# why do resonant inductive coupling circuit operate at high frequencies?

Just as the title says. Whenever I read a research paper on wireless power transfer via resonant inductive coupling the authors just mention frequencies that range in the kHz and Mhz range, but none of them explain why high frequencies must be used.

• in terms of electronics, kHz and MHz is hardly 'high frequencies'. In fact, in my field, that is all considered 'that DC rubbish we have to get rid of'. – Joren Vaes Oct 6 '18 at 9:07
• Can you please tell me why you don't use these low frequencies in your field? I am having a hard time understanding the advantages of high frequency... – DigiNin Gravy Oct 6 '18 at 9:14
• That in-and-of-itself is a question I have literally written chapters of books about, and would be too broad for a stack exchange question. It mainly comes down to bandwidth and wavelength (and corresponding antenna size). – Joren Vaes Oct 6 '18 at 9:19
• Above 20 kHz has the advantage that it's mostly inaudible. Lower frequencies would make an annoying whine from the inductors. Listen to the 400/800 Hz tone on top of the cabin announcements in a plane. – tomnexus Oct 6 '18 at 9:41

• @AndyAka, all the information mentioned in the answer is relevant. But I think, probably the most important reason relevant to the question (I presume OP is about inductive power transfer) is the power transfer capability. When two inductors are coupled, the induced voltage at the secondary is proportional to the frequency; $V_{secondary} = j \omega M I_{primary}$ – Pojj Oct 7 '18 at 18:27