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K Scheffler - One of the best experts on this subject based on the ideXlab platform.
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9 4 t double tuned 13 c 1 h human head array using a combination of surface loops and Dipole Antennas
NMR in Biomedicine, 2021Co-Authors: N I Avdievich, Georgiy Solomakha, L Ruhm, A Henning, K SchefflerAbstract:MRI at ultra-high field (UHF, ≥7 T) provides a natural strategy for improving the quality of X-nucleus magnetic resonance spectroscopy and imaging due to the intrinsic benefit of increased signal-to-noise ratio. Considering that RF coils require both local transmission and reception at UHF, the designs of double-tuned coils, which often consist of several layers of transmit and receive resonant elements, become quite complex. A few years ago, a new type of RF coil, ie a Dipole antenna, was developed and used for human body and head imaging at UHF. Due to the mechanical and electrical simplicity of Dipole Antennas, combining an X-nucleus surface loop array with 1 H Dipoles can substantially simplify the design of a double-tuned UHF human head array coil. Recently, we developed a novel bent folded-end Dipole transceiver array for human head imaging at 9.4 T. The new eight-element Dipole array demonstrated full brain coverage, and transmit efficiency comparable to that of the substantially more complex 16-element surface loop array. In this work, we developed, constructed and evaluated a double-tuned 13 C/1 H human head 9.4 T array consisting of eight 13 C transceiver surface loops and eight 1 H transceiver bent folded-end Dipole Antennas all placed in a single layer. We showed that interaction between loops and Dipoles can be minimized by placing four 1 H traps into each 13 C loop. The presented double-tuned RF array coil substantially simplifies the design as compared with the common double-tuned surface loop arrays. At the same time, the coil demonstrated an improved 1 H longitudinal coverage and good transmit efficiency.
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evaluation of short folded Dipole Antennas as receive elements of ultra high field human head array
Magnetic Resonance in Medicine, 2019Co-Authors: Nikolai I Avdievich, Georgiy Solomakha, L Ruhm, A Henning, K SchefflerAbstract:PURPOSE To improve the receive (Rx) performance of a human head transceiver (TxRx) array at 9.4T without compromising its transmit (Tx) performance, a novel 16-element array was developed, constructed, and tested. METHODS We designed and constructed a phased array, which consists of 8 TxRx surface loops placed in a single row and circumscribing a head, and 8 Rx-only short folded Dipole Antennas. Dipoles were positioned along the central axis of each transceiver loop perpendicular to its surface. We evaluated the effect of Rx Dipoles on the Tx efficiency of the array and maximum local specific absorption rate (SAR) as compared to the array of 8 surface loops only. We also compared the new array to a 16-channel array of the same size consisting of 8 TxRx surface loops and 8 Rx-only vertical loops in terms of Tx efficiency, SAR, and signal-to-noise ratio (SNR). RESULTS The new array improves both peripheral (up to 2 times) and central (1.17 times) SNR as compared to the 16-element array of the same geometry consisting of 8 TxRx surface loops and 8 Rx-only vertical loops. We demonstrated that an addition of actively detuned Rx-only Dipole elements produces only a small decrease (~7%) of the B1+ transmit field and a small increase (<7%) of the maximum local SAR. CONCLUSION As a proof of concept, we developed and constructed a prototype of a 9.4T (400 MHz) head array consisting of 8 TxRx surface loops and 8 Rx-only short optimized folded Dipoles. We demonstrated that at ultra-high field, Dipoles outperformed Rx-only vertical loops in vivo.
A Henning - One of the best experts on this subject based on the ideXlab platform.
