Printed, dual-loop magnetic field sniffer probe for bench measurements on radio frequency MRI coils

This work describes an open-source design for decoupled dual-loop radio frequency (RF) probes which are common tools in the RF lab. In magnetic resonance (MR) applications dual-loop probes are used to measure the tuning frequency and quality factor of RF coils and associated electronics. Traditional dual-loop probes, however, are delicate and not readily available commercially because they are made using semi-rigid or hand-formable coaxial cable, and they require skill and experience to build well. Our dual-loop probe design is tough, reliable, and can be mass-produced inexpensively, thus allowing new and established labs to obtain these probes with minimal effort. We used two overlapped shielded loops fabricated with multilayer printed circuit board technology. Design files are published under an open-hardware license. The printed probe achieves the required levels of durability and high isolation (better than 50 dB up to 500 MHz) which are equivalent to those achieved with traditional probes, and much more resistant to degradation.