From: sbharris@ix.netcom.com(Steven B. Harris)
Newsgroups: alt.folklore.urban,sci.skeptic,rec.food.cooking,sci.med,
	alt.parenting.solutions,misc.survivalism
Subject: Re: milk carcinogenic in microwave?
Date: 5 May 1999 06:18:20 GMT

In <7gnjb9$4kr$1@holly.prod.itd.earthlink.net> "Marvin Margoshes"
<physchem@earthlink.net> writes:

>This model is a useful one, but not to be taken literally. The quantum
>world is not like the macro world that we know from our senses. I can
>think of molecules rotating and vibrating in a gaseous state, but not in
>a liquid or solid where the molecules don't have a lot of space for such
>motions.

    True for rotation, but there's plenty of space for vibration in
solids, since the first couple of vibration modes above the fundamental
don't change the average distance bewteen atoms much, as compared with
the usual distance between molecules in solid or liquid phase.  Which
is why polar molecular solids and liquids often have IR absorption
bands quite identifiable as the same ones (though shifted) as they are
found to have as gases.

From: sbharris@ix.netcom.com(Steven B. Harris)
Newsgroups: alt.folklore.urban,sci.skeptic,rec.food.cooking,sci.med,
	alt.parenting.solutions,misc.survivalism
Subject: Re: milk carcinogenic in microwave?
Date: 5 May 1999 07:40:13 GMT

In <eyh90b4ke7u.fsf@liddell.cstr.ed.ac.uk> Richard Caley
<spt@cstr.ed.ac.uk> writes:
>
>In article <MPG.11942c418fb0c2319896d6@news>, Tony Pelliccio (tp) writes:
>
>tp> Bzzzttt.... the microwaves are at about the right freguency (2.4GHz) to
>tp> be resonant with water molecules. When they resonate they're doing so at
>tp> high frequency causing some friction with other water molecules and
>tp> matter near it.


   Microwaves at 2.45 GHz are not at the right frequency to be
resonnant with anything in water.  And if they, were they'd have to
detune them, since absorption would be so strong as to deposit all heat
in a small surface volume, which would cause overcooked exteriors and
underdone interiors.  Lower frequencies than 2.45 GHz work perfectly
well in heating foods, BTW, and are even more pentrative.  They are not
used in the home only because the magnetrons and waveguides would be
too big (these are scaled in terms of wavelength and not working when
one dimension is much below wavelength). It's likely your soda crackers
were dried by radio-wave heating at around 100 MHz, though.



>Er, friction? You have your levels of abstraction massively
>crossed. Friction is what we call the gross effects of molecules
>pulling on each other. Molecules themselves don't rub against each
>other with friction. They are mostly empty space after all.


   Empty space defended by electrons which resist being in the same
bound quantum state with incoming electrons.  They might as well be
thought of as filling that space.

    As for friction, of course you are right, but analogous to friction
is the rate at which kinetic energy in a gas (say a beam or cold gas
molecules) is equilibrated when it is mixed in a target cold gas.
Energy of motion goes into heat (in which it is equilibrated with
vibration) quite fast, due to conversion of kinetic to thermal energy
(vibration, intra and extra molecular).



>>> Microwave photons don't.
>
>tp> Photons? You are very misinformed.
>
>Microwaves come in photons, like any other EM radiation.


   Yep.  (AC power, however, does not.  Unless you count virtual
photons as photons).  Strictly speaking, it's not radiation.   If
something didn't pick that energy up and make it real, it would never
leave.  This is not true of EM radiation.

From: sbharris@ix.netcom.com(Steven B. Harris)
Newsgroups: alt.folklore.urban,sci.skeptic,rec.food.cooking,sci.med,
	misc.survivalism
Subject: Re: milk carcinogenic in microwave?
Date: 5 May 1999 21:35:53 GMT

In <372FFF14.EEA1D164@home.com> ray hastings <rayhastings@home.com>
writes:

>I'm glad that I don't have to know or remember everything...just know
>where to look for the answers.
>Microwave Heating: The microwaves strike molecules of water in the
>forrd. Each wave of energy causes the water molecules to ALIGN and then
>REVERSE alignment. The extremely rapid and repeated twisting produces
>heat.



