Abstract
The radiofrequency field homogeneity and quality factor ( Q) of a number of high-pass resonator designs are compared theoretically and experimentally for small-bore coils. It was found that for high-pass resonators with the number of distributed capacitors greater than eight, a significant and unacceptable decrease in Q resulted. A number of schemes are proposed and investigated to improve the homogeneity of eight-capacitor high-pass resonators, thus balancing Q and homogeneity. These designs include variation in rung width, interrung feeding, a new hybrid coil design, and the use of internal guard rings. Eleven high-pass resonators were modeled and built to test the designs. The current density in each conductor was calculated using a novel numerical technique based on the inverse finite Hilbert transform which implicitly includes the effects of RF eddy currents. It was found that the effect of such eddy currents is important in coils of small geometry. RF fields were calculated from the current densities by using a retarded-potential solution to the free-space Maxwell equations. The interrung-fed hybrid coil design with guard rings was found to be superior to conventional designs.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call