RE: 2. 4 GHz cordless telephone, question of general interest
I once was in a hurry to get out the door to a racquetball game. My shorts were still damp and I got to thinking about how microwave ovens work and their effects of the on water content of items. Rapidly following a flawed string of logic I decided the microwave would a quick solution to my problem. Not being a complete idiot (please I know many of you will have some pretty interesting things to say on the point but spare me for the moment if you will!) I put them in the oven and set it for a minute. Pulled them out, and discovered it was working, tried two minutes. - still working so now I am on to a plan. About this time a neighbor showed up and needed some tools in my garage. Flush with my recent success I set the ol' microwave to 5 minutes and I'm off in the garage digging for tools and pointing out to my neighbor what a clever fellow I was. I gave him the tools and returned to the kitchen, yanked open the microwave and was greeted by small puffs of smoke rolling out of the oven door. It seems I had failed to account for the nylon stitching around the garment halves and waste band. Five minutes was enough to build enough heat in those areas to scorch the cloth. Some of the hems were on the centerline front to back but I was out of time; and widely thought I should be the hell out of the kitchen before my wife discovered all of this, so off I went. Once at the gym I put on the shorts and headed for the court. Well, given the burn patterns a lot of folks just assumed I had the worse case of burrito gas discharge and vaporization they had ever witnessed. The extra attention didn't help my game any, and now I'm not allowed in the kitchen. Gary -Original Message- From: Cortland Richmond [mailto:72146@compuserve.com] Sent: Monday, April 23, 2001 7:36 AM To: David Instone; ieee pstc list Subject: Re: 2. 4 GHz cordless telephone, question of general interest 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:david_inst...@uk.xyratex.com Subj: Re: 2. 4 GHz cordless telephone, question of general interest Chrg: $0.00 Imp: Norm Sens: StdReceipt: NoParts: 1 List-Post: emc-pstc@listserv.ieee.org Date: Mon, 23 Apr 2001 09:05:38 +0100 From: david_inst...@uk.xyratex.com (David Instone) Subject: Re: 2. 4 GHz cordless telephone, question of general interest Reply-To: david_inst...@uk.xyratex.com (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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual
Re: 2. 4 GHz cordless telephone, question of general interest
Several years ago I went to warm up some peanut butter I kept in the fridge so that it would spread easier. I had not noticed or forgotten that the (metallized) security wrap underneath the plastic lid had not completely detached from the jar lip. I got a spectacular light show right through the opaque plastic lid. Potentials induced on the remnant metal strips were high enough to arc over... -- From: umbdenst...@sensormatic.com To: emc-p...@ieee.org Subject: RE: 2. 4 GHz cordless telephone, question of general interest Date: Mon, Apr 23, 2001, 9:49 AM I once warmed up some leftover take-out Chinese food in the take-out containers with the metal handle. The laws of physics worked -- the handle burned the container. Water is apparently resonant at 2450 MHz, but metal also reacts to EM waves. Your dishes may have metallic compounds in the glazes or substrate. This will definitely warm up the fajita platter. :-) Don Umbdenstock -- From: Ken Javor[SMTP:ken.ja...@emccompliance.com] Reply To: Ken Javor Sent: Monday, April 23, 2001 9:50 AM To: dinst...@uk.xyratex.com Cc: emc-p...@ieee.org Subject: Re: 2. 4 GHz cordless telephone, question of general interest Microwave safe dishes do not heat if put in an oven without food on them to heat by conduction; melmac cannot be pt in a microwave because it does absorb - I don't know what's in melmac but it must have some water content that does absorb energy. Maybe the same goes for your pottery. It's REALLY hazy, chemistry was one of my worst subjects, but some compounds have a structure where they are bound to H2O molecules as in CaCO3*H2O (I just made up that combination for illustration). Such a compound could be completely dry but still retain H2O content. This is purely supposition on my part. -- From: david_inst...@uk.xyratex.com (David Instone) To: Ken Javor ken.ja...@emccompliance.com Cc: emc-p...@ieee.org Subject: Re: 2. 4 GHz cordless telephone, question of general interest Date: Mon, Apr 23, 2001, 3:05 AM 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Heald