   This is correct.  However, note that the effect works for EM waves
of any frequency. There is no coupling to rotational states.  No
special tuning is required for this kind of heating, which has much in
common with the kind of heating produced by diathermy (changing
electric field), or induction coil (magnetic field).  The difference is
that a microwave oven uses far-field EM _radiation_, in which the E and
B fields are in fixed ratio (E = cB).  In induction heating the B field
is far stronger than E/c, and in diathermy the E field is far stronger
than cB.

    Using far-field radiated EM waves (microwaves or radiowaves) allows
a fairly large range of radio power to be generated, with very little
difference in load change on the magnetron (not the case with inductive
or capacitative heating, which feeds back far more to the source).
Otherwise the effect is more or less the same.  Polar molecules are
twisted back and forth by field changes, and in the process of turning
they strike other molecules and give them a kick.  The kinetic energy
eventually is disipated and distributed as kinetic and vibrational
motion in neighboring molecules (heat).

From: "Steve Harris" <sbharris@ix.RETICULATEDOBJECTcom.com>
Newsgroups: sci.physics.electromag,sci.med,sci.physics,sci.chem
Subject: Re: Sterilization by microwave oven
Date: Wed, 24 Apr 2002 16:40:53 -0700
Message-ID: <aa7fs8$64e$1@slb1.atl.mindspring.net>

Repeating Decimal wrote in message ...

>One must really distinguish between radiative transfer and inductive
>transfer of power. A microwave oven is somewhere on the edge. IIRC MW ovens
>work at about 1.2 GHz.

2.4 or 5.8 in the US. There is also some industrial microwave drying at 915
MHz


>That is a wavelenth of about 25 cm and much longer
>than many objects heated. Moreover, many food items to not get heated
>internally very well.

Penetration is inversely with the amount of liquid water per volume. As with
any dye.

>I conclude, without having done any real experimentation, that such
>highly conductive foods, such as salty roasts etc, are not heated
>internally because of skin effect.

Ion conductivity decreases penetration inasmuch as are additional modes of
absorbing energy from the electric field. One of these is inductive as you
say. Another is ion drag in liquid water.

> That is, heating is by induction rather than by resonant
>radiative absorption.

Induction, which is basically ion drag currents working against resistance,
is additive to dielectric heating. Both effects operate, but only dielectric
heating is important in the several GHz range. This is basically too high
frequency to have good "ionic eddy currents" and inductive losses due them.
There is nothing "resonant" about microwave absorption by water in these
bands. It's dielectric or ion drag (if any). No real spectroscopy.

>The less conductive or dryer the material is, the
>deeper the penetration.

Yes, but only because it's water tha absorbs, and there's less of it.


>For good conductors, there truly is a skin effect. For copper, the
>penetration is only about 6 mm and decreases inversely as the square root
>of the frequency. Thus, for small food pieces, you get dielectric
>heating, not resonant radio frequency absorption.

You don't get resonant radio frequency absorption in an oven. This is a
great urban myth.


>The depth also inversely proportional
>to the square root of the conductivity.

Not really. Dielectric heating of distilled water in your microwave is not
much slower than if you spike it with salt, even though the conductivity
changes by many, many orders of magnitude. That's because at these
frequencies (as noted) ion drag heating (which is proportional to ionic
conductivity) is not as important as dielectric heating (which does NOT
depend on conductivity-- and even works for fats and alcohols). Go below 100
MHz (as in diathermy which is far below this), and ion drag and induction
start to get important.

SBH


--
I welcome email from any being clever enough to fix my address. It's open
book.  A prize to the first spambot that passes my Turing test.

