Q Value of an Inductor (Coil)

The Q value is a parameter that indicates the quality of an inductor. The “Q” stands for “Quality Factor”. Coils pass direct current, but act as a resistor to alternating current which is called inductive reactance. The higher the frequency of the alternating current, the higher the inductive reactance.

Although the coil is a conductor, the wire winding has certain resistance components ( R ). The ratio between the resistance components and the frequency-dependent inductance (R/2πf L) is called the loss factor, and its inverse number is the Q value (Q=2πf L/R). Because f is the frequency of the current flowing through the coil, the Q value will differ according to the frequency. In simple terms, a higher Q value means lower losses and better suitability for use as a high frequency inductor.

To find a Q value of a coil use this equation:

Another factor in Q value is the substrate material. Coils can have a substrate made of ferrite or ceramic material. In the frequency range of several hundred MHz and above, ferrite substrates cannot be used, and ceramics are used instead. Below is a graph showing the Q value and frequency response of inductors with the different material.

On the Digi-key website we have a filter in our adjustable inductors, fixed inductors and wireless charging coils that allow you to choose a Q value at a certain frequency.

By selecting one of the Q values at a certain frequency, you can narrow your search down from thousands of parts.

For other information on how to filter and find parts on our website you can read this article: How to Use Digi-Key’s Part Search More Efficiently or the Part search help.

Content and images provided courtesy of TDK’s FAQ.