Electromagnetic Field Simulation Research Articles

A Comparative Study of Birdcage RF Coil Configurations for Ultra-High Field Magnetic Resonance Imaging.

Improvements in transmission and reception sensitivities of radiofrequency (RF) coils used in ultra-high field (UHF) magnetic resonance imaging (MRI) are needed to reduce specific absorption rates (SAR) and RF power deposition, albeit without applying high-power RF. Here, we propose a method to simultaneously improve transmission efficiency and reception sensitivity of a band-pass birdcage RF coil (BP-BC RF coil) by combining a multi-channel wireless RF element (MCWE) with a high permittivity material (HPM) in a 7.0 T MRI. Electromagnetic field (EM-field) simulations, performed using two types of phantoms, viz., a cylindrical phantom filled with oil and a human head model, were used to compare the effects of MCWE and HPM on BP-BC RF coils. EM-fields were calculated using the finite difference time-domain (FDTD) method and analyzed using Matlab software. Next, to improve RF transmission efficiency, we compared two HPM structures, namely, a hollow cylinder shape HPM (hcHPM) and segmented cylinder shape HPM (scHPM). The scHPM and MCWE model comprised 16 elements (16-rad BP-BC RF coil) and this coil configuration demonstrated superior RF transmission efficiency and reception sensitivity along with an acceptable SAR. We expect wider clinical application of this combination in 7.0 T MRIs, which were recently approved by the United States Food and Drug Administration.

A Preliminary Study for Reference RF Coil at 11.7 T MRI: Based on Electromagnetic Field Simulation of Hybrid-BC RF Coil According to Diameter and Length at 3.0, 7.0 and 11.7 T.

Magnetic resonance imaging (MRI) systems must undergo quantitative evaluation through daily and periodic performance assessments. In general, the reference or standard radiofrequency (RF) coils for these performance assessments of 1.5 to 7.0 T MRI systems have been low-pass-type birdcage (LP-BC) RF coils. However, LP-BC RF coils are inappropriate for use as reference RF coils because of their relatively lower magnetic field (B1-field) sensitivity than other types of BC RF coils, especially in ultrahigh-field (UHF) MRI systems above 3.0 T. Herein, we propose a hybrid-type BC (Hybrid-BC) RF coil as a reference RF coil with improved B1-field sensitivity in UHF MRI system and applied it to an 11.7 T MRI system. An electromagnetic field (EM-field) analysis on the Hybrid-BC RF coil was performed to provide the proper dimensions for its use as a reference RF coil. Commercial finite difference time-domain program was used in EM-field simulation, and home-made analysis programs were used in analysis. The optimal specifications of the proposed Hybrid-BC RF coils for them to qualify as reference RF coils are proposed based on their B1+-field sensitivity under unnormalized conditions, as well as by considering their B1+-field uniformity and RF safety under normalized conditions.

Ultranarrow dual-band metamaterial perfect absorber and its sensing application

In this paper, a dual-band metamaterial absorber (MMA) with wide-angle and high absorptivity is proposed. The MMA consists of two silver layers separated by a dielectric layer. Its top resonant element is constituted by two concentric ring resonators connected with four strips. Based on electromagnetic field simulation, the proposed MMA has two narrow absorption peaks with an absorption rate of 99.9% at 711 nm and 99.8% at 830 nm, and the corresponding line width of the two absorption peaks are only 9.7 and 9.8 nm. The dual-band MMA shows high absorptivity under wide incident angles. The simulated field pattern shows that dual-band perfect absorption is the combined result of the interaction of two concentric ring resonators and unit cell coupling. In addition, the hexapole plasmon mode can be observed at the outer ring at one absorption peak. The narrow plasmon resonance has a potential application in optical sensing, and can be used to measure the concentration of aqueous glucose with two frequency channels. The proposed MMA with high absorptivity is simple to manufacture, and has other potential applications, such as narrow-band filters, energy storage device, and so on.