Re: 2. 4 GHz cordless telephone, question of general interest
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 72146@compuserve.com To: David Instone david_inst...@uk.xyratex.com, ieee pstc list emc-p...@ieee.org 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:david_inst...@uk.xyratex.com Subj: Re: 2. 4 GHz cordless telephone, question of general interest Chrg: $0.00 Imp: Norm Sens: StdReceipt: NoParts: 1 Date: Mon, 23 Apr 2001 09:05:38 +0100 From: david_inst...@uk.xyratex.com (David Instone) Subject: Re: 2. 4 GHz cordless telephone, question of general interest Reply-To: david_inst...@uk.xyratex.com (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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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:ken.ja...@emccompliance.com == 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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
RE: 2. 4 GHz cordless telephone, question of general interest
I once warmed up some leftover take-out Chinese food in the take-out containers with the metal handle. The laws of physics worked -- the handle burned the container. Water is apparently resonant at 2450 MHz, but metal also reacts to EM waves. Your dishes may have metallic compounds in the glazes or substrate. This will definitely warm up the fajita platter. :-) Don Umbdenstock -- From: Ken Javor[SMTP:ken.ja...@emccompliance.com] Reply To: Ken Javor Sent: Monday, April 23, 2001 9:50 AM To: dinst...@uk.xyratex.com Cc: emc-p...@ieee.org Subject: Re: 2. 4 GHz cordless telephone, question of general interest Microwave safe dishes do not heat if put in an oven without food on them to heat by conduction; melmac cannot be pt in a microwave because it does absorb - I don't know what's in melmac but it must have some water content that does absorb energy. Maybe the same goes for your pottery. It's REALLY hazy, chemistry was one of my worst subjects, but some compounds have a structure where they are bound to H2O molecules as in CaCO3*H2O (I just made up that combination for illustration). Such a compound could be completely dry but still retain H2O content. This is purely supposition on my part. -- From: david_inst...@uk.xyratex.com (David Instone) To: Ken Javor ken.ja...@emccompliance.com Cc: emc-p...@ieee.org Subject: Re: 2. 4 GHz cordless telephone, question of general interest Date: Mon, Apr 23, 2001, 3:05 AM 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: 2. 4 GHz cordless telephone, question of general interest
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:david_inst...@uk.xyratex.com Subj: Re: 2. 4 GHz cordless telephone, question of general interest Chrg: $0.00 Imp: Norm Sens: StdReceipt: NoParts: 1 List-Post: emc-pstc@listserv.ieee.org Date: Mon, 23 Apr 2001 09:05:38 +0100 From: david_inst...@uk.xyratex.com (David Instone) Subject: Re: 2. 4 GHz cordless telephone, question of general interest Reply-To: david_inst...@uk.xyratex.com (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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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:ken.ja...@emccompliance.com == 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: 2. 4 GHz cordless telephone, question of general interest
Microwave safe dishes do not heat if put in an oven without food on them to heat by conduction; melmac cannot be pt in a microwave because it does absorb - I don't know what's in melmac but it must have some water content that does absorb energy. Maybe the same goes for your pottery. It's REALLY hazy, chemistry was one of my worst subjects, but some compounds have a structure where they are bound to H2O molecules as in CaCO3*H2O (I just made up that combination for illustration). Such a compound could be completely dry but still retain H2O content. This is purely supposition on my part. -- From: david_inst...@uk.xyratex.com (David Instone) To: Ken Javor ken.ja...@emccompliance.com Cc: emc-p...@ieee.org Subject: Re: 2. 4 GHz cordless telephone, question of general interest Date: Mon, Apr 23, 2001, 3:05 AM 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: 2. 4 GHz cordless telephone, question of general interest
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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
RE: 2. 4 GHz cordless telephone, question of general interest
