Decoupling methods for radio frequency antennas in ultra-high-field MRI

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School of Electrical Engineering | Doctoral thesis (article-based) | Defence date: 2021-09-03
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Date

2021

Department

Elektroniikan ja nanotekniikan laitos
Department of Electronics and Nanoengineering

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Mcode

Degree programme

Language

en

Pages

138 + app. 198

Series

Aalto University publication series DOCTORAL DISSERTATIONS, 88/2021

Abstract

For further development of many applications, such as multi-input multi-output (MIMO), radio frequency identification (RFID), wireless power transfer (WPT), and ultra-high-field magnetic resonance imaging (UHF MRI), decoupling of closely located antennas without significant changes of radiation pattern is a key task. In magnetic resonance imaging, there is a trend to increase the magnetic field strengths to obtain better spatial resolution of the image and perhaps smaller scan time. Since by increasing dc magnetic field, the frequency of the B1 field (created by dipole and loop antennas) necessary increases, the use of standard radio antennas applied in usual MRI is not allowed. Challenges of B1 field inhomogeneity arising at high frequencies and low efficiency of antennas in the new range are currently addressed by using so-called transmit-arrays driven by multiple independent channels and phase-amplitude steering. However, the mutual coupling results in considerable power losses and up to now poses a constraint on the density of these arrays. This dissertation focuses on developing new techniques for decoupling closely located dipole and loop antennas. In the first part, decoupling of closely located dipole antennas using passive scatterers is analyzed. The possibility of decoupling using passive scatterers and the effect of decoupling on the B1 field is comprehensively studied. In the second part, the decoupling of loop antennas is discussed. For that, shielded loop antennas with modified shields are analyzed. These shielded loop antennas suppress the mutual coupling between antennas without any damage on the B1 field. In general, using a metasurface of resonant dipoles, two closely located dipole antennas are decoupled while the presence of metasurface does not affect the B1 field significantly. Moreover, transceiver shielded loop antennas with self-decoupling feature are designed which does not change the B1 field. Besides ultra-high-field MRI application, the possibility of employing this method for wireless power transfer application has been numerically and experimentally checked.

Description

Supervising professor

Simovski, Constantin, Prof., Aalto University, Department of Electronics and Nanoengineering, Finland

Keywords

electrical engineering, radio frequenqy antennas

Other note

Parts

  • [Publication 1]: M. S. M. Mollaei, A. Hurshkainen, S. Kurdjumov, S. Glybovski and C. Simovski, “Passive electromagnetic decoupling in an active meta- surface of dipoles,” Photonics and Nanostructures - Fundamentals and Applications, vol. 32, pp. 53-61, October 2018.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-201811025575
    DOI: 10.1016/j.photonics.2018.10.001 View at publisher
  • [Publication 2]: M. S. M. Mollaei, A. Hurshkainen, S. Kurdjumov, S. Glybovski and C. Simovski, “Decoupling of two closely located dipole antennas by a split-loop resonator,” Radio Science, vol. 53, no. 11, pp. 1398-1405, October 2018.
    DOI: 10.1029/2018RS006679 View at publisher
  • [Publication 3]: M. S. M. Mollaei, A. Hurshkainen, S. Kurdjumov and C. Simovski, “Double-resonance decoupling method in very dense dipole arrays,” Photonics and Nanostructures - Fundamentals and Applications, vol. 39, p. 100767, May 2020.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-202002122137
    DOI: 10.1016/j.photonics.2020.100767 View at publisher
  • [Publication 4]: M. S. M. Mollaei, S. Kurdjumov, A. Hurshkainen and C. Simovski, “Decoupling of two closely located dipoles by a single passive scatterer for ultra-high field MRI,” Progress In Electromagnetics Research, vol. 164, pp. 164-166, April 2019.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-201906203877
    DOI: 10.2528/PIER18101703 View at publisher
  • [Publication 5]: M. S. M. Mollaei, S. Kurdjumov, A. Hurshkainen and C. Simovski, “Decoupling of two closely located dipoles using metasurfaces of resonant dipoles and split-loop resonators,” Metamaterials 2018: 12-th International Congress on Artificial Metamaterials for Novel Wave Phenomena, Espoo, Finland, pp. 355-357, August 2018.
    DOI: 10.1109/MetaMaterials.2018.8534082 View at publisher
  • [Publication 6]: A. Hurshkainen, M. S. M. Mollaei, M. Dubois, S. Kurdjumov, R. Abdeddaim, S. Enoch, S. Glybovski and C. Simovski, “Decoupling of closely-spaced dipole antennas for ultra-high field MRI with meta- surfaces,” IEEE Transactions on Antennas and Propagation, vol. 69, no. 2, pp. 1094-1106, February 2021.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-202102262035
    DOI: 10.1109/TAP.2020.3016495 View at publisher
  • [Publication 7]: M. S. M. Mollaei, C. C. van Leeuwen, A.J.E. Raaijmakers and C. Simovski, “Analysis of high impedance coils both in transmission and reception regimes,” IEEE Access, vol. 8, pp. 129754-129762, July 2020.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-202008285197
    DOI: 10.1109/ACCESS.2020.3009367 View at publisher
  • [Publication 8]: M. S. M. Mollaei, A. S. M. Mollaei and C. Simovski, “Dual-band transceiver high impedance coil,” submitted to IEEE Transactions on Antennas and Propagation, January 2021
  • [Publication 9]: M. S. M. Mollaei, P. Jayathurathnage, S. A. Tretyakov and C. Simovski, “High impedance wireless power transfer transmitter for freely positioning receivers,” IEEE Access, vol. 9, pp. 42994-43000, March 2021.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-202103312686
    DOI: 10.1109/ACCESS.2021.3064212 View at publisher

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https://urn.fi/URN:ISBN:978-952-64-0430-1

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[diss] Sähkötekniikan korkeakoulu / ELEC