Nearby Conductor Research Articles

Crosstalk in an uncompensated gapped-core contactless current transducer

A detailed analysis of the crosstalk in an uncompensated gapped-core current transducer is presented in this paper. A cut-core current transducer with a magnetic field sensor in the airgap is widely used to measure current in industry and in laboratories. Crosstalk is the effect of a nearby current-carrying conductor on the reading of this type of sensor. We present a study of the dependence of the crosstalk on the position of the external conductor, the core material, and the core geometry, including the number of airgaps. A 3D Finite Element Method (FEM) based model is used to analyze the crosstalk, and the results are compared with measurements.Using a low-permeability ferrite core with two 2 mm airgaps and a single Hall sensor results in a maximum crosstalk error of 18 %. This error can be reduced to 1 % either by using a differential Hall sensor pair, or surprisingly by using a single 4 mm airgap. This error can be further reduced to 0.15 % by using an FeSi core with larger permeability. However, this type of sensor is very sensitive to the position of the Hall sensor in the center of the airgap. Displacement or an angular mismatch can increase the error to 1.5 %, as demonstrated on a commercial sensor.

Characteristic Mode Formulations of Composite PEC and Lossy Dielectric Objects

Lossy dielectric substrate affects the performance of a nearby perfect electric conductor (PEC) antenna. This letter presents a set of formulae for characteristic mode analysis (CMA) of composite PEC and lossy dielectric objects. It is based on the volume-surface integral equation and substructure treatment that separates the radiation and dissipation powers of the composite structure. A narrow PEC plate (that represents a dipole antenna) is placed in proximity of a thick, lossy dielectric material, and CMA of this structure is presented as an example. The separation gap between the PEC and dielectric objects affects the resonance and radiation efficiency of the antenna, and it is shown that CMA accurately captures those effects. The influence of dielectric loss on the modal orthogonality is discussed. Since the PEC item dominates over the coupling one in the substructure operator, the computed modes maintain good orthogonality with low-loss dielectrics. Owing to the physical insights of CMA, it has many potential applications associated with lossy materials.

Decoherence mitigation by real-time noise acquisition

We present a scheme to neutralize the dephasing effect induced by classical noise on a qubit. The scheme builds upon the key idea that this kind of noise can be recorded by a classical device during the qubit evolution, and that its effect can be undone by a suitable control sequence that is conditioned on the measurement result. We specifically demonstrate this scheme on a nitrogen-vacancy center that strongly couples to current noise in a nearby conductor. By conditioning the readout observable on a measurement of the current, we recover the full qubit coherence and the qubit's intrinsic coherence time T2. We demonstrate that this scheme provides a simple way to implement single-qubit gates with an infidelity of 10−2 even if they are driven by noisy sources, and we estimate that an infidelity of 10−5 could be reached with additional improvements. We anticipate this method to find widespread adoption in experiments using fast control pulses driven from strong currents, in particular, in nanoscale magnetic resonance imaging, where control of peak currents of 100 mA with a bandwidth of 100 MHz is required.

Influence of a nearby conductor on shape and length of a microwave plasma jet.

This Rapid Communication reports on the observation of an interesting phenomenon: the shape, especially the length, of a microwave plasma jet (MPJ) can be clearly influenced by simply placing a conductor near the plasma source, particularly when the nearby conductor is in contact with the external conductor of the coaxial microwave plasma generator, accompanied by a significant change in microwave reflection power from the terminal. To further investigate this discovery, the relationships between the length of the plume and some important factors, such as the conductivity and length of the nearby conductor, microwave input power, and gas flow velocity, are analyzed, and we find nonlinear rules of influence of these factors on the jet. Measurements of the electric potential around the jet reveal the nonuniform and non-neutral charge distribution inside the visible plasma plume, which plays a vital role in uncovering the mechanism underlying this phenomenon. The results are helpful for providing a deeper understanding of microwave plasma jet characteristics. More importantly, it provides guidelines to control the MPJ using simple structures.

Energy harvester for use on nearby current-carrying conductors

We report a concept of a new electret-based energy harvester that can extract energy from a nearby conductor carrying a time-varying current. In the harvester, a permanent magnet located near an electret is made move relative to the electret by the magnetic interaction of the circumferential time-varying magnetic field produced by the current flow and the static magnetic field of the permanent magnet. The advantage of this harvester over harvesters that employ piezoelectric elements is that piezoelectric materials are known to fatigue over time, whereas electrets having extremely long lifetimes are possible.

