scholarly journals Current control of systems with a Peierls distortion by magnetic field

2018 ◽  
Vol 98 (15) ◽  
Author(s):  
Ryuji Takahashi ◽  
Naoyuki Sugimoto
Keyword(s):  
Magnetic Field ◽  
Current Control ◽  
Peierls Distortion

scholarly journals FFC NMR Relaxometer with Magnetic Flux Density Control

2019 ◽  
Vol 9 (3) ◽  
pp. 22
Author(s):  
António Roque ◽  
Duarte M. Sousa ◽  
Pedro Sebastião ◽  
Elmano Margato ◽  
Gil Marques
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Flux Density ◽  
Low Cost ◽  
Current Control ◽  
Magnetic Flux Density ◽  
Density Control ◽  
Earth Magnetic Field ◽  
Innovative Solution ◽  
Field Cycling

This paper describes an innovative solution for the power supply of a fast field cycling (FFC) nuclear magnetic resonance (NMR) spectrometer considering its low power consumption, portability and low cost. In FFC cores, the magnetic flux density must be controlled in order to perform magnetic flux density cycles with short transients, while maintaining the magnetic flux density levels with high accuracy and homogeneity. Typical solutions in the FFC NMR literature use current control to get the required magnetic flux density cycles, which correspond to an indirect magnetic flux density control. The main feature of this new relaxometer is the direct control of the magnetic flux density instead of the magnet current, in contrast with other equipment available in the market. This feature is a great progress because it improves the performance. With this solution it is possible to compensate magnetic field disturbances and parasitic magnetic fields guaranteeing, among other possibilities, a field control below the earth magnetic field. Experimental results validating the developed solution and illustrating the real operation of this type of equipment are shown.

Experimental Investigation of the Transient Behavior of MR Fluids

2011 ◽  
Author(s):  
Ju¨rgen Maas ◽  
Dirk Gu¨th
Keyword(s):  
Magnetic Field ◽  
Experimental Investigation ◽  
Response Time ◽  
Dynamic Properties ◽  
Transient Behavior ◽  
Current Control ◽  
Large Signal ◽  
Carrier Fluid ◽  
Mr Fluids ◽  
The Magnetic Field

The transient behavior of MRF actuators is an important property for certain applications that is mainly affected by three delays, occurring from the dynamic properties of the coil current, the magnetic field and the torque generation by the MRF. In order to investigate the transient behavior of the generated torque with respect to the magnetic field, which is mainly affected by the motion of the MR particles in the carrier fluid, the mentioned response time of the electrical and magnetic domains must be in an appropriated ratio in comparison to the MRF response time to obtain reliable results by experiments. Therefore a special disc-type test actuator with outstanding dynamics is designed that minimizes the delays by the use of an ultrafast current control and a magnetic core made of soft ferrite material for preventing the effects of eddy currents. For the experimental investigation of the transient behavior of MR fluids, the small signal as well as the large signal behavior is analyzed for different test signals and load conditions of the actuator. Various results of the investigated transient behavior are shown finally for two different MR fluids featuring response times of about 1 ms for the fluid itself and switching times of about 4 ms for the MRF actuator.

Remote Field Eddy Current Control Using Rotating Magnetic Field Transducer: Application to Pressure Tubes Examination

2008 ◽  
Vol 19 (4) ◽  
pp. 202-218 ◽  
Author(s):  
Raimond Grimberg ◽  
Lalita Udpa ◽  
Adriana Savin ◽  
Rozina Steigmann ◽  
Petrica Vizureanu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Eddy Current ◽  
Current Control ◽  
Rotating Magnetic Field ◽  
Pressure Tubes ◽  
Magnetic Field Transducer ◽  
Transducer Application

scholarly journals Discrete Current Control Strategy of Permanent Magnet Synchronous Motors

2013 ◽  
Vol 2013 ◽  
pp. 1-9
Author(s):  
Yan Dong ◽  
Kai Jing ◽  
Hexu Sun ◽  
Yi Zheng
Keyword(s):  
Magnetic Field ◽  
Permanent Magnet ◽  
Control Strategy ◽  
Direct Torque Control ◽  
Current Control ◽  
Torque Control ◽  
Rotating Magnetic Field ◽  
Permanent Magnet Synchronous Motors ◽  
Magnetomotive Force ◽  
Synchronous Motors

A control strategy of permanent magnet synchronous motors (PMSMs), which is different from the traditional vector control (VC) and direct torque control (DTC), is proposed. Firstly, the circular rotating magnetic field is analyzed on the simplified model and discredited into stepping magnetic field. The stepping magnetomotive force will drive the rotor to run as the stepping motor. Secondly, the stator current orientation is used to build the control model instead of rotor flux orientation. Then, the discrete current control strategy is set and adopted in positioning control. Three methods of the strategy are simulated in computer and tested on the experiment platform of PMSM. The control precision is also verified through the experiment.

