MULTIGAP PARALLEL-PLATE BRACELET RESONATOR FREQUENCY DETERMINATION AND APPLICATIONS

A loop made from a length of transmission line with alternate electric al discontinuities (gaps) on the two conductors behaves as a resonator whose resonant frequency is a function of the transmission line param eters as well as its form and the number (n) of gaps. For a given loop diameter, one can thus design a wide range of resonant frequency by c hoice of n and the characteristic impedance Z(c) of the line. The anal ysis is illustrated by a parallel-plate transmission line resonator in the form of a bracelet. Experimental resonant frequencies obtained fr om resonators of various dimensions are in good agreement with calcula ted values. Two resonators were tested on a 3 T NMR imager: A 11 cm di ameter H-1 surface coil, yielding results comparable to those obtained from a lumped capacitor coil and a 13 cm diameter volume coil to perf orm in vivo muscle C-13 spectroscopy without H-1 decoupling.