Simulation analysis and experimental research on the safety distance of UAV inspection on transmission lines

In recent years, unmanned aerial vehicle (UAV) inspection has become one of the main means of daily operation and maintenance of overhead transmission lines. Since the key components of the UAV inspection system are composed of electronic components, it relies on data communication to realize data link transmission. In the actual operation process, the complex electromagnetic field environment has an obvious impact on its control and communication performance, especially when inspecting near the DC line. In this paper, combined with the research on the safety assurance technology of UAV inspection operations, the electromagnetic field simulation model of the UAV inspection operation on DC transmission lines is established. The electromagnetic field distribution around the wire is analyzed when the UAV is at different inspection distances, and the influence range and degree of the DC electromagnetic field on UAV inspection system are obtained. A true test platform for the inspection safety distance of the ±500 kV line UAV inspection was built, and the inspection safety distance test and research of the small rotary-wing UAV with a typical size, structure, and material was carried out. Through the test, when the current of the transmission line is 3 kA, the minimum safety distance of the UAV inspection operation of the ±500 kV DC transmission line straight tower is 3 m, and the distance is corrected in combination with the current. The research results of this paper can provide technical support for the inspection operation of small multi-rotor UAVs on ±500 kV transmission lines.

Towards an integrated neonatal brain and cardiac examination capability at 7 T: electromagnetic field simulations and early phantom experiments using an 8-channel dipole array

ObjectiveNeonatal brain and cardiac imaging would benefit from the increased signal-to-noise ratio levels at 7 T compared to lower field. Optimal performance might be achieved using purpose designed RF coil arrays. In this study, we introduce an 8-channel dipole array and investigate, using simulations, its RF performances for neonatal applications at 7 T.MethodsThe 8-channel dipole array was designed and evaluated for neonatal brain/cardiac configurations in terms of SAR efficiency (ratio between transmit-field and maximum specific-absorption-rate level) using adjusted dielectric properties for neonate. A birdcage coil operating in circularly polarized mode was simulated for comparison. Validation of the simulation model was performed on phantom for the coil array.ResultsThe 8-channel dipole array demonstrated up to 46% higher SAR efficiency levels compared to the birdcage coil in neonatal configurations, as the specific-absorption-rate levels were alleviated. An averaged normalized root-mean-square-error of 6.7% was found between measured and simulated transmit field maps on phantom.ConclusionThe 8-channel dipole array design integrated for neonatal brain and cardiac MR was successfully demonstrated, in simulation with coverage of the baby and increased SAR efficiency levels compared to the birdcage. We conclude that the 8Tx-dipole array promises safe operating procedures for MR imaging of neonatal brain and heart at 7 T.

Effects of Electromagnetic Fields Generated from Transcutaneous Transformer:

Transcutaneous energy transfer system (TETS) is one of the methods to supply electric power to an assisted heart. In this study, we analyzed the effects of electric fields in the body on biological tissues around the TETS. Using an electromagnetic field simulator, biological tissue models consisting of Dry-Skin, Wet-Skin, Fat, and Muscle were fabricated. When the frequency was fixed at 400 kHz and the transmission distance at 20 mm, the analysis was conducted by changing the transmitting coils from 2 to 4 layers and the receiving coils from 1 to 4 layers in order to suppress the electric field strength inside the body. The results showed that the lowest internal electric field was observed at 2 layers of transmitting and 4 layers of receiving coils, and the maximum internal electric field was 77.07 V/m. This result was below the occupational of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guideline.

Coil Efficiency for Inductive Peripheral Nerve Stimulation.

Magnetic stimulation of peripheral nerves is evoked by electric field gradients caused by high-intensity, pulsed magnetic fields created from a coil. Currents required for stimulation are very high, therefore devices are large, expensive, and often too complex for many applications like rehabilitation therapy. For repetitive stimulation, coil heating due to power loss poses a further limitation. The geometry of the magnetic coil determines field depth and focality, making it the most important factor that determines the current required for neuronal excitation. However, the comparison between different coil geometries is difficult and depends on the specific application. Especially the distance between nerve and coil plays a crucial role. In this investigation, the electric field distribution of 14 different coil geometries was calculated for a typical peripheral nerve stimulation with a 27 mm distance between axon and coil. Coil parameters like field strength and focality were determined with electromagnetic field simulations. In a second analysis, the activating function along the axon was calculated, which quantifies the efficiency of neuronal stimulation. Moreover, coil designs were evaluated concerning power efficacy based on ohmic losses. Our results indicate that power efficacy of magnetic neurostimulation can be improved significantly by up to 40% with optimized coil designs.

