  Specialized radio-frequency coils and sensors placed inside the magnetic
resonance imaging (MRI) scanner considerably extend its functionality. However,
since cable connected in-bore devices have several disadvantages compared to
wireless ones, the latter currently undergo active development. One of the
promising concepts in wireless MRI coils is energy harvesting that relies on
converting the energy carried by the radio-frequency MRI field without the need
for additional transmitters as in common wireless power transfer realizations.
In this Article, we propose a compact harvesting coil design based on the
combination of the loop and butterfly coils that allows energy harvesting of a
circularly polarized field. By performing numerical simulations and experiments
with commonly used Siemens Espree and Avanto 1.5 Tesla MRI scanners, we
demonstrate that the proposed approach is safe, efficient, does not decrease
the quality of MRI images, and allows doubling the harvested voltage compared
to linearly polarized setups.
