Electromagnetic Field Simulation Research Articles

Dispersion analysis of the solid helical pulse-forming line

AbstractIn this paper, a solid helical pulse-forming line (HPFL) is described. The electromagnetic (EM) dispersion theory is used to calculate the important parameters of the HPFL based on tape helix model. Dispersion effects on the important EM parameters of HPFL, such as electric length and characteristic impedances, are analyzed. When Al2O3 ceramic is applied to be the dielectric in the HPFL, the pulse width of the HPFL is calculated nearly 50 ns only with the length of 305 mm. EM field simulation can draw the dispersion curve of the HPFL directly, which can describe the dispersion effect on the electric length of HPFL. Furthermore, the EM field simulation and experiments are carried out to verify the theoretical calculations of the pulse wide and characteristic impedances. Both simulation and experimental results can prove the EM analyses and calculations in this paper.

Numerical Simulation of Electromagnetic Field and Flow Pattern in a Continuous Slab Caster with In-roll Type Strand Electromagnetic Stirring

The electromagnetic field and flow analysis model were developed to simulate the electromagnetic field and the flow pattern in a vertical curved continuous slab caster with the in-roll type strand electromagnetic stirring. The transient electromagnetic field distribution and the induced electromagnetic force were numerically described. The effects of stirring current, stirring frequency, and different stirrer configurations on the electromagnetically driven flow field in the strand were investigated and the optimization of the stirring parameters was discussed by performing a relative comparison of numerical results. Results show that the in-roller type strand electromagnetic stirrer (SEMS) pair generates the fluctuating magnetic fields, penetrating through the cast slab and periodically parallel shifting along the slab wide face with time evolution. The transient induced electromagnetic forces travels toward the magnetic flux shifting direction. Different stirring parameters (i. e. current and frequency) and stirrer configurations affect the stirring strength and the flow recirculation pattern in the strand, which are closely related to metallurgical performances of the stirrers. There is an optimum frequency to obtain the maximum stirring. The present model provides a relatively theoretical insight into the in-roll type strand electromagnetic stirring system for best operating.

Eight-channel transceiver RF coil array tailored for ¹H/¹⁹F MR of the human knee and fluorinated drugs at 7.0 T.

The purpose of this study was to evaluate the feasibility of an eight-channel dual-tuned transceiver surface RF coil array for combined (1)H/(19)F MR of the human knee at 7.0 T following application of (19)F-containing drugs. The (1)H/(19)F RF coil array includes a posterior module with two (1)H loop elements and two anterior modules, each consisting of one (1)H and two (19)F elements. The decoupling of neighbor elements is achieved by a shared capacitor. Electromagnetic field simulations were performed to afford uniform transmission fields and to be in accordance with RF safety guidelines. Localized (19)F MRS was conducted with 47 and 101 mmol/L of flufenamic acid (FA) – a (19)F-containing non-steroidal anti-inflammatory drug – to determine T1 and T2 and to study the (19)F signal-to-dose relationship. The suitability of the proposed approach for (1)H/(19)F MR was examined in healthy subjects. Reflection coefficients of each channel were less than -17 dB and coupling between channels was less than -11 dB. Q(L)/Q(U) was less than 0.5 for all elements. MRS results demonstrated signal stability with 1% variation. T1 and T2 relaxation times changed with concentration of FA: T1 /T2 = 673/31 ms at 101 mmol/L and T1 /T2 = 616/26 ms at 47 mmol/L. A uniform signal and contrast across the patella could be observed in proton imaging. The sensitivity of the RF coil enabled localization of FA ointment administrated to the knee with an in-plane spatial resolution of (1.5 × 1.5) mm(2) achieved in a total scan time of approximately three minutes, which is well suited for translational human studies. This study shows the feasibility of combined (1)H/(19)F MRI of the knee at 7.0 T and proposes T1 and T2 mapping methods for quantifying fluorinated drugs in vivo. Further technological developments are necessary to promote real-time bioavailability studies and quantification of (19)F-containing medicinal compounds in vivo.

