High Frequency Coil Research Articles

Hybrid simulation of the plasma characteristics in a dual‐frequency dual‐antenna inductively coupled plasma discharge

AbstractDual‐frequency (DF) dual‐antenna inductively coupled plasma (ICP) sources have been proposed as one of the methods to produce large‐area uniform plasma. In this study, a hybrid model, consisting of a fluid module and an electron Monte Carlo (eMC) module, is used to further investigate the modulation of the plasma characteristics (i.e., induced electric field, electron energy distribution, electron heating mechanism, electron temperature, and plasma density) by the low‐frequency (LF) and high‐frequency (HF) currents in a DF argon discharge. When the inner LF current increases from 12 to 22 A at a fixed outer HF current of 10 A, the induced electric field is strengthened near the LF coil and weakened near the HF coil. The fraction of high‐energy electrons at different spatial positions increases with the increase of LF current, which is caused by the sufficient collision heating in the skin layer of LF source, leading to an increase in electron temperature. When the outer HF current rises from 7 to 13 A with the inner LF current fixed at 17 A, the induced electric field is enhanced near the HF coil and weakened near the LF coil. The fraction of low‐energy electrons at different positions increases with the increase of HF current since the energetic electrons from the skin layer of HF source are cooled due to the ionization, excitation, and stepwise ionization collisions between electrons and neutral particles, as well as the weakened induced electric field near the LF coil. As a result, the electron temperature drops with the increase of HF current. Moreover, when the LF and HF currents increase, the plasma density increases, and the distribution of plasma density is also significantly modulated.

POWER SUPPLIES BASED FULL-BRIDGE LLC RESONANT CONVERTER PERFORMANCE FOR IH APPLICATIONS

This paper describes the analysis and performance of a full-bridge LLC resonant converter based on power supplies for IH applications. The analysis contains five components: half bridge inverter, resonant tank, high frequency transformer, rectifier and coil. The switching bridge generates a square waveform to excite the LLC resonant tank, which will produce a resonant sinusoidal current which is transferred to the secondary of the converter through a high-frequency transformer. As it scales the voltage up or down according to the output requirements. The load represented by the equivalent circuit of the coil and work-piece is fed by the current transformed by the rectifiers. Considering that load parameters and resonant frequency vary greatly in all phases of system operation, this paper provides improved knowledge of output power control for high temperature applications. The validity of the analyzed converter parameters had been simulated and tested using MATLAB-SIMULINK software. The results of testing demonstrated that the proposed scheme and assembly has good efficiency, and it is well suited for magnetic induction heating systems

Optimization and Analysis of High-frequency Data Receiver Coil for Artificial Retina

High-frequency coils are vital parts of the wireless data transfer system of implantable electronics for achieving higher data rates. Coil structure and its geometrical parameters are the deciding factors of the optimized coil design. In this paper, the physical parameters of the coil are optimized to resonate at a high frequency. A simple parametric approach is used to extract the physical parameters of the coil for optimizing the coil features at high frequency using MATLAB. The key challenges associated with the disparity in coil characteristics after implantation in the eye are being investigated. Tissue layers that mimic the human eyeball are modelled using HFSS software. The coil is simulated in the tissue environment to evaluate the electrical characteristics of the coil in the biological medium. To validate the simulation model, the implant coil is characterized in the porcine eye to analyse the electrical behaviour of the coil in tissue media. The measured Q factor of the coil in the air is 19.69 and in the tissue is 3.3. Experimental results of the coil implanted in the porcine eye show that the resonant frequency of the coil is reduced by 20%, which limits the operation of the coil at higher frequencies when implanted. This exploratory study on the interaction of biological medium with the electrical behaviour of the coil can be used to predict energy losses in tissues and hence aid in devising compensation techniques for improving the data transmission efficiency of the artificial retinal system.

