Helmholtz Coils Research Articles

A Uniformed DC Magnetic Generator Using Ferromagnetic Slot Cage by Geomagnetism Distortion Cancellation

A widely uniform and highly ambient robust DC magnetic field generator for precise motion sensors using inertial measurement units (IMUs) is newly proposed in this paper. Chronic problems such as low uniformity of magnetic field and geomagnetic disturbance of conventional Helmholtz, Merritt, Rubens, Lee-Whiting, and Tetra coils can be significantly mitigated by the proposed uniform DC magnetic field generator (UFG). Different from the previous air coils, the proposed UFG adopts a core-cage so that a strong and uniform DC magnetic field distribution can be generated inside the cage and that the UFG may be quite magnetically robust to ambient changes such as geomagnetic field and ferromagnetic objects. A dedicated power supply was developed for providing not only a DC current to generate the required magnetic field but also an exponentially decaying AC current to demagnetize the residual magnetic field in the core-cage. Design procedures for the UFG are fully established, considering the manufacturing cost, performance, and mechanical robustness for commercialization. Detailed designs of the UFG for magnetic field generation, enhancing uniformity, geomagnetic cancellation, and demagnetizing of the UFG are provided. Experimental results verified by a 30 cm × 30 cm × 30 cm prototype UFG showed that the geomagnetic field inside the UFG was significantly attenuated by 22 dB while the DC magnetic field uniformity (θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>t</i></sub> < 5.0°) was achieved over 85% of the total volume of 27,000 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .

A Magnetic Sensor Calibration System Based on a Closed-Loop Tri-Axial Field Simulator

Magnetism is an omnipresent phenomenon with potential applications in various fields. Immense research has gone into the ways in which magnetism can be used for practical applications. Apart from day-to-day applications such as mobile phones, laptops, railways etc., it finds applications in the aerospace sector as well, for interplanetary studies, navigation, and space robotics. Accurate sensing of the magnetic field is essential for these applications, for which efficient magnetic sensors are used. The precise calibration of these sensors is necessary to quantify various parameters and associated uncertainties to ensure accuracy. For this, a field simulator which can generate a highly accurate and controlled magnetic field is essential. The design and development of a Tri-axis Helmholtz coil field simulator based on Model Reference Adaptive Controller (MRAC) is presented here. It provides a simple, compact, and cost-effective solution for aerospace magnetic sensor calibration. The proposed system offers a uniform magnetic field with 0.1% uniformity within a cubic volume space of 3375cm³. The intensity of the magnetic field can be varied within the full-scale range of 200&#x03BC;T with a resolution of 0.01&#x03BC;T by appropriate current control. The MRAC was finalized after a detailed analysis with various types of controllers such as basic PI, PID and LQI, as it provides precise closed loop control and field stability, which is of paramount importance for aerospace magnetic sensor calibration. It exhibits lesser computational complexity, lower settling time, better adaptability to external field disturbances, lesser overshoot and higher phase margin indicating better closed loop stability compared to other controllers.

Elliptic Helmholtz coil

Elliptic Helmholtz coil

Elliptic Helmholtz coil

Elliptic Helmholtz coil

Design and Development of a Helmholtz Pair System for Production of a Low-Magnetic Field of up to 7.5 mT

In this study, the design, numerical modelling, and construction of various Helmholtz pair coil systems were investigated to produce a homogeneous magnetic field. The magnetic field was simulated using three different Helmholtz coil systems including 2-coil, 3-coil, and 4-coil combinations in order to optimize the field homogeneity and strength over a region of interest that consists of a cylindrical geometry with a height of 700 mm and a diameter of 90 mm. The simulated magnetic field created by the 4-coil system was found to be more homogenous than 3-coil and 2-coil systems over the region of interest. The 4-coil system was constructed and tested by using two commercially available low-power (P=600 W) DC power supplies. For further optimization, the number of turns and diameter of coil elements were simulated. The optimum number of turns and elements were determined to be 140 and 80 turns for the outer pair and inner pair of the 4-coil system, respectively. Finally, the produced magnetic field strength was measured using a hand-held gaussmeter and compared to the simulated magnetic field. We found that the system can produce a magnetic field of B=7.5047 ± 0.0562 mT, and the correlation between simulated and measured magnetic fields were calculated to be R=0.9824 with (p<0.001) suggesting a statistically significant agreement.