22 GHz is the resonant frequency of water folks. Not 2.45 GHz. uwave ovens heat by way of dielectric heating. Oils heat much faster than water. That's why your uwave food mfrs load up on the oils and salts in the food. Which by the way, hasn't been looked into as far as a high fat diet contributing to cancer. Or has it? Also, the higher above 1GHz you go, the more surface heating of a human body happens. Not deeper. Deep tissue heating combined with surface tissue heating happens below that. Ionization of atoms and molecules require much higher freqs which translates to higher levels of eVs. Typical eV's that occur during normal chemical reactions with STP (standard temp and pressure) is about 15 eV. The photo-electric work function of say Tungsten = 4.58 eV = 2694 Angstroms = 0.27 cm. Pretty damn small in my opinion. And you have to get far above approx 10 mW/cm^2 to really start being a problem. 1 mW/cm^2 I think is the limit. I worked the numbers out with one uwave oven which I thought had exceedingly high emissions, and it turned out to be pretty benign in terms of W/cm^2. More like uW/cm^2. Higher freqs are required to actually start perturbation at the atomic level. At the low GHz range, you're only perturbing the general molcular structure en masse. You have to go much higher to start doing the funky thing with an atom. Trying to consider that *only* uwave ovens are even involved with the whole cancer thing leaves out many many other factors to the point of being ignored. All the above of course, IMHO. And opinions may vary at any speed. Regards, Doug McKean -Original Message- From: owner-emc-p...@ieee.org [mailto:owner-emc-p...@ieee.org]On Behalf Of Ken Javor Sent: Friday, April 20, 2001 2:40 PM To: emc-p...@ieee.org Subject: 2. 4 GHz cordless telephone, question of general interest Someone on this forum likely knows the answer to this question... I was at Wal-Mart the other day and they had 2.4 GHz cordless phones on clearance. My home cordless phones are 900 MHz. One is multiple channels, the other is some kind of spread spectrum. 2.4 GHz is very close to 2450 MHz, the microwave oven frequency that resonates with H2O molecules. Is 2.4 GHz close enough to 2450 MHz to cause significantly more heating than 900 MHz (in the human head adjacent to the head/handset antenna)? I realize this is very low power relative to a cell phone, but I wonder if the issue was ever addressed. Another way of asking this question is, what is the Q of H20 resonance? If it is much better than 50, the problem is not important. If it is 50 or less, then 2.4 GHz would transfer more energy to head tissue than 900 MHz. One way of measuring this effect would be to time how long it takes to raise the temperature of a beaker of water a set amount at 2450 MHz, and then time how long it takes at 2400 MHz... But this all must have been done already... --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: 2. 4 GHz cordless telephone, question of general interest
Two points regarding this question. I understand that 2.4 GHz is not a resonant frequency of the water molecule which resonates at a much higher frequency. 2.4 GHz is just the ISM frequency. Also the depth of penetration is only a few cm at 2.4 GHz and issomewhat higher at 900 MHz. 27 MHz diathermy gives a very good depth of penetration and more even heating through human joints. Regards John Cronin From: "Ralph Cameron" <ral...@igs.net> Reply-To: "Ralph Cameron" <ral...@igs.net> To: "Ken Javor" <ken.ja...@emccompliance.com>, <emc-p...@ieee.org> Subject: Re: 2. 4 GHz cordless telephone, question of general interest Date: Fri, 20 Apr 2001 22:39:29 -0400 In terms of heating ( cooking ) 900Mhz is more efficient but its a question then of density of tissue , I understand that between 70-90Mhz the human body absorbs most energy and that first microwave ovens were designed around 450Mhz but 2.4 Ghz was an I.S.M. band so permitted limitless power. The leakage in the average Microwave oven should be so small that you'd never hear it on a 2.4Ghz cell phone (i.e. 50Mhz off frequency) many offie type 2.4Ghz cordless phone use 900mw on the base unit and 200mw on the handset. I would suspect the field intensity that close to the head could be substantial. Ralph Cameron - Original Message - From: "Ken Javor" <ken.ja...@emccompliance.com> To: <emc-p...@ieee.org> Sent: Friday, April 20, 2001 5:40 PM Subject: 2. 4 GHz cordless telephone, question of general interest Someone on this forum likely knows the answer to this question... I was at Wal-Mart the other day and they had 2.4 GHz cordless phones on clearance. My home cordless phones are 900 MHz. One is multiple channels, the other is some kind of spread spectrum. 