Efficiency Considerations of LLC Resonant Converter for Induction Heating Application

Due to the high efficiency, high power density and low EMI provided by the LLc resonant converter, it has been widely used by researchers in many fields such as induction heating (IH). This converter is based on a resonant circuit consisting of a capacitor (Cr) and two inductors Lr, Lm operating in wide output load regulating ranges for the purpose of achieving good efficiency for very high power systems using a high operating frequency. This paper aims to present a half-bridge LLC resonant converter based on power supplies for IH applications. The analysis contains five components: half bridge inverter, resonant tank, high frequency transformer, rectifier and coil. The switching bridge generates a square waveform to excite the LLC resonant tank, which will produce a resonant sinusoidal current which is transferred to the secondary of the converter through a high-frequency transformer. as it scales the voltage up or down according to the output requirements. The load represented by the equivalent circuit of the coil and work-piece is fed by the current transformed by the rectifiers. This paper provides an improved knowledge of the control of the output power for high-temperature applications through numerical simulation Considering that the load parameters and resonant frequency vary substantially throughout the system operation. The results of testing demonstrated that the proposed scheme and assembly has good efficiency, and it is well suited for magnetic induction heating systems.

Advanced characterization of magnetization dynamics in iron oxide magnetic nanoparticle tracers.

Characterization of the magnetization dynamics of single-domain magnetic nanoparticles (MNPs) is important for magnetic particle imaging (MPI), magnetic resonance imaging (MRI), and emerging medical diagnostic/therapeutic technologies. Depending on particle size and temperature, nanoparticle magnetization relaxation time constants span from nanoseconds to seconds. In solution, relaxation occurs via coupled Brownian and Néel relaxation mechanisms. Even though their coexistence complicates analysis, the presence of two timescales presents opportunities for more direct control of magnetization behavior if the two processes can be understood, isolated, and tuned. Using high frequency coils and sample temperature tunability, we demonstrate unambiguous determination of the specific relaxation processes for iron oxide nanoparticles using both time and frequency domain techniques. Furthermore, we study the evolution of the fast dynamics at ≈ 10 nanosecond timescales, for magnetic field amplitudes relevant to MPI.

Optimal design of a high homogeneous and small-size shim coil for atomic spin gyroscope based on 0-1 linear programming

It is necessary to develop a high homogeneous, low power consumption, high frequency and small-size shim coil for high precision and low-cost atomic spin gyroscope (ASG). To provide the shim coil, a multi-objective optimization design method is proposed. All structural parameters including the wire diameter are optimized. In addition to the homogeneity, the size of optimized coil, especially the axial position and winding number, is restricted to develop the small-size shim coil with low power consumption. The 0-1 linear programming is adopted in the optimal model to conveniently describe winding distributions. The branch and bound algorithm is used to solve this model. Theoretical optimization results show that the homogeneity of the optimized shim coil is several orders of magnitudes better than the same-size solenoid. A simulation experiment is also conducted. Experimental results show that optimization results are verified, and power consumption of the optimized coil is about half of the solenoid when providing the same uniform magnetic field. This indicates that the proposed optimal method is feasible to develop shim coil for ASG.

Fault analysis and improved design of JET in-vessel Mirnov coils

In vessel Mirnov coils are an essential diagnostic in present day tokamaks. Their use in ITER and future Fusion reactors presents some disadvantages linked to the high radiation environment. Furthermore large Electro Magnetic (EM) forces can be experienced by the coil, due to the pulsed operation of the tokamak device (Van Nieuwenhove and Vermeeren, 2003, Vayakis et al., 2011 [1,2]), and disruptions (Gerasimov et al., 2015 [3]). Since the operation with the ITER-like wall, JET has experienced severe faults in the high-bandwidth Ti wire coils. During 2016-17 new coils have been designed and installed. These can be replaced using remote handling, and they use Cu alloy wire.The presented work includes the failure analysis and modelling, motivating the design differences between old and new coils. The latter will provide valuable information on the long term effects of EM loads during disruptions, as well as chemical degradation processes that will be encountered for ITER High Frequency (HF) coils, which are characterized by the same materials.