Computational and experimental analysis of high gain antenna for WLAN/WiMAX applications

In this paper a new microstrip-fed planar triple-band antenna has been proposed which is applicable for wireless communication standards WLAN/WiMAX applications. The proposed antenna is composed of radiating patch loaded with open square-loop and arc slots and rectangular full length ground plane with defect on it. The geometry of the designed antenna has been parametrically analyzed and optimal dimensions are obtained through numerical computations by using a commercial electromagnetic field simulator. On the basis of conceptual design, a physical module of the antenna has been realized on ceramic filled polytetrafluoroethylene based dielectric substrate of $$\varepsilon _{r} = 10.2$$?r=10.2 and loss tangent, $$tan\delta = 0.0023$$tan?=0.0023. The measurement results from the antenna prototype show $$-10$$-10dB impedance bandwidths of 630 MHz (2.16---2.79 GHz), 600 MHz (3.27---3.87 GHz) and 690 MHz (5.28---5.97 GHz) which can simultaneously cover the bandwidth requirements for all WLAN/WiMAX standards. The designed antenna exhibits nearly symmetric and omnidirectional radiations patterns over the three operating bands. The antenna prototype has shown maximum radiation gains at the frequency bands of 2.49, 3.54 and 5.6 GHz are about 5.71, 6.16, and 6.48 dBi. The experimental results are in good agreement with the results obtained from numerical computation and the designed antenna can be a good candidate for multiband operations in 2.4/5.2/5.8 GHz WLAN and 2.5/3.5/5.5 GHz WiMAX standard wireless applications.

Investigation of a circular TE11-TE01-mode converter in stepped waveguide technique

A compact and broadband TE11-TE01-mode converter, suitable for various industrial applications like bypass level measurements, is presented in this contribution. Based on stepped waveguide technique, the main advantages of the recommended converter design and the specific field distribution of the TE01-mode are discussed in detail. The converter is presented exemplary for a frequency range from 23 to 28 GHz, which corresponds to a bandwidth of approximately 20 % of the center frequency. Numerous three-dimensional electromagnetic field simulations are performed to optimize the converter and to investigate its reflection and transmission behavior. Realized by six different single elements and 11 parts in total, fast and effective simulations can be performed with CST Microwave Studio. Considering realistic production process parameters, like fillets or tolerances, a good return loss better 17 dB, an insertion loss of 0.1 dB, and an excellent mode purity are achieved. Compared with back-to-back, realistic disturber scenario, and far-field measurements with a first prototype, the expected excellent converter behavior can be validated without limitations. Hence, the suitability of the presented converter design is proven and the feasibility is demonstrated.

The Planar Multipole Resonance Probe: Challenges and Prospects of a Planar Plasma Sensor

A novel compact plasma sensor applicable for the supervision and control of industrial plasma processes is presented in this contribution. Based on the multipole resonance probe (MRP), the new planar MRP (pMRP) is introduced as a powerful and economical monitoring tool, flush-mounted into the reactor wall. Hence, it can be used for an effective suppression of disturbances of the plasma process itself. Using 3D electromagnetic field simulations with CST Microwave Studio, the pMRP is investigated and challenges as well as prospects of the new sensor design are discussed in detail. Three different sensor versions are presented and compared with the resonance behavior of the MRP. Furthermore, limitations concerning position tolerances are shown and the suitability of the pMRP is proven. Measurements in a double inductive coupled plasma, with argon as process gas and varying excitation powers, demonstrate the suitability of the pMRP for monitoring purposes.

A method for the determination of the complex permittivity by detuned ring resonators for bulk materials up to 110 GHz

An accurate characterization of microwave materials is essential for reliable high-frequency circuit design. This paper presents a measurement setup, which enables a quick and accurate determination of the relative permittivity of dielectric bulk materials up to 110 GHz. A ring-resonator is manufactured on a well-characterized substrate, serving as reference resonator. The material under test (MUT) is placed on top of the ring, which increases the effective permittivity and therefore introduces a shift of the resonance frequency of the resonator. In case of moderate to large dielectric losses of the MUTs, the quality factor of the resonator decreases perceptibly, which provides conclusions about the dielectric losses. Electromagnetic field simulations with different heights and relative permittivities of the MUTs provide a look-up table for the measured resonance frequencies. The functionality of the proposed measurement setup is validated by measurement results of different MUTs.