2.4 GHz is very close to 2450 MHz, the microwave oven frequency that resonates with H2O molecules. Is 2.4 GHz close enough to 2450 MHz to cause significantly more heating than 900 MHz (in the human head adjacent to the head/handset antenna)? I realize this is very low power relative to a cell phone, but I wonder if the issue was ever addressed. Another way of asking this question is, what is the "Q" of H20 resonance? If it is much better than 50, the problem is not important. If it is 50 or less, then 2.4 GHz would transfer more energy to head tissue than 900 MHz. One way of measuring this effect would be to time how long it takes to raise the temperature of a beaker of water a set amount at 2450 MHz, and then time how long it takes at 2400 MHz... But this all must have been done already... --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall," Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com. --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on "Virtual Conference Hall,"
Re: 2. 4 GHz cordless telephone, question of general interest
In terms of heating ( cooking ) 900Mhz is more efficient but its a question then of density of tissue , I understand that between 70-90Mhz the human body absorbs most energy and that first microwave ovens were designed around 450Mhz but 2.4 Ghz was an I.S.M. band so permitted limitless power. The leakage in the average Microwave oven should be so small that you'd never hear it on a 2.4Ghz cell phone (i.e. 50Mhz off frequency) many offie type 2.4Ghz cordless phone use 900mw on the base unit and 200mw on the handset. I would suspect the field intensity that close to the head could be substantial. Ralph Cameron - Original Message - From: Ken Javor ken.ja...@emccompliance.com To: emc-p...@ieee.org Sent: Friday, April 20, 2001 5:40 PM Subject: 2. 4 GHz cordless telephone, question of general interest Someone on this forum likely knows the answer to this question... I was at Wal-Mart the other day and they had 2.4 GHz cordless phones on clearance. My home cordless phones are 900 MHz. One is multiple channels, the other is some kind of spread spectrum. 2.4 GHz is very close to 2450 MHz, the microwave oven frequency that resonates with H2O molecules. Is 2.4 GHz close enough to 2450 MHz to cause significantly more heating than 900 MHz (in the human head adjacent to the head/handset antenna)? I realize this is very low power relative to a cell phone, but I wonder if the issue was ever addressed. Another way of asking this question is, what is the Q of H20 resonance? If it is much better than 50, the problem is not important. If it is 50 or less, then 2.4 GHz would transfer more energy to head tissue than 900 MHz. One way of measuring this effect would be to time how long it takes to raise the temperature of a beaker of water a set amount at 2450 MHz, and then time how long it takes at 2400 MHz... But this all must have been done already... --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
Re: 2. 4 GHz cordless telephone, question of general interest
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, 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. -- From: Rich Nute ri...@sdd.hp.com To: ken.ja...@emccompliance.com Cc: emc-p...@ieee.org Subject: Re: 2. 4 GHz cordless telephone, question of general interest Date: Fri, Apr 20, 2001, 5:27 PM Hi Ken: Here are some quotes: http://www.eskimo.com/~billb/weird/microexp.html#demo: Q: Aren't these ovens tuned to a special frequency so they only heat water? A: No. The usual operating frequency of a microwave oven is nowhere near the resonant frequency of water, and the RF energy will heat other substances. For example, drops of grease on a plastic microwave dish can be heated far hotter than 100C, and this causes the mysterious scarring which frequently occurs on plastic utensils. Any molecule which is polar and has positive and negative ends will be rotated to align with the electric field of the radio waves in the oven. The vibrating electric field rotates (vibrates) the water molecules (and any other polar molecules) within the food. Microwave ovens have difficulty melting ice, presumably because the water molecules are bound together and cannot be easily rotated by the e-fields. If the oven was tuned to the water resonance frequency, then the water would become far more opaque to the wave energy. The water in the food's thin