A Novel Magnetic Stimulator Using Parallel Excited Coils and Capable of High Frequency Stimulation

2013 ◽  
Vol 8 (1) ◽  
Author(s):  
Syrpailyne Wankhar ◽  
Suresh Devasahayam ◽  
Srinivasa Babu
Keyword(s):  
Magnetic Field ◽  
Nerve Stimulation ◽  
High Frequency ◽  
Compound Muscle Action Potential ◽  
Current Control ◽  
High Frequency Stimulation ◽  
Circuit Element ◽  
Inductive Load ◽  
Frequency Stimulation ◽  
A Current

Magnetic stimulators are used for transcranial and peripheral stimulation of nerves for diagnostic, therapeutic, and research purposes. Stimulation is achieved by generating a rapidly changing magnetic field to induce a current at the nerve of interest. Effective nerve stimulation requires a current transient of about 108A/s. This current is obtained by switching the current through a thyristor or an insulated gate bipolar transistor (IGBT). Insulated gate bipolar transistors have better turn off characteristics than thyristors. Due to the large currents, fast switching, and inductive load required in magnetic stimulators, spike voltages can occur and cause device damage. Therefore, they require elaborate protection circuitry. Contemporary magnetic stimulators are large, bulky, and give a current wave that is constrained by the device characteristics rather than decided by physiology. Recent instruments using IGBTs have addressed this question. However, the IGBTs require special considerations to protect them against damage. No magnetic stimulators reported so far can stimulate at rates greater than 60 Hz (Magstim Rapid2, two linked stimulators). A novel magnetic stimulator design is presented in this paper which uses a set of stacked coils driven by independent but synchronized electronic circuits to distribute the current so that only a fraction of the required current flows through any given circuit element. The coils can be arranged in several different geometries, depending on the location and shape of the nerves to be stimulated. While such paralleling of coils and control circuits is not so important for the thyristor circuit design, in the case of the IGBT design it allows the use of smaller IGBTs and better transient control. The design of the coils and independent excitation improves the current control and the magnetic field that is generated. The result is a portable instrument with well controlled rectangular pulse shapes. This stimulator is also capable of much higher frequencies (tested up to 100 Hz) than previously reported. Experimental tests have been compared with the biophysical analysis of stimulation with this instrument. Peripheral nerve stimulation and the elicited compound muscle action potential was used to validate the instrument. The instrument has been tested for the controlled recruitment of a compound nerve at up to 100 Hz. In this paper we present a portable magnetic stimulator capable of high frequency stimulation and rectangular stimulation pulse. These features should give fresh momentum to the use of magnetic stimulation in neurological investigations and interventions. In particular, we expect that it will find wide clinical use such as in pediatric neurology, psychiatry, and neuromodulation.

Scattering of radio frequency waves by cylindrical filaments with general orientation relative to the magnetic field

2018 ◽  
Vol 84 (6) ◽  
Author(s):  
S. I. Valvis ◽  
A. K. Ram ◽  
K. Hizanidis ◽  
P. Papagiannis ◽  
A. Papadopoulos ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Radio Frequency ◽  
Plasma Heating ◽  
Current Control ◽  
Density Fluctuations ◽  
Cylindrical Shape ◽  
Infinite Length ◽  
Poloidal Magnetic Field ◽  
Turbulent Layer ◽  
Wide Range

Radio frequency (RF) waves are routinely used in tokamak fusion plasmas for plasma heating, current control, as well as in diagnostics. These waves are excited by antenna structures placed near the tokamak’s wall and they have to propagate through a turbulent layer known as the scrape-off layer, before reaching the core plasma (which is their target). This layer exhibits coherent density fluctuations in the form of filaments and blobs. The scattering processes of RF plane waves by a single filament is studied with the assumption that the filament has a cylindrical shape and infinite length. Furthermore, besides the major toroidal component of the externally imposed magnetic field, there is also a small poloidal magnetic field component. Considering also that the cylindrical filament’s axis is not necessarily aligned with the toroidal direction, the total magnetic field is in general neither aligned with the axis of the cylinder nor with the toroidal direction. The investigation concerns the case of electron cyclotron (EC) waves (of frequency $f_{0}=170~\text{GHz}$) for tokamak applications. The study covers a variety of density contrasts between the filament and the ambient plasma, different magnetic field inclinations with respect to the cylinder axis (for the same magnitude of magnetic induction $B=4.5T$) and a wide range of filament radii.