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9 4 t double tuned 13 c 1 h human head array using a combination of surface loops and Dipole Antennas
NMR in Biomedicine, 2021Co-Authors: N I Avdievich, Georgiy Solomakha, L Ruhm, A Henning, K SchefflerAbstract:MRI at ultra-high field (UHF, ≥7 T) provides a natural strategy for improving the quality of X-nucleus magnetic resonance spectroscopy and imaging due to the intrinsic benefit of increased signal-to-noise ratio. Considering that RF coils require both local transmission and reception at UHF, the designs of double-tuned coils, which often consist of several layers of transmit and receive resonant elements, become quite complex. A few years ago, a new type of RF coil, ie a Dipole antenna, was developed and used for human body and head imaging at UHF. Due to the mechanical and electrical simplicity of Dipole Antennas, combining an X-nucleus surface loop array with 1 H Dipoles can substantially simplify the design of a double-tuned UHF human head array coil. Recently, we developed a novel bent folded-end Dipole transceiver array for human head imaging at 9.4 T. The new eight-element Dipole array demonstrated full brain coverage, and transmit efficiency comparable to that of the substantially more complex 16-element surface loop array. In this work, we developed, constructed and evaluated a double-tuned 13 C/1 H human head 9.4 T array consisting of eight 13 C transceiver surface loops and eight 1 H transceiver bent folded-end Dipole Antennas all placed in a single layer. We showed that interaction between loops and Dipoles can be minimized by placing four 1 H traps into each 13 C loop. The presented double-tuned RF array coil substantially simplifies the design as compared with the common double-tuned surface loop arrays. At the same time, the coil demonstrated an improved 1 H longitudinal coverage and good transmit efficiency.
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evaluation of short folded Dipole Antennas as receive elements of ultra high field human head array
Magnetic Resonance in Medicine, 2019Co-Authors: Nikolai I Avdievich, Georgiy Solomakha, L Ruhm, A Henning, K SchefflerAbstract:PURPOSE To improve the receive (Rx) performance of a human head transceiver (TxRx) array at 9.4T without compromising its transmit (Tx) performance, a novel 16-element array was developed, constructed, and tested. METHODS We designed and constructed a phased array, which consists of 8 TxRx surface loops placed in a single row and circumscribing a head, and 8 Rx-only short folded Dipole Antennas. Dipoles were positioned along the central axis of each transceiver loop perpendicular to its surface. We evaluated the effect of Rx Dipoles on the Tx efficiency of the array and maximum local specific absorption rate (SAR) as compared to the array of 8 surface loops only. We also compared the new array to a 16-channel array of the same size consisting of 8 TxRx surface loops and 8 Rx-only vertical loops in terms of Tx efficiency, SAR, and signal-to-noise ratio (SNR). RESULTS The new array improves both peripheral (up to 2 times) and central (1.17 times) SNR as compared to the 16-element array of the same geometry consisting of 8 TxRx surface loops and 8 Rx-only vertical loops. We demonstrated that an addition of actively detuned Rx-only Dipole elements produces only a small decrease (~7%) of the B1+ transmit field and a small increase (<7%) of the maximum local SAR. CONCLUSION As a proof of concept, we developed and constructed a prototype of a 9.4T (400 MHz) head array consisting of 8 TxRx surface loops and 8 Rx-only short optimized folded Dipoles. We demonstrated that at ultra-high field, Dipoles outperformed Rx-only vertical loops in vivo.
Richard W Ziolkowski - One of the best experts on this subject based on the ideXlab platform.
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dual band linearly polarized electrically small huygens Dipole Antennas
IEEE Transactions on Antennas and Propagation, 2019Co-Authors: Mingchun Tang, Ting Shi, Richard W ZiolkowskiAbstract:Two electrically small, dual-band Huygens Dipole Antennas are reported. In both designs, two pairs of magnetic and electric near-field resonant parasitic (NFRP) elements are combined organically within an electrically small, low profile package. The NFRP elements are excited effectively using only one coaxial-fed-driven element. One dual-band Huygens system produces parallel, linearly polarized (LP) fields at its two operating frequencies. The other dual-band system produces two orthogonal LP fields. Additional parasitic elements are introduced to mitigate the mutual coupling effects between the pairs of NFRP elements. The measured values for prototypes of both Antennas in the L-band demonstrate their electrically small size ( $ka ) and low profile ( $\sim 0.03\lambda _{0}$ ). They also confirm their broadside radiation and polarization performance characteristics, as well as the isolation between each operating frequency. Their fractional bandwidths, peak realized gains, front-to-back ratios, and radiation efficiencies are, respectively, ~0.6%, > 2 dBi, > 10 dB, and > 60% at both frequencies. These dual-band systems would provide multifunctional performance in a variety of portable, compact wireless devices.
