scholarly journals An Antenna-Theory Method for Modeling High-Frequency RF Coils: A Segmented Birdcage Example

2008 ◽  
Vol 2008 ◽  
pp. 1-10 ◽  
Author(s):  
Xin Chen ◽  
Victor Taracila ◽  
Timothy Eagan ◽  
Hiroyuki Fujita ◽  
Xingxian Shou ◽  
...  
Keyword(s):  
High Frequency ◽  
Dipole Antenna ◽  
Rf Coils ◽  
Optimized Design ◽  
Theory Method ◽  
Rf Coil ◽  
Field Approach ◽  
Antenna Theory ◽  
Target Field ◽  
Tem Mode

We suggest that center-fed dipole antenna analytics can be employed in the optimized design of high-frequency MRI RF coil applications. The method is illustrated in the design of a single-segmented birdcage model and a short multisegmented birdcage model. As a byproduct, it is shown that for a long single-segmented birdcage model, the RF field within it is essentially a TEM mode and has excellent planar uniformity. For a short shielded multisegmented birdcage model, the RF field is optimized with a target-field approach with an average SAR functional. The planar homogeneity of the optimized RF field is significantly improved compared with that of a single-segmented birdcage model with the same geometry. The accuracy of the antenna formulae is also verified with numerical simulations performed via commercial software. The model discussed herein provides evidence for the effectiveness of antenna methods in future RF coil analysis.

scholarly journals A Low-Profile HF Meandered Dipole Antenna with a Ferrite-Loaded Artificial Magnetic Conductor

2021 ◽  
Vol 11 (5) ◽  
pp. 2237
Author(s):  
Oh Heon Kwon ◽  
Won Bin Park ◽  
Juho Yun ◽  
Hong Jun Lim ◽  
Keum Cheol Hwang
Keyword(s):  
High Frequency ◽  
Dipole Antenna ◽  
Unit Cell ◽  
Operating Frequency ◽  
High Permeability ◽  
Magnetic Conductor ◽  
Artificial Magnetic Conductor ◽  
Low Profile ◽  
Compact Size ◽  
Binary Genetic Algorithm

In this paper, a low-profile HF (high-frequency) meandered dipole antenna with a ferrite-loaded artificial magnetic conductor (AMC) is proposed. To operate in the HF band while retaining a compact size, ferrite with high permeability is applied to the unit cell of the AMC. The operating frequency bandwidth of the designed unit cell of the AMC is 1.89:1 (19–36 MHz). Thereafter, a meandered dipole antenna is designed by implementing a binary genetic algorithm and is combined with the AMC. The overall size of the designed antenna is 0.06×0.06×0.002 λ3 at the lowest operating frequency. The proposed dipole antenna with a ferrite-loaded AMC is fabricated and measured. The measured VSWR bandwidth (<3) covers 20–30 MHz on the HF band. To confirm the performance of the antenna, a reference monopole antenna which operates on the HF band was selected, and the measured receiving power is compared with the result of the proposed antenna with the AMC.

scholarly journals Development of a Cryogen-Free Compact 3 T Superconducting Magnet for an Electromagnetic Property Measurement System

2021 ◽  
Vol 11 (7) ◽  
pp. 3074
Author(s):  
Jae Young Jang ◽  
Myung Su Kim ◽  
Young Jin Hwang ◽  
Seunghyun Song ◽  
Yojong Choi ◽  
...  
Keyword(s):  
High Temperature ◽  
Measurement System ◽  
Electromagnetic Property ◽  
Superconducting Magnet ◽  
Optimized Design ◽  
Magnet System ◽  
Superconducting Tape ◽  
High Temperature Superconducting ◽  
Target Field ◽  
Property Measurement

A cryogen-free portable 3 T high-temperature superconducting magnet for an electromagnetic property measurement system has been developed to serve as a user facility at the Korea Basic Science Institute. The metallic insulation method was adopted to reduce the charging delay without sacrificing the self-protecting feature. A genetic-algorithm-aided optimized design was carried out to minimize the superconducting tape consumption while satisfying several design constraints. After the design, the compact high-temperature superconducting magnet composed of eight double-pancake coil modules was wound with high-temperature superconducting tape and stainless steel tape, and integrated with a two-stage cryo-cooler. The 3 T magnet was successfully cooled to approximately 20 K with a cryo-cooler and reached the target field of 3 T without any problems. Long-term measurements and a range of other tests were also implemented to verity the performance of the magnet. Test results demonstrated the feasibility of a cryogen-free portable high-temperature superconducting magnet system for electromagnetic property measurement experiments.

scholarly journals Improvement of Risk Assessment Using Numerical Analysis for an Offshore Plant Dipole Antenna

Symmetry ◽  
2018 ◽  
Vol 10 (12) ◽  
pp. 681
Author(s):  
Yun-Jeong Cho ◽  
Kichang Im ◽  
Dongkoo Shon ◽  
Daehoon Park ◽  
Jong-Myon Kim
Keyword(s):  
Risk Assessment ◽  
Numerical Analysis ◽  
High Frequency ◽  
Dipole Antenna ◽  
Effective Field ◽  
Initial Assessment ◽  
International Electrotechnical Commission ◽  
Test Procedures ◽  
High Frequency Structure Simulator ◽  
Site Test

