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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 Q factors, 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
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 factors, 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
An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire (likely copper) wound into a electromagnetic coil, coil. A current through the wire creates a magnetic ...
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 (sometimes called B-field) is a physical 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 ...
. 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 by tumbling, as is done in the manufacture ofjewelry
Jewellery (or jewelry in American English) consists of decorative items worn for personal adornment such as brooches, ring (jewellery), rings, necklaces, earrings, pendants, bracelets, and cufflinks. Jewellery may be attached to the body or the ...
.
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
An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire (likely copper) wound into a electromagnetic coil, coil. A current through the wire creates a magnetic ...
.
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