Load Resistance RL Research Articles

Injection of anomalous-Hall current into a load circuit

The anomalous-Hall current injection is studied in a Hall device contacted to a lateral load circuit. This anomalous-Hall current is generated inside a Co75Gd25 ferrimagnetic Hall bar and injected into a lateral load circuit contacted at the edges. The current, the voltage, and the power are measured as a function of the magnetization states, the load resistance Rl, and the temperature. It is shown that (1) the resistance associated with the anomalous-Hall current flowing inside the Hall bar is that of the portion of the ferrimagnet located between the lateral contacts, (2) the role of the non-uniformity of the current due to the lateral contacts is small, (3) the maximum power efficiency of the current injection into the load circuit corresponds to the condition of the resistance matching of the two sub-circuits, and (4) this maximum power efficiency is of the order of the square of the anomalous-Hall angle. These observations are in agreement with recent predictions based on a non-equilibrium variational approach.

Analysis of electrical transients in the fourth quadrant of thin films photovoltaics: The case of organic bulk heterojunction solar cell

Current-voltage (J-V) measurements under illumination are essential for studying solar cells. They directly provide fundamental parameters of the solar cell, as the short-circuit current (JSC), the open-circuit voltage (VOC), and the fill-factor (FF); but a deeper investigation of transport phenomena along the fourth quadrant is hampered by the tight linear scale, limited between zero to ~1 V. In this work, we present transient measurements carried out in an organic solar cell (ITO/PEDOT:PSS/PTB7-Th:PC71BM/Ca/Al), which allows to analyze J-V curves, by extending the scale from a linear to a logarithmic scale. For this, we used a circuit similar to that used in transient measurements, by replacing the voltage source by a variable load resistance RL (from 50 Ω to 1 MΩ). A voltage transient ΔV(t) and its time decay τ are measured over each RL, and τ-RL curves were obtained, keeping the device under different intensities of sunlight. Each τ-RL curve is divided in three distinct zones: one in which the extraction dominates the photocurrent; the second where a competition between extraction and non-geminate recombination is established; and the third, dominated by recombination and diffusion. An equivalent circuit is used to analyze the τ-RL curves, in which the diode resistance plays a relevant role, especially in the region close to VOC. Not only recombination mechanisms can be better analyzed through this new approach, but also the distinction between drift and diffusion transports.

A Multifunction Robot Based on the Slider-Crank Mechanism: Dynamics and Optimal Configuration for Energy Harvesting

An electromechanical robot based on the modified slider-crank mechanism with a damped spring hung at its plate terminal is investigated. The robot is first used for actuation operation and for energy harvesting purposes thereafter. Mathematical modeling in both cases is proposed. As an actuator, the robot is powered with a DC motor, and the effect of the voltage supply on the whole system dynamics is found out. From the numerical simulation based on the fourth-order Runge-Kutta algorithm, results show various dynamics of the subsystems, including periodicity, multi-periodicity, and chaos as depicted by the bifurcation diagrams. Applications can be found in industrial processes like sieving, shaking, cutting, pushing, crushing, or grinding. Regarding the case of the robot functioning as an energy harvester, two different configurations of the electrical circuit for both single and double loops are set up. The challenge is to determine the best configuration for the high performance of the harvester. It comes from theoretical predictions and experimental data that the efficiency of the robot depends on the range values of the electrical load resistance RL. The double loop circuit is preferable for the low values of RL50 Ohm) while the single loop is convenient for high values of RL ≥ 50 Ohm.

Explicit Numerical Model of Solar Cells to Determine Current and Voltage

This paper deals with the extraction of the physical parameters of solar cells (a single diode model) from the equivalent circuit of the cell. The extraction is carried out by three different numerical methods with a comparison between them. The first and second methods are a difference of the Newton Raphson algorithm (NRM) and Aitken’s extrapolation algorithm (AEM), respectively. The roots of the nonlinear equation of this cell have been described and solved using the three methods. The proposed method is tested to solve the output voltage; current and power of this cell from the roots of this equation with the various values of load resistance RL.

Search for power-efficient wide-range reversible resistance modulation of VO2 single crystals

The abrupt metal insulator transition in VO2 is attracting considerable interest from both fundamental and applicative angles. We report on DC I–V characteristics measured on VO2 single crystals in the two-probe configuration at several ambient temperatures below the insulator–metal (I–M) transition. The insulator-mixed-metal-insulator transition is induced by Joule heating above ambient temperature in the range of negative differential resistivity (NDR). In this range the stability of I(V) is governed by the load resistance RL. Steady state I(V) is obtained for RL > |dV/dI|max in the NDR regime. For RL < |dV/dI|max there is switching between initial and final steady states associated with peaks in the Joule power, that are higher the lower RL is. The peaks caused by steep switching are superfluous and damaging the samples. On the other hand, the large RL needed for steady state is the main power consumer in the circuit at high currents. The present work is motivated by the need to avoid damaging switching in the NDR regime while reducing the power consumption in the circuit. Large resistance modulation can be obtained under steady state conditions with reduced power consumption by increasing the ambient temperature of the device above room temperature. Under steady state conditions, the transition to the mixed metal-insulator state is smooth and is followed closely by appearance of sliding domains.

