High Frequency Magnetic Field Research Articles

A Wide Range Dual-Output Power Management Circuit for I-Shaped High Frequency Magnetic Field Energy Harvester

A Wide Range Dual-Output Power Management Circuit for I-Shaped High Frequency Magnetic Field Energy Harvester

In Situ Forming of Nitric Oxide and Electric Stimulus for Nerve Therapy by Wireless Chargeable Gold Yarn-Dynamos.

Endogenous signals, namely nitric oxide (NO) and electrons, play a crucial role in regulating cell fate as well as the vascular and neuronal systems. Unfortunately, utilizing NO and electrical stimulation in clinical settings can be challenging due to NO's short half-life and the invasive electrodes required for electrical stimulation. Additionally, there is a lack of tools to spatiotemporally control gas release and electrical stimulation. To address these issues, an "electromagnetic messenger" approach that employs on-demand high-frequency magnetic field (HFMF) to trigger NO release and electrical stimulation for restoring brain function in cases of traumatic brain injury is introduced. The system comprises a NO donor (poly(S-nitrosoglutathione), pGSNO)-conjugated on a gold yarn-dynamos (GY) and embedded in an implantable silk in a microneedle. When subjected to HFMF, conductive GY induces eddy currents that stimulate the release of NO from pGSNO. This process significantly enhances neural stem cell (NSC) synapses' differentiation and growth. The combined strategy of using NO and electrical stimulation to inhibit inflammation, angiogenesis, and neuronal interrogation in traumatic brain injury is demonstrated in vivo.

Superconducting Synchronous Motor Development for Airplane Applications - Mechanical and Electrical Design of a Prototype 100 kW Motor

A 100 kW, 4500 RPM synchronous superconducting motor is being built at the Paihau-Robinson Research Institute, Victoria University of Wellington, New Zealand. The motor has superconducting excitation field coils on the rotor and a conventional stator winding. To minimize mass the motor is an air-core type, meaning no ferromagnetic materials are employed inside the motor. Some of the salient features of this motor include: 1) field winding coils employing REBCO CORC conductor; 2) field coils powered with a contactless superconducting dynamo exciter; 3) an EM shield on the rotor for protecting the field coils from high frequency magnetic fields due to stator harmonics and the switching of the drive electronics; 4) a unique single-layer winding design for the stator winding, where the stator coils are made with copper Litz wire and are liquid-cooled. This paper describes the electrical design and 3D simulation of the motor including the superconducting dynamo, and highlights stator and rotor coil developments that will be validated in the prototype. Sensitivity to critical design parameters has been assessed in simulation and initial sub-system prototypes manufactured for testing. Preliminary design is projecting this motor diameter and axial length as 360 mm and 550 mm respectively, with an efficiency of 96.4 % at the rated load. These numbers may be comparable with permanent magnet motors of similar rating, but this motor is being built to serve as a test-bed for evaluating different technologies for rotor and stator components. The ultimate goal for this program is a 3.0 MW machine with superconducting armature and field windings. In comparison with the permanent magnet motor in 2.5 - 3.0 MW range, the superconducting motors are expected to be 4 to 5 times smaller in size and mass with efficiency exceeding 99 %.

Vortex dynamics in NbTi films at high frequency and high DC magnetic fields

We report on the characterization of NbTi films at sim 11 GHz and in DC magnetic fields up to 4 T, performed by means of the coplanar waveguide resonator technique, providing quantitative information about the penetration depth, the complex impedance, and the vortex-motion-induced complex resistivity. This kind of characterization is essential for the development of radiofrequency cavity technology. To access the vortex-pinning parameters, the complex impedance was analyzed within the formalism of the Campbell penetration depth. Measurements in this frequency range allowed us to determine the complete set of vortex-pinning parameters and the flux flow resistivity, both analyzed and discussed in the framework of high-frequency vortex dynamics models. The analysis also benefits from the comparison with results obtained by a dielectric-loaded resonator technique on similar samples and by other ancillary structural and electromagnetic characterization techniques that provide us with a comprehensive picture of the material. It turns out that the normalized flux flow resistivity follows remarkably well the trend predicted by the time dependent Ginzburg-Landau theory, while the pinning constant exhibits a decreasing trend with the field which points to a collective pinning regime.