scholarly journals Nano-photoluminescence of natural anyon molecules and topological quantum computation

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Alexander M. Mintairov ◽  
Dmitrii V. Lebedev ◽  
Alexei S. Vlasov ◽  
Alexei O. Orlov ◽  
Gregory L. Snider ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Fault Tolerant ◽  
Current Control ◽  
Molecular Structures ◽  
Quantum Field Theories ◽  
Many Body ◽  
Single Vortex ◽  
Charge Sensing ◽  
Topological Quantum ◽  
Topological Quantum Computation

AbstractThe proposal of fault-tolerant quantum computations, which promise to dramatically improve the operation of quantum computers and to accelerate the development of the compact hardware for them, is based on topological quantum field theories, which rely on the existence in Nature of physical systems described by a Lagrangian containing a non-Abelian (NA) topological term. These are solid-state systems having two-dimensional electrons, which are coupled to magnetic-flux-quanta vortexes, forming complex particles, known as anyons. Topological quantum computing (TQC) operations thus represent a physical realization of the mathematical operations involving NA representations of a braid group Bn, generated by a set of n localized anyons, which can be braided and fused using a “tweezer” and controlled by a detector. For most of the potential TQC material systems known so far, which are 2D-electron–gas semiconductor structure at high magnetic field and a variety of hybrid superconductor/topological-material heterostructures, the realization of anyon localization versus tweezing and detecting meets serious obstacles, chief among which are the necessity of using current control, i.e., mobile particles, of the TQC operations and high density electron puddles (containing thousands of electrons) to generate a single vortex. Here we demonstrate a novel system, in which these obstacles can be overcome, and in which vortexes are generated by a single electron. This is a ~ 150 nm size many electron InP/GaInP2 self-organized quantum dot, in which molecules, consisting of a few localized anyons, are naturally formed and exist at zero external magnetic field. We used high-spatial-resolution scanning magneto-photoluminescence spectroscopy measurements of a set of the dots having five and six electrons, together with many-body quantum mechanical calculations to demonstrate spontaneous formation of the anyon magneto-electron particles (eν) having fractional charge ν = n/k, where n = 1–4 and k = 3–15 are the number of electrons and vortexes, respectively, arranged in molecular structures having a built-in (internal) magnetic field of 6–12 T. Using direct imaging of the molecular configurations we observed fusion and braiding of eν-anyons under photo-excitation and revealed the possibility of using charge sensing for their control. Our investigations show that InP/GaInP2 anyon-molecule QDs, which have intrinsic transformations of localized eν-anyons compatible with TQC operations and capable of being probed by charge sensing, are very promising for the realization of TQC.

Ion source with hot filament and magnetic field. Model-based anode current control

Vacuum ◽  
2002 ◽  
Vol 69 (1-3) ◽  
pp. 445-447 ◽  
Author(s):  
Nikolai Donkov ◽  
Zdravko Dinkov ◽  
Kamen Ivanov
Keyword(s):  
Magnetic Field ◽  
Field Model ◽  
Ion Source ◽  
Current Control ◽  
Anode Current ◽  
Model Based ◽  
Magnetic Field Model ◽  
Hot Filament

Dating of Sediments by physics methods Electron Paramagnetic Resonance (EPR) in the region of Iguape – Cananéia, Brazil.

2021 ◽  
Vol 9 (1A) ◽  
Author(s):  
Bruna Cortez
Keyword(s):  
Magnetic Field ◽  
Electron Paramagnetic Resonance ◽  
Sea Level ◽  
Energy Difference ◽  
Current Control ◽  
Sediment Dating ◽  
Quaternary Period ◽  
Paramagnetic Resonance ◽  
Electron Paramagnetic ◽  
The Magnetic Field

Dating of sediments was used by physics method in this work, in the physics methods the radioactivity is present, but usually it is method based on the storage of energy of radiation in the solid, in which will be employed. In the present work, Icapara sediment dating was used Electron Paramagnetic Resonance (EPR) method, in this technique the energy absorption occurs when the frequency of the incident wave is in resonance with the energy difference made by the magnetic field between the parallel and antiparallel directions to this field with the irradiated sample that creates defects in its structure.  In the state of S˜ao Paulo, in the region of Iguape on the southeast coast, it is a place called Icapara, a large sand terrace that was formed due to sea level fluctation that ocorred more than 130 thousand years ago. A sample was taken from a point about 9 meters above the current control of the sea. An age of about 38,000 ±12,000 and 46,000 ± 7,000 years were obtained (EPR) to correlate with the Quaternary period and will be presented to the data obtained.

Sign in / Sign up

Export Citation Format

Share Document