Pair Of Helmholtz Coils Research Articles

Passive magnetic field cancellation device by multiple high-Tc superconducting coils

A passive magnetic field cancellation device (PMFCD) is designed. The PMFCD could automatically cancel the field as an active cancellation system did; however it requires no power sources and feedback systems. The capability of the PMFCD is based on the principle that a closed loop can resist flux variation and keep the flux constant inside. The closed loop in the PMFCD is formed by connecting two pairs of high temperature superconductor Helmholtz coils with different radii in series. More important thing is that the ratio of the radius and the turn number between the coils has to satisfy a number of conditions, with which 100% cancellation can be reached. Theoretical methods to obtain the turn number ratio and radius ratio are the major part of the paper. Numerical simulation was followed, aiming to evaluate field distribution under a cancellation state and correct the theoretical values.

Design and fabrication of a high Tc BSCCO based square helmholtz coil

A square Helmholtz coil has been designed and fabricated using commercial grade HTS BSCCO tape with double pancake configuration. The present work is aimed at generating uniform magnetic field with a square Helmholtz coil pair useful in laboratory applications. It has an advantages over the circular Helmholtz coil which had been fabricated and validated by us earlier in terms of field uniformity. This coil is intended to be used as a background field/magnet for circular Helmholtz coil and possible characterization of High T c tapes. Design parameters details, magnetic field generated and the fabrication techniques of this square Helmholtz coil have been described in this paper. Measured current voltage (I-V) characteristics following 1.0 μV/cm criteria and magnetic field profiles of the square Helmholtz coil have been presented in this report in greater detail. From the I-V characteristics, the critical current based on self field dependent of HTS co il is found to be 84 A. The maximum magnetic field is found to be 0.05 T from the magnetic field characteristics.

Novel electromagnetic actuation (EMA) method for 3-dimensional locomotion of intravascular microrobot

A new electromagnetic actuation (EMA) method is proposed for 3-dimensional locomotion of a microrobot. Generally, the EMA system uses Helmholtz coils and Maxwell coils. The Helmholtz coil pair generates a uniform magnetic flux density and the Maxwell coil pair generates a uniform gradient magnetic flux. The microrobot can be aligned to the desired direction by the Helmholtz coils and then, be propelled in the aligned direction by the Maxwell coils. However, many previous EMA systems have been restricted to 2-dimensional planar actuation. The EMA system proposed in this paper consists of a pair of stationary Helmholtz–Maxwell coils and a pair of rotational Helmholtz–Maxwell coils. This new EMA system can manipulate a microrobot in 3-dimensional space. For accurate actuation of a microrobot, the gravitational force, which influences the motion of microrobot, has to be analyzed and compensated. Through various experiments, the performance of the proposed EMA system was evaluated. Finally, a microrobot was test-driven in a blood vessel phantom, and the result of the test drive verified the feasibility of 3-dimensional motion of a microrobot by the new EMA system.

전자기 구동 유영 마이크로로봇

The various electromagnetic based actuation(EMA) methods have been proposed for actuating microrobot. The advantage of EMA is that it can provide wireless driving to microrobot. In this reason a lot of researchers have been focusing on the EMA driven microrobot. This paper proposed a swimming microrobot driven by external alternating magnet field which is generated by two pairs of Helmholtz coils. The microrobot has a fish-like shape and consists of a buoyant robot body, a permanent magnet, and a fin. The fin is directly linked to the permanent magnet and the magnet is swung by the alternating magnet field, which makes the propulsion and steering power of the robot. In this paper, firstly, we designed the locomotive mechanism of the microrobot boy EMA. Secondly, we set up the control system. Finally, we demonstrated the swimming robot and evaluated the performance of the microrobot by the experiments.

Two-dimensional locomotion of a microrobot with a novel stationary electromagneticactuation system

In this paper, we study the locomotion of a microrobot for intravascular therapy. Asan intravascular microrobot has to be small, a conventional actuator, such asa micro-motor, and a battery cannot be integrated. To solve this integrationproblem, we analyze a microrobot with an electromagnetic actuation (EMA) system.Previously, an EMA system using two stationary coil pairs was proposed for the2-dimensional (D) planar locomotion of a microrobot. The EMA system used twostationary pairs of Helmholtz coils and two stationary pairs of Maxwell coils in thex- andy-direction, respectively. This paper proposes a novel stationary EMA system using twopairs of Helmholtz coils and one pair of Maxwell coils. The 2D locomotion of themicrorobot using the proposed EMA system is analyzed and verified by variousexperiments. The microrobot actuated by the proposed EMA system was able to move inthe desired direction on the desired path. The comparison between the proposed EMAsystem and the previous EMA system showed that the proposed system had an 18%smaller volume and used 91% less coil current for the same actuation force than theprevious EMA system. The proposed EMA system produced 2D locomotion of themicrorobot, while having a small volume and a lower power consumption than the previousEMA system.