A design for significantly improving the measurable sensitivity of LOG-periodic dipole antenna arrays for optical electric field sensors

Using our improved Optical Electric Field Sensor (OEFS) that incorporates our Log-Periodic Dipole Antenna Array (LPDA-type), it is now possible to accurately measure Electromagnetic Field Interference (Hidaka et al., IEICE Trans Commun (2014) 253–262). However, accurately evaluating the sensitivity characteristics of the LPDA-type OEFS via a standard electromagnetic field simulator resulted in an excellent but less than perfect outcome (Hidaka et al., IEICE Trans Commun (2014) 253–262). In this article, we show that a more accurate and reliable method of assessing the sensitivity characteristics of the OEFS via our software can be achieved using a detailed simulation model that prevents large errors. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1386–1390, 2015

On the interplay of gas dynamics and the electromagnetic field in an atmospheric Ar/H2 microwave plasma torch

A complementary simulation and experimental study of an atmospheric pressure microwave torch operating in pure argon or argon/hydrogen mixtures is presented. The modelling part describes a numerical model coupling the gas dynamics and mixing to the electromagnetic field simulations. Since the numerical model is not fully self-consistent and requires the electron density as an input, quite extensive spatially resolved Stark broadening measurements were performed for various gas compositions and input powers. In addition, the experimental part includes Rayleigh scattering measurements, which are used for the validation of the model. The paper comments on the changes in the gas temperature and hydrogen dissociation with the gas composition and input power, showing in particular that the dependence on the gas composition is relatively strong and non-monotonic. In addition, the work provides interesting insight into the plasma sustainment mechanism by showing that the power absorption profile in the plasma has two distinct maxima: one at the nozzle tip and one further upstream.

Contactless Ultrasound Generation in a Crucible

Ultrasound treatment is used in light alloys during solidification to refine microstructure, remove gas, or disperse immersed particles. A mechanical sonotrode immersed in the melt is most effective when probe tip vibrations lead to cavitation. Liquid contact with the probe can be problematic for high temperature or reactive melts leading to contamination. An alternative contactless method of generating ultrasonic waves is proposed, using electromagnetic (EM) induction. As a bonus, the EM force induces vigorous stirring distributing the effect to treat larger volumes of material. In a typical application, the induction coil surrounding the crucible—also used to melt the alloy—may be adopted for this purpose with suitable tuning. Alternatively, a top coil, immersed in the melt (but still contactless due to EM force repulsion) may be used. Numerical simulations of sound, flow, and EM fields suggest that large pressure amplitudes leading to cavitation may be achievable with this method.

Large scale uniform electromagnetic field simulation based on Helmholtz coil

Considering the technical requirements of the space physical environment simulation system,a square Helmholtz coil was built by a pair of axis symmetric rectangular coils which had the same turns,side length,height and thickness,based on the principle of Helmholtz coils. Combining with the constant current source and MCU control technology,the electromagnetic field simulation system was designed. Adopting finite element analysis software ANSYS Workbench,the magnetic field distribution of the square Helmholtz coil was simulated,and the emphasis of the study was on the electromagnetic field distribution of the coil X-axis,Y-axis and near the surface of the coil. Based on the analysis results,the structure parameters of the square Helmholtz coil were designed. The magnetic flux density of 12 key points was measured inside the designed coil. The results show that the magnetic flux density and uniformity of the magnetic field inside the coil could satisfy the requirements of the space environmental simulation systems.

Advanced Power Control Scheme in Wireless Power Transmission for Human Protection From EM Field

The wireless power transmission (WPT) system must guarantee human protection from the electromagnetic (EM) field around the system in proportion to the increase of the transmit power. This paper presents an advanced power control scheme to reduce the EM field. The basic operation of the proposed scheme is the automatic control of the transmit power according to the proximity of the human body within a certain distance from the WPT system. For the initial design, the EM field simulation is carried out using the HFSS 3-D EM simulator. The initial regions around the system are set up according to the EM field simulation results and the human exposure guideline of the 1998 International Commission on Non-Ionizing Radiation Protection (ICNIRP). A WPT system is designed and implemented using the magnetic resonance in order to measure the EM field and confirm the final scheme. The system is operated at 1.8-MHz band to charge a 24-V 40-Ah lead-acid battery embedded in a docent robot. A laser sensor is also used to detect the proximity of the human body. Two communication schemes are used for automatic wireless charging and power control scheme. By the EM field measurement results of the WPT system, the power control scheme is finally confirmed. The performance measurement with a final scheme shows that the EM field is adaptively reduced to less than the guideline value depending on the proximity of the human body.