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crossed Dipole Antennas a review
IEEE Antennas and Propagation Magazine, 2015Co-Authors: Ikmo Park, Richard W ZiolkowskiAbstract:Crossed Dipole Antennas have been widely developed for current and future wireless communication systems. They can generate isotropic, omnidirectional, dual-polarized (DP), and circularly polarized (CP) radiation. Moreover, by incorporating a variety of primary radiation elements, they are suitable for single-band, multiband, and wideband operations. This article presents a review of the designs, characteristics, and applications of crossed Dipole Antennas along with the recent developments of single-feed CP configurations. The considerations of profile miniaturization, radiation pattern control, bandwidth enhancement, and multiband operation are emphasized.
K M Luk - One of the best experts on this subject based on the ideXlab platform.
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linearly polarized and circularly polarized wideband Dipole Antennas with reconfigurable beam direction
IEEE Transactions on Antennas and Propagation, 2018Co-Authors: Hang Wong, K M LukAbstract:Linearly polarized (LP) and circularly polarized (CP) Dipole Antennas with switchable beams are presented. The beam-switchable reconfigurability is realized by electronically controlling the state of switches on the side apertures of a square substrate integrated waveguide (SIW). Four wide Dipoles are loaded in front of the four apertures. To generate one desired unidirectional radiation beam, the corresponding aperture is switched ON, which excites the corresponding Dipole. Meanwhile, the other three apertures are switched off and perform as electric walls in the SIW. In this way, the other three Dipoles work as reflectors of the excited Dipole. Wide bandwidths and good directional radiation patterns can be obtained. Two fully functional LP and CP antenna prototypes with more than 47% bandwidths are developed and tested. The measurement result demonstrates Antennas with measured gains of approximately 4.5 dBi and radiation efficiencies of approximately 80% over the operating band. Owing to the symmetrical antenna structures, the two designs are capable of switching the radiation beam at every 90° in the azimuth plane with identical patterns. In addition, the proposed designs possess compact antenna sizes, i.e., $0.51\lambda _{0}\times 0.51\lambda _{0}\times 0.39\lambda _{0}$ for the LP antenna and $0.95\lambda _{0}\times 0.95\lambda _{0}\times 0.46\lambda _{0}$ for the CP antenna, where $\lambda _{0}$ represents the free-space wavelength at the center frequency of 2.2 GHz.
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magnetoelectric Dipole Antennas with dual open ended slot excitation
IEEE Transactions on Antennas and Propagation, 2016Co-Authors: Hau Wah Lai, Hang Wong, Chi Hou Chan, K M LukAbstract:Designs of novel magnetoelectric Dipole Antennas excited by dual open-ended slots for both single and dual linear polarizations are presented in this paper. The antenna can be interpreted as a dual complementary source that exhibits lower profile and higher gain while maintaining excellent radiation characteristics of the original ME Dipole, including wideband, low back radiation, and high polarization purity. In addition, high isolation is obtained in the dual polarization design. All the above characteristics show that the proposed Antennas can be regarded as potential candidates for various wireless applications. Prototypes are fabricated and measured to confirm the simulation results.
G. Tuttle - One of the best experts on this subject based on the ideXlab platform.
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Dipole Antennas on photonic band gap crystals experiment and simulation
Microwave and Optical Technology Letters, 1997Co-Authors: M M Sigalas, Rana Biswas, S. Mccalmont, D D Crouch, W Y Leung, Russ Jacobswoodbury, Brian Lough, Sam Nielsen, G. TuttleAbstract:The radiation patterns of Dipole Antennas on three-dimensional photonic crystal substrates have been measured and calculated with the finite-difference-time-domain method. The photonic band-gap crystal behaves as a perfectly reflecting substrate, and all the Dipole power is radiated into the air side when driven at frequencies in the stop band. The radiation pattern is found for dfferent positions and orientations of the Dipole antenna. Antenna configurations with desirable patterns are identified. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 15: 153–158, 1997.
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Optimized Dipole Antennas on photonic band gap crystals
Applied Physics Letters, 1995Co-Authors: Shi-di Cheng, Ekmel Ozbay, Rana Biswas, S. Mccalmont, G. TuttleAbstract:Photonic band gap crystals have been used as a perfectly reflecting substrate for planar Dipole Antennas in the 12–15 GHz regime. The position, orientation, and driving frequency of the Dipole antenna on the photonic band gap crystal surface, have been optimized for antenna performance and directionality. Virtually no radiated power is lost to the photonic crystal resulting in gains and radiation efficiencies larger than Antennas on other conventional dielectric substrates.