Motivation: Existing power amplifiers for multi-coil shim arrays suffice for B0 inhomogeneity mitigation but cannot support novel supplementary spatial encoding techniques requiring 10x higher bandwidth and coil current. Goal(s): Our goal was to develop an MR-compatible shim amplifier capable of 50kHz bandwidth and 50A current without active cooling. Approach: We select multi-MHz switching frequencies to avoid imaging bands and eliminate ferromagnetic inductor cores, and use a parallel-interleaved circuit topology to increase control bandwidth and distribute losses to facilitate thermal management. Results: We demonstrate feasibility of 50A passively-cooled operation and high open-loop bandwidth. Acquired images have minor artifacts which may be mitigated through additional filtering. Impact: An MR-compatible power amplifier for multi-coil shim arrays with 10x the bandwidth and output current without active cooling will provide the MR community with a key hardware component to bridge the gap between multi-coil imaging technique development and clinical realization.
Chew et al. (Tue,) studied this question.