Analysis of the proximity and skin effects on copper loss in a stator core

Abstract Accurate prediction of power loss distribution within an electrical device is highly desirable as it allows thermal behavior to be evaluated at the early design stage. Three-dimensional (3-D) and two-dimensional (2-D) finite element analysis (FEA) is applied to calculate dc and ac copper losses in the armature winding at high-frequency sinusoidal currents. The main goal of this paper is showing the end-winding effect on copper losses. Copper losses at high frequency are dominated by the skin and proximity effects. A time-varying current has a tendency to concentrate near the surfaces of conductors, and if the frequency is very high, the current is restricted to a very thin layer near the conductor surface. This phenomenon of nonuniform distribution of time-varying currents in conductors is known as the skin effect. The term proximity effect refers to the influence of alternating current in one conductor on the current distribution in another, nearby conductor. To evaluate the ac copper loss within the analyzed machine a simplified approach is adopted using one segment of stator core. To demonstrate an enhanced copper loss due to ac operation, the dc and ac resistances are calculated. The resistances ratio ac to dc is strongly dependent on frequency, temperature, shape of slot and size of slot opening.

Relieving pain in rheumatology patients: Repetitive transcranial magnetic stimulation (rTMS), a developing approach

Transcranial magnetic stimulation (TMS) is a non-invasive method for activating specific areas of the brain. There are two variants, repetitive TMS (rTMS) and direct TMS. Rapid changes in an electrical current induce a magnetic field, which in turn induces an electrical current in a nearby conductor. When a coil is positioned over the brain, rTMS delivers very brief and painless magnetic pulses to the brain. Initially, rTMS was developed as a treatment for depression. Since then, potential indications have been extended to the treatment of chronic pain, most notably in patients with rheumatic diseases. Thus, active research is being conducted into rTMS effects in fibromyalgia, chronic low back pain, and type I complex regional pain syndrome. Studies have established that rTMS is safe; provides pain relief, at least in the short-term; and improves the psychological correlates of chronic pain. These data support further development efforts with the goal of using rTMS in patients with chronic pain, including those with rheumatic diseases. French physicians have shown a high level of interest in rTMS, and the first French recommendations for using this method were issued in 2011. Further research is needed to determine the optimal stimulation parameters, session frequency, and session duration, as well as the best indications. Physicians who see many patients with chronic pain, such as rheumatologists, should be aware of this developing non-pharmacological and safe treatment modality, which can be of considerable help to their patients.

Electromechanical Energy Scavenging From Current-Carrying Conductors

This paper describes a novel method for scavenging energy for electric power systems sensing applications by the use of permanent magnets that couple to the magnetic field generated by an alternating current flowing through a nearby conductor. The resulting mechanical energy is converted to electrical energy using piezoelectric transduction. This electromechanical AC energy scavenging method is an attractive alternative to coil-based AC energy scavengers in cases where the scavengers cannot encircle the conductor. In such cases, the electromechanical AC energy scavenger has the potential to produce significantly more power than comparable coil-based methods. The components of an electromechanical AC energy scavenger are described in detail, and experimental data from prototypes that are fabricated and tested in our laboratory are shown. The 20 cm3 prototypes generated up to 2.7 mW of power each from 20 A of nearby current. Theoretical power densities of electromechanical AC energy scavengers are compared to the power densities of representative coil-based methods, showing that in some cases the electromechanical AC scavengers can generate an order-of-magnitude more power than coil-based AC scavengers. This paper demonstrates that electromechanical AC energy scavenging is a potential method for powering small size low cost stick-on wireless sensor networks.

A Case Study on Lightning Protection, Current Injection Measurements, and Model

A newly built pharmaceutical plant has been investigated by measurements. Currents of 0.3 kA were injected in the lightning protection grid on the roof. Inside the building, test cables of 100 m length followed a path typical for cables belonging to the installation. We measured induced cable currents and voltages. A reduced model of the building incorporated most of the designed current paths. Measurements and model showed that the roof steel skeleton carried about 80% of the current and the intended lightning conductors 20%. The calculated current through a cable support was larger than measured. This is explained by also considering a nearby nonintended conductor. For three types of cables, we determined the transfer impedances. The measurements and model have been combined and extrapolated to actual lightning.