Accurate Multipole Field Reconstruction Methods Based on 3-D Electromagnetic Field Simulation Results

This paper proposes the extraction of surrogate field models from 3-D electromagnetic simulation results, for use in a Vlasov beam-dynamics code. Each accelerator component is represented by a dedicated surrogate field model based on a series expansion of its 3-D field distribution. The obtained beam-dynamics simulation results are validated against a particle-in-cell tracking code that integrates a 3-D field distribution of the corresponding accelerator component.

Iterative multi-channel radio frequency pulse calibration with improving B1 field uniformity in high field MRI.

BackgroundIn high field MRI capable of multi-channel radio frequency (RF) transmission, B1 shimming is a time-consuming job because conventional B1 shimming techniques require B1 mapping for each channel. After acquiring the complex-numbered B1 field maps, the optimal amplitude and phase of the driving RF pulse are determined for each channel to maximize the B1 field uniformity in conventional B1 shimming. However, time-consuming B1 shimming procedures at the pre-scan may not be tolerated in the clinical imaging in which patient throughput is one of the important factors.MethodsTo avoid the time-consuming B1 mapping, the first spin echo and the stimulated echo were repeatedly acquired in the slice-selective stimulated echo sequence without imaging gradients. A cost function of the amplitudes and phases of the driving RF pulse for every channel was defined in a way that the ratio between the spin echo and stimulated echo amplitudes rapidly converged to √ 2. The amplitude and phase of the driving RF pulse were iteratively modified over the repeating RF pulse sequence so that the cost function was minimized.ResultsFrom the finite-difference-time-domain (FDTD) electromagnetic field simulations with a human body model placed in a birdcage coil operating at 3 T, it was observed that the RF pulse calibration with iterative cost function minimization can give improvement of B1 field uniformity as well as flip-angle calibration. The experiments at 3 T also showed improvement of RF field uniformity in the phantom imaging studies.ConclusionsSince the proposed RF pulse calibration is not based on B1 mapping, the RF pulse calibration time could be much shorter than the B1-mapping based methods. The proposed method is expected to be a practical substitute for the B1-mapping-based B1 shimming methods when long pre-scan time is not tolerable.

Numerical Analysis of Electromagnetically Induced Heating and Bioheat Transfer for Magnetic Fluid Hyperthermia

In this paper, we study the computational modeling of electromagnetically induced heating in magnetic fluid hyperthermia. Owing to the Brownian rotation and Neel relaxation of induced magnetic moments, ferrofluids can generate heat when exposed to an alternating current magnetic field. To destroy all tumors cells while preventing deleterious physiological responses, input parameters such as the frequency and intensity of magnetic fields and the complex susceptibility of ferrofluids should be determined precisely. In this paper, a solution to Maxwell’s equation for a model of a tumor and its neighboring tissues are coupled as input to Penne’s bioheat equation. Both sets of equations are solved using the finite element analysis method with perfectly matched layers for isothermal boundary conditions in COMSOL. We use a bilayered spherical model with blood perfusion and metabolism to simulate the temperature distribution in tumor regions during hyperthermia therapy. Power density due to electromagnetic field simulation serves as input to the bioheat transfer equation and determines the heat generated by the ferrofluids. The obtained results indicate that tumor regions are heated without adversely affecting healthy regions.

GA-Optimized Compact Broadband CRLH Band-Pass Filter Using Stub-Inserted Interdigital Coupled Lines

The design of a new compact band-pass filter is proposed, which is based on the microstrip composite right- and left-handed transmission-line (CRLH-TL) structure. Particularly, the interdigital coupled (IDC) lines of the CRLH geometry are proposed to be parted by inserting open stubs to meet the specifications on the passband. In addition, there is another pair of stubs to complete the design in a limited space. These are considered in the TL-based analysis and the design parameters are calculated by genetic algorithm optimization. The measurement is shown to be acceptable and agreeable with the circuit and electromagnetic field simulations. In addition, the zerothorder resonance (ZOR) phenomenon is verified.

Nonreciprocal perfect absorber based on an ultra-compact nonsymmetry cavity structure

In this paper, the transmission and absorption properties of nonsymmetrical cavity structure with metal material have been studied through transfer matrix method and electromagnetic (EM) field simulations. The absorption is found to be dependent on the cavity resonance effect. For a nonsymmetrical structure, the EM wave can be totally absorbed from one incidence direction, at the same time the EM wave is totally reflected from the opposite incidence direction. The reasons of the nonreciprocal absorption are analyzed in detail.

