skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

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. 2016. "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 = 2016,
month = 8
}
  • The authors used a sapphire dielectric resonator with a copper cylindrical shield and two endplates replaced by HTS layers for very accurate surface resistance measurements of TBCCO films made by the two step method. This technique allows for the preparation of high quality 2-in diameter Tl-2223 superconducting films with surface resistance values (R{sub s}) smaller than 100 {micro}{Omega} at 5.6 GHz and 77 K. The use of these films in sapphire dielectric resonators yields resonators for the C-band with very high unloaded quality factors (Q{sub o} > 2 {times} 10{sup 6} at 77 K). Such high Q{sub o}-values are notmore » reached with any conventional resonators of comparable size.« less
  • We have studied damping in polycrystalline Al nanomechanical resonators by measuring the temperature dependence of their resonance frequency and quality factor over a temperature range of 0.1-4 K. Two regimes are clearly distinguished with a crossover temperature of 1 K. Below 1 K we observe a logarithmic temperature dependence of the frequency and linear dependence of damping that cannot be explained by the existing standard models. We attribute these phenomena to the effect of the two-level systems characterized by the unexpectedly long (at least two orders of magnitude longer) relaxation times and discuss possible microscopic models for such systems. Wemore » conclude that the dynamics of the two-level systems is dominated by their interaction with one-dimensional phonon modes of the resonators.« less
  • We investigate the terahertz electromagnetic responses of fractal meta-atoms (MAs) induced by different mode coupling mechanisms. Two types of MAs based on concentric rectangular square (CRS) resonators are presented: independent CRS (I-CRS) and junctional-CRS (J-CRS). In I-CRS, each resonator works as an independent dipole so as to result in the multiple resonance modes when the fractal level is above 1. In J-CRS, however, the generated layer is rotated by π/2 radius to the adjacent CRS in one MA. The multiple resonance modes are coupled into a single mode resonance. The fractal level increasing induces resonance modes redshift in I-CRS whilemore » blueshift in J-CRS. When the fractal level is below 4, the mode Q factor of J-CRS is in between the two modes of I-CRS; when the fractal level is 4 or above, the mode Q factor of J-CRS exceeds the two modes of I-CRS. Furthermore, the modulation depth (MD) decreases in I-CRS while it increases in J-CRS with the increase in fractal levels. The surface currents analysis reveals that the capacitive coupling of modes in I-CRS results in the modes redshift, while the conductive coupling of modes in J-CRS induces the mode blueshift. A high Q mode with large MD can be achieved via conductive coupling between the resonators of different scales in a fractal MA.« less