Inner Intrinsically Safe Criterion and Design Considerations of Buck Converter Based on Equivalent Inductance

To obtain the intrinsic safety criterion of the Inner-intrinsic-Safety-Buck-Converter (ISBC) based on equivalent-inductance to guide its optimal design, the Inductor Disconnected Discharge (IDD) behavior of ISBC is researched, and the Equivalent-Simple-Inductive-Circuit (ESIC) based on the equivalent inductance is defined. According to ESIC based on the equivalent-current and the energy equivalence, the expression of the equivalent inductance L ei is derived. The effect of the inductance L, the capacitance C, the input voltage V i and the load resistance R L on L ei is deeply studied, and it’s pointed out that L ei increases with the increase of V i, L, C, and R L, respectively. According to the minimal ignition current curve of the Simple-Inductive-Circuit (SIC), the nonexplosive intrinsically safe criterion based on L ei is proposed. Combining the proposed criterion, the output ripple voltage and the expression of L ei, the design region of the capacitance and inductance of the Buck converter meeting the demands of both inner intrinsic safety and electric performance is obtained. The feasibility of the design method and the proposed criterion is proved by the simulation and experimental results.

Power dissipation in the mixed metal-insulator state of self-heated VO2 single crystals and the effect of sliding domains

The mixed metal-insulator state in VO2 sets on within the current-controlled negative differential resistivity regime of I-V loops traced at ambient temperature. In this state, the stability of I(V) and/or spontaneous switching between initial and final steady states are governed by the load resistance RL in series with the sample. With increasing current (decreasing voltage), the power P = IV reaches a maximum (Pmax) and drops to a minimum (Pmin) along a path that depends on RL. For low enough RL, the ratio Pmax/Pmin may exceed by far the contrast in thermal emissivity from films of VO2 over the metal-insulator transition as reported in Kats et al. [Phys. Rev. X 3, 041004 (2013)]. The minimum is followed by a range of currents where the power increases with current. The return path overlaps the original path and continues towards backward switching. For a few samples, there is evidence from optical microscopy that the portion of the P(I) loop between Pmin and backward switching coincides with the range of currents where semiconducting domains slide within a metallic background. Damage induced in crystals by repeated I-V cycling suppresses domain sliding and flattens P(I) in the respective range of currents. This is consistent with the current dependent excess power dissipation being induced by the sliding domains.

Determination of the dissipation in superconducting Josephson junctions

The results relative to macroscopic quantum tunneling rate, out of the metastable state of Josephson junctions, are examined in view of determining the effect of dissipation. We adopt a simple criterion in accordance to which the effect of dissipation can be evaluated by analyzing the shortening of the semiclassical traversal time of the barrier. In almost all the considered cases, especially those with relatively large capacitance values, the relative time shortening turns out to be about 20% and with a corresponding quality factor Q ≃ 5.5. However, beyond the specific cases here considered, still in the regime of moderate dissipation, the method is applicable also to different situations with different values of the quality factor. The method allows, within the error limits, for a reliable determination of the load resistance RL, the less accessible quantity in the framework of the resistively and capacitively shunted junction model, provided that the characteristics of the junction (intrinsic capacitance, critical current, and the ratio of the bias current to the critical one) are known with sufficient accuracy.

Performance analysis of photovoltaic–thermoelectric hybrid system with and without glass cover

This paper establishes a theoretical model for assessing the performance of glazed/unglazed photovoltaic–thermoelectric (PV–TE) hybrid system. To enhance the heat removal, nanofluid is served as heat sink. Firstly, a performance comparison between glazed and unglazed system is given. It is suggested that, under the condition of higher figure of merit Z and concentration ratio C, as well as enhanced transmissivity of glass cover, glazed system may be competitive or even superior to the unglazed one. Environmental effect such as wind velocity, is also a significant factor which may be ignored in the existing researches. Therefore, considering the coupling effect of wind velocity and nanofluid flow rate, the impacts of some key parameters on the system overall efficiency are examined in the following part. It is found for certain TE modules, a higher figure of merit Z may still cause a decrease in the system overall efficiency resulting from the different parameter values, that is, Seebeck coefficient s, electrical resistivity ρ and thermal conductivity λ. When thermoelectric efficiency ηTE reaches maximum, the obtained optimal load resistance Rl is larger than that corresponding to maximum overall efficiency η. With varying wind velocity, the maximum overall efficiency could achieve at maximum or minimum wind velocity, corresponding to Z=0.0021K−1 and Z=0.0085K−1 conditions, respectively. In addition, nanofluid shows better performance than water.