High sensitivity surface enhanced Raman spectroscopy of R6G on in situ fabricated Au nanoparticle/graphene plasmonic substrates

Plasmonic gold nanoparticles (AuNP) with controllable dimensions have been fabricated in situ on graphene at moderately elevated temperature for high sensitivity surface enhanced Raman spectroscopy (SERS) of Rhodamine 6G (R6G) dye molecules. Significantly enhanced Raman signature of R6G dyes were observed on AuNP/graphene substrates as compared to the case without graphene with an improvement factor of 400%, which is remarkably greater than previous results obtained in ex situ fabricated SERS substrate. Simulation of localized electromagnetic field around AuNPs with and without the underneath graphene layer reveals an enhanced local electromagnetic field due to the plasmonic effect of AuNPs, while additional Ohmic loss occurs when graphene is present. The enhanced local electromagnetic field by plasmonic AuNPs is unlikely the dominant factor contributing to the observed high SERS sensitivity on R6G/AuNP/graphene substrate. Instead, the p-doped graphene, which is supported by the large positive Dirac point shift away from “zero” observed in AuNP/graphene field effect transistors, promotes SERS signals through enhanced molecule adsorption and non-resonance molecular–substrate chemical interaction.

Optimal Design of Wireless Power Transmission Links for Millimeter-Sized Biomedical Implants.

This paper presents a design methodology for RF power transmission to millimeter-sized implantable biomedical devices. The optimal operating frequency and coil geometries are found such that power transfer efficiency (PTE) and tissue-loss-constrained allowed power are maximized. We define receiver power reception susceptibility (Rx-PRS) and transmitter figure of merit (Tx-FoM) such that their multiplication yields the PTE. Rx-PRS and Tx-FoM define the roles of the Rx and Tx in the PTE, respectively. First, the optimal Rx coil geometry and operating frequency range are identified such that the Rx-PRS is maximized for given implant constraints. Since the Rx is very small and has lesser design freedom than the Tx, the overall operating frequency is restricted mainly by the Rx. Rx-PRS identifies such operating frequency constraint imposed by the Rx. Secondly, the Tx coil geometry is selected such that the Tx-FoM is maximized under the frequency constraint at which the Rx-PRS was saturated. This aligns the target frequency range of Tx optimization with the frequency range at which Rx performance is high, resulting in the maximum PTE. Finally, we have found that even in the frequency range at which the PTE is relatively flat, the tissue loss per unit delivered power can be significantly different for each frequency. The Rx-PRS can predict the frequency range at which the tissue loss per unit delivered power is minimized while PTE is maintained high. In this way, frequency adjustment for the PTE and tissue-loss-constrained allowed power is realized by characterizing the Rx-PRS. The design procedure was verified through full-wave electromagnetic field simulations and measurements using de-embedding method. A prototype implant, 1 mm in diameter, achieved PTE of 0.56% ( -22.5 dB) and power delivered to load (PDL) was 224 μW at 200 MHz with 12 mm Tx-to-Rx separation in the tissue environment.

Numerical study of remote detection outside the magnet with travelling wave Magnetic Resonance Imaging at 3T

The use of the travelling wave approach for high magnetic field magnetic resonance imaging has been used recently with very promising results. This approach offer images one with greater field-of-view and a reasonable signal-to-noise ratio using a circular waveguide. This scheme has been proved to be successful at 7 T and 9.4 T with whole-body imager. Images have also been acquired with clinical magnetic resonance imaging systems whose resonant frequencies were 64 MHz and 128 MHz. These results motivated the use of remote detection of the magnetic resonance signal using a parallel-plate waveguide together with 3 T clinical scanners, to acquired human leg images. The cut-off frequency of this waveguide is zero for the principal mode, allowing us to overcome the barrier of transmitting waves at lower frequency than 300 MHz or 7 T for protons. These motivated the study of remote detection outside the actual magnet. We performed electromagnetic field simulations of a parallel-plate waveguide and a phantom. The signal transmission was done at 128 MHz and using a circular surface coil located almost 200 cm away for the magnet isocentre. Numerical simulations demonstrated that the magnetic field of the principal mode propagate inside a waveguide outside the magnet. Numerical results were compared with previous experimental-acquired image data under similar conditions.