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Transcranial magnetic stimulation (TMS) is a noninvasive and painless treatment for some neurological or psychiatric disorders. The rodent model of TMS provides the possibility to reveal the mechanism of TMS at cellular and molecular levels. However, their application has been hampered by lack of stimulation coils with appropriate focus and intensity. In this study, we analyzed various forms of coils and proposed conductive shield and iron core materials to improve the coil performance. The results showed that the combination of “Halo” coil and “Figure of Eight” coil with shield and iron core could generate better stimulus focus (30.44 mm2) and intensity (87.6 V/m). [ABSTRACT FROM AUTHOR]

In order to couple external circuits to edge-element discretized electromagnetic models, with full field equations, global constraints involving voltages or currents need to be enforced. There is no canonical way to impose a voltage or a current without additional modeling information on the distribution of field sources that rely on topological concepts. In this article, a fast solution of field sources within massive conductors in static and dynamic problems is proposed. Global basis functions, required to cope with non-trivial coil topologies, are directly generated by an iterative solver rather than pre-computing source fields, e.g., by tree–cotree decomposition. [ABSTRACT FROM AUTHOR]

In this study, the NdxFe1−xNy materials are applied for the magnetic core of the series resonance circuit of GaN wireless power transmission (WPT) for the first time. At over 10 MHz, the inductance of the fabricated Nd2Fe17N3 coil is stable at $1.15~\mu \text{H}$ and the effective magnetic permeability of the Nd2Fe17N3 is estimated to be 2.6. At the same inductance, the number of turns of the Nd2Fe17N3 coil can be decreased as compared with that of the air-core coil, and the coil size can be reduced by 0.7 times by using the Nd2Fe17N3 material. At the 13.56 MHz GaN-WPT operation, the successful WPT waveforms can be obtained, and the drastic reduction of the energy loss at the coil is achieved due to the low imaginary part of the magnetic permeability. The Nd-Fe-N materials are considered indispensable to GaN high-frequency switching circuits. [ABSTRACT FROM AUTHOR]

This paper investigates the feasibility of novel data-driven deep learning (DL) models to predict the solution of Maxwell’s equations for low-frequency electromagnetic (EM) devices. With ground truth (empirical evidence) data being generated from a finite-element analysis solver, a deep convolutional neural network is trained in a supervised manner to learn a mapping for magnetic field distribution for topologies of different complexities of geometry, material, and excitation, including a simple coil, a transformer, and a permanent magnet motor. Preliminary experiments show DL model predictions in close agreement with the ground truth. A probabilistic model is introduced to improve the accuracy and to quantify the uncertainty in the prediction, based on Monte Carlo dropout. This paper establishes a basis for a fast and generalizable data-driven model used in the analysis, design, and optimization of EM devices. [ABSTRACT FROM AUTHOR]

This paper proposes and implements an accurate position detection method in wireless power transfer (WPT) for implant applications. Since the technique of WPT via magnetic resonant coupling makes it possible to non-invasively supply electricity for implants from an external tramsitter, an accurate position detection of an invisible receiver from the external transmitter is highly desirable to enhance the transfer efficiency and reduce the magnetic leakage. The magnetoresistive (MR) sensor has been widely used to detect the magnetic field variation due to its low power consumption and high accuracy. In this paper, the compact-in-size MR sensor array in plane with the transmitter is developed to directly detect the magnetic field variation caused by the coil misalignment. Thus, definite advantages of efficient and compact position detection in WPT for implants can be achieved. Since the computation process is straightforward, the coil-misalignment position can be intuitively and easily determined by analyzing the output amplitude of MR sensors. [ABSTRACT FROM AUTHOR]

A high-efficiency post-processing method for computing the magnetic flux in coils is discussed and applied to magnetodynamic problem analysis. The method separates the contribution of magnetic flux in a coil into three parts, respectively, generated by source coils, the magnetization of magnetic region, and eddy currents in conductive region. The computation of the three components of the magnetic flux in coils can be transformed to coil-region-independent integrals, which can help to reduce the mesh size used around the coil, thus increasing the computational efficiency. The method is well adapted to any numerical techniques, such as the finite-element and volume integral methods. A typical electromagnetic shielding problem is used to validate the performance of the post-processing magnetic flux computational method at low-frequency application. [ABSTRACT FROM AUTHOR]

