16,832 research outputs found
Design and construction of a measurement system of hall effect DC and AC
No full textEn este trabajo se presenta el diseño y la construcción de un sistema de medida de efecto Hall (SMEH) basado en un Sistema Delta Mode (Instrumentos Keithley 6221-2182A). Las técnicas de medición SMEH incluyen voltaje Hall, resistividad, curvas voltaje-corriente, concentración de portadores, movilidad y el método de Van Der Pauw. El SMEH opera tanto en modo de corriente continua como en alterna (0.001–1 Hz). Un software altamente integrado con el ambiente de LabView fue desarrollado para la operación del sistema y la adquisición de datos. El software permite al usuario graficar el voltaje Hall, la densidad y la movilidad de portadores en función de la corriente, del campo magnético y la frecuencia. Un imán permanente Phylatex es utilizado para generar campos magnéticos (H) de hasta 800 mT. El SMEH se puso a prueba utilizando una muestra de cobre (Cu) y se utilizó para estudiar las propiedades de transporte eléctrico a temperatura ambiente de cintas magnéticas blandas de Co64Fe21B15 y Co71Fe4B15Si10, y de Fe73.5Si13.5B9Nb3-xMoxCu1 para x = 0, 1.5, 2, 3. (Texto tomado de la fuente)The design and building of a Hall Effect measurement (HEMS) system based in a Delta Mode System (Keithley Instruments 6221–2182A) is presented. The HEMS measurement techniques include Hall voltage, resistivity, I-V curves, carrier concentration, mobility and the Van Der Pauw method. The HEMS was operated in both dc and ac (0.001–1 Hz) current modes. Highly integrated software using LabView environment was developed for system operation and data acquisition. The software enables the user to graphic Hall voltage, density and mobility of carriers in function of current, magnetic field and frequency. A permanent magnet Phylatex was employed to generate magnetic fields (H) up to 800 mT. The HEMS was tested using a standard sample of Cu and was used to study the room temperature transport properties of the soft magnetic ribbons of Co64Fe21B15 and Co71Fe4B15Si10, and of Fe73.5Si13.5B9Nb3-xMoxCu1 for x = 0, 1.5, 2, 3Maestrí
Hall-Effect Sensor Technique for No Induced Voltage in AC Magnetic Field Measurements Without Current Spinning
No full textAccurately sensing AC magnetic field signatures poses a series of challenges to commonly used Hall-effect sensors. In
particular, induced voltage and lack of high-frequency spinning methods are bottlenecks in the measurement of AC
magnetic fields. We describe a magnetic field measurement technique that can be implemented in two ways: 1) the current
driving the Hall-effect sensor is oscillating at the same frequency as the magnetic field, and the signal is measured at the
second harmonic of the magnetic field frequency, and 2) the frequency of the driving current is preset, and the measured
frequency is the magnetic field frequency plus the frequency of the current. This method has potential advantages over
traditional means of measuring AC magnetic fields used in power systems (e.g., motors, inverters), as it can reduce the
components needed (subsequently reducing the overall cost and size) and is not frequency bandwidth limited by current
spinning. The sensing technique produces no induced voltage and results in a low offset, thus preserving accuracy and
precision in measurements. Experimentally, we have shown offset voltage values between 8 and 27 μT at frequencies
ranging from 100 Hz to 1 kHz, validating the potential of this technique in both case
Optimal football strategies: AC Milan versus FC Barcelona
No full textIn a recent UEFA Champions League game between AC Milan and FC Barcelona, played in Italy (final score 2-3), the collected match statistics, classified into four offensive and two defensive strategies, were in favour of FC Barcelona (by 13 versus 8 points). The aim of this paper is to examine to what extent the optimal game strategies derived from some deterministic, possibilistic, stochastic and fuzzy LP models would improve the payoff of AC Milan at the cost of FC Barcelona.football game; offensive & defensive strategies; Deterministic LP; fuzzy LP; stochastic LP; Nash equilibria;
Influence of ac ageing on space charge dynamics in LDPE
No full textPolymeric materials have been widely used as insulation in power industry due to their excellent electrical properties. However, these properties deteriorate in time irreversibly when the material is subjected to electric stress. Although space charge is believed to play an important role in ac ageing, exact mechanisms are poorly understood due to very limited experimental data. In the present work efforts have been made to investigate the influence of ac ageing on space charge dynamics in low-density polyethylene (LDPE). LDPE films with 200mm were aged at 50 kV/mm at 50 Hz for various times at ambient temperature. Space charge dynamics in the samples prior to and after ageing were monitored using the pulsed electroacoustic (PEA) technique under dc electric stress. The results indicate that there is a significant amount of homocharge accumulation in the unaged sample due to charge injection. These injected charges are the captured by the deep traps originated from the interface between crystalline and amorphous regions in LDPE. Ageing under ac condition does not necessarily lead to an increase in amount of charge in the bulk but leads to an increase in mobility of charge carriers. Chemical analysis by infrared spectroscope (FTIR) reveals there are chemical changes taken place in the bulk of the material after ac ageing. It is believed that the chemical changes introduce shallow traps which promote the movement of charge carriers in the bulk. Consequently, the injected charges spread across the sample
