Metamaterial-based non-ferrite RF circulator

Superconducting radio frequency (SRF) accelerators at modern scientific facilities use cavities with quality factors approaching 1011. These cavities require reliable and high-precision instruments to measure such a high Q-factor. A typical diagnostic system includes a ferrite-based circulator, which limits the accuracy of Q-factor measurements due to the power dependence of the ferrite’s material properties, resulting in match and directivity parameters dependence. RadiaBeam proposes to replace the ferrite material with metamaterial media that has similar properties, where the incident EM wave is split into two modes that coherently cancel each other in one port and add to each other in another port. One way is to construct a metamaterial that provides excitation of magnetization by an orthogonal H-field component, enabling a symmetric real-valued permeability tensor, which mimics the ferrite behavior. In Phase I we will perform the numerical RF design and optimization of the metamaterial and verify the permeability tensor and frequency splitting with numerical simulations. Then, we will perform an experimental demonstration of frequency splitting by fabricating 2D PCBs, assembling them into a 3D metamaterial array, and measuring the frequency response of this array placed into a cylindrical resonator. In Phase II, we plan to build a full-scale circulator prototype and test it with an actual high-Q-factor SRF cavity at Fermilab to prove the desirable accuracy. The developed high precision diagnostic system will be a strong contender for measuring the next generation of very high Q superconducting cavities, and will find application in a number of large DOE projects. The circulator can be broadly used in microwave technologies outside of accelerator applications. In addition, the metamaterials could be used for radars, antennas, magnetic mirrors and other industrial and military applications.