Conditional statistics of electron transport in interacting nanoscale conductors

Interactions between nanoscale semiconductor structures form the basis for charge detectors in the solid state. Recent experimental advances have demonstrated the on-chip detection of single electron transport through a quantum dot (QD). The discreteness of charge in units of e leads to intrinsic fluctuations in the electrical current, known as shot noise. To measure these single-electron fluctuations a nearby coherent conductor, called a quantum point contact (QPC), interacts with the QD and acts as a detector. An important property of the QPC charge detector is noninvasiveness: the system physically affects the detector, not visa-versa. Here we predict that even for ideal noninvasive detectors such as the QPC, when a particular detector result is observed, the system suffers an informational backaction, radically altering the statistics of transport through the QD as compared to the unconditional shot noise. We develop a theoretical model to make predictions about the joint current probability distributions and conditional transport statistics. The experimental findings reported here demonstrate the reality of informational backaction in nanoscale systems as well as a variety of new effects, such as conditional noise enhancement, which are in essentially perfect agreement with our model calculations. This type of switching telegraph process occurs abundantly in nature, indicating that these results are applicable to a wide variety of systems.

Charge fluctuations in open chaotic cavities

We present a discussion of the charge response and the charge fluctuations of mesoscopic chaotic cavities in terms of a generalized Wigner-Smith matrix. The Wigner-Smith matrix is well known in investigations of time-delay of quantum scattering. It is expressed in terms of the scattering matrix and its derivatives with energy. We consider a similar matrix but instead of an energy derivative we investigate the derivative with regard to the electric potential. The resulting matrix is then the operator of charge. If this charge operator is combined with a self-consistent treatment of Coulomb interaction, the charge operator determines the capacitance of the system, the non-dissipative ac-linear response, the RC-time with a novel charge relaxation resistance, and in the presence of transport a resistance that governs the displacement currents induced into a nearby conductor. In particular these capacitances and resistances determine the relaxation rate and dephasing rate of a nearby qubit (a double quantum dot). We discuss the role of screening of mesoscopic chaotic detectors. Coulomb interaction effects in quantum pumping and in photon assisted electron-hole shot noise are treated similarly. For the latter we present novel results for chaotic cavities with non-ideal leads.

Controlling ac losses in quantum Hall effect devices

When measured with ac at kilohertz frequencies the quantized Hall resistance (QHR) of a quantum Hall effect (QHE) device is usually found to be current- and frequency-dependent. This is a limitation on its use as a quantum impedance standard. We develop a model for the principal ac losses arising in the QHE device and show how they are responsible for the observed QHR current and frequency coefficients. We believe that losses are mainly caused by dissipative ac charging of the device along its edges. Charging is induced by the passage of the Hall current and by capacitive coupling between an edge and any nearby conductor maintained at an ac potential different to that of the edge, as for example at shield potential. The loss power is proportional to frequency and increases more rapidly than the square of the applied voltage or current. We model losses in terms of in-phase loss currents, which are a function of the amplitude of the ac charge reaching or leaving edges. The QHR frequency coefficient is zero only when the loss current for one portion of the high-potential edge and that for a corresponding portion of the low-potential edge are equal and of opposite sign. We propose a simple method for approaching that balance condition: gates are located under the device edges and their ac potentials adjusted so that the QHR current coefficient, evaluated at a constant frequency, is zero. We report measurements of the residual QHR frequency coefficients obtained after adjustment for GaAs/GaAlAs devices of two different types. For five different devices of the most favourable type, the QHR frequency coefficients do not exceed ±2 parts in 108 per kilohertz.

Miniature circulatory support power transformer.

