(YIG) Yttrium-iron garnet is a synthetic crystalline ferrite containing yttrium and iron (Y3Fe6O16). If a single crystal sphere of YIG is immersed in a magnetic field, and RF energy is coupled into it via a magnetic loop, the crystal will resonate at a frequency linearly proportional to the magnetic field strength. In practical YIG-tuned oscillators and filters, the magnetic field is derived from an electromagnet and the resonant frequency of the YIG sphere is proportional to the current flowing through the magnetic coil.