Analysis of coplanar line-type thin-film magnetic field sensor by electromagnetic field simulation

Analysis of coplanar line-type thin-film magnetic field sensor by electromagnetic field simulation

Increasing the waste heat absorption performance in the refrigeration system using electromagnetic effect

This paper enables a simulation model for analyzing and predicting magnetic field patterns and their magnetic flux density on the pipe. Different types of arrangements of magnets like series, parallel, and Halbach arrays are utilized and their magnetic flux density and magnetic field intensity are compared on the respective pipes. Electromagnetic field simulation software calculates different magnetic fields and circuit parameters. Using this software, accurate results can be obtained such as the perfect arrangement of magnets and so on. For this experimentation, Neodymium-35 type magnets are used which have appropriate and stable magnetic strength as compared to other magnets. Diffusion absorption refrigeration systems can also be used alternatively in domestic refrigeration, thus replacing conventional vapor compression refrigeration systems. Thus, results obtained by using different magnetic arrangements will be highly beneficial to choose the proper magnetic arrangement in diffusion absorption refrigeration system for various cooling applications.

Hand Blockage Impact on 5G mmWave Beam Management Performance

Modelling and managing user-induced rotation and blockage in handheld multi-antenna panel devices are some of the pivotal challenges of future narrow beam millimeter wave (mmWave) communications. While studies have been conducted separately on multi-panel beam management (BM) performance and mmWave user blockage loss, no study has been made to date, to the best of the authors’ knowledge, on how hand blockage influences beam alignment accuracy in the context of 5G new radio (NR). This paper presents a link-level evaluation on the impact of user hand grip in BM performance under a 5G NR standard compliant signalling and measurement framework. A high-detail handset model is employed, equipped with multiple panels and different hand grips obtained with CST Microwave Studio, a 3D electromagnetic field simulation tool. Additionally, this study incorporates aspects such as intra-cell mobility, device rotation, hand grip variability and changing propagation conditions. Results show that hand blockage can significantly degrade beam alignment performance, particularly for dual-hand grips in predominantly line-of-sight (LOS) environments. Finally, results suggest that the current blockage model proposed by 3GPP must be further enhanced to account for blockage on a per-panel basis. This would allow a more accurate portrayal of user hand behaviour, which would support the analysis and design of effective solutions to overcome the user’s unpredictable shadowing effects at mmWave frequencies.

Blood Hemoglobin Concentration Sensing by Optical Nano Biosensor-Based Plasmonic Metasurface: A Feasibility Study

Erratic in concentration of the blood hemoglobin (Hb) is pernicious and common disease in many humans worldwide. The establishment of Hb measurement led to finding bio-optics mechanisms for tunable and high sensitivity dual-band plasmonic metasurface (PM) configuration that studied for Hb concentration detection of blood and formed by a semiconductor integrated with metal and dielectric layers. However, finding particularly useful mechanisms without surgery is a safe method with several potentials in biomedical applications. In this paper, a biosensor based on surface plasmon resonances (SPRs) that is a label-free detection method is proposed to measure Hb concentration of blood. The presented sensing method is susceptible to being a dual-bands metasurface perfect absorber at room temperature to adjust the optical properties of the integrated semiconductor plasmonic structure. The modeling and numerical performance have been fulfilled based on the finite element method (FEM) using an electromagnetic field simulation software (CST). Also, to validate the numerical results, the transfer matrix method (TMM) was introduced as an analytical model. The analytical and numerical results show a good agreement. Results indicate maximum sensitivity, figure of merit (FoM), and quality factor ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> ) as 315 nm/RIU, 398.8, and 1407.6, respectively. By controlling and harnessing the light-matter interaction in near-infrared (NIR) region, we obtained the giant electric field intensity enhancement (EFIE) as 5000 and the maximum absorption close to 1 in the first resonance peak of λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> = 1.126 µm which is the best track of optical operation in NIR regime. By adding samples to the biosensor, different Hb concentrations of 0 g/L to 260 g/L have been detected from 1.11 µm to 1.17 µm. Furthermore, the proposed optical metasurface design can be utilized as a biosensor to measure the different content of Hb concentration in whole blood on a g/L scale, making it one of the best candidates for the future optical biosensors for biomedical applications.