surface would absorb all the energy, and only the outside surface of foods would be heated. The thin outer surface of meat would become a blast of steam, and the inside would remain ice cold. But because water does not resonate with the microwave frequency, the waves can travel an inch or so into the meat before being absorbed. See also: http://hypertextbook.com/facts/HowardCheung.shtml Here's another quote: http://rabi.phys.virginia.edu/HTW//microwave_ovens.html My science book said that a microwave oven uses a laser resonating at the natural frequency of water. Does such a laser exist or was that a major typo? It's a common misconception that the microwaves in a microwave oven excite a natural resonance in water. The frequency of a microwave oven is well below any natural resonance in an isolated water molecule, and in liquid water those resonances are so smeared out that they're barely noticeable anyway. It's kind of like playing a violin under water--the strings won't emit well-defined tones in water because the water impedes their vibrations. Similarly, water molecules don't emit (or absorb) well-defined tones in liquid water because their clinging neighbors impede their vibrations. Instead of trying to interact through a natural resonance in water, a microwave oven just exposes the water molecules to the intense electromagnetic fields in strong, non-resonant microwaves. The frequency used in microwave ovens (2,450,000,000 cycles per second or 2.45 GHz) is a sensible but not unique choice. Waves of that frequency penetrate well into foods of reasonable size so that the heating is relatively uniform throughout the foods. Since leakage from these ovens makes the radio spectrum near 2.45 GHz unusable for communications, the frequency was chosen in part because it would not interfere with existing communication systems. As for there being a laser in a microwave oven, there isn't. Lasers are not the answer to all problems and so the source for microwaves in a microwave oven is a magnetron. This high-powered vacuum tube emits a beam of coherent microwaves while a laser emits a beam of coherent light waves. While microwaves and light waves are both electromagnetic waves, they have quite different frequencies. A laser produces much higher frequency waves than the magnetron. And the techniques these devices use to create their electromagnetic waves are entirely different. Both are wonderful inventions, but they work in very different ways. The fact that this misleading information appears in a science book, presumably used in schools, is a bit discouraging. It just goes to show you that you shouldn't believe everything read in books or on the web (even this web site, because I make mistakes, too). On the other hand: http://www.sciencenet.org.uk/database/Physics/EMandLight/p00571b.html How does a microwave oven work? Everything has what is called a natural frequency. When you hold a ruler over the edge of a table
Re: 2. 4 GHz cordless telephone, question of general interest
Hi Ken: Here are some quotes: http://www.eskimo.com/~billb/weird/microexp.html#demo: Q: Aren't these ovens tuned to a special frequency so they only heat water? A: No. The usual operating frequency of a microwave oven is nowhere near the resonant frequency of water, and the RF energy will heat other substances. For example, drops of grease on a plastic microwave dish can be heated far hotter than 100C, and this causes the mysterious scarring which frequently occurs on plastic utensils. Any molecule which is polar and has positive and negative ends will be rotated to align with the electric field of the radio waves in the oven. The vibrating electric field rotates (vibrates) the water molecules (and any other polar molecules) within the food. Microwave ovens have difficulty melting ice, presumably because the water molecules are bound together and cannot be easily rotated by the e-fields. If the oven was tuned to the water resonance frequency, then the water would become far more opaque to the wave energy. The water in the food's thin surface would absorb all the energy, and only the outside surface of foods would be heated. The thin outer surface of meat would become a blast of steam, and the inside would remain ice cold. But because water does not resonate with the microwave frequency, the waves can travel an inch or so into the meat before being absorbed. See also: http://hypertextbook.com/facts/HowardCheung.shtml Here's another quote: http://rabi.phys.virginia.edu/HTW//microwave_ovens.html