A Concept for the Characterization and Analysis of the Permeability of Soft Magnetic Thin-Films

A simple approach for accomplishing soft thin film magnetic measurements is evaluated. A modular system based on a pair of HELMHOLTZ coils taken from an existing magnetometer was designed. To characterize it, a quantitative comparison between analytic calculations, Finite Element Methode (FEM) simulation and measurements was conducted. The field uniformity over the measured area of 10 cm along the x-axis was found to be within1.6% of toleration; a sampling rate of 50 kSPS and 50 Hz external magnetic field excitation frequency were used. The system setup and analysis methods were analyzed. The system shows high correlations to other magnetometers, that allows easy calibration with commercial HALL sensors and other magnetometers. The measurement of electroplated NiFe samples fabricated in thin-film technology at the imt demonstrated the validity of the approach.

Characterization of bacterial magnetotactic behaviors by using a magnetospectrophotometry assay.

Magnetotactic bacteria have the unique capacity of synthesizing intracellular single-domain magnetic particles called magnetosomes. The magnetosomes are usually organized in a chain that allows the bacteria to align and swim along geomagnetic field lines, a behavior called magnetotaxis. Two mechanisms of magnetotaxis have been described. Axial magnetotactic cells swim in both directions along magnetic field lines. In contrast, polar magnetotactic cells swim either parallel to the geomagnetic field lines toward the North Pole (north seeking) or antiparallel toward the South Pole (south seeking). In this study, we used a magnetospectrophotometry (MSP) assay to characterize both the axial magnetotaxis of "Magnetospirillum magneticum" strain AMB-1 and the polar magnetotaxis of magneto-ovoid strain MO-1. Two pairs of Helmholtz coils were mounted onto the cuvette holder of a common laboratory spectrophotometer to generate two mutually perpendicular homogeneous magnetic fields parallel or perpendicular to the light beam. The application of magnetic fields allowed measurements of the change in light scattering resulting from cell alignment in a magnetic field or in absorbance due to bacteria swimming across the light beam. Our results showed that MSP is a powerful tool for the determination of bacterial magnetism and the analysis of alignment and swimming of magnetotactic bacteria in magnetic fields. Moreover, this assay allowed us to characterize south-seeking derivatives and non-magnetosome-bearing strains obtained from north-seeking MO-1 cultures. Our results suggest that oxygen is a determinant factor that controls magnetotactic behavior.

Chicks incubated in hypomagnetic field need more exogenous noradrenaline for memory consolidation

The geomagnetic field (GMF) is one of the essential characteristics of the terrestrial environment but does not apply in outer space. The elimination of GMF may interfere with the normal activities of life in many aspects. Previous behavioral experiments have found that long-term memory is impaired in chicks incubated in a near-zero magnetic environment (i.e. hypomagnetic field or HMF). The present study was designed to evaluate the possible involvement of noradrenergic change in the functional abnormality observed before. A HMF space was produced by nullifying the natural GMF with three pairs of Helmholtz coils. The one-trial passive avoidance learning paradigm was performed on day-old chicks incubated in either the HMF space or the natural GMF. Exogenous noradrenaline was administered by intracerebral injections and the effect on memory consolidation was compared between the two categories of subjects. In the behavioral paradigm, the HMF chicks had a higher elimination rate than the GMF chicks and displayed a significant reduction in overall responsiveness. The administration of moderate doses (0.1–0.5 nmol/hemisphere) of noradrenaline led to fairly good memory retention in GMF chicks but had little effect on HMF chicks. However, long-term memory of HMF chicks could be elevated to the normal level by much higher doses (1.0–1.75 nmol/hem) of the drug. These results suggest that prolonged exposure to HMF may induce disorders in the noradrenergic system in the brain and indicate a potentiality of counteracting the ill-effect of GMF deprivation with appropriate pharmacological manipulation.

Improvement of temporal resolution for three-dimensional continuous-wave electron paramagnetic resonance imaging

This paper describes improved temporal resolution for three-dimensional (3D) continuous-wave electron paramagnetic resonance (EPR) imaging. To improve temporal resolution, the duration of magnetic filed scanning that is used to obtain an EPR spectrum for each projection was reduced to 40 ms. The Helmholtz coil pair for field scanning was driven by triangular waves. The uniform distribution of projections was also used to reduce the number of projections for 3D image reconstruction. The reduction reaction of 4-hydroxy-2,2,6,6-tetramethyl-piperidinooxy with ascorbic acid was visualized by improved 3D EPR imaging techniques with a temporal resolution of 5.8 s.