Beam Measurements of the Tianlai Dish Radio Telescope Using an Unmanned Aerial Vehicle [Antenna Applications Corner

Precision measurement of the beam pattern of an antenna is very important for many applications. While traditionally such measurement is often made in a microwave anechoic chamber or at a test range, measurement using an unmanned aerial vehicle offers a number of advantages: the measurement can be made for the assembled antenna on site, thus reflecting the actual characteristics of the antenna of interest, and more importantly, it can be performed for larger antennas which cannot be steered or easily measured using the anechoic chamber and test range. Here we report our beam measurement experiment with UAV for a 6 meter dish used in the Tianlai array, which is a radio astronomy experiment. Due to the dish's small collecting area, calibration with an astronomical source only allows for determining the antenna beam pattern over a very limited angular range. We describe in detail the setup of the experiment, the components of the signal transmitting system, the design of the flight path and the procedure for data processing. We find the UAV measurement of the beam pattern agrees very well with the astronomical source measurement in the main lobe, but the UAV measurement can be extended to the fourth side lobe. The measured position and width of each lobe also shows good agreement with electromagnetic field simulation. This UAV-based approach of beam pattern measurement is flexible and inexpensive, and the technique may also be applied to other experiments.

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.

Research on Electromagnetic Force of Hybrid Electromagnetic Levitation Needle Driving System

Hybrid electromagnetic levitation drive system is the core of the needle drive structure, and its performance directly determines the size of the needle drive force. According to the initial design results, the simulation model of the needle drive is established in the electromagnetic field simulation software Maxwell, and the influence of the structural parameters of the hybrid electromagnetic drive system:, the material of the iron core, the number of coil turns on its static characteristics is analyzed. The simulation results show that at the same height, when the isolation ring material is aluminum, the time for the permanent magnet needle to rise to the highest position is the shortest.

Design of 1*4 Microstrip Antenna Array on the Human Thigh with Gain Enhancement

In this paper, at first attempted to design and simulate a stacked circular microstrip patch antenna for high gain at frequency 2.45 GHz, to apply on the industrial, scientific, and medical (ISM) applications. The antenna needs to be minimized for the array mounted on the human thigh, which has high gain and pattern scan capability. The substrate with a high relative permittivity is used for the designed antenna to minimize the dimension of the antenna. A 1*4 array antenna is designed for mount on the human thigh. The amplitude and phase of each antenna are obtained using the maximum-gain theorem to achieve the maximum gain of this array antenna. The coaxial feed is used to achieve good impedance matching, low cross-polarization, and easy control of the amplitude and phase of the element. For designing this entire array antenna, three-dimensional electromagnetic field simulation software Ansoft HFSS based on the finite element method is applied. To experimentally verify the performance, a prototype of the array antenna is fabricated and measurement is performed. The realized gain of the designed array antenna at the resonant frequency is 11 dB. This array structure can be mounted on a human thigh, waist, or head for medical applications, depending on the specific radius.

Small Triple-Band Meandered PIFA for Brain-Implantable Biotelemetric Systems: Development and Testing in a Liquid Phantom

We present a meandered triple-band planar-inverted-F antenna (PIFA) for integration into brain-implantable biotelemetric systems. The target applications are wireless data communication, far-field wireless power transfer, and switching control between sleep/wake-up mode at the Medical Device Radiocommunication Service (MedRadio) band (401–406 MHz) and Industrial, Scientific and Medical (ISM) bands (902–928 MHz and 2400–2483.5 MHz), respectively. By embedding meandered slots into the radiator and shorting it to the ground, we downsized the antenna to the volume of 11 × 20.5 × 1.8 mm3. We optimized the antenna using a 7-layer numerical human head model using full-wave electromagnetic field simulation. In the simulation, we placed the implant in the cerebrospinal fluid (CSF) at a depth of 13.25 mm from the body surface, which is deeper than in most works on implantable antennas. We manufactured and tested the antenna in a liquid phantom which we replicated in the simulator for further comparison. The measured gain of the antenna reached the state-of-the-art values of −43.6 dBi, −25.8 dBi, and −20.1 dBi at 402 MHz, 902 MHz, and 2400 MHz, respectively.