Simulations of the Behaviour of Steel Ferromagnetic Fibres Commonly Used in Concrete in a Magnetic Field

The efficiency of fibre reinforcement in concrete can be drastically increased by orienting the fibres using a magnetic field. This orientation occurs immediately after pouring fresh concrete when the fibres can still move. The technique is most relevant for manufacturing prefabricated elements such as beams or columns. However, the parameters of such a field are not immediately apparent, as they depend on the specific fibre reaction to the magnetic field. In this study, a numerical model was created in ANSYS Maxwell to examine the mechanical torque acting on fibres placed in a magnetic field with varying parameters. The model consists of a single fibre placed between two Helmholtz coils. The simulations were verified with an experimental setup as well as theoretical relationships. Ten different fibre types, both straight and hook-ended, were examined. The developed model can be successfully used to study the behaviour of fibres in a magnetic field. The fibre size plays the most important role together with the magnetic saturation of the fibre material. Multiple fibres show significant interactions.

In situ size measurement of a magnetically trapped single superconducting microparticle by Mie scattering

Light scattering by a single superconducting microparticle trapped in a quadrupole magnetic field has been observed. The angular distributions of the scattering light were recorded for multiple colors of the incident light and were well reproduced by using the Mie scattering theory with the refractive indices for normal conducting metals. This analysis provides us with the radius of the trapped particle.

Design and simulation of Helmholtz coil and Maxwell coil for low cost and low magnetic field MRI machine

Design and simulation of Helmholtz coil and Maxwell coil for low cost and low magnetic field MRI machine

Soft and Hard Iron Compensation for the Compasses of an Operational Towed Hydrophone Array without Sensor Motion by a Helmholtz Coil.

Usually, towed hydrophone arrays are instrumented with a set of compasses. Data from these sensors are utilized while beamforming the acoustic signal for target bearing estimation. However, elements of the hydrophone array mounted in the neighborhood of a compass can affect the Earth’s magnetic field detection. The effects depend upon the materials and magnetic environment present in the vicinity of the platform hosting the compass. If the disturbances are constant in time, they can be compensated for by means of a magnetic calibration procedure. This process is commonly known as soft and hard iron compensation. In this paper, a solution is presented for carrying out the magnetic calibration of a COTS (Commercial Off the Shelf) digital compass without sensor motion. This approach is particularly suited in applications where a physical rotation of the platform that hosts the sensor is unfeasible. In our case, the platform consists in an assembled and operational towed hydrophone array. A standard calibration process relies on physical rotation of the platform and thus on the use of the geomagnetic field as a reference during the compensation. As a variation on this approach, we generate an artificial reference magnetic field to simulate the impractical physical rotation. We obtain this by using a tri-axial Helmholtz coil, which enables programmability of the reference magnetic field and assures the required field uniformity. In our work, the simulated geomagnetic field is characterized in terms of its uncertainty. The analysis indicates that our method and experimental set-up represent a suitably accurate approach for the soft and hard iron compensation of the compasses equipped in the hydrophone array under test.

A Compensation Method for Magnetic Localization on Capsule Robot in Medical Application

Aiming at the magnetic positioning accuracy of capsule robot and the magnetic coupling between capsule robot and external driving magnetic field, according to the requirements of capsule robot for position and attitude information, a magnetic positioning compensation method of capsule robot based on magnetic driving system is proposed. This method deduces the error formula according to the magnetic dipole model, optimizes the formula, reduces the number of unknowns, optimizes the calculation process and improves the positioning accuracy. At the same time, a compensation is added to solve the magnetic coupling problem between the external driving magnetic field three-axis Helmholtz coil and the capsule robot. Finally, several groups of experiments verify the effectiveness of the algorithm.

Fabrication and evaluation of bilateral Helmholtz radiofrequency coil for thermo-stable breast image with reduced artifacts.

PurposeThe positron emission tomography (PET)‐magnetic resonance (MR) system is a newly emerging technique that yields hybrid images with high‐resolution anatomical and metabolic information. With PET‐MR imaging, a definitive diagnosis of breast abnormalities will be possible with high spatial accuracy and images will be acquired for the optimal fusion of anatomic locations. Therefore, we propose a PET‐compatible two‐channel breast MR coil with minimal disturbance to image acquisition which can be used for simultaneous PET‐MR imaging in patients with breast cancer.Materials and MethodsFor coil design and construction, the conductor loops of the Helmholtz coil were tuned, matched, and subdivided with nonmagnetic components. Element values were optimized with an electromagnetic field simulation. Images were acquired on a GE 600 PET‐computed tomography (CT) and GE 3.0 T MR system. For this study, we used the T1‐weighted image (volunteer; repetition time (TR), 694 ms; echo time (TE), 9.6 ms) and T2‐weighted image (phantom; TR, 8742 ms; TE, 104 ms) with the fast spin‐echo sequence.ResultsThe results of measuring image factors with the proposed radiofrequency (RF) coil and standard conventional RF coil were as follows: signal‐to‐noise ratio (breast; 207.7 vs. 175.2), percent image uniformity (phantom; 89.22%–91.27% vs. 94.63%–94.77%), and Hounsfield units (phantom; ‐4.51 vs. 2.38).ConclusionsOur study focused on the feasibility of proposed two‐channel Helmholtz loops (by minimizing metallic components and soldering) for PET‐MR imaging and found the comparable image quality to the standard conventional coil. We believe our work will help significantly to improve image quality with the development of a less metallic breast MR coil.

