This kind of heating specifically relies on eddy current induction. A solenoidally wound coil is placed around the cylindrical work-piece, which is concentric with the induction coil. If you work out the vectors, the eddy currents circulate around the circumference of the work-piece, heating it. I'm guessing one reason for using such a high frequency as opposed to a more typical 150 kHz is skin depth. With a much smaller skin depth, the eddy currents flow closer to the surface. The increased current density increases the resistive heating effect.
From: "Price, Ed" <[email protected]> List-Post: [email protected] Date: Thu, 15 Sep 2005 16:41:12 -0700 To: [email protected] Cc: [email protected] Subject: RE: When is a cable shield not a cable shield? The principle is demonstrated by industrial induction heaters, where a few seconds of 13 MHz eddy current loss will turn the end of an auto engine valve cherry red. Ed Price [email protected] WB6WSN NARTE Certified EMC Engineer & Technician Electromagnetic Compatibility Lab Cubic Defense Applications San Diego, CA USA 858-505-2780 (Voice) 858-505-1583 (Fax) Military & Avionics EMC Is Our Specialty > -----Original Message----- > From: Robert A. Macy [mailto:[email protected]] > Sent: Thursday, September 15, 2005 3:28 PM > To: Ken Javor > Cc: [email protected] > Subject: Re: When is a cable shield not a cable shield? > > Eddy currents exist everywhere the conductor looks like a > shorted turn on a transformer. > > Imagine a perfectly balanced pair of wires, driven in a > perfetly balanced manner. A wire down, a wire back - a loop. > That pair will radiate right out through its loop. > A simple plate of conductor placed over the loop will get > eddy currents generated in it that "cancels" to lower radiation. > > The plate does not have to be terminated to have this effect. > Simply covering the surface of the loop is sufficient. Plus > with the wires perfectly balanced and the drive pervectly > balanced there will be no residual signal put upon the plate, > so the plate does not radiate, or reradiate. > > - Robert - - 2005 IEEE Symposium on Product Safety Engineering 3-4 October Schaumburg, IL http://www.ieee-pses.org/symposium ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc - 2005 IEEE Symposium on Product Safety Engineering 3-4 October Schaumburg, IL http://www.ieee-pses.org/symposium ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