Triple Frequency Impedance Matching by Frequency Transformation

ABSTRACTThe purpose of this article is to bring to the attention of students and teachers of circuit theory, as well as of practising design engineers, a recently reported technique for impedance matching at multiple frequencies. This will be done through a specific example, namely that of design of a lumped network for matching a given load resistance RL to a given source resistance RS at three given frequencies ω1, ω2, and ω3. The method is based on application of the frequency transformation technique, commonly used in analog filter design, to a basic single frequency matching network. By comparison with the existing approach of assuming a network configuration and solving a set of simultaneous equations, as reported in a recent paper, the new method is shown to have the advantages of design by synthesis, elegance, and simplicity. Further, by virtue of the synthesis approach, the method allows a number of alternative networks to be designed, so that the best one can be selected on the basis of a predetermined criterion.

Output short-circuit spark discharging energy and output intrinsic safety criterion of Buck converters

To obtain the output intrinsic safety criterion of Buck converters, the experimental research on its output-short circuit discharge characteristics is conducted by using the safety spark test apparatus. It is found that its spark discharge process can be divided into four stages, i.e., the dielectric-breakdown, spark-generation, spark-keeping and spark-extinguishment. According to the obtained spark discharge characteristics, the output short-circuit spark discharging energy (OSSDE) is deeply analyzed. It is indicated that the OSSDE of the Buck converter with a given inductance is a concave function of load resistance RL when RL is less than the critical resistance RLC corresponding to this inductance, while that is a convex function of RL in the case of RL &gt; RLC. Considering the actual parameter range of the Buck converter, it is further pointed out that when RL RLC, the OSSDE increases with the increase of RL and reaches its maximum in the case of RL=RLC; when RL &gt; RLC, the OSSDE first increases and then decreases with the increase of RL and reaches its maximum in the case of RL, DCM. The most dangerous operating conditions of the converter in whole dynamic range are obtained, i.e., the converter operates in DCM when the input voltage is the highest and RL=RL, DCM. Meanwhile, the maximum OSSDE is achieved. According to the energy equivalence, an output intrinsic safety criterion for Buck converter is proposed by modeling the output short-circuit discharging behaviour as a simple capacitive circuit. The theoretical analysis and proposed criterion are verified by the simulation and experimental results.

Overheating of an optically triggered SiC thyristor during switch-on and turn-on spread

A simple adiabatic model of the switch-on and turn-on spread in an optically triggered SiC thyristor has been developed. The model makes it possible to evaluate the overheating of the structure with consideration for the switched current Imax, the rate of current increase dI/dt, the power/energy of the UV light source used for switching, the area initially switched-on by light, and the switch-on time constant τ of the thyristor. The applicability of the adiabatic approximation to evaluation of the device overheating is substantiated. It is shown that the instantaneous maximum power density is approximately inversely proportional to the area of the initially switched-on portion of the thyristor. The estimates obtained demonstrate that, to preclude the inadmissible overheating of the structure, the maximum current density during switch-on, jmax, should not exceed ∼(2–3) × 104 A cm−2. With jmax ≈ Imax/πr02 ≈ U0/πrr02Rl taken for estimation, it is possible to estimate the radius of the optical window r0 for a given voltage U0 at which the structure is switched on and a chosen load resistance Rl.

A Fluid-Thermo-Electric Coupled Field Analysis of a Novel Integrated Thermoelectric Device

Thermoelectric elements made of semiconductor plates laminated with a highly electrically and thermally conducting inter-connector with a flow channel configuration can be treated as integrated Thermoelectric Device (TED). Elements with constructed bulk crystalline n-type and p-type (Bismuth-Telluride-Selenium) semiconducting materials and copper as a conducting material are considered. In this study, the thermoelectric performance of such an element using fluid-thermo-electric coupled field numerical methods has been investigated. The TED is subjected to constant cold temperature at the bottom and top surfaces while the inter-connector channel walls are exposed to hot fluid flow; the remaining surfaces are kept adiabatic. The performance of the integrated TED element is studied in terms of power output P0 , heat input, Qh conversion efficiency η and produced electric voltage V for different load resistances, RL inlet hot fluid temperatures Tin and flow rates ReDh . For a fixed Tin , optimum η is shown at a load resistance RL which is slightly lesser than total internal resistance Rin value. An increase in Tin results in an enhancement in P0 and η, however, it has a minimal effect on the variation of optimum load resistance RoptmL. At higher Tin values, the increment in RL showed a significant change in the heat input Qh values. The ReDh had a prominent effect on TED performance predictions. The P0 increased nearly three-fold at ReDh =500 in comparison to ReDh =100. It is recommended that for an accurate modeling, design and optimization of state-of-the-art TED with flow channels to be carried out using fluid-thermo-electrical coupling field simulations.