This paper proposes a numerical analysis method for improving risk assessment of radio frequency (RF) hazards. To compare the results of conventional code analysis, the values required for dipole antenna risk assessment, which is widely used in offshore plants based on the British standards (BS) guide, are calculated using the proposed numerical analysis. Based on the BS (published document CENELEC technical report (PD CLC/TR) 50427:2004 and international electrotechnical commission (IEC) 60079 for an offshore plant dipole antenna, an initial assessment, a full assessment, and on-site test procedures are performed to determine if there is a potential risk of high-frequency ignition. Alternatively, numerical analysis is performed using the Ansys high frequency structure simulator (HFSS) tool to compare results based on the BS guide. The proposed method computes the effective field strength and power for the antenna without any special consideration of the structure to simplify the calculation. Experimental results show that the proposed numerical analysis outperforms the risk assessment based on the BS guide in accuracy of the evaluation.

scholarly journals Low-Profile Spidron Fractal Dipole Antenna with a Ferrite-Loaded Artificial Magnetic Conductor for Manpack Applications

2020 ◽  
Vol 10 (24) ◽  
pp. 8843
Author(s):  
Oh Heon Kwon ◽  
Keum Cheol Hwang
Keyword(s):  
High Frequency ◽  
Dipole Antenna ◽  
Magnetic Conductor ◽  
Very High Frequency ◽  
Artificial Magnetic Conductor ◽  
Received Power ◽  
Low Profile ◽  
Profile Characteristics ◽  
Very High ◽  
Good Agreement

In this paper, a Spidron fractal dipole antenna with a ferrite-loaded artificial magnetic conductor (AMC) is presented. By applying ferrite composed of nickel–zinc with a high permeability value, a compact AMC that operates in the broadband frequency range within the high-frequency/very-high-frequency/ultra-high-frequency (HF/VHF/UHF) bands was designed. A Spidron fractal-shaped dipole antenna with a quasi-self-complementary structure was designed and combined with a miniaturized ferrite-loaded AMC. This allowed the designed AMC-integrated dipole antenna to operate in a wide frequency band, covering the HF/VHF/UHF bands, with low-profile characteristics. A prototype of the proposed Spidron fractal dipole antenna with the AMC was manufactured and measured and found to meet low VSWR (voltage standing wave radios) specifications of <3.5 within the 20–500 MHz bandwidth range. The simulated and measured results are in good agreement. The size of the Spidron fractal dipole antenna with the AMC is 0.03×0.026×0.001λ3 relative to the wavelength of the lowest operating frequency. The received power of the Spidron fractal dipole antenna with the AMC was also measured when it was applied to relatively small applications, such as a manpack in this case.

scholarly journals Networks of high frequency inhomogeneous transmission lines

2015 ◽  
Vol 13 ◽  
pp. 189-195
Author(s):  
F. Ossevorth ◽  
H. G. Krauthäuser ◽  
S. Tkachenko ◽  
J. Nitsch ◽  
R. Rambousky
Keyword(s):  
Numerical Simulations ◽  
Transmission Lines ◽  
High Frequency ◽  
Electrical Network ◽  
Wave Method ◽  
Transmission Line Theory ◽  
Full Wave ◽  
Tem Mode ◽  
Line Theory ◽  
Nonuniform Transmission Lines

Abstract. It is well known from classical transmission line theory, that transmission lines can be folded into impedances and thereby used in an electrical network setting. But it is also possible to create large networks of transmission lines consisting of tubes and junctions. The tubes contain the transmission lines and the junctions consider the mutual influences of the adjacent tubes or the terminals. The calculation of the currents and voltages at the junctions can be performed with the help the BLT-equation. So far this method is not applicable for nonuniform transmission lines described in a full wave method, because the lack of a distinct voltage gives no possibility for junctions. Junctions only make sense, when the considered network offers the possibility to propagate a TEM-Mode. If this requirement is fullfilled, nonuniform transmission lines could be included in an electrical network. This approach is validated in this paper in form of numerical simulations as well as measurements.

scholarly journals Coplanar Stripline-Fed Wideband Yagi Dipole Antenna with Filtering-Radiating Performance

Electronics ◽  
2020 ◽  
Vol 9 (8) ◽  
pp. 1258
Author(s):  
Yong Chen ◽  
Gege Lu ◽  
Shiyan Wang ◽  
Jianpeng Wang
Keyword(s):  
High Frequency ◽  
Dipole Antenna ◽  
Frequency Selectivity ◽  
Antenna Design ◽  
Initial Structure ◽  
Coplanar Stripline ◽  
Half Wavelength ◽  
Yagi Antenna ◽  
Operating Bandwidth ◽  
Good Agreement

In this article, a wideband filtering-radiating Yagi dipole antenna with the coplanar stripline (CPS) excitation form is investigated, designed, and fabricated. By introducing an open-circuited half-wavelength resonator between the CPS structure and dipole, the gain selectivity has been improved and the operating bandwidth is simultaneously enhanced. Then, the intrinsic filtering-radiating performance of Yagi antenna is studied. By implementing a reflector on initial structure, it is observed that two radiation nulls appear at both lower and upper gain passband edges, respectively. Moreover, in order to improve the selectivity in the upper stopband, a pair of U-shaped resonators are employed and coupled to CPS directly. As such, the antenna design is finally completed with expected characteristics. To verify the feasibility of the proposed scheme, a filtering Yagi antenna prototype with a wide bandwidth covering from 3.64 GHz to 4.38 GHz is designed, fabricated, and measured. Both simulated and measured results are found to be in good agreement, thus demonstrating that the presented antenna has the performances of high frequency selectivity and stable in-band gain.

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