RF - Invisible Inductors

Introduction In MR Imaging the RF coupling properties of reactive components like inductors and capacitors used for building Phased Array Coils are very important. Ideally these components must have lump circuit characteristics only, without manifesting any stray radiation. These goals might appear to be contradictory since inductors and capacitors with higher inductances and capacitances respectively must have bigger volumes and a certain surrounding volume for magnetic and respectively electric fields confinement [1]. In this work we address the question of the “invisible” inductors – inductors with highly confined magnetic field, which still have satisfactory inductive characteristics. A classical inductor (Figure1a) is usually a loop with one or multiple turns. The magnetic field exhibited by such an inductor is primarily a magnetic dipole type. Inductors used in MRI cannot contain magnetic cores, because of very tight B0 distortion requirements. With an air core approach on the other hand, it is difficult to obtain a high inductance at the same time having a very confined magnetic field.