Dual‐band RFID tag antenna based on the Hilbert‐curve fractal for HF and UHF applications

A novel single-radiator card-type tag is proposed which is constructed using a series Hilbert-curve loop and matched stub for high frequency (HF)/ultra high frequency (UHF) dual-band radio frequency identification (RFID) positioning applications. This is achieved by merging the series Hilbert-curve for implementing the HF coil antenna, and square loop structure for implementing the UHF antenna to form a single RFID tag radiator. The RFID tag has directivity of 1.75 dBi at 25 MHz, 2.65 dBi at 785 MHz, 2.82 MHz at 835 MHz and 2.75 dBi at 925 MHz. The tag exhibits circular polarisation with −3 dB axial-ratio bandwidth of 14, 480, 605 and 455 MHz at 25, 785, 835 and 925 MHz, respectively. The radiation characteristics of the RFID tag is quasi-omnidirectional in its two orthogonal planes. Impedance matching circuits for the HF/UHF dual-band RFID tag are designed for optimal power transfer with the microchip. The resulting dual-band tag is highly compact in size and possesses good overall performance which makes it suitable for diverse applications.

A novel sputtering technique: Inductively Coupled Impulse Sputtering (ICIS)

Sputtering magnetic materials with magnetron based systems has the disadvantage of field quenching and variation of alloy composition with target erosion. The advantage of eliminating magnetic fields in the chamber is that this enables sputtered particles to move along the electric field more uniformly. Inductively coupled impulse sputtering (ICIS) is a form of high power impulse magnetron sputtering (HIPIMS) without a magnetic field where a high density plasma is produced by a high power radio frequency (RF) coil in order to sputter the target and ionise the metal vapour. In this emerging technology, the effects of power and pressure on the ionisation and deposition process are not known. The setup comprises of a 13.56 MHz pulsed RF coil pulsed with a duty cycle of 25 %. A pulsed DC voltage of 1900 V was applied to the cathode to attract Argon ions and initiate sputtering. Optical emission spectra (OES) for Cu and Ti neutrals and ions at constant pressure show a linear intensity increase for peak RF powers of 500 W – 3400 W and a steep drop of intensity for a power of 4500 W. Argon neutrals show a linear increase for powers of 500 W – 2300 W and a saturation of intensity between 2300 W – 4500 W. The influence of pressure on the process was studied at a constant peak RF power of 2300 W. With increasing pressure the ionisation degree increased. The microstructure of the coatings shows globular growth at 2.95×10−2 mbar and large-grain columnar growth at 1.2×10−1 mbar. Bottom coverage of unbiased vias with a width of 0.360 μm and aspect ratio of 2.5:1 increased from 15 % to 20 % for this pressure range. The current work has shown that the concept of combining a RF powered coil with a magnet-free high voltage pulsed DC powered cathode is feasible and produces very stable plasma. The experiments have shown a significant influence of power and pressure on the plasma and coating microstructure.

Modelling and Control Techniques for a Shorted Turn to Improve High Frequency Coil Response

Electromagnetic coils are used in a wide variety of engineering applications. The magnitude of current (and hence magnetic field strength) is inherently frequency-dependent; above the coil’s breakpoint frequency current reduces in proportion to frequency. This effect often limits the high-frequency performance of devices. A magnetically-coupled conducting loop (“shorted-turn”) may produce beneficial effects of reducing the primary coil’s electrical impedance at high frequencies. This shorted turn effect was modelled using linear transfer function analysis and shown to have close agreement to experimental frequency-response measurements. Parameter sensitivity analysis was conducted to identify the effect of individual shorted-turn variables on the frequency response of a primary coil. Experimental variation of shorted-turn parameters confirmed the theoretical analysis, with thicker-walled, lower-resistance loops providing a more pronounced modification of primary coil response. These results and analysis provide a framework to design shorted-turns within electrical devices to optimise high-frequency behaviour.