Recently, there has been an increase in the demand for high-efficiency miniature electronic equipment such as personal computers. Therefore, using high drive frequencies and reducing copper loss have become important in meeting the demand. In this paper, we propose the use of magnetocoated wires (MCWs) for coil windings fabricated using the spray method. MCW coils reduce the resistance due to the proximity effect because a magnetic layer leads a magnetic field. As a result, the resistances of the copper wire (COW) and MCW coils at the frequency f = 2.5 MHz are 668 and 447 \text{m}\Omega , respectively, which show a reduction of 33% from resistance of COW to MCW. The resistances of the MCW coils at the frequency f = 20$ kHz and the current $I = 8$ A decreased by 10% compared with the resistances of the COW. The temperature increment of the MCW coils decreased by 5 °C compared with that of COW. This was because MCWs decrease the ac resistance of coils. The magnetic saturation was examined in detail using the finite-element method from the measured value of complex permeability. From the calculated magnetic field and measured magnetization curve, we show the absence of magnetic saturation in coils of nine turns. [ABSTRACT FROM AUTHOR]

The 3-D analytical calculations are proposed using Green’s function (integral approach) for determining magnetic flux densities, mutual inductances, or interaction energies and magnetic force components between different polygon-shaped coils with a rectangular cross section. The basic concept is the determination of the cited magnetic quantities from elementary linear conductors with arbitrary orientations in desired planes. The process is described by using the space transformation matrices of the different axes in which the conductors have previously been defined. The developed results are validated by comparison with those issued from 3-D finite-element methods (Flux 3-D Software). The calculated mutual inductances for some applications are also compared with realized experimental measures. [ABSTRACT FROM AUTHOR]

In this paper, an electromagnetic (EM) vibration energy harvester (VEH) employing the Halbach arrays magnetic circuits to convert a low-frequency vibration energy into an electrical energy is presented. The VEH is made up of the Halbach arrays magnetic circuits, a coil, and a cantilever beam. The Halbach arrays magnetic circuits can concentrate the magnetic field on one side while canceling out the magnetic field on the other side. An analytical model is developed to analyze the distribution of the magnetic field of the Halbach arrays magnetic circuits. The electric output performances of the VEH have been investigated. Compared with the traditional EM VEH, the proposed VEH can significantly increase output power and power density. When coil diameter $d$ , turns number N$ , and cantilever length L_{c} are 20 mm, 1400, and 80 mm, we obtain the optimum output power of 90.35 mW and the power density of 0.55 mW/cm3 at 12.65 Hz under 0.5 g, respectively. Remarkably, the proposed low-frequency resonant EM VEH employing the Halbach arrays has great potential for applying in intelligent wireless sensor networks. [ABSTRACT FROM AUTHOR]

In this paper, we propose a microrobot powered by wireless power transfer (WPT) system which can generate propulsion force and torque as well as electrical energy to perform complex missions. The magnetic field and the induced current from the WPT coils can be utilized into the propulsion force and the Lorentz force for implementing rotational movement. The generated propulsion force and the torque are verified by 3-D finite-element simulations and experimental measurements. [ABSTRACT FROM AUTHOR]

We demonstrate a vector-potential coil and a vector-potential transformer that each use a long flexible solenoid wound around a hollow cylinder. The long flexible solenoid has a current-return wire that runs through the core of the solenoid itself. These devices generate a curl-free vector potential in the hollow cylinder without a magnetic field. In the space within the cylinder where no magnetic field exists, the vector potential is detected by observing a voltage across a secondary conductor that is proportional to the time rate of change of the primary current. We also present the transparency properties of the vector potential through a thick metal whose thickness is larger than the skin depth at the test frequency. [ABSTRACT FROM AUTHOR]

Transcranial magnetic stimulation (TMS) uses transient magnetic field to activate brain regions by inducing an electric field across and an electric current through neurons. Functional magnetic resonance imaging (fMRI) allows the measurement of brain activity making it a potentially useful tool in combination with TMS to analyze the sites of stimulation within the brain. TMS typically utilizes a high current pulse up to 8 kA at approximately 2.5 kHz to induce an electric field inside the brain sufficient for neural stimulation. Lorentz forces are created on the TMS coil and are increased in the presence of a high external magnetic field from the MRI magnet. This study implements a realistic coil model developed from X-ray images of a commercial figure-of-eight TMS coil. The Lorentz forces and stress profile inside the current carrying material of this realistically modeled coil are presented. Results show that the maximum Lorentz force density is significantly larger than previously calculated, by a factor of more than 3. [ABSTRACT FROM AUTHOR]

This paper presents a new real-time control model for the magnetically levitated ironless planar motor. The corner segments of the coil are taken into account in this model. The theory of the composite numerical integration and the Newton-Leibniz formula are used to derive the model. The model is verified by using the harmonic model. Compared with the well-known model, the new model has higher accuracy, and is suitable for real-time control, which can be used in improving the control accuracy of the magnetically levitated ironless planar motor. [ABSTRACT FROM AUTHOR]

