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Title: Meta-metallic coils and resonators: Methods for high Q-value resonant geometries

Abstract

A novel method of decreasing ohmic losses and increasing Q-value in metallic resonators at high frequencies is presented. The method overcomes the skin-depth limitation of rf current flow cross section. The method uses layers of conductive foil of thickness less than a skin depth and capacitive gaps between layers. The capacitive gaps can substantially equalize the rf current flowing in each layer, resulting in a total cross-sectional dimension for rf current flow many times larger than a skin depth. Analytic theory and finite-element simulations indicate that, for a variety of structures, the Q-value enhancement over a single thick conductor approaches the ratio of total conductor thickness to skin depth if the total number of layers is greater than one-third the square of the ratio of total conductor thickness to skin depth. The layer number requirement is due to counter-currents in each foil layer caused by the surrounding rf magnetic fields. We call structures that exhibit this type of Q-enhancement “meta-metallic.” In addition, end effects due to rf magnetic fields wrapping around the ends of the foils can substantially reduce the Q-value for some classes of structures. Foil structures with Q-values that are substantially influenced by such end effects are discussedmore » as are five classes of structures that are not. We focus particularly on 400 MHz, which is the resonant frequency of protons at 9.4 T. Simulations at 400 MHz are shown with comparison to measurements on fabricated structures. The methods and geometries described here are general for magnetic resonance and can be used at frequencies much higher than 400 MHz.« less

Authors:
 [1];  [2]; ;  [1]
  1. Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
22597654
Resource Type:
Journal Article
Resource Relation:
Journal Name: Review of Scientific Instruments; Journal Volume: 87; Journal Issue: 8; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; COUNTER CURRENT; CROSS SECTIONS; DEPTH; END EFFECTS; FINITE ELEMENT METHOD; FOILS; GEOMETRY; K1-1270 MESONS; K1-1400 MESONS; LAYERS; MAGNETIC FIELDS; MAGNETIC RESONANCE; MHZ RANGE 100-1000; PROTONS; Q-VALUE; RESONATORS; THICKNESS

Citation Formats

Mett, R. R., Department of Physics and Chemistry, Milwaukee School of Engineering, Milwaukee, Wisconsin 53202, Sidabras, J. W., and Hyde, J. S.. Meta-metallic coils and resonators: Methods for high Q-value resonant geometries. United States: N. p., 2016. Web. doi:10.1063/1.4961573.
Mett, R. R., Department of Physics and Chemistry, Milwaukee School of Engineering, Milwaukee, Wisconsin 53202, Sidabras, J. W., & Hyde, J. S.. Meta-metallic coils and resonators: Methods for high Q-value resonant geometries. United States. doi:10.1063/1.4961573.
Mett, R. R., Department of Physics and Chemistry, Milwaukee School of Engineering, Milwaukee, Wisconsin 53202, Sidabras, J. W., and Hyde, J. S.. Mon . "Meta-metallic coils and resonators: Methods for high Q-value resonant geometries". United States. doi:10.1063/1.4961573.
@article{osti_22597654,
title = {Meta-metallic coils and resonators: Methods for high Q-value resonant geometries},
author = {Mett, R. R. and Department of Physics and Chemistry, Milwaukee School of Engineering, Milwaukee, Wisconsin 53202 and Sidabras, J. W. and Hyde, J. S.},
abstractNote = {A novel method of decreasing ohmic losses and increasing Q-value in metallic resonators at high frequencies is presented. The method overcomes the skin-depth limitation of rf current flow cross section. The method uses layers of conductive foil of thickness less than a skin depth and capacitive gaps between layers. The capacitive gaps can substantially equalize the rf current flowing in each layer, resulting in a total cross-sectional dimension for rf current flow many times larger than a skin depth. Analytic theory and finite-element simulations indicate that, for a variety of structures, the Q-value enhancement over a single thick conductor approaches the ratio of total conductor thickness to skin depth if the total number of layers is greater than one-third the square of the ratio of total conductor thickness to skin depth. The layer number requirement is due to counter-currents in each foil layer caused by the surrounding rf magnetic fields. We call structures that exhibit this type of Q-enhancement “meta-metallic.” In addition, end effects due to rf magnetic fields wrapping around the ends of the foils can substantially reduce the Q-value for some classes of structures. Foil structures with Q-values that are substantially influenced by such end effects are discussed as are five classes of structures that are not. We focus particularly on 400 MHz, which is the resonant frequency of protons at 9.4 T. Simulations at 400 MHz are shown with comparison to measurements on fabricated structures. The methods and geometries described here are general for magnetic resonance and can be used at frequencies much higher than 400 MHz.},
doi = {10.1063/1.4961573},
journal = {Review of Scientific Instruments},
number = 8,
volume = 87,
place = {United States},
year = {Mon Aug 15 00:00:00 EDT 2016},
month = {Mon Aug 15 00:00:00 EDT 2016}
}