Quantitative EPR by Gareth R. Eaton Sandra S. Eaton David P. Barr & Ralph T. Weber

Author:Gareth R. Eaton, Sandra S. Eaton, David P. Barr & Ralph T. Weber
Language: eng
Format: epub
Publisher: Springer Vienna, Vienna

7.2 Loaded Q and Unloaded Q

For EPR the most useful Q-factor expression is called the “loaded Q” of a resonator. This term is sometimes used incorrectly in the magnetic resonance literature to mean the Q of a resonator “loaded” with a lossy sample, such as an animal. The electrical engineering definition of “loaded Q” is the Q of a resonator coupled to a transmission line. The “unloaded Q” is the term used for the resonator when it is not coupled to a transmission line and is twice the value of the loaded Q. Sometimes subscripts L and U are used to denote the loaded and unloaded Q values, but since the loaded Q is so commonly used, the L subscript is often omitted. Caution should be exercised in citing Q values unless they are clearly defined.

There are many ways to express the Q of a resonator. Each provides useful insight, so several expressions are provided here.

In terms of an RLC circuit, the resonator Q is given by:

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