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Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
At the front of your head there is a matched pair of fluid-filled microwave energy absorbing sensors (I like to call them cornea's) maybe you could experiment to determine sensitivity to drying-out or boiling vs. leakage power?
For liability reasons I should point out that the above is (raw/un-cooked) tongue-in-cheek.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
The lenses in your eyes have no cooling mechanism. Blood or other fluid cools most other organs.
When the lenses are heated, they solidify and turn opaque like egg white does when heated. This is irreversible and leads to an inability to focus and blindness.
The wavelength of 2.45 GHz microwaves is several centimetres, if I remember correctly. about the size of your head. Your head will act like a tuned length antenna, and absorb a considerable amount of energy. Shorter wavelengths will heat the eyes or lenses more, due to this effect.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
The wavelength of 2.45 GHz microwaves is several centimetres , if I remember correctly
λ 2.45GHz = 12.24 cm
Ash Small wrote ...
about the size of your head.
Surely not another case of microcephaly on the forum...
Ash Small wrote ...
Your head will act like a tuned length antenna, and absorb a considerable amount of energy.
So the heads of children could be expected to absorb more RF energy than the larger heads of adults?
Is that the clanking alarm of the Bolloxometer I hear sounding off?
Try to get out of this one, Caped Crusader:
Health Phys. 1998 Feb;74(2):160-8. Differences in energy absorption between heads of adults and children in the near field of sources. Schönborn F, Burkhardt M, Kuster N. Swiss Federal Institute of Technology, Zurich.
Abstract This paper was motivated by a recent article in which the levels of electromagnetic energy absorbed in the heads of mobile phone users were compared for children and adults at the frequencies of 835 MHz and 1,900 MHz. Significant differences were found, in particular substantially greater absorption in children's heads at 835 MHz. These findings contradict other studies in which no significant changes had been postulated. The clarification of this issue is crucial to the mobile communications industry since current SAR evaluations as required by the FCC are only performed with phantoms based on the heads of adults. In order to investigate the differences in absorption between adults and children due to their differing anatomies, simulations have been performed using head phantoms based on MRI scans of an adult (voxel size 2 x 2 x 1 mm3) and two children (voxel size 2 x 2 x 1.1 mm3) of the ages of 3 and 7 y. Ten different tissue types were distinguished. The differences in absorption were investigated for the frequencies of 900 MHz and 1,800 MHz using 0.45 lambda dipoles instead of actual mobile phones. These well-defined sources simplified the investigation and facilitated the comparison to previously published data obtained from several numerical and experimental studies on phantoms based on adults. All simulations were performed using a commercial code based on the finite integration technique. The results revealed no significant differences in the absorption of electromagnetic radiation in the near field of sources between adults and children. The same conclusion holds when children are approximated as scaled adults.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Proud Mary wrote ...
Ash Small wrote ...
The wavelength of 2.45 GHz microwaves is several centimetres , if I remember correctly
λ 2.45GHz = 12.24 cm
Ash Small wrote ...
about the size of your head.
Surely not another case of microcephaly on the forum...
Ash Small wrote ...
Your head will act like a tuned length antenna, and absorb a considerable amount of energy.
So the heads of children could be expected to absorb more RF energy than the larger heads of adults?
Is that the clanking alarm of the Bolloxometer I hear sounding off?
Try to get out of this one, Caped Crusader:
Health Phys. 1998 Feb;74(2):160-8. Differences in energy absorption between heads of adults and children in the near field of sources. Schönborn F, Burkhardt M, Kuster N. Swiss Federal Institute of Technology, Zurich.
Abstract This paper was motivated by a recent article in which the levels of electromagnetic energy absorbed in the heads of mobile phone users were compared for children and adults at the frequencies of 835 MHz and 1,900 MHz. Significant differences were found, in particular substantially greater absorption in children's heads at 835 MHz. These findings contradict other studies in which no significant changes had been postulated. The clarification of this issue is crucial to the mobile communications industry since current SAR evaluations as required by the FCC are only performed with phantoms based on the heads of adults. In order to investigate the differences in absorption between adults and children due to their differing anatomies, simulations have been performed using head phantoms based on MRI scans of an adult (voxel size 2 x 2 x 1 mm3) and two children (voxel size 2 x 2 x 1.1 mm3) of the ages of 3 and 7 y. Ten different tissue types were distinguished. The differences in absorption were investigated for the frequencies of 900 MHz and 1,800 MHz using 0.45 lambda dipoles instead of actual mobile phones. These well-defined sources simplified the investigation and facilitated the comparison to previously published data obtained from several numerical and experimental studies on phantoms based on adults. All simulations were performed using a commercial code based on the finite integration technique. The results revealed no significant differences in the absorption of electromagnetic radiation in the near field of sources between adults and children. The same conclusion holds when children are approximated as scaled adults.
