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Yttrium iron garnet spheres (YIG spheres) serve as magnetically tunable filters and resonators for microwave frequencies. YIG filters are used for their high
YIG Tuned Oscillators
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Experimenting with a Stellex YIG OscillatorA simple approach to YIG oscillators
{{Authority control Microwave technology Filter theory Wireless tuning and filtering Iron(III) compounds
Yttrium iron garnet spheres (YIG spheres) serve as magnetically tunable filters and resonators for microwave frequencies. YIG filters are used for their high Q factor
In physics and engineering, the quality factor or ''Q'' factor is a dimensionless parameter that describes how underdamped an oscillator or resonator is. It is defined as the ratio of the initial energy stored in the resonator to the energy los ...
s, typically between 100 and 200. A sphere made from a single crystal of synthetic yttrium iron garnet acts as a resonator.
The field from an electromagnet changes the resonance frequency of the sphere and hence the frequency it will allow to pass. The advantage of this type of filter is that the garnet can be tuned over a very wide frequency range by varying the strength of the magnetic field
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
. Some filters can be tuned from 3 GHz up to 50 GHz.
Construction
The YIG spheres themselves are on the order of 0.5 mm in diameter and are manufactured from slightly larger cubes of diced material bytumbling
Tumble or tumbling may refer to:
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, 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.
The input and output coils are oriented at right angles to one another around the YIG crystal. They are cross-coupled when energized by the ferrimagnetic resonance frequency, which depends on the external magnetic field supplied by an electromagnet.
YIG filters usually consist of several coupled stages, each stage consisting of a sphere and a pair of loops.
Applications
YIG filters are often used as preselectors. YIG filters tuned by a sweep current are used in spectrum analyzers. Another YIG application is YIG oscillators, where the sphere acts as a tunable frequency-determining element. It is coupled to an amplifier which provides the required feedback for oscillation./ref>
References
Further reading
*External links
Experimenting with a Stellex YIG Oscillator
{{Authority control Microwave technology Filter theory Wireless tuning and filtering Iron(III) compounds