High-Frequency Magnetic Field Energy Imaging of Magnetic Recording Head by Alternating Magnetic Force Microscopy (A-MFM) with Superparamagnetic Tip

Recent progress in the development of high-frequency (HF) magnetic materials and devices requires the HF imaging of magnetic field and magnetic field response with high spatial resolution. In this work, we proposed HF Alternating Magnetic Force Microscopy (A-MFM) with a superparamagnetic tip to image magnetic field energy near the sample surface. Magnetic field with a frequency from 100 kHz to 1 GHz was emanated by a writing head used for perpendicular magnetic recording. Applied HF magnetic field is amplitude modulated, and magnetic energy determines the frequency modulation of cantilever oscillation in the framework of A-MFM. The frequency modulated oscillation was caused by low frequency alternating magnetic force, which was generated by the interaction between the amplitude modulated AC magnetic field and superparamagnetic tip.

Role of interface in optimisation of polyamide-6/Fe[formula omitted]O[formula omitted] nanocomposite properties suitable for induction heating

Induction heating of magnetic nanoparticles (MNPs) and localised melting of the surrounding high temperature engineering polymer matrix by generating microscopic or macroscopic eddy currents during magnetisation of a polymer nanocomposite (PMC) is crucial for realising induction heating aided structural bonding. However, the polymer heating should be homogeneous and efficient to avoid local pyrolysis of the polymer matrix, which results in degraded mechanical properties, or requiring a large coil for generating a high frequency magnetic field. Increasing the interfacial area by homogeneously dispersing the MNPs in the polymer matrix provides many microscopic eddy currents to dissipate the power through magnetisation and polarisation, leading to micro eddy current induced uniform heating of the PMC. However, the application of a hydrophobic coating on MNPs to aid dispersion can perturb the generation of eddy currents and affect the crystallinity and size of the crystallites responsible for the mechanical properties. In this work, the dielectric and magnetic properties, as well as the degree/size of crystallinity of a PMC containing oleic acid (OA) (22 and 55 w/w%) and silica coated (Stöber and reverse emulsion method) Fe3O4 MNPs were measured to evaluate the effect of the interfacial coating and its chemistry. The correlation between the measured properties and dispersion state of the MNPs was established to demonstrate the comprehensive effects of interfacial coating on the PMC and this is a unique method to select a suitable PMC for induction aided structural bonding applications. The results showed that the lower amount of OA (22 w/w%) helped achieve the best dispersion to reduce the crystallinity size and increase degree of crystallinity, and to give the best candidate for achieving mechanical properties of the bonded carbon fibre reinforced polymer (CFRP). Moreover, the low concentration of OA helped achieve high polarisation for dielectric heating as well as eddy current formation due to the relatively high magnetic saturation. The silica coating proportionally reduced the magnetic response and electric polarisation of the PMC, which could affect its eddy current generation that is responsible for induction heating.

Visualization of Current Paths by High-Frequency Magnetic Fields Using the Down-Conversion Method

Subsurface magnetic imaging using the electromagnetic field reconstruction is a non-destructive evaluation methods for electric components and circuits. Subsurface magnetic imaging has a considerable limitation because the resolution depends on both the measurement distance and sensitivity of magnetic sensor. In principle, it is difficult to evaluate electronic components and circuits with currents that exceed the response frequency of the sensor. In this study, we propose a down-conversion method for the magnetic field distribution and electric current path images of an isolated DC-DC power conversion circuit, with currents exceeding the response frequency of the magnetic sensor. The circuit was measured with a connected resistance and open circuit condition. The magnetic field distribution and the current path images accurately show that the magnetic field transferred the energy from the input side to the output terminal. Furthermore, the electric current path image shows that there is no electric current flow to the output when the terminal was in open circuit condition.

Study of the B-Dot Sensor for Aircraft Surface Current Measurement.