Galfenol material properties and impact on transducer design.

A simple measurement technique to accurately characterize magnetostrictive materials such as Terfenol‐D and Galfenol is required as they become more widely used. A technique was developed that measures the magnetostrictive d33, μ33T, s22H, and Qm constants using a pair of Helmholtz coils, a laser vibrometer, and a sense coil. Unlike previous methods, this technique does not require that the magnetostrictive sample be built into a transducerlike apparatus. A matrix of magnetostrictive material properties as a function of magnetic bias and ac drive amplitude can be created using the developed method. To demonstrate the usefulness of this technique, stress annealed laminated Fe–18.4%Ga rods were tested. Property trends observed for these samples will be reported as well as their impact on transducer performance. [This work was sponsored by the Office of Naval Research (Contract No. N00014‐06‐1‐0530) and by Etrema Products, Inc.]

Verification of a method for measuring magnetostrictive parameters for use in transducer design modeling.

Previous studies have initiated an investigation into a new method of measuring the d33, μ33T, and s33H magnetostrictive constants of a given sample using a pair of Helmholtz coils, a laser vibrometer, and a sense coil. These parameters are calculated from measurements made as a function of dc magnetic bias and ac drive amplitude. This method contrasts with the traditional measurement technique which involves building the sample into a transducerlike device. The new method was demonstrated for laminated stress‐annealed Galfenol rods of high aspect ratio. Measurements obtained by this method appear credible and demonstrate good repeatability. For verification, the authors have returned to the established approach and designed a simple transducer using one of the measured Galfenol rods. The transducer was driven in air as a function of dc magnetic bias and ac drive amplitude. Data obtained from this transducer are compared to an analytical model that uses the material properties obtained experimentally with the new method. [This work was sponsored by the Office of Naval Research (Contract N00014‐06‐1‐0530) and by Etrema Products, Inc.]

Volume Generation of $\hbox{H}^{-}$ Ions in a Magnetized Sheet Plasma Source

A sheet plasma of several-millimeter thickness and an area of ~600 cm2 is produced by a combination of a pair of strong dipole magnets (~1.5 kG on the surface) with opposing fields and a pair of Helmholtz coils producing a magnetic mirror field. The dipole magnets are located at a perpendicular distance of 10 cm away from the sheet plasma core, and the Helmholtz coils are positioned at each end of the extraction chamber, which are separated at 40 cm. H- is formed in the extraction chamber via the excitation of hydrogen molecules by energetic electrons and the subsequent dissociative attachment of the molecules with cold electrons. The ions produced at different neutral gas pressures and discharge conditions were extracted at various probe distances relative to the sheet plasma core. The effects of a noble gas, argon, and sputtered magnesium to H- ion yield were determined. The optimum H- current density extracted at 3.0 cm from the plasma core and 3-A plasma current increased by 4.2 times to 0.63 A/m2 with 10% argon seeding. Argon-hydrogen plasma was then seeded with magnesium (Mg). A Mg disk with an effective area of 22 cm2 is placed at the anode of the extraction region and subjected to sputtering. The optimum H- current density at 3.0 cm from the core plasma is further increased by 4.9 times to 3.09 A/m2. The increase in electron density (from 2.76 times 1012 m-3 to 2.90 times 1015 m-3) of cold electrons with an effective electron temperature of about 3 eV is conducive for DA reactions, leading to the enhanced yield.

Radial characterization of the electron energy distribution in a helicon source terminated by a double layer

Electron energy probability functions (EEPFs) are measured across the radius (0⩽r<6.85cm) of a low pressure (0.3mTorr) helicon plasma source terminated by a current-free double layer. The source field of about 130G is generated using a Helmholtz coil pair and the radio frequency (rf) power is maintained at 250W. All EEPFs exhibit a distribution with a temperature Tebulk out to a break energy εbreak and a relatively depleted distribution for higher energies with a lower temperature Tetail. Tebulk and Tetail are about 8eV and 5eV, respectively, for r<4cm and increase up to about 14eV and 9eV near the source wall, i.e., near the rf antenna. εbreak is found to correspond to the potential drop of the double layer for the central part of the source and to the sheath potential near the wall.

A Novel Rotating Magnetic Field Generator for Driving Magnetic Micro-Machine

In order to make magnetic micro-machine swim more flexibly, we designed a rotating magnetic field generator with tunable angular frequency and magnetic flux density in arbitrary spatial plane by computation and simulation. A device which consists of power supply and three pairs of Helmholtz coils which are pair-wise orthogonal would be applied. Triphase sinusoidal currents were chosen to obtain a rotating magnetic field with an arbitrary rotation axis. The magnetic flux density, angular frequency and rotation axis can be modulated by tuning the amplitude and frequency of each phase current. The device can achieve a rotating magnetic field with arbitrary rotation axis to drive magnetic micro-machine. And through driving experiments, the generator can rotate magnetic micro-machine and move.