Accurate prediction of EUV lithographic images and 3D mask effects using generative networks

Background: As extreme ultraviolet lithography (EUV) lithography has progressed toward feature dimensions smaller than the wavelength, electromagnetic field (EMF) solvers have become indispensable for EUV simulations. Although numerous approximations such as the Kirchhoff method and compact mask models exist, computationally heavy EMF simulations have been largely the sole viable method of accurately representing the process variations dictated by mask topography effects in EUV lithography. Aim: Accurately modeling EUV lithographic imaging using deep learning while taking into account 3D mask effects and EUV process variations, to surpass the computational bottleneck posed by EMF simulations. Approach: Train an efficient generative network model on 2D and 3D model aerial images of a variety of mask layouts in a manner that highlights the discrepancies and non-linearities caused by the mask topography. Results: The trained model is capable of predicting 3D mask model aerial images from a given 2D model aerial image for varied mask layout patterns. Moreover, the model accurately predicts the EUV process variations as dictated by the mask topography effects. Conclusions: The utilization of such deep learning frameworks to supplement or ultimately substitute rigorous EMF simulations unlocks possibilities of more efficient process optimizations and advancements in EUV lithography.

Analysis and design of parallel-coupled high-gradient structure for ultrashort input power pulses

Shortening the pulse length of input power is a possible approach to raise the accelerating gradient limit of normal conducting structures. We present a novel design of a parallel-coupled structure that operates at ultrashort input power pulses. The principle of the design is to shorten the filling time of the whole structure by feeding the cells individually so that the duration of power transmission between cells can be saved. An X-band (11.994 GHz) parallel-coupled structure design with a 10 ns pulse length is presented in this work. Previous high-power tests of X-band structure prototypes show that a gradient of $120\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ could be achieved for a 200 ns pulse length. Based on the law requiring that ${E}^{30}{t}^{5}=\text{constant}$, this 10-ns-structure design should be able to reach a gradient of $200\text{ }\text{ }\mathrm{MV}/\mathrm{m}$. A detailed circuit model and real-time electromagnetic field simulation methods for designing the parallel-coupling structure are also presented and discussed in this paper.

Effective electrodynamical parameters and microwave heating of radially heterogeneous pellets containing EAF dust and biochar

In this work, we investigated the effect of microwave radiation with radially heterogeneous pellets consisting of electric arc furnace (EAF) dust and biochar. We reviewed the possible content of EAF dust in terms of permittivity and permeability of its components and calculated effective permittivity and permeability of EAF dust by an effective medium approach. Using obtained values we calculated dependencies of effective permittivity and permeability of EAF dust - biochar composite mixture on the volume fraction of EAF dust and conductivity of biochar. Taking into account these dependencies we simulated electromagnetic field and temperature distribution within pellet with a radial dependency of volume fraction of EAF dust and effective permittivity correspondingly.

Design, Manufacture and Performance Evaluation of HTS Electromagnet Wound by YBCO Tape

Heat generation and serious energy consumption of normal-conductive suspension electromagnets influence the performance and stability of suspension systems. With the development of second generation (2G) high temperature superconducting (HTS) technologies, HTS suspension electromagnets are being considered for energy saving purpose. In this paper, a suspension system with three suspension electromagnets is designed, which is comprised of two normal-conductive suspension electromagnets and a 2G-HTS suspension electromagnet. A three-dimensional (3D) electromagnetic field simulation based on finite element method (FEM) is carried out, and the force test platform of suspension electromagnet is built for performance evaluation of the HTS suspension electromagnet. The experimental results show that the current of HTS suspension electromagnet is steady loaded from 0 A to 70 A under 77 K working conditions, with the suspension force meet the requirements. This work provides a certain theoretical and practical foundation for the future superconducting suspension projects.