The B-dot sensor is a type of Rogowski coil widely used in the measurement of current. However, the accuracy of the B-dot for measuring aircraft high-frequency lightning current is greatly affected by factors such as numerical integration drift, high-frequency oscillation, and calibration. In this study, a new design and optimization for improving the B-dot measuring accuracy was carried out. To correct the drift of the numerical integral of the measurement signal in differential mode, the measuring current was reconstructed based on the nonlinear least squares method. The sensor was then optimized by isolating the sampling resistance and matching the impedance with a voltage follower. A low-cost coaxial loop calibration system was also designed to calibrate the high frequency and strong magnetic fields more accurately. Finally, the optimized B-dot sensor accuracy was greatly improved with a measuring range of 30 kA/m, an error of 3.1%, and a high-frequency response of 50 MHz. Our study greatly increases the accuracy of measuring aircraft high-frequency lightning current.

Reduced graphene oxide nanosheets decorated with core-shell of Fe3O4-Au nanoparticles for rapid SERS detection and hyperthermia treatment of bacteria

In this study, the core–shell of Fe3O4-Au nanoparticles (NPs) were prepared by seeding AuNPs onto Fe3O4 NPs modified with poly-ethylenimine (PEI). Later, Fe3O4-Au NPs were attached to cationic poly(dimethyldiallylammonium chloride) (PDDA)-modified graphene oxide (GO) nanosheets through in situ self-assembly behaviors, termed as Fe3O4-Au@RGO nanocomposites, for surface-enhanced Raman scattering (SERS) detection and hyperthermia treatment of bacteria. The resulting Fe3O4-Au@RGO nanocomposites were evaluated systematically by transmission electron microscope, zeta potential, X-ray diffraction, X-ray photoelectron spectroscopy, and vibrating sample magnetometer. It revealed that the core–shell structured Fe3O4-Au NPs were dispersed homogeneously on the surface of the GO nanosheets. Furthermore, the rapid SERS detection for small biomolecules and bacteria was conducted by Raman spectroscopy. The results showed that the greatest SERS intensity was fne tuned at the weight ratio of Fe3O4-Au/RGO nanosheets was 20/1, displaying the optimal interparticle gap of AuNPs to induce the huge hot-spots effect. The magnetic inductive heating capability of Fe3O4-Au@RGO nanocomposites was produced under high frequency magnetic field exposure and can kill high than 90% of the bacteria at 10 min. Hence, the newly developed Fe3O4-Au@RGO nanocomposites were demonstrated to be viable for SERS detection of biomolecules and microbes and potential applications for magnetically capturing and hyperthermia treatment of bacteria.

Generation of a rotating high frequency magnetic field designed for use in magnetic hyperthermia

The paper presents two issues: a new method of generating a rotating magnetic field of high frequency and describes the influence of the rotating magnetic field high frequency on energy losses in a magnetic fluid. This new generation method uses a closed magnetic circuit with ferrite elements. It is powered by two high-frequency power amplifiers through transformers with ferrite cores. As a result, it is relatively easy to obtain high amplitude values ​​of the rotating magnetic field intensity. The article describes the results of the operation of rotating magnetic fields in the frequency range from 38 kHz to 370 kHz, with an amplitude of intensity up to 16 kA·m−1 on energy losses in a magnetic fluid. The obtained results indicate that at a constant frequency f the values ​​of the temperature rate increase dT/dt are proportional to the square of intensity of magnetic field ∝H2. Likewise, the values ​​of the rate of temperature increase dT/dt measured with the constant intensity of the rotating magnetic field H are proportional to the square of frequency ∝f2. It was found that in the area of ​​the low magnetic field intensity, energy losses resulting from magnetic relaxation prevail, which decrease with the increase of the field strength H, and then the share of losses due to magnetic hysteresis increases. A comparison of the calorimetric effect in a rotating and alternating magnetic field shows that the rotating field releases 75% more heat energy than the alternating field.

