Meta-metallic coils and resonators: Methods for high Q-value resonant geometries
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, Wisconsin 53226 (United States)
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.
- OSTI ID:
- 22597654
- Journal Information:
- Review of Scientific Instruments, Vol. 87, Issue 8; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA); ISSN 0034-6748
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
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