Spin Backflow and ac Voltage Generation by Spin Pumping and the Inverse Spin Hall Effect
No full textThe spin current pumped by a precessing ferromagnet into an adjacent normal metal has a constant polarization component parallel to the precession axis and a rotating one normal to the magnetization. The former is now routinely detected as a dc voltage induced by the inverse spin Hall effect (ISHE). Here we compute ac ISHE voltages much larger than the dc signals for various material combinations and discuss optimal conditions to observe the effect. The backflow of spin is shown to be essential to distill parameters from measured ISHE voltages for both dc and ac configurations.QN/Quantum NanoscienceApplied Science
A power sharing series power BJT array with isolated low voltage control for AC power control applications
No full textA technique for a continuously variable AC resistance using a series BJT array is presented. This array provides high power dissipation capability and uniform voltage and power distribution across the individual transistors. The array, controlled using a set of optoisolators to maintain the electrical isolation between the control circuits and the power stage, could be used as the basis to develop several useful techniques including a solid state AC regulator with comparable performance to the commonly used ferro-resonant systems; a linear AC electronic load suitable for testing UPS and other power conditioners; and, in other AC power control applications such as switching capacitors in AC resonant circuits
AC transport at holographic quantum hall transitions
No full textWe compute AC electrical transport at quantum Hall critical points, as modeled by intersecting branes and gauge/gravity duality. We compare our results with a previous field theory computation by Sachdev, and find unexpectedly good agreement. We also give general results for DC Hall and longitudinal conductivities valid for a wide class of quantum Hall transitions, as well as (semi)analytical results for AC quantities in special limits. Our results exhibit a surprising degree of universality; for example, we find that the high frequency behavior, including subleading behavior, is identical for our entire class of theories.Peer reviewe
Crossover of the Hall-voltage distribution in AC quantum Hall effect
No full textThe distribution of the Hall voltage induced by low-frequency AC current is studied theoretically in the incoherent linear transport of quantum Hall systems. It is shown that the Hall-voltage distribution makes a crossover from the uniform distribution to a concentrated-near-edges distribution as the frequency is increased or the diagonal conductivity is decreased. This crossover is also reflected in the frequency dependence of AC magnetoresistance
Experimental High-Frequency Parameter Identification of AC Electrical Motors
No full textIn order to predict conducted electromagnetic interference in inverter-motor drive systems, high-frequency (HF) motor models are requested and the involved parameters have to be available. In previous studies, the authors have presented an accurate HF model for induction motors and they have defined the procedures to identify the model parameters. In this paper, these results are extended to several types and sizes of industrial ac motors such as induction, synchronous reluctance (without interior permanent magnets), and brushless motors. The model parameter-identification procedure has been improved, and it is based on a least-squares data fitting applied to the measured magnitude and phase-frequency-response curves of the phase-to-ground and the phase-to-neutral impedances. The aim of this paper is to provide quick indications to select the suitable values of the HF model parameters, with reference to the size and type of the ac motor, to evaluate the HF voltage and current components in inverted-fed ac motor system
Development of Graphene Quantum Hall Effect AC Metrology at RISE
No full textWe present the first steps taken towards a graphene quantum Hall effect ac resistance standard at RISE. A new measurement setup has been developed including a graphene quantum Hall effect device suitable for the kilohertz range and a coaxial cryoprobe to be used together with a coaxial impedance bridge based on inductive voltage dividers. 1:1 ratio resistance measurements of the graphene device against a 12.9 kΩ ac resistance standard resulted in a linear frequency dependent (≈ 0.2(μΩ/Ω)/kHz) deviation from the quantized dc value.</p
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