Reduction of Switching Frequency Vibration of Induction Machines by Auxiliary Winding With Capacitors

The switching action of power electronic devices causes high frequency current, magnetic field, vibration and annoying noise of induction machines fed by inverters, and these high-frequency components concentrate around the switching frequency and its multiple times. Adding auxiliary winding with capacitors is an effective way to reduce the high frequency vibration by weakening the high frequency magnetic field. In order to analyze the vibration mitigation effect of adding auxiliary winding with capacitors, this method is systematically and theoretically analyzed in the paper. The accurate equivalent circuit of induction machines with auxiliary winding is proposed considering the mutual leakage inductance between stator main winding and auxiliary winding. The transfer function of electromotive force and its frequency response are used to illustrate the effect of vibration reduction. To verify the correctness of the analysis, two induction machines with different auxiliary winding arrangements are prototyped and tested.

The Multifunctionally Graded System for a Controlled Size Effect on Iron Oxide-Gold Based Core-Shell Nanoparticles.

We report that Fe3O4@Au core-shell nanoparticles (NPs) serve as a multifunctional molecule delivery platform. This platform is also suitable for sensing the doxorubicin (DOX) through DNA hybridization, and the amount of carried DOX molecules was determined by size-dependent Fe3O4@Au NPs. The limits of detection (LODs) for DOX was found to be 1.839 nM. In our approach, an Au nano-shell coating was coupled with a specially designed DNA sequence using thiol bonding. By means of a high-frequency magnetic field (HFMF), a high release percentage of such a molecule could be efficiently achieved in a relatively short period of time. Furthermore, the thickness increase of the Au nano-shell affords Fe3O4@Au NPs with a larger surface area and a smaller temperature increment due to shielding effects from magnetic field. The change of magnetic property may enable the developed Fe3O4@Au-dsDNA/DOX NPs to be used as future nanocarrier material. More importantly, the core-shell NP structures were demonstrated to act as a controllable and efficient factor for molecule delivery.

Thermal Traits of MNPs under High-Frequency Magnetic Fields: Disentangling the Effect of Size and Coating.

We investigated the heating abilities of magnetic nanoparticles (MNPs) in a high-frequency magnetic field (MF) as a function of surface coating and size. The cobalt ferrite MNPs were obtained by a hydrothermal method in a water–oleic acid–ethanol system, yielding MNPs with mean diameter of about 5 nm, functionalized with the oleic acid. By applying another cycle of hydrothermal synthesis, we obtained MNPs with about one nm larger diameter. In the next step, the oleic acid was exchanged for 11-maleimidoundecanoic acid or 11-(furfurylureido)undecanoic acid. For the heating experiments, all samples were dispersed in the same solvent (dichloroethane) in the same concentration and the heating performance was studied in a broad interval of MF frequencies (346–782 kHz). The obtained results enabled us to disentangle the impact of the hydrodynamic, structural, and magnetic parameters on the overall heating capabilities. We also demonstrated that the specific power absorption does not show a monotonous trend within the series in the investigated interval of temperatures, pointing to temperature-dependent competition of the Brownian and Néel contributions in heat release.

Anomalous Losses in Thin Metal Shells Due to High-Frequency Magnetic Fields and Related Phenomena

Losses in very thin metal shells induced by high-frequency electromagnetic fields have been analyzed. It has been shown, in addition to the existing literature, that the loss dependence on the shell thickness has both minima and maxima. The latter are attained at thicknesses two orders of magnitude smaller than skin depth, or at units of micrometers at several tens of kHz in aluminum and copper. In shielding applications, an inopportune choice of the shield may result in very high losses, bringing about shield overheat, melting, and even evaporation within fractions of a second. Both analytical and numerical analyses are presented, supported by an experimental demonstration. It is shown, in particular, that specific losses maximize with decreasing thickness, and remain independent of it after a certain threshold. It is also shown that even in moderate fields of the order of tens of kA/m specific losses can be so high that the energy of vaporization can be exceeded in milliseconds. Thus, useful applications of the noted effect can also be envisioned, especially in pulsed power, such as the controlled explosion of thin metal foils and films for circuit breaking, forming nanopowders, ultrafast local heating, etc. The obtained results are valid within the limitations of the macroscopic Maxwell equations.