From: "Steve Harris" <sbharris@ix.RETICULATEDOBJECTcom.com>
Newsgroups: sci.physics.electromag,sci.med,sci.physics,sci.chem
Subject: Re: Sterilization by microwave oven
Date: Wed, 24 Apr 2002 11:31:46 -0700
Message-ID: <aa6toj$823$1@nntp9.atl.mindspring.net>

Edward Green wrote in message
<2a0cceff.0204232147.1ef9b137@posting.google.com>...>Peter Hanely
<hanelyp@no-spam.calweb.com> wrote in message
news:<3CBD80BD.1030703@no-spam.calweb.com>...

>MWR heats by vibrating the individual water molecules???
>
>Damn sure that an individual water molecule is a poor antenna, if a
>fruit fly is!  Do microwaves couple to individual molecules or not?
>Can you superheat steam in the microwave (I mean after liquid water is
>gone, not by placing it under pressure in the presence of liquid, so
>T_equil > 100 C).
>
>Someone straighten me out, please.
>
>Hint to myself:  must be some ambiguity in "couple".  Molecular
>dipoles clearly can "couple" strongly to slowly oscillating electric
>fields; whose wavelengths might be in meters.  They simply will follow
>the field.  And "slowly" here might extend down to microwave range.
>Then there is the sense of "couple" as in resonance, as in a loss
>peak.



COMMENT:

Microwaves can be absorbed by any dipole, if the dipole has some way of
disposing of the energy. A single free water vapor molecule has no good way
to get rid of 2 or 3 GHz oscillations unless it bumps into others while
swinging around. Thus, it "couples" in the sense of seeing the field, but
doesn't absorb energy because to do so would require the energy to be
transduced to something else somehow. This is basically why ice is such a
poor microwave absorber-- it's not that the individual molecules don't
couple-- rather they are locked into place and can't transduce any of it
into motion. H2O gas is too free to absorb well; ice is not free enough.

--
I welcome email from any being clever enough to fix my address. It's open
book.  A prize to the first spambot that passes my Turing test.

From: "Steve Harris" <sbharris@ix.RETICULATEDOBJECTcom.com>
Newsgroups: sci.physics.electromag,sci.med,sci.physics,sci.chem
Subject: Re: Sterilization by microwave oven
Date: Wed, 24 Apr 2002 11:09:51 -0700
Message-ID: <aa6sfi$1d8$1@slb7.atl.mindspring.net>

Edward Green wrote in message
<2a0cceff.0204240947.2495e7f3@posting.google.com>...

>I was simply throwing out the random observation which may or may not
>be helpful here.  I'm interested about the "lossy" part... if
>reorienting dipoles is lossy, then that is like any other loss to
>electrical resistance, hence a possible heating mechanism.  Would that
>be the most accurate way to describe the heating of water by a
>microwave oven?

Yes, that's the main effect at GHz frequencies.  Capacitative heating also
happens in high frequency capacitors.  There are diathermy machines that
work this way: basically just two big plates.  At microwave frequencies the
main effect is from water molecule dipole orientation/re-orientation. At the
lower diathermy frequencies (10 Mhz or so) this happens, but there's another
E-field heating effect in ionic solutions-- ion drag. Charged particles like
ions get dragged through the field back and forth and bump into water.  If
the frequency is too high (> 100 Mhz or so) this doesn't have *time* to
happen significantly (the ion doesn't get going fast enough in one cycle to
hit anything and transfer energy). And of course, it's not a factor in pure
water since there are few ions.

There are also diathermy machines which work on induction-- they have an RF
generator and a big coil. This depends on induced current, and I suppose
couples well only to conductive solutions such as are in your body, and also
would not work well in pure water.

I'm flabbergasted that enough RF power to heat your tissues by induction, or
capacitative alternating E-field coupling (dipole or ion drag), doesn't
cause some kind of horrible biological effects. Hell, you'd think it would
do SOMETHING. But nobody's yet found anything reliable.

SBH
--
I welcome email from any being clever enough to fix my address. It's open
book.  A prize to the first spambot that passes my Turing test.