Direct power delivery to intracorporeal circulatory support devices risks infection. Electrical transformers spanning the integument (skin or mucosa) have long been attractive means of circumventing this risk. Yet all existing skin surface transformers leak substantial magnetic flux, with an intrinsic risk of battery draining cross-coupling by any nearby conductor, requiring strict control of surroundings. In a progression of designs, we have used the walls of a small pouch, surgically formed from ileum, rather than skin, as a barrier. Previously, we reported a torroidal design with complete magnetic circuits, having zero flux leakage and unmatched heat dissipation in a 2 week canine trial. This work was in three parts: (1) Devices were placed in eight dogs for 9-12 weeks to document performance of the existing design. (2) Based on these results, the device was further miniaturized. Iterative computational modeling was applied to material selection and design. Simultaneously, practical techniques for surgically constructing tiny accommodating ileal pouches were explored in cadavers, by using polymer "mock-ups" of potential designs. (3) The final design was tested by acute implantation in a live 52 kg goat and by in vitro testing of electrical transfer function. IN VIVO TRIALS: The earlier design demonstrated 97.2% AC/AC and 84.2% DC/DC efficiency with contiguous tissue warming of 0.1 degrees C. DESIGN AND PERFORMANCE: A transformer with a Square Permalloy torroidal core (6 cm3, 23 grams, both coils eight turns) was designed, by using human cadaver trials to optimize geometry. Input and output were 6 V, 12W at 9.2 kHz with AC-AC efficiency 96%. OPERATIVE PLACEMENT TRIAL: The primary coil easily fit into an isolated, vascularized, but otherwise disconnected "blind" ileal pouch < 2 cm long with a slender extension to a miniature stoma. With secondary turns, the pouch and transformer fit easily into the abdominal wall. This tiny system seems compatible with near "forgettable" power delivery allowing unprecedented freedom of environment and activity in circulatory support dependent people.

Double quantum dots as detectors of high-frequency quantum noise in mesoscopic conductors

We propose a measurement setup for detecting quantum noise over a wide frequency range using inelastic transitions in a tunable two-level system as a detector. The frequency-resolving detector consists of a double quantum dot which is capacitively coupled to the leads of a nearby mesoscopic conductor. The inelastic current through the double quantum dot is calculated in response to equilibrium and nonequilibrium current fluctuations in the nearby conductor, including zero-point fluctuations at very low temperatures. As a specific example, the fluctuations across a quantum point contact are discussed.

The transfer impedance of cables with a nearby return conductor and a noncentral inner conductor

The transfer impedance Z/sub t/ of a cable is often assumed to be a characteristic of the shield only. We investigate the limits of this assumption by calculations and measurements. The first test cable was formed by a solid copper tube (shield) and a wire inside; several positions, also non-central, were chosen for the wire. The common mode current (between 10 Hz and 100 kHz) through the tube had as return path a single wire, which was placed at several positions, near and at some distance from the shield. A second cable with a braided shield was tested as well. The results show that both the differential mode and the common mode circuit have to be carefully defined for a particular Z/sub t/. Varying either circuit may alter Z/sub t/ drastically. Consequently, the Z/sub t/ of a particular cable measured in a triaxial setup, is a characteristic of that setup and cannot always be used in another setup as in for instance cable bundles. >

Toroid detectors in pressure probes

The utility of toroid resonators for NMR has been discussed in several reports (I, 2). Most recently, using “0 NMR, Glass and Dom (3) have shown an SINadvantage of 3-5 for toroids compared with Helmholtz detectors. However, realization of this advantage for narrow-line nuclides was limited by poor B0 field homogeneity, since typical linewidths achieved were 45-70 Hz, which could only be reduced to a best value of 11.7 Hz with use of a specially designed shim system (4). Were it not for the B. field homogeneity problem, we suspected that toroids, due to their greater coil efficiency and their confinement of the B, field to the internal regions of the coil, would be particularly useful in metal pressure vessels, since this confinement would also be expected to avoid losses due to magnetic coupling with the vessel. Here, we report 2H static linewidths near 1.0 Hz for several toroid detectors, even though mounted within a Be-Cu pressure vessel, with 13C sensitivities significantly better than that of a commercial 10 mm ambient pressure multinuclear probe. The spectra were recorded using a General Electric GN300/89 spectrometer with an Oxford 89 mm magnet and standard shim system. Magnetic coupling of a transmitter coil to a nearby conductor results in loss of energy to the conductor in the form of eddy currents. In addition, the coupling also allows pickup of thermal or other noise from the conductor when the coil is used to receive signals. Magnetic coupling decreases the coil’s inductance and quality factor. To alleviate these problems, Hoult (5) recommends that detector coils be located at least a distance equal to their largest dimension from nearby conductors. The recommendation applies to metal pressure vessels in that their walls are conductive. Significantly, it essentially triples the required inside diameter and wall thickness of the pressure vessel and one designed for 10 mm sample sizes for use in magnets of 7.05 T or above would be difficult to achieve. Jonas’ high-pressure NMR probes have their detectors far removed from the walls of the vessel (6, 7). To investigate the potential advantages of toroids for use in high-pressure NMR probes, the pressure vessel in Fig. 1 was fabricated from Berylco alloy 25 (tensile strength; 192,000 psi). The vessel is intended for homogeneous catalysis studies involving reactions of gases and liquids under pressure and is designed to receive effluent from a separate stirred reactor where gas and liquid mixing occur. It uses standard l/l 6 in. compression fittings (Parker or single ferrule Swagelok) in both the gas connections and in the RF feedthroughs; however, the feedthroughs used VespelSP 1 reducing ferrules (Alltech Associates, 1 / 16 in. to 1 .O mm) in place of the standard