Studies on the measurement of grain moisture using high frequency coil

Studies on the measurement of grain moisture using high frequency coil

Studies on the measurement of grain moisture using high frequency coil (part 1)

Studies on the measurement of grain moisture using high frequency coil (part 1)

Magnetic probe construction using thick-film technology

Thick-film technology has been successfully adapted for the design and fabrication of magnetic probes of a new type suitable for use in the simultaneous ultrahigh vacuum and high temperature environment of a nuclear fusion device. The maximum usable temperature is expected to be around 900 °C. This new probe has a specific sensitivity (coupling area per unit volume) an order of magnitude higher than a conventional coil. The new probe in one implementation is capable of simultaneously measuring magnetic field in three orthogonal directions about a single spatial point and in two frequency ranges. Low frequency coils have a measured coupling area of 296–323 cm2, and a frequency response of about 300 kHz. High frequency coils have a design coupling area of 12–15 cm2.

Studies on the Measurement of Grain Moisture Using High Frequency Coil (part 2)

Studies on the Measurement of Grain Moisture Using High Frequency Coil (part 2)

Magnetism in high-resolution NMR probe design. II: HR MAS

Various issues affecting nuclear magnetic resonance probe resolution are discussed, with emphasis on high-resolution or magic angle spinning (MAS) in this part. Symmetric positioning of chip capacitors at the magic angles addresses the largest B0 perturbation with ultra-low-inductance decoupling coils, and symmetric spinner drive designs with silicon-nitride coilforms are shown to be extremely beneficial in reducing spinning-, decoupling-, and variable temperature-induced thermal gradients. Other factors discussed include MAS sample cell design, high frequency (HF) coils, centrifugation, shimming, B1 homogeneity, B0 stability, and geometric compensation for variable angle spinning resolution. ©1998 John Wiley & Sons, Inc. Concepts Magn Reson 10: 239–260, 1998

RF front end for a 4.1 Tesla clinical NMR spectrometer

With increased signal-to-noise, spatial, temporal, and spectral resolution, blood oxygenation level contrast, and other benefits of high field NMR, 4T NMR systems enhance the potential for using multinuclear imaging and spectroscopy for medical science and clinical diagnostics. A new NMR spectrometer is needed however. The magnet aside, the key difference between present clinical or animal systems, and 4T+ clinical systems is the RF front end. Including the power amplifier, transmit/receive (T/R) switch, preamplifier, and RF coils, the front end is required to operate at power levels, bandwidths, and circuit lengths unique in the NMR field. New technology has been developed for these components to optimize the performance of the spectrometer. To cover broader spectral bandwidths, and to compensate for chemical shift dispersion error, two 15 kW solid state amplifiers have been developed for implementation on a "home-built" 4.1T clinical system. A stripline transformed, nonmagnetic, tuned GaAsFET preamp has been built for achieving high gain and low noise at the RF coil. A nonmagnetic dual quadrature hybrid-PIN diode T/R switch was developed to isolate the RF power amplifier from the receiver. New high frequency coils have made use of tuned cavities and transmission lines.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

5427103 MRI apparatus for receiving nuclear-magnetic resonance signals of a living body

There is provided an apparatus for receiving nuclear magnetic resonance signals by applying high frequency energy to a living body placed in a static magnetic field. The distal end portion of the insertion section of the endoscope has a rigid distal end portion and a bendable portion. A housing portion for housing a high frequency coil is provided between the rigid distance portion and the bendable portion. This structure makes it possible to assemble the high frequency coil into the endoscope in a compact manner and can reduce a patient's burden when the insertion section is inserted in the body cavity of the patient.

5245288 Magnetic resonance examination apparatus with wireless transmission of spin resonance signals from high frequency coil system processing unit

A magnetic resonance examination apparatus includes a coil system (10) for receiving spin resonance signals generated in an examination zone, and a processing unit remote from the examination zone for processing the signals received in the coil system. Disturbing effects are liable to occur when a coil system is connected to the processing unit via a cable. These disturbing effects are avoided in that in the direct vicinity of the coil system there is arranged a transmitter for transmitting the spin resonance signals. This transmitter cooperates in a wireless fashion with a receiver to which the processing unit is connected.

4748412 High-frequency coil for nuclear magnetic resonator

4748412 High-frequency coil for nuclear magnetic resonator

4746866 High-frequency coil system for a magnetic resonance imaging apparatus

4746866 High-frequency coil system for a magnetic resonance imaging apparatus