YIG sphere

Yttrium iron garnet spheres (YIG spheres) serve as magnetically tunable filters and resonators for microwave frequencies. These filters are used for their high Q factors, typically between 100 and 200. A sphere made from a single crystal of synthetic yttrium iron garnet acts as a resonator. These spheres are on the order of 0.5 mm in diameter and are manufactured from slightly larger cubes of diced material by tumbling, as is done in the manufacture of jewelry. The garnet is mounted on a ceramic rod, and a pair of small loops around the sphere couple fields into and out of the sphere; the loops are half-turns, positioned at right-angles to each other to prevent direct electromagnetic coupling between them and each is grounded at one end.