Numerical Simulation of the Plasma Current Quench Following a Disruptive Energy Loss

The plasma/electromagnetic interaction with poloidal field coils and nearby passive conductor loops during the current quench following a disruptive loss of plasma energy is simulated. By solving a differential/algebraic system consisting of a set of circuit equations (including the plasma circuit) coupled to a plasma energy balance equation and an equilibrium condition, the electromagnetic consequences of an abrupt thermal quench are observed. Limiters on the small and large major radius sides of the plasma are assumed to define the plasma cross section. The presence of good conductors near the plasma and a small initial distance (i.e., 5 to 10% of the plasma minor radius) between the plasma edge and an inboard limiter are shown to lead to long current decay times. For a plasma with an initial major radius R0 = 4.3 m, aspect ratio A = 3.6, and current Ip = 4.0 MA, introducing nearby passive conductors lengthens the current decay from milliseconds to hundreds of milliseconds.

Two-dimensional plasma equilibria

Complex-variable, hodograph methods are used to solve the free-boundary problem of a plasma confined by its own skin currents and the field due to two parallel external conductors. In one extreme case the external field is a quadrupole field in the vicinity of the plasma; another extreme case describes the local perturbation of a large plasma by a single, nearby conductor.

Self-induced interaction of magnetic domains and bubbles with a neighboring current

It was recently pointed out that magnetic domains tend to move parallel with the current in a nearby conductor; the motion is due to Hall currents set up in the conductor by the domain field and is independent of any field gradients due to the unperturbed current. The magnitude of the force that produces this drift is here calculated for the cases of a single straight domain wall and of a circular magnetic bubble. The force is found to be strong enough to produce controlled motion of a magnetic bubble, provided that the magnetic material is optically flat and the current carriers in the conductor have a high mobility.

Audio-Frequency Current Comparator for Instrument Transformer Calibration

A special six-terminal ribbon resistor which makes it possible to measure accurately any current ratio from 1 to 1, up to 10 to 1, in the lower audio-frequency range, has been devised and constructed. Circuits have been designed and tested which permit the calibration of ratio and phase angle of current transformers without reference to a standard whose ratio and phase angle are known. In the experimental work it was necessary to devise methods for minimizing effects due to 1) extraneous EMFs induced in the detector circuit by magnetic fields produced from any nearby current-carrying conductor, 2) extraneous currents caused by stray capacitance--mostly between transformer windings, and 3) changes in resistance of the ribbon resistor caused by current flow. It was found that errors caused by these effects could be almost entirely eliminated at ratios near unity, but their magnitude would increase as ratio increased. By using a battery-operated tuned null detector of high sensitivity, a resolution of 1 ppm in ratio could easily be attained. At ratios near unity the estimated uncertainty in ratio was within 5 ppm. At higher ratios the uncertainty increases, but by having two sets of transformers and comparing secondary currents, it is possible to "boot strap" to higher ratios using only ratios up to 2 to 1 on the test equipment. In the present work the uncertainty in each boot-strap operation was thought to be less than 10 ppm in ratio at 60 Hz.