Editing Magnetic core (section)

=== Air ===
<!-- arguably this is not a magnetic core, but the articles need a section to explain the downsides of magnetic cores, and why high permeable cores are not always used, and 'air core' is a well recognized term of art. --->
A coil not containing a magnetic core is called an ''air core''.  This includes coils wound on a plastic or ceramic form in addition to those made of stiff wire that are self-supporting and have air inside them. Air core coils generally have a much lower [[inductance]] than similarly sized ferromagnetic core coils, but are used in [[radio frequency]] circuits to prevent energy losses called [[core loss]]es that occur in magnetic cores.  The absence of normal core losses permits a higher [[Q factor]], so air core coils are used in high frequency [[resonant circuit]]s, such as up to a few megahertz. However, losses such as [[proximity effect (electromagnetism)|proximity effect]] and [[dielectric losses]] are still present. Air cores are also used when field strengths above around 2 Tesla are required as they are not subject to saturation.