RAM absorbs rf energy by virtue of a controlled conductivity via impregnated carbon, but it is a broadband effect, just as you state. 2450 MHz is the frequency which excites vibration in H2O molecules, so H2O is PARTICULARLY efficient at absorbing energy at that frequency. Certainly other media may absorb the energy as well, but at greatly reduced efficiency relative to H2O. Pure distilled H2O will resonate at 2450 MHz. It is not the impurities in the water which cause the effect, but the nature of the polar H2O molecule itself.
---------- >From: Cortland Richmond <[email protected]> >To: David Instone <[email protected]>, ieee pstc list <[email protected]> >Subject: Re: 2. 4 GHz cordless telephone, question of general interest >Date: Mon, Apr 23, 2001, 9:35 AM > > > A lump of coal will heat up in a microwave oven. No water needed. It is the > bulk resistivity of an object which allows circulating currents to generate > heat, and while water can help (when we wet something, its chemical bonds > are a source of electrons) it is not the only thing that is heated in a > microwave oven. > > The cones from our chambers don't have water in them (better not, anyway) > and they'll not only heat up in the microwave, but burn with a nasty, nasty > smell. The carbon conducts, the foam that holds it burns. Not to denigrate > water's action; I remember reading that a serviceable Radar Absorbing > Material may be made by wetting foam urethane. But the frequency of > microwave ovens wasn't chosen for resonance with water. > > (PURE, distilled water is an insulator. I wonder if 2450 is close enough to > even warm it up?) > > Cortland > > > ====================== Original Message Follows ==================== > > >> Date: 23-Apr-01 02:07:07 MsgID: 1078-34037 ToID: 72146,373 > From: David Instone >INTERNET:[email protected] > Subj: Re: 2. 4 GHz cordless telephone, question of general interest > Chrg: $0.00 Imp: Norm Sens: Std Receipt: No Parts: 1 > > Date: Mon, 23 Apr 2001 09:05:38 +0100 > From: [email protected] (David Instone) > Subject: Re: 2. 4 GHz cordless telephone, question of general interest > Reply-To: [email protected] (David Instone) > > > Ken Javor wrote: >> >> Just goes to show you can find anything on the net. I have measured > leakage >> from microwave ovens and every one was at 2450 MHz. And that IS a > resonant >> frequency for water and water alone. That's why you can put waterless > items >> in and they won't heat up, > > Hm, now I wonder how the the totally dry and empty pottery plate I put > in the microwave to heat (before I put my non microwave cooked food on > it) gets too hot to hold after just 60 seconds at 650W. > > >> and also why you should never run a microwave >> oven without a water load: with no load you get high vswr and the > magnetron >> can be damaged by reflected energy. > -- > Regards > > Dave Instone. Compliance Engineer > Storage Systems Development, MP24/22 > Xyratex, Langstone Rd., Havant, Hampshire, P09 1SA, UK. > Tel: +44 (0)23-92-496862 (direct line) > Fax: +44 (0)23-92-496014 > http://www.xyratex.com Tel: +44 (0)23-92-496000 > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: [email protected] > Dave Heald [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.rcic.com/ click on "Virtual Conference Hall," > > > > **Primary Recipient: > Ken Javor INTERNET:[email protected] > > ====================== End of Original Message ===================== > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: [email protected] > Dave Heald [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.rcic.com/ click on "Virtual Conference Hall," > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [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.rcic.com/ click on "Virtual Conference Hall,"