My science book said that a microwave oven uses a laser resonating at the natural frequency of water. Does such a laser exist or was that a major typo? It's a common misconception that the microwaves in a microwave oven excite a natural resonance in water. The frequency of a microwave oven is well below any natural resonance in an isolated water molecule, and in liquid water those resonances are so smeared out that they're barely noticeable anyway. It's kind of like playing a violin under water--the strings won't emit well-defined tones in water because the water impedes their vibrations. Similarly, water molecules don't emit (or absorb) well-defined tones in liquid water because their clinging neighbors impede their vibrations. Instead of trying to interact through a natural resonance in water, a microwave oven just exposes the water molecules to the intense electromagnetic fields in strong, non-resonant microwaves. The frequency used in microwave ovens (2,450,000,000 cycles per second or 2.45 GHz) is a sensible but not unique choice. Waves of that frequency penetrate well into foods of reasonable size so that the heating is relatively uniform throughout the foods. Since leakage from these ovens makes the radio spectrum near 2.45 GHz unusable for communications, the frequency was chosen in part because it would not interfere with existing communication systems. As for there being a laser in a microwave oven, there isn't. Lasers are not the answer to all problems and so the source for microwaves in a microwave oven is a magnetron. This high-powered vacuum tube emits a beam of coherent microwaves while a laser emits a beam of coherent light waves. While microwaves and light waves are both electromagnetic waves, they have quite different frequencies. A laser produces much higher frequency waves than the magnetron. And the techniques these devices use to create their electromagnetic waves are entirely different. Both are wonderful inventions, but they work in very different ways. The fact that this misleading information appears in a science book, presumably used in schools, is a bit discouraging. It just goes to show you that you shouldn't believe everything read in books or on the web (even this web site, because I make mistakes, too). On the other hand: http://www.sciencenet.org.uk/database/Physics/EMandLight/p00571b.html How does a microwave oven work? Everything has what is called a natural frequency. When you hold a ruler over the edge of a table and ping it, it will bounce up and down at a certain rate. If the length of ruler is kept the same, the frequency of the bounce will be the same however hard the ruler is struck. This frequency is called the natural frequency. A swing in a children's playground also has a preferred frequency. In fact, it is extremely difficult to make it swing at any other frequency. On a much smaller scale, water molecules also have a natural frequency at which they prefer to rotate from side to side. One way to cook a potato, is to stick it into a hot oven. Heat energy from the oven is transferred to the potato and the particles inside the potato
2. 4 GHz cordless telephone, question of general interest
Someone on this forum likely knows the answer to this question... I was at Wal-Mart the other day and they had 2.4 GHz cordless phones on clearance. My home cordless phones are 900 MHz. One is multiple channels, the other is some kind of spread spectrum. 2.4 GHz is very close to 2450 MHz, the microwave oven frequency that resonates with H2O molecules. Is 2.4 GHz close enough to 2450 MHz to cause significantly more heating than 900 MHz (in the human head adjacent to the head/handset antenna)? I realize this is very low power relative to a cell phone, but I wonder if the issue was ever addressed. Another way of asking this question is, what is the Q of H20 resonance? If it is much better than 50, the problem is not important. If it is 50 or less, then 2.4 GHz would transfer more energy to head tissue than 900 MHz. One way of measuring this effect would be to time how long it takes to raise the temperature of a beaker of water a set amount at 2450 MHz, and then time how long it takes at 2400 MHz... But this all must have been done already... --- 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: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson:pstc_ad...@garretson.org Dave Healddavehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://www.rcic.com/ click on Virtual Conference Hall,