Performance optimization of indirectly heated cathode based electron gun by controlling high voltage surface flashover and beam positioning at target plane

In this paper, an improved design of a practical 2700-bent, 60 kV, 60 kW, indirectly heated cathode-based electron gun has been proposed in order to reduce high voltage breakdown in the electron gun. This ensures reliable and uninterrupted operation of the electron gun for melting and evaporation applications. For this purpose, 1) shield electrodes have been optimally designed for gun insulators in order to provide desired voltage grading/shielding and 2) optimization of positioning of the gun electrodes and optimal current in Helmholtz coil in order to ensure desired 2700-bent electron beam at the target plane, have been achieved. A new optimization technique incorporating formulation of a 3-D cost function is developed and is implemented by using an open-source web application utilizing python script. Electrostatic and electromagnetic 3-D gun simulations are carried out by using CST Studio Particle Tracking Module with modified parameters. Trial experiments have been conducted to monitor breakdown signal which showed improvement in surface flashover performance of electron gun. Molybdenum tablets were successfully melted at target plane by achieving the desired 2700-bent electron beam. Dimensions of molybdenum melt pool and simulation results showed good correspondence.

Magnetically triggered release of active TGF-B from spin vortex microdiscs

Transforming Growth Factor-β (TGF-β) has been implicated in a variety of cellular functions, including control of cell cycle, cell proliferation, extracellular matrix formation, and even stem cell differentiation. TGF-β is also a contributor for combinatorial cellular responses, including cellular senescence, cellular apoptosis, and tumor progression. As a result, spatial and temporal control of TGF-β delivery has the potential to lead to greater control over cell signaling while minimizing the potential for undesirable off-target effects. We recently reported magnetically triggered release of active TGF-β from TGF-β Latent Complex conjugated to high-specific absorption rate (SAR) magnetic nanoparticles via magnetic hyperthermia; here we redirected our approach to spin vortex discs. Planar, gold-coated Permalloy (Ni80Fe20) microdiscs (∼2.0 µm diameter, 70 nm thick) were fabricated via standard lithography techniques and thin-film deposition. The discs were then bioconjugated with latent TGF-β via gold-thiol conjugation chemistry, and shear stress on the attached latent TGF-β was induced via magnetic actuation of the discs. This magnetic actuation was achieved via application of a spatially uniform dual pulsating magnetic field (∼1 mT) using two perpendicular pairs of Helmholtz coils at a frequency of 20 Hz for 1 h. Preliminary results of the bioconjugated discs shown here indicate a significant increase in the release of active TGF-β compared to the baseline passive release. Further studies will focus on investigating non-invasive remote activation and direction of TGF-β by a magnetic field, as well as investigating the potential of expanding this work to other growth factors that exist in latent and active forms.

Разработка экспериментальной установки для исследования магниторецепции у серых тюленей

The assumption was made that Cetaceans, both whales and dolphins, are using geomagnetic field of Earth for orientations during migration. Pinnipeds also make long-distance migrations in open seas without apparent reference point. That may be an evidence of magnetic sense in pinnipeds. In this paper we describe development and construction of experimental installation based on Helmholtz coil for gray seal magnetoreception research. A technique of “selection of an object with specified characteristics” is described, adapted for conduction of experiments with pinnipeds.

Towards Magnetic Field Gradient-Based Imaging and Control of In-Body Devices.

This papers reports a magnetic field gradient-based imaging system for in-body devices which takes inspiration from the localization principles of magnetic resonance imaging. By applying three orthogonal magnetic field gradients, the location of a device inside the body can be determined by measuring the magnetic fields in the device and transmitting this information to an external reader. The proposed system consists of one pair of Helmholtz coils and two pairs of saddle coils and is capable of generating the three orthogonal gradient fields. To emulate an implantable device, a miniature sensor module was designed using off-the-shelf components and semi-passive UHF RFID. The proposed localization system produces magnetic field gradients up to 187.4 G/m while consuming 1 A and achieves an average localization error of 80 μm.