Inductive Thermography as Non-Destructive Testing for Railway Rails

Inductive thermography is a non-destructive testing method, whereby the specimen is slightly heated with a short heating pulse (0.1–1 s) and the temperature change on the surface is recorded with an infrared (IR) camera. Eddy current is induced by means of high frequency (HF) magnetic field in the surface ‘skin’ of the specimen. Since surface cracks disturb the eddy current distribution and the heat diffusion, they become visible in the IR images. Head checks and squats are specific types of damage in railway rails related to rolling contact fatigue (RCF). Inductive thermography can be excellently used to detect head checks and squats on rails, and the method is also applicable for characterizing individual cracks as well as crack networks. Several rail pieces with head checks, with artificial electrical discharge-machining (EDM)-cuts and with a squat defect were inspected using inductive thermography. Aiming towards rail inspection of the track, 1 m long rail pieces were inspected in two different ways: first via a ‘stop-and-go’ technique, through which their subsequent images are merged together into a panorama image, and secondly via scanning during a continuous movement of the rail. The advantages and disadvantages of both methods are compared and analyzed. Special image processing tools were developed to automatically fully characterize the rail defects (average crack angle, distance between cracks and average crack length) in the recorded IR images. Additionally, finite element simulations were used to investigate the effect of the measurement setup and of the crack parameters, in order to optimize the experiments.

Tribological Properties of EN-GJV-400 Cast Iron after TIG Welding in a High-Frequency Magnetic Field

Experimental values are derived for the tribological characteristics of EN-GJV-400 cast iron, as well as its surfaces modified by melting, alloying with copper and nickel, and tungsten inert gas (TIG) welding in a high-frequency magnetic field. The latter process considerably improves the wear resistance.

Internal Temperature Measurements by X-Ray Diffraction on Magnetic Nanoparticles Heated by a High-Frequency Magnetic Field

There is a theoretical and experimental controversy on the possibility for magnetic nanoparticles (MNPs) heated by high-frequency magnetic fields to reach a temperature much larger than the one of ...

Research of the tribotechnical properties of EN-GJV-400 cast iron modified by the TIG method in a high-frequency magnetic field

The tribological parameters of EN-GJV-400 cast iron and its modified surfaces obtained by melting, surface alloying with copper and nickel, as well as TIG welding in a high frequency magnetic field are studied. It is determined, that TIG welding in a high frequency magnetic field significantly increases the wear resistance of the material. Keywords cast iron, TIG welding, ledeburite, wear resistance. fashirzadov@beu.edu.az, a_sadixov05@rambler.ru

Optimal SQUID Loop Size in Arrays of HTS SQUIDs

Arrays of Superconducting interference devices (SQUIDs) deserve much attention for high frequency magnetic field detection because of the combined advantages of wideband radiofrequency operation and improved dynamic range compared to single SQUID magnetometers. Indeed, in principle the dynamic range should scale as the square root of the number of SQUIDs. It is well-known that the size of a SQUID designed for magnetometry has an optimum resulting from a trade-off between large magnetic flux in its loop and small loop inductance. Among the factors affecting this optimum when using arrays of SQUIDs, we discuss the impact of Josephson junction characteristic dispersion, experimentally observed with high temperature superconductors (HTS) and wideband requirement. Both limit the SQUID size to lower values, in particular for arrays of SQUIDs connected in series.

Effects of electromagnetic and magnetic stresses on zebrafish samples

In this work, zebrafish (Danio rerio) embryos were subjected to different physical stresses, consisting of a static and two low frequency magnetic fields, and two radio frequencies. Specifically, embryos were exposed to static (Bo, 0 Hz), very low frequency (VLF, 0.2 Hz), low frequency (LF, 270 kHz), very high frequency (VHF, 100 MHz) and ultra-high frequency (UHF, 900 MHz) magnetic field irradiations for up to 5 days. The field intensities were 40 mT, 40 mT, 470 μT, 240 nT and 240 nT, respectively. Untreated embryos were used as control (n = 10 for each condition).