High-power ceramic materials for piezoelectric transformers

Considering the characteristics of materials required for piezoelectric transformers, and introducing the maximum vibration velocity vmax that generates a fixed temperature rise, we can express the maximum output power of a piezoelectric transformer as the product of this v2max, the square of the power coefficient on the output side A2 and the load resistance RL. Moreover, the power coefficient on the output side A2 is proportional to the product of the square root of Young's modulus YE, the square root of the electromechanical coupling coefficient k, and the permittivity ϵ33. This is verified by using two types of piezoelectric transformers in an inverter where the output section may be of the Rosen type or the transverse-effect type. It is shown that the contributions made by the structure of the piezoelectric transformer and the load resistance differ in each case. The Rosen structure is used in the piezoelectric transformer for the inverter, and it is shown that a material with large maximum vibration velocity vmax is useful in this case. © 1999 Scripta Technica, Electron Comm Jpn Pt 3, 82(11): 86–92, 1999

Generating properties of Al-Tb2GeS5-Ge MIS structures

The nature of ac generation in an aluminum-amorphous terbium thiogermanate-monocrystalline germanium structure is discussed. An expression obtained for the frequency (f) of the generated current satisfactorily describes the experimentally observed dependences of f on the load resistance RL, temperature, thickness of the Tb2GeS5 film, and the area of contact with it (S). The specific rate of carrier generation in the germanium space-charge region is calculated from plots of f−1 against RL and S.

A transmission line transformer having frequency independent matching properties

AbstractIn this paper, we present a new transmission line transformer which is capable of matching a load resistance RL to a given source of internal resistance Rg in a frequency independent manner. This matching can be made perfect at all frequencies if RL/Rg = 4; for RL/Rg ≠ 4, the matching can still be made frequency independent but the power transferred to the load becomes less than the maximum available power.

Pyroelectric response to single infrared laser pulses in triglycine sulphate and strontium-barium niobate

Expressions are derived for the pyroelectric (PE) voltage response to single ir laser signals much shorter than the thermal time constant τT of the PE sample. It is shown both analytically and experimentally that when the electronic time constant τe is much shorter than the time characteristics of the signal, then the response exactly follows the signal and has a peak voltage Vp proportional to the load resistance RL. In the opposite case, the response rises as long as the signal persists, reaching a peak value proportional to absorbed energy but independent of RL, then decays exponentially with falltime τe ∝ RL, as long as τe≪τT.

Pyroelectric Voltage Response to Step Signals of Infrared Radiation in Triglycine Sulphate and Strontium-Barium Niobate

Theoretical and experimental analysis of voltage transients obtained in triglycine sulphate and strontium-barium niobate in response to step radiation signals yields information important for pyroelectric ir detection. The response transients are shown to be symmetrical with respect to the electronic and thermal time constants τe and τT of the samples. When τe and τT differ appreciably, the rise of the response and its decay are exponentials whose time constants are, respectively, the smaller and the larger one from among τT and τe. The peak voltage values are proportional to the load resistance RL when τe≪τT; they become independent of RL and proportional to τT when τe≫τT. The initial slope of the response in a given sample is found to be independent of RL for a given radiation flux. The pyroelectric coefficient of a material, divided by the product of its permittivity, density, and specific heat is shown to be a figure of merit for use in pyroelectric ir detection

Analysis of magnetic amplifiers with diodes

It has been demonstrated1 that the behavior of magnetic amplifiers without diodes can be analytically described by a set of linear difference equations relating the average values of voltages and currents at the ports. For most circuits this representation gives values which are accurate to within 1 or 2% of actual even for a large variety of waveforms of port and supply voltages. The reason for this rather remarkable accuracy of representation can be attributed to three factors: 1. The control circuit resistance R1 the output circuit resistance R2, and the load resistance RL are small compared to the magnetizing resistance Rm. 2. Almost all practical amplifiers of this type employ an interconnection of basic elements such that quiescent currents tend to cancel at the ports. 3. The state of the saturable inductor, saturated or unsaturated, depends on the integral of the inductor voltage rather than the inductor voltage itself.