New applications for transcranial magnetic stimulation (TMS) are rapidly being developed for diagnostic and therapeutic purposes but are restricted by a number of technical limitations. The ability to reliably perform TMS concurrently with functional magnetic resonance imaging (fMRI) would be a valuable tool for researchers. However the forces experienced by TMS coils during normal operation due to large transient magnetic fields which are produced, are problematic. When operated within a large external field, such as in an fMRI scanner these forces can result in mechanical failure of the coils. This paper presents calculations of these forces to form a basis from which coil failure can be prevented. [ABSTRACT FROM AUTHOR]

This paper concerns the analysis of the force between a rectangular coil and a cuboidal permanent magnet. The magnetic flux density distribution due to the permanent magnet is determined using the surface charge method, and an analytical equation is obtained for the Lorentz force on a cuboidal current carrying volume. These analytical results are used to calculate the Lorentz force on a rectangular coil modeled using four current carrying volumes. The calculations are verified both by measurements and numerical integration. These results can be used in the design and real-time control of planar actuators for industrial levitation/positioning platforms or other (ironless) actuators. [ABSTRACT FROM AUTHOR]

Inductive proximity sensors are noncontact sensing devices used to detect the approach of a target by an increase in coil resistance due to eddy current loss. Extending the operating distance of these sensors is demanded. In this paper, we propose the use of a magnetoplated wire (MPW) as a sensing coil. The MPW is a copper wire, whose circumference is plated with a magnetic thin film. We analyze the impedance of a proximity sensor using a copper wire (COW) and MPW coils by a finite element method. The use of the MPW results in a decrease in AC resistance due to the proximity effect, an increase in inductance, and the generation of a higher flux than when the COW is used. Therefore, it is possible to increase the quality factor Q of the MPW coil. As a result, the operating distances of the MPW and COW coils are 5.0 and 3.8 mm, respectively. The operating distance of the MPW coil is 1.3-fold that of the COW coil. [ABSTRACT FROM AUTHOR]

This paper deals with experiments and calculations performed in order to investigate the influence of the electromagnetic hardening of payloads in a railgun. This is a complex task: besides the large amplitudes of the in-bore magnetic fields due to the pulsed current, the exit of the projectile from the muzzle and the consequences of plasma arcs have to be considered. At the muzzle the magnetic induction can drop from several Teslas to zero within some microseconds, leading to very high induced voltages and electric fields in the metallic parts of the projectile. On the other hand, the electric contact established by solid armatures tends to develop into electric arcs at high velocities during the launch. These plasma arcs as well as the closing switch transients of the railgun circuit are a source of electromagnetic radiation in a broad spectral range. Some electronic devices were selected and tested with static setups corresponding to the previous conditions. In a first phase a series of static railgun experiments (no projectile movement) was performed. In a second phase, static experiments simulating the muzzle exit conditions were carried out. Finally, the influence of electromagnetic waves emitted during railgun experiments on electronic devices was investigated, using a static setup with a conventional spark gap. [ABSTRACT FROM AUTHOR]

In eddy-current sensors and eddy-current testing, it is important to analyze the magnetic field of the coil. Toward this end, we analyzed magnetic fields in various coils, such as circular and rectangular coils. We used the double Fourier transformation and applied it to the eddy-current problem of coils facing a sheet conductor. However, only a limited number of coil shapes could be analyzed by this method. We therefore devised a method of magnetic field analysis that could be applied to a variety of coils by double Fourier transformation. We focused attention on the generated magnetic field of the coil, which is a basic characteristic. Our analysis method is made applicable to a much larger variety of coil shapes by defining a completely new type of function, called shape functions. We verified the validity of the analytical results experimentally. Although the Biot-Savart law may be used to analyze magnetic fields of coils, the law is not applicable when the coil faces a sheet conductor. [ABSTRACT FROM AUTHOR]

We describe a new permeameter to evaluate all components of a permeability tensor. The permeameter consists of a shorted microstrip line and a revolving coil, which can operate well up to 300 MHz. All μijr(i, j = x, y, and z) of a relative permeability tensor of a magnetic thin film were evaluated by the permeameter. The measurements show that the sample has large off-diagonal components compared with diagonal ones, indicating that the examination of such off-diagonal components by the permeameter can be used to design new devices with high accuracy. [ABSTRACT FROM AUTHOR]

The reusable linear magnetic flux compressor has been regarded as a preferred pulsed power supply for the electric gun. Some papers have discussed models for optimal design of this compressor. However, none of them have discussed the resistance calculation of the compressor coil particularly, which is the key issue of the compressor design. Based on a two-dimensional finite element model which can simulates current distributions a in the conductors of the compressor coil, this paper presents a method for the resistance calculation of the compressor coil. In order to verify the proposed method, a physical model of the compressor coil has been built in the laboratory. The comparisons between the calculated and measured results show that the proposed method is an effective tool for resistance calculation of the compressor coil. [ABSTRACT FROM AUTHOR]