Vortex formation in a spin–orbit-coupled Bose–Einstein condensates with static quadrupole magnetic field

The ground-state phases of Rashba spin–orbit (SO)-coupled Bose–Einstein condensates (BECs) in a quadrupole magnetic field are studied. The coupling of quadrupole magnetic field and spin induces local nonzero gauge particle current, accompanied by the generation of equal and opposite canonical particle current, and leads to the spontaneous nucleation of quantized vortices. The condensates exhibit a variety of rich density patterns and vortex arrangements resulting from the competition among quadrupole magnetic field, SO coupling, and interatomic interactions. Novel vortex structures, such as static vortex dipole, three-vortex molecule and the structure of a cross-arranged vortices and anti-vortices surrounded by a density annulus are found in the condensates. These structures greatly enrich the ground-state phases of SO-coupled BECs, and help to understand the superfluid behavior of a BEC and the nonlinear behavior of coherent matter waves.

Innovative Wireless Charging System for Implantable Capsule Robots

This article deals with an innovative wireless charging system for an implanted capsule robot. The transmitting coil is given by a combination of a Helmholtz coil and a birdcage coil. This coil configuration generates a magnetic field with all nonzero field components for any location within the human torso. Therefore, a single axis receiving coil wound around a cylindrical shaped ferrite core is able to receive a significant quantity of electrical energy for any capsule orientation and position. Design guidelines are provided and illustrative examples are given. Assuming a capsule of 2 cm length and 1 cm diameter we can transfer at least 1 W to the load with a minimum power transfer efficiency larger than 10% without considering electronic losses. Finally, compliance with electromagnetic field safety limits is assessed by a numerical dosimetric analysis.

Real time display with the ferrolens of homogeneous magnetic fields

In our previous published research we have studied the applications of the ferrolens for the observation and qualitative analysis of non-homogeneous magnetic fields. Latest developments over the last few years of the ferrolens increased multifold the sensitivity of this device allowing it to display magnetic fields as low as 10mT in strength and therefore it is possible now to observe also the homogeneous (i.e. straight parallel magnetic flux lines of uniform density in space) magnetic field existing inside air solenoids and between N-S poles of two attracting separated permanent magnets. We present and analyze herein these novel observations of homogeneous magnetic fields with the ferrolens and as a potential new application of this device. The ferrolens can now display the projected magnetic field on air from a distance without needing to be in physical contact with the field source. Experiments were carried out to demonstrate these new capabilities of the ferrolens as a nanomagnetic flux viewer, real-time physical device and scientific qualitative tool. We compare the geometry of magnetic fields of condensed matter ferromagnets with that of magnetic fields inside electrical air solenoids. Specifically, the homogeneous field between two N-S attracting magnets at a distance as well as inside air solenoids and Helmholtz coils and also the non-homogeneous total field of single dipole permanent magnets were observed using a latest generation very sensitive ferrolens. The unique feature of this magneto optic fluid thin film physical device is that it can display discrete magnetic flux lines of the macroscopic field. Also we show how the ferrolens can be used to detect qualitatively the symmetry center of a non ideal homogeneous magnetic field.

The influence of the Earth\u2019s magnetic field on strapdown inertial gravimetry using Q-Flex accelerometers: static and dynamic experiments

In recent strapdown airborne and shipborne gravimetry campaigns with servo accelerometers of the widely used Q-Flex type, results have been impaired by heading-dependent measurement errors. This paper shows that the effect is, in all likelihood, caused by the sensitivity of the Q-Flex type sensor to the Earth’s magnetic field. In order to assess the influence of magnetic fields on the utilised strapdown IMU of the type iMAR iNAV-RQH-1003, the IMU has been exposed to various magnetic fields of known directions and intensities in a 3-D Helmholtz coil. Based on the results, a calibration function for the vertical accelerometer is developed. At the example of five shipborne and airborne campaigns, it is outlined that under specific circumstances the precision of the gravimetry results can be strongly improved using the magnetic calibration approach: The non-adjusted RMSE at repeated lines decreased from 1.19 to 0.26 mGal at a shipborne campaign at Lake Müritz, Germany. To the knowledge of the authors, a significant influence of the Earth’s magnetic field on strapdown inertial gravimetry is demonstrated for the first time.

Design of highly uniform three-dimensional square magnetic field coils for external magnetic shielding of magnetometers

This work uses an intelligent algorithm named the wolf pack algorithm (WPA) in the design of multiple pairs of square Helmholtz coil structures to generate highly uniform magnetic fields within a limited volume for external magnetic shielding of magnetometers. Square Helmholtz coils are widely used in magnetic shielding, magnetic navigation, and aerospace applications, among others. The coil structure is simple, and the generated magnetic field is convenient to calculate. Simultaneously, we set the appropriate penalty function and boundary conditions as well as add the necessary design parameters to achieve the final design. Compared with the traditional design, this method solves the problem of coil assembly to generate a highly uniform magnetic field under various structural and process constraints. The results show that the uniformity of multiple pairs of coils is better than that of a single pair for the same volume and the uniformity of the coil designed by the WPA is better than that designed by the PSO. The measured results of the device are nearly consistent with the theoretical values.