A Scalarizing One-Stage Algorithm for Efficient Multi-Objective Optimization

A novel kriging-assisted algorithm is proposed for computationally expensive multi-objective optimization problems, such as those which arise in electromagnetic design. The algorithm combines the multiple objectives into a single objective, which it then optimizes using a one-stage method from single-objective optimization. Inequality and equality constraint handling techniques are included, as is a method for dealing with failed iterations. Its efficiency is demonstrated on the constrained optimization of a pair of Helmholtz coils.

Two-dimensional magnetic field dependence of current-voltage characteristics of rectangular, hexagonal and triangle shape superconducting junctions and DC-SQUIDs

Modulation characteristics of Josephson current through rectangular, hexagonal and triangle shape superconducting junctions and dc-SQUIDs by two-dimensional scanning of external magnetic field have been studied. Two pairs of Helmholtz coils were controlled by two current sources with GPIB (General Purpose Interface Bus) system to obtain the magnetic field dependence automatically. In the case of rectangular shape junction, the dependence of Josephson current on Hx-Hy plane has become the product of the two Fraunhofer patterns in the direction Hx, Hy parallel to each edge of this rectangular shape. The periods of these modulations were inversely proportional of each length of the rectangular shape perpendicular to the magnetic field. In the case of hexagonal shape junction, we have found hexagonal symmetry in the dependence of Josephson current on the Hx-Hy plane. Six ridges of the modulation surface were clearly observed in the directions of six edges of the hexagonal shape (0, 60, 120, 180, 240 300 degrees). In triangle shape junctions, six ridges of the modulation surface were also clearly observed in the directions of three edges of the triangle shape. In the case of dc-SQUIDs, the modulation pattern was the product of the sensitive modulation of the period of the magnetic flux quantization of the hole of the vertical dc-SQUID and the insensitive modulation pattern of each square junction itself.

Why do Electromagnetic Pulses Enhance Bone Growth?

The excitation probability of substrate molecules involved in the production of growth factors influencing the division of chondrocytes in the growth layer of bone under the influence of pulsed electromagnetic fields is studied theoretically in a quantum mechanical model calculation. In this model matrix elements and anti-bonding energy levels are assumed known and the dynamics of the interaction with pulsed electromagnetic fields is derived. The derivation makes it clear that continuous pulsing or large driving currents can overwhelm local diffusive transport to the growth plane resulting in a loss of its enhancement properties. Optimal locations within a pair of Helmholtz coils for enhancement of bone growth are also investigated and found to be close to the coils. The work presented here is believed to be the first derivation in a model calculation of a physical basis for the effects of pulsed electromagnetic fields on bone growth and fusion.

Novel Compensated Moment Detection Coil

We constructed a coil system providing a homogeneity of the sixth order and a compensation of the second order to measure the magnetic dipole moment. The coil system consists of six circular filaments connected in series; two of them are connected with the other four in opposition. This coil system is highly insensitive to external magnetic disturbances, even if they are inhomogeneous, whereas its sensitivity inside the coil is constant over a large part of its volume. In this paper, we report our optimization calculation for the system, calculation of the performance, and measurement results. We measured the influence of a magnet and of an iron plate close to the coil on the magnetic dipole moment for the coil system and also for a pair of Helmholtz coils and compared the results with the calculated values. By reason of the principle of inversion, the coil system can also be used as a field-generating coil, where the decay of the field strength outside the system is much more rapid than for noncompensated systems.

Experimental Demagnetizing Factors for Disk Samples Magnetized Along a Diameter

Demagnetizing factors for disk samples of a commercial 80Ni permalloy have been measured using a vibrating sample magnetometer with fields provided by a Helmholtz coil pair. The range of values of m (diameter/thickness) is from 12.5 to 385. The experimental values of N are significantly higher than those calculated for an ellipsoid, but lower than those calculated assuming uniform magnetization

A square-loop Helmholtz coil system for the evaluation of a single-layer second-order high- Tc SQUID gradiometer

We have designed and fabricated a square-loop Helmholtz coil system to balance and calibrate a second-order SQUID gradiometer, and measured the field distribution in the midplane. It consists of two pairs of identical square loops, one for generating uniform fields, which is a Helmholtz coil pair, and the other for generating the second-order field gradient by subtracting the Helmholtz coils’ field with equal magnitude at the center. We obtained analytical expressions in power series up to the fourth-order of the fields in the midplane and along the coil axis, and measured the field distributions for both Helmholtz and second-order gradient modes.