The above article doesn't mention 2.45 GHz radiation. The wavelengths mentioned are much longer that the 12.5 cm figure you gave.
I've been doing quite a bit of reading up on this subject recently, as I'm planning to build a magnetron powered plasma/ion source, as I'm sure you recall from other threads where you provided some useful links on waveguides, etc.
I found several references to the fact that the human body will act as an antenna to wavelengths in the region of 5'-6', and that organs such as the head will also act as antennas for corresponding wavelengths. I've also been advised that 2.45 GHz has too long a wavelength to effectively heat organs such as the lens of the eye, etc. from others on this forum in the chatroom. (I won't mention names, I'll leave it up to them if they wish to comment.)
I would suggest the example you gave above has little relevance here as it doesn't mention 2.45 GHz radiation, however, if you do come across anything that is relevant, especially if it refutes what I posted above, please post it as I'm interested in this subject.
I enjoy nothing better than to be proved wrong, as a day spent not learning anything is a day wasted, however, on this occasion, that doesn't appear to be the case.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
I don't think I could bear it if you were to drop me from your Christmas card list, so just to prove I'm not the Queen of Mean here's a bit of free grist for your mill:
Joines, William T.; Spiegel, Ronald J.; Resonance Absorption of Microwaves by the Human Skull Biomedical Engineering, IEEE Transactions on Vol BME-21 Issue:1 pp 46 - 48 Jan. 1974 pp 46 - 48
Abstract
Resonance absorption of microwaves by the human skull is examined by making computerized calculations of theoretical models of the skull. The calculated relative absorption versus frequency is plotted and compared for homogeneous and inhomogeneous skull models. At a frequency of maximum power absorption, the spatial distribution of intracranial field intensity (based upon the theoretical model) is also calculated and plotted.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Electric current and electric field induced in the human body when exposed to an incident electric field near the resonant frequency
King, R.W.P.; Gordon McKay Lab., Harvard Univ., Cambridge, MA
Abstract The electric field and current density induced in the human body when this is exposed to electric fields near the resonant frequency, 53 MHz, are determined analytically. Since this frequency range includes an important amateur radio band of 50-60 MHz and exposure to electric fields at this frequency has been shown to be hazardous, the study has a specific motivation. A cylindrical model of the body is used to derive formulas for the total axial current and current density induced in the body subject to skin effect. Tabulations and graphical representations illuminate the results
This abstract appears to re-inforce what I posted above, however, I've been unable to read the full text of any of the above articles as I don't have a subscription to the IEEE digital library.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
Electric current and electric field induced in the human body when exposed to an incident electric field near the resonant frequency
King, R.W.P.; Gordon McKay Lab., Harvard Univ., Cambridge, MA
Abstract The electric field and current density induced in the human body when this is exposed to electric fields near the resonant frequency, 53 MHz, are determined analytically. Since this frequency range includes an important amateur radio band of 50-60 MHz and exposure to electric fields at this frequency has been shown to be hazardous, the study has a specific motivation. A cylindrical model of the body is used to derive formulas for the total axial current and current density induced in the body subject to skin effect. Tabulations and graphical representations illuminate the results
Isn't 53 MHz unreasonably further away from 2.45 GHz than the 1.8 GHz examined in the paper you disallowed? 53 MHz is a wavelength of 5.66 m, and it's not easy to see what resonant relationship to the dimensions of the human body - or parts thereof - it might have.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
It would appear so, yes. Whether this has something to do with 1/4 wavelength dipoles, or whatever the correct terminology is, I don't know.
As I said previously, I've been trying to discover more about this phenomenon before I run any tests using a magnetron, and I don't yet consider that I know enough about it to be confident that my proposed setup is safe.
These papers do seem to suggest, though, that different wavelengths are absorbed to a greater or lesser extent by the human body, and by different organs, depending on resonance.
Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
I'm fairly sure that because water absorbs the radiation from a µwave oven so strongly there wouldn't be much resonance, so the size of the head wouldn't matter much. In effect, none would reach the back of the head- the penetration depth s only a few cm. After that (and that basically means behind your eyes) the tissue in front has acted as a (sacrificial) shield.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
I figure that door seal could be so easily misaligned, that it's just not worth taking the risk of staring at your food behind the door day after day. After all, my eyes are my third favourite organ, do I really want to use them as a sacrificial microwave leakage indicator? I also insist, much to my daughter's hurumph, that she unplugs, not just switches off, the hand-held blender when changing the blades. The chances of losing body parts is pretty small, but why bother with the risk at all?
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Standing in front of the microwave
