostatic mode. A decrease in electrolysis voltage requirements proportional to the current or potential imposed in the auxiliary circuit was observed on carbon and noble metal catalysts. This was only observed when the auxiliary current or potential was in the opposite direction compared to the electrolyser circuit current or potential. Cathode potential measurements were reported in triode operation. It appears that triode operation improved the electro-oxidation through the electrochemical pumping of protons and proton spillover. This improvement could not be explained by intrinsic membrane or solution conductivity enhancements due to greater proton concentrations. The mechanism behind the triode enhancement needs clarifications. Triode operation may lead to electrolysis cost reduction through the use of smaller amounts or no precious metal catalyst while maintaining an adequate performance.

Novel tapered macrogate structure for carbon nanotube based field emission display

The tapered macrogate (TMG) structure is proposed to overcome the difficulties in carbon nanotube (CNT) based field emission display (FED) with high-voltage phosphors used in cathode ray tube screens. In order to achieve an ideal triode operation for field emission devices, the TMG was designed to have a very thick gate insulator with the inclined gate holes compared with the CNT emitters. The inclined gate holes with a narrower outlet than the bottom of the hole were shown to protect the CNT emitters from the anode field perfectly, enabling the authors to apply a high anode voltage over 10 kV needed for high-voltage FED. Also, the TMG structure had additional useful functions such as an electron-beam self-focusing and high durability against electrical damage. The authors successfully fabricated and demonstrated a 5 in. active-matrix CNT-FED panel with the TMG, showing color moving images with a low addressing voltage of about 15 V using amorphous silicon thin-film transistor as a switching device.

Tunable Highly Linear Floating-Gate CMOS Resistor Using Common-Mode Linearization Technique

In this paper, an implementation of a tunable highly linear floating resistor that can be fully integrated in CMOS technology is presented. The second-order effects of a single MOS transistor operating in the triode operation regime are described, and a common-mode linearization technique is applied to suppress these nonlinearities. This technique is implemented by utilizing a low-power circuit design strategy that exploits the capacitive coupling and the charge storage properties of floating-gate transistors. The resistance of the proposed circuit is tuned by utilizing the Fowler-Nordheim tunneling and hot-electron injection quantum-mechanical phenomena. We demonstrate the use of this resistor in highly linear amplifier. We present experimental data from the chips that were fabricated in a 0.5- CMOS process. We show that this resistor exhibits 0.024% total harmonic distortion (THD) for a sine wave with amplitude. Also, we show the programmability of the amplifier gain using the proposed tunable resistor.

High field emission reproducibility and stability of carbon nanosheets and nanosheet-based backgated triode emission devices

The authors have characterized field emission properties of freestanding, 1nm thick graphene layers, called carbon nanosheets (CNSs), which were grown perpendicular to the growth surface using a radio-frequency plasma-enhanced chemical vapor deposition technique. The CNSs are metallic impurity-free and have uniform height distribution (standard deviation of &amp;lt;10%). The authors have demonstrated reproducibility and stability of the CNSs for a period of &amp;gt;200h at 1.3mA emission current level. Over this time, no degradation has been observed, the variability of the individual I-V curves is small among 7216 voltage cycles, and the standard deviation at the maximum current was no more than 2.3%. A nanosheet-based backgated triode emission device has been developed to take advantage of the nanosheet field emission performance. Prototype devices have confirmed triode operation and stable electron emission.

High Linearity BiCMOS Multiplier/Transconductor Structures

A new wide-input range BiCMOS analog multiplier is proposed based on the triode and saturation region operation of the MOS transistors. The new circuit can also be reconfigured to operate as a versatile Operational Transconductance Amplifier, OTA, with independent current bias control for N stages. The novel design involves the use of attenuators at the input stage to boost the input linear range. It also utilizes a high output impedance subtractor setup at the output stage to obtain a single-ended output. The new circuit is characterized by its large input range, its high linearity and ability to operate at low voltages as well as high frequencies. HSPICE simulation results of the circuit, using the MOSIS 2 µm process parameters, resulted in an input range of ±4 V (±5 V supply), ±1.9 V (±3 V supply) and ±1 V (±2 V supply), with linearity error less than 0.5%. It’